comparative pathogenesis of autoimmune diabetes in …

Comparative Pathogenesis of Autoimmune Diabetes inHumans NOD Mice and Canines Has a Valuable AnimalModel of Type 1 Diabetes Been OverlookedAllison L OrsquoKell1 Clive Wasserfall2 Brian Catchpole3 Lucy J Davison4 Rebecka S Hess5

Jake A Kushner6 and Mark A Atkinson2

Diabetes 2017661443ndash1452 | httpsdoiorg102337db16-1551

Despite decades of research in humans andmousemodelsof disease substantial gaps remain in our understanding ofpathogenic mechanisms underlying the development oftype 1 diabetes Furthermore translation of therapies frompreclinical efforts capable of delaying or halting b-cell de-struction has been limited Hence a pressing need existsto identify alternative animal models that reflect humandisease Canine insulin deficiency diabetes is in somecases considered to follow autoimmune pathogenesissimilar to NODmice and humans characterized by hyper-glycemia requiring lifelong exogenous insulin therapyAlso similar to human type 1 diabetes the canonical ca-nine disorder appears to be increasing in prevalenceWhereas islet architecture in rodents is distinctly differentfrom humans canine pancreatic endocrine cell distribu-tion is more similar Differences in breed susceptibilityalongside associations with MHC and other canine im-mune response genes parallel that of different ethnicgroups within the human population a potential benefitover NOD mice The impact of environment on diseasedevelopment also favors canine over rodent modelsHerein we consider the potential for canine diabetes toprovide valuable insights for human type 1 diabetes interms of pancreatic histopathology impairment of b-cellfunction and mass islet inflammation (ie insulitis) andautoantibodies specific for b-cell antigens

The incidence of type 1 diabetes (T1D) is increasingworldwide (1) and despite immense research efforts the

inciting cause remains elusive Animal models in particularthe NOD mouse are often used to study T1D pathogenesisand have proven quite informative given certain similaritiesin disease-associated features with humans (2) Howeverthe impact of physiological variances between mice andhumans (eg immune system components islet architec-ture metabolism) taken together with limited success sto-ries involving preclinical translation of therapies has causedincreasing concerns (3) Thus a need exists for alternativeanimal models that may add additional insights to the hu-man disease with companion animals providing one poten-tial avenue to fill this role With this Perspective weconsider the current knowledge of naturally occurring ca-nine diabetes and following comparison with humans andthe NOD mouse model of T1D propose it may serve as aninformative model of the human disease

CLINICAL AND METABOLIC FEATURES

Diabetes mellitus is one of the most common endocrinediseases affecting pet dogs (4) Similar to human T1D (5)the incidence of canine diabetes also appears to be increas-ing in the US the prevalence of canine diabetes at veter-inary teaching hospitals increased from 19 per 10000 to64 per 10000 cases between 1970 and 1999 (6) Virtuallyall dogs require insulin therapy at diagnosis (47) regardlessof the underlying cause Canine diabetes can be classifiedinto two major categories insulin deficiency diabetes andinsulin resistance diabetes (4) A canine equivalent to hu-man type 2 diabetes does not seem to occur and although

1Department of Small Animal Clinical Sciences College of Veterinary MedicineUniversity of Florida Gainesville FL2Department of Pathology Immunology and Laboratory Medicine University ofFlorida Gainesville FL3Department of Pathology and Pathogen Biology Royal Veterinary CollegeHatfield UK4Department of Veterinary Medicine University of Cambridge Cambridge UKand Wellcome Trust Centre for Human Genetics University of Oxford Oxford UK5Department of Clinical Studies School of Veterinary Medicine University ofPennsylvania Philadelphia PA

6McNair Medical Institute and Department of Pediatric Diabetes and Endocrino-logy Baylor College of Medicine Texas Childrenrsquos Hospital Houston TX

Corresponding author Mark A Atkinson atkinsonufledu

Received 14 December 2016 and accepted 15 March 2017

copy 2017 by the American Diabetes Association Readers may use this article aslong as the work is properly cited the use is educational and not for profit and thework is not altered More information is available at httpwwwdiabetesjournalsorgcontentlicense

Diabetes Volume 66 June 2017 1443

PERSPECTIVESIN

DIA

BETES

obesity is associated with insulin resistance this doesnot progress to overt diabetes unless other predisposingfactors are present (4) A variety of causes of insulin re-sistance diabetes have been suggested which primarily in-volve hormonal antagonism of insulin activity related tothe diestrus period (progesterone associated) exogenous orendogenous excess of glucocorticoids or the presence ofacromegaly (4) Some studies report a female predominance(689) whereas others have not demonstrated a sex pre-dilection (1011) This discrepancy may be due to geo-graphic location of the study population as dogs inEurope are more likely to remain sexually intact (and atrisk for diestrus diabetes) than dogs in the US There isno strong sex predilection in human T1D but geographicvariation exists with Finland Sardinia and Sweden havingthe highest incidence of childhood-onset T1D (12) In theNOD mouse however a clear association with sex existswith 60ndash90 of females and 10ndash65 of males developingthe disorder (1314)

Most diabetic dogs suffer from insulin deficiency di-abetes with the underlying cause of the pancreatic b-cellloss or destruction most likely a result of an inflammatoryprocess in the exocrine or endocrine tissues and autoimmu-nity suspected in some cases (4) Pancreatitis may be di-agnosed concurrently with diabetes in some cases (15) Therole of autoimmunity is currently less clear than in humanT1D and the NOD mouse in which an immune-mediatedpathogenesis is well established (1416) The majority ofdogs are middle-aged to older (5ndash7 years) at diagnosis(681011) although a relatively uncommon juvenile orcongenital form of insulin deficiency diabetes has been re-ported in some breeds (4) This contrasts with the juvenileonset that is more common than adult-onset disease inpeople (16) though there is an emerging realization thatT1D onset occurs more frequently in adults than once be-lieved (17) It also parallels the late (postsexual maturation)onset of disease in the NOD mouse at 10ndash26 weeks of age(1314)

Similar to humans the reference range for normal bloodglucose in dogs is 81ndash118 mgdL (45ndash66 mmolL) (Table1) Clinical signs of symptomatic diabetes in all three speciesare similar (polyuria polydipsia polyphagia and weightloss) (41316) Canine diabetes is classically diagnosedwhen hyperglycemia (typically250 mgdL [139 mmolL])(1819) and glucosuria are identified in the presence ofclinical signs (Table 1) This is similar to NOD mice inwhich a diagnosis is typically made when blood glucoseis 250 mgdL (139 mmolL) on two consecutive readings(Table 1) (20) however no single diagnostic criterion exists(21) Diabetes in people can be diagnosed using specificcriteria for hemoglobin A1C or plasma glucose (16) (Table1) and thus may be more likely to be recognized prior tothe onset of symptoms As glucosuria in dogs does notusually develop until blood glucose is between 180 and220 mgdL (10 and 122 mmolL) (7) dogs that mayhave early or subclinical diabetes are often not identifiedKetoacidosis may be present at diagnosis or may develop

during therapy (4) This is comparable to human T1D inwhich diabetic ketoacidosis remains a somewhat commonfeature of clinical presentation (22) The NOD mouse de-velops ketosis without insulin therapy (132324) butthrough evaluation for ketoacidosis in the literature thiscomplication appears rare (24)

Few reports exist describing b-cell function in dogs Inthe majority of diabetic dogs baseline fasting C-peptide wassimilar to or lower than healthy control canines whereasthe insulin and C-peptide response to glucagon stimulationwas blunted indicating insulin deficiency (2526) Theseresults parallel findings in human T1D in which there isinsulin deficiency assessed using C-peptide as a marker ofb-cell function (27) and lifelong insulin therapy is requiredat diagnosis (22) Although the NOD mice can survive forseveral weeks without insulin therapy after diabetes onset(23) insulin therapy markedly prolongs survival (13) Inaddition to the NOD mouse several other rodent modelsare used to study autoimmune diabetes most notably theBioBreeding (BB) rat (142328) Although an in-depth de-scription of the BB rat is beyond the scope of this Perspec-tive important characteristics are summarized in Table 1

PANCREATIC ISLET PATHOLOGY

Islet ArchitectureThe basic islet characteristics for each of the three speciesare summarized in Table 2 Canine islets have on average78 b-cells 11 a-cells 11 d-cells (29) and 4 pan-creatic polypeptide (PP) cells (30) In comparison humanislets have fewer b-cells and more a-cells averaging 50b-cells 40 a-cells 10 d-cells and rare PP cells (3031)NOD mice fall somewhere in between with an average of60ndash80 b-cells 15ndash20 a-cells 10 d-cells and 1PP cells in their islets (30) Islet endocrine cell distributionis strikingly different between humans and mice In miceb-cells are located in the center of the islet and a- andd-cells on the periphery (Fig 1A) whereas in humans en-docrine cells are generally distributed throughout theislets without a distinct central and peripheral zone(Fig 1B) (3031) Canine islets do not have a distinct zonaldistribution with b-cells commonly located in the centerof the islet but also in the periphery a-cells located in ei-ther the center or periphery and d-cells having a randomdistribution (Fig 1C) (293233) In humans and dogs thedistribution of cell types varies with the region of the pan-creas (3334) Both species have a PP cellndashdominant regionthat is located in the uncinate process of the head of thepancreas in humans (34) and in the right limb of the pan-creas in dogs which is analogous to the head of the humanpancreas (33)

Pancreatic Histopathology in T1DThe histopathological characteristics reported in thepancreata of diabetic dogs have been variable Histori-cally studies reported a slight to marked decrease in isletnumber and mild to marked reduction in b-cells withnormal to proportionately decreased numbers of a- and

1444 Autoimmune Diabetes in Mice Dogs and Humans Diabetes Volume 66 June 2017

Table

1mdashCharacteristics

ofT1D

inhum

ansdogsNOD

miceand

BB

rats

Hum

anDog

NOD

mouse

BBrat

Genetic

susceptibility+

++

+

Presence

ofautoantibodies

++2

++

Insulitis+

+2+

+

Disease

heterogeneity+

+mdash

mdash

InbredoutbredOutbred

Outbredinbred

InbredInbred

Sex

predilectionmdash

mdash+(fem

ale)mdash

Diagnosis

a)Hem

oglobinA1C

$65

(48mmolm

ol)b)Fasting

plasmaglucose

126

mgdL

(70mmolL)

c)2-hplasm

aglucose

$200

mgdL

(111mmolL)

duringan

oralglucosetolerance

testd)R

andomplasm

aglucose

$200

mgdL

(111mmolL)

with

classicsym

ptoms

Con

firmdiagnosis

byab

orcwith

repeattesting

Presence

ofhyperglycem

ia(typically

250

mgdL

[139mmolL])glucosuria

andclinicalsigns

(normal

fastingreference

range81

ndash118mgdL

[45ndash66

mmolL])

Blood

glucose250

mgdL

(139mmolL)

ontw

oconsecutive

readings

Glucosuria

(4+)incom

binationwith

bloodglucose

250

mgdL

(139mmolL)

Ketoacidosis

common

++

+

Insulinrequired

atonset

++

++

Thistable

doesnotinclude

congenitalb-cellde

ficiencyorinsulin

resistancediabetes

(eggestationalprogesteroneorglucocorticoid

induced)Atthe

timeofthis

writingthere

isno

publishedstandard

rangefor

caninesThe

rangereported

hereis

fromthe

Endocrinology

Section

Diagnostic

Center

forPopulation

andAnim

alHealthM

ichiganState

University

LansingMI

diabetesdiabetesjournalsorg OrsquoKell and Associates 1445

d-cells compared with healthy control animals (3536)Remaining b-cells were described as swollen vacuolatedand degranulated (35) Inflammatory mononuclear islet in-filtrates (described as insulitis) were observed in 6 of13 dogs (36) These studies included female dogs with noinformation on breed or neutering status and it is possiblethat some of these cases represented diestrus-related dia-betes which is considered to have a different pathogenesisthan the adult-onset insulin deficiency diabetes that is thefocus of this discussion Ahlgren et al (37) reported similarfindings of varying numbers of b-cells in the islets of di-abetic dogs as well as enlarged and vacuolated islets but noinsulitis The majority of these dogs were female and neu-tering status was again unknown so some of these dogsmay also have had diestrus-related diabetes A more recentstudy including predominantly males and neutered femalesreported small islets with few b-cells (Fig 2A) (29) Thecomposition of the islets in diabetic dogs (30 b-cells40 a-cells and 30 d-cells and PP cells) were markedlydifferent than in controls (78 b-cells 11 a-cells 11d-cells (29) and 4 PP cells) (30) Additionally diabeticislets were poorly defined compared with controls andthere was no evidence of lymphocyte infiltration exceptfor in a single young puppy (29) Insulitis in a diabeticpuppy has been reported previously but appears to be anuncommon finding in juvenile dogs (Fig 2B) (38) Dogswith long-standing disease were essentially devoid ofb-cells (29) Importantly most pathological studies includefew dogs at symptomatic onset even then it is plausiblethat a period of active insulitis early in disease (even priorto clinical diagnosis) may no longer be detectable

The findings thus far in dogs contrast with pathologicalfindings in human patients with T1D and the NOD mousein which insulitis is a defining feature Insulitis is identifiedby the presence of a lymphocytic infiltrate affecting theperiphery (peri-insulitis) or the interior of the islet (intra-insulitis) (39) A consensus definition in people requires$15 CD45+ cellsislets in a minimum of 3 islets for diag-nosis of insulitis combined with the presence of b-celldevoid islets (pseudo-atrophic islets) (Fig 2C and D) (39)Usually 10 of all islets predominantly insulin-positiveislets (ie those with b-cells) are affected (39) The fre-quency of insulitis is reportedly higher in young patientswith disease duration less than 1 month with one reviewevaluating the collective literature suggesting 73 ofthose 14 years old having insulitis compared with 29

of those aged 15ndash40 years (40) Other studies howevernoted a higher prevalence of insulitis with shorter diseaseduration but no correlation with age (41) With respect tothe natural history of b-cell loss although T1D patientshave reduced b-cell area residual b-cells exist for decadesafter the symptomatic onset of disease (42) which con-trasts to the current findings in canine diabetes

Insulitis is a prominent feature of diabetes in the NODmouse and pathological characteristics have been far morewidely and thoroughly studied than in humans or dogsbecause of the availability of pancreatic samples Classicallydefined mononuclear infiltration begins at approximately4 weeks of age prior to the onset of diabetes (1443)however recent efforts have noted that cells of the innateimmune system may enter as early as 2 weeks of age (44)Initially the inflammatory infiltrate is predominantly lo-cated in the peri-islet region and begins focally (1443)This focal mononuclear accumulation (predominantly lym-phocytes) progresses to surround the islet and forms aldquotertiary lymphoid organrdquo structure (43) As the mice ageintraislet lymphocyte invasion becomes prominent alongwith a marked loss of b-cells by approximately 12 weeksof age (14) At the time of clinical onset of disease (ie 10ndash26 weeks of age) b-cell mass is severely decreased pseudo-atrophic islets are present and virtually all islets areaffected by insulitis (Fig 2E and F) (43) Islet diameterdecreases as duration of disease increases along with themagnitude of lymphocytic infiltration similar to humansislets without b-cells often lack insulitis (45) Mice that donot develop diabetes also develop insulitis but with highvariability in severity (45)

Concurrent exocrine pancreatic changes have beenfound in conjunction with diabetes in all three speciesThere is somewhat conflicting evidence of a role forexocrine pancreatic disease as a predisposing factorfor the b-cell loss seen in canine diabetes Some histopath-ological studies have reported no or minimalvery focalareas of pancreatitis (2937) whereas in others 20ndash33of dogs demonstrated acute or chronic pancreatitis withvariable fibrosis (3536) In the latter studies it is unclearwhether these lesions were severe or diffuse enough in allcases to cause diabetes (3536) In dogs with histopatholog-ically confirmed chronic pancreatitis 5 of 14 (36) hadconcurrent diabetes of which 2 also had exocrine pancreaticinsufficiency (15) b-Cell function was decreased in 5 of6 (83) nondiabetic dogs with chronic pancreatitis based

Table 2mdashIslet characteristics in humans dogs and NOD mice

a-Cells b-Cells d-Cells PP cells

Human 40 core + periphery 50 core + periphery 10 core + periphery Core + periphery rare except inuncinate process of head

Dog 11 core + periphery 78 core periphery 11 core + periphery 4 core + periphery predominantlyright limbhead lobe

Mouse 15ndash20 periphery 60ndash80 core 10 periphery 1 periphery

Adapted with permission from Steiner et al (30) Information generated from refs 29ndash3134


on glucagon stimulation testing (46) Thus the evidencesupports pancreatitis as a cause or contributing factor indiabetes in some dogs although the overall prevalence andsignificance of exocrine inflammation as a cause of b-celldestruction is unclear In people inflammatory infiltrates(eg lymphocytes and dendritic cells) can be found in theexocrine pancreas in patients with and without insulin-containing islets (47) The NOD mouse has the most welldefined and consistent changes described Prior to the onsetof diabetes exocrine pancreas is affected by mononuclearinfiltration including infiltration of exocrine pancreatic ve-nules periductular infiltrates and focal inflammation inconnective tissue (focal pancreatitis) (48) In contrast toboth dogs and people however at the time of disease onsetextraislet inflammation is absent (48)

In NOD mice a prominent distinguishing feature fromhuman and canine diabetes is the concurrent increase inlymphocytes in peripheral lymphoid organs blood otherendocrine tissues and glands (1443) including lacrimaland salivary glands (ie a model of Sjoumlgren syndrome)(49) a disorder not associated with T1D in humans or dogs

GENETICS

The genetic basis for canine diabetes is not fully establishedand similar to both humans and the NOD mouse hasproven to be somewhat complex Compared with the NODmouse dogs have much higher genetic diversity and aredivided into breeds with variable predisposition to diseases(50) There are remarkable breed differences in susceptibil-ity to canine diabetes suggesting an underlying geneticcomponent (4) (Table 3) Dog leukocyte antigen (DLA)genes coding for MHC class II have been associated withboth disease susceptibility and protection (51) Three dif-ferent DLA haplotypes involving the DRB1-DQA1-DQB1loci have been shown to confer increased risk among avariety of dog breeds along with one protective haplotype(51) It is unclear at this time however whether these DLAhaplotypes are markers of a susceptible or resistant breedrather than a susceptible or resistant individual (51) Thepossibility exists that genetic risk is fixed within a breedand thus case-control studies within a breed may not be thebest means to study genetic association To date associa-tions between breedgenetics and autoimmune markers(autoantibodies insulitis) have not been reported in dia-betic dogs In humans genes coding for human leukocyteantigen (HLA analogous to DLA) are the most establishedgenetic risk factor for T1D (52) Similar to dogs theDRB1-DQA1-DQB1 loci in the HLA class II region has thestrongest association with several different haplotypesconferring susceptibility or protection (reviewed in Nobleand Valdes [52]) There is also evidence that HLA class I andIII loci contribute to disease susceptibility although stronglinkage disequilibrium in the HLA region leads to challengesin analyzing these alleles individually (5354) In the NODmouse MHC alleles (H2g7) similarly confer the strongestsusceptibility and this region (termed Idd1) containsMHC class I and II genes (255) To the authorsrsquo knowledge

Figure 1mdashNormal islet architecture Representative immunofluores-cent images show islet composition for mice (A) humans (B) andcanines (C) without diabetes A Insulin green glucagon red somato-statin blue Adapted with permission from Novikova et al (45) BInsulin red glucagon blue somatostatin green Previously unpub-lished image kindly provided by Dr Martha Campbell-Thompson ofUniversity of Florida) C Insulin green glucagon red somatostatinyellow Adapted with permission from Shields et al (29) Scale bars =100 mm (A and C) and 20 mm (B)


there have been no published investigations into MHCclass I or III in dogs

More than 60 other loci have been associated with T1Drisk in humans (56) highlighting the complexity of geneticdeterminants of the disease Those with the highest oddsratios include INS CTLA4 IL2RA PTPN22 and IFIH1 (57)These genes aside from insulin (an apparent key autoan-tigen) are associated with the immune response and arealso implicated in other autoimmune diseases (57) In the

NOD mouse a number of other candidate genes have alsobeen identified including genes encoding IL-2 IL-21 CTLA-4 T-cell receptor CD30 TNFR2 and b2-microglobulin(reviewed in refs 255) Although only some of these geneshave orthologs in human T1D identification of these geneshas improved understanding of the immunopathogenesis ofthe disease (2) Efforts to identify other candidate genes indogs similar to those contributing to risk in humans havenot found conclusive associations although there may be

Figure 2mdashIslet architecture in diabetes Representative immunofluorescent images (A C E) show islet composition and immunohistochemicalstaining (B D F) shows insulitis for canines with insulin deficiency diabetes (A and B) humans with T1D (C and D) and NOD mice with diabetes(E and F) Panel B represents the rare finding of insulitis in a juvenile diabetic dog A Insulin green glucagon red somatostatin yellow Adaptedwith permission from Shields et al (29) B CD3 brown Adapted with permission from Jouvion et al (38) C Insulin green glucagon redUnpublished image kindly provided by Dr Peter Inrsquot Veld of Brussels Free University (previously available at httpwwwdiapediaorgtype-1-diabetes-mellitus2104434133long-term-changes) D CD3 brown glucagon red Previously unpublished image acquired from the Network forPancreatic Organ Donors with Diabetes (nPOD) online Aperio viewing platform which is freely available with log-in credentials (nPOD 6396) EInsulin green glucagon red somatostatin blue Progressive loss of insulin staining 1 week (top) and 3 weeks (bottom) after diabetes onsetAdapted with permission from Novikova et al (45) F CD3 brown Adapted with permission from Koulmanda et al (84)


breed-specific genetic factors that are masked when assess-ing the diabetic dog population as a whole An analysis of18 genes associated with monogenic diabetes in humans didnot find consistent associations in a large cohort of dogs(58) A large single nucleotide polymorphism (SNP)-basedanalysis of the human candidate genes PTPN22 IL10IL12B IL6 IL4 RANTES IFNG INS IL1A TNFA andIGF2 found 24 SNPs linked to susceptibility and 13 SNPsthat were protective in dogs (59) However the findingswere variable comparing breeds with some SNPs associatedwith increased susceptibility in one breed but protective inanother (59) A similar cohort of dogs was further assessedfor association of diabetes risk with SNPs related to genesencoding IFN-g IL-10 IL-12b IL-4 and CTLA-4 and sev-eral susceptibility and protective associations were found ina variety of breeds (6061) These findings are intriguinggiven the involvement of these genes in the immune re-sponse and similarities to observations in human T1Dhowever the significance of any functional effects of thesepolymorphisms is unknown at this time The investigatorscautioned that these results require replication and should

be interpreted with caution until further investigation intothe associated genes can occur with focus on genetic factorsin individual breeds (59ndash61)

IMMUNOPATHOGENESIS

The role of autoimmunity in the pathogenesis of diabetes indogs has received far less study than in humans and miceand although evidence for autoimmunity is present inmultiple studies the results to date are somewhat in-consistent Evaluation of humoral immunity has primarilyfocused on circulating autoantibodies that have beendocumented in humans with T1D In untreated diabeticdogs circulating islet cell autoantibodies (ICA) were notdetected using either frozen human or canine pancreas(37) Using purified islets from rat insulinoma as an anti-gen approximately 12 of 23 (52) untreated diabetic dogsdemonstrated serum antindashb-cell antibodies detected via im-munofluorescence (62) This may be analogous to humanswho are positive for ICA yet negative for the other autoan-tibodies (63) Insulin autoantibodies have been detectedin 3 of 109 (3) (64) and 5 of 40 (125) (65) untreateddiabetic dogs Proinsulin autoantibodies were found in 8 of15 (53) untreated and 6 of 15 (375) insulin-treateddiabetic dogs but also in 3 of 15 (20) of control dogs(66) Currently it is unclear whether the latter is an in-cidental finding or a possible predictor of future diabetesdevelopment In newly diagnosed untreated diabetic dogsautoantibodies against canine GAD65 or IA-2 were found in4 of 30 (13) and 3 of 30 (10) respectively (67) in apopulation selected for those suspected as having insulindeficiency diabetes However in another study only 1 of122 (08) treated diabetic dogs had GAD antibodies (37)although this population of dogs likely included a propor-tion that were affected with insulin resistance diabetes andblood samples were obtained at variable (sometimes substan-tial) periods of time after diagnosis Using human GAD IA-2and ZnT8 antibody assays in a recent report none of 15 di-abetic dogs had evidence of autoantibodies but 3 of 15 con-trol dogs were GAD antibody positive (68) These findingscontrast with humans in which autoantibodies to at leastone of the major autoantigens (insulin GAD65 IA-2 ZnT8)are present in 90 of patients at diagnosis (226970) Anumber of additional autoantigens have been reported butwith much lower sensitivity (69) These autoantibodies areoften present prior to the symptomatic onset of disease andcan be used to identify at-risk patients (70ndash72) In the NODmouse only insulin autoantibodies have been documentedreliably despite findings of insulin GAD and IA-2 as targetautoantigens (73) Insulin is likely an early autoantigen inthe NOD mouse as in humans (2) but whether the sameholds true for dogs is currently less well defined Autoanti-bodies themselves are not thought to be directly involvedin disease pathogenesis and are more likely a biomarkerof b-cell autoimmunity in humans (69) Similarly NODtransgenic mice with B lymphocytes that cannot secreteantibodies still develop diabetes (74) B lymphocytes doheighten the immune response toward b-cells in NOD

Table 3mdashReported susceptible and protected dog breeds

Susceptible breeds Protected breeds

Samoyed Golden Retriever

Australian Terrier Boxer

Tibetan Terrier German Shepherd

Cairn Terrier German Shorthaired Pointer

Miniature Schnauzer Springer Spaniel

Standard Schnauzer Airedale Terrier

Miniature Poodle American Pit Bull Terrier

Toy Poodle Pekingese

Yorkshire Terrier Collie

Pug Shetland Sheepdog

Fox Terrier Bulldog

Keeshond Great Dane

Border Terrier Cocker Spaniel

Bichon Frise English Pointer

Border Collie Norwegian Elkhound

Finnish Spitz Old English Sheepdog

Siberian Husky Brittany Spaniel

Shih Tzu

Boston Terrier

Irish Setter

Doberman Pinscher

Dalmatian

Basset Hound

Labrador Retriever

English Setter

Beagle

As determined from refs 4685 Most studies were harmonious inreporting those with variance are noted with


mice (55) and research suggests that B lymphocytes mayplay a role in human T1D likely through antigen presenta-tion (75) To date no studies have specifically investigatedB lymphocytes in canine diabetes

Other indirect evidence of autoimmunity in dogs wasdocumented using mouse islets exposed to serum fromdiabetic dogs in vitro the serum contained complement-fixing ICA that caused decreased stimulated insulin releaseand lysis of the islet cells (76) None of the minor autoan-tibodies in humans have been tested in dogs and screeningof an array of autoantigens may aid in picking out canine-unique or -specific autoantibodies Given that autoanti-bodies have been detected in some diabetic dogs indicatinga component of autoimmunity in a proportion of patientsthis area is worth pursuing with additional studies andnovel methodologies that may lead to more canine-specificindicators of autoimmunity in this disease

Cellular immunity has had limited study in diabetic dogsUsing mouse islets in vitro canine mononuclear cells causedincreased basal insulin release and decreased stimulatedinsulin release suggesting possible b-cell damage and func-tional impairment (76) Peripheral blood T-cell proinflam-matory responses to insulin were found in two of fourdiabetic dogs quantified by IFN-g production (68) Al-though two of four control dogs also showed a responsepreactivation of T cells was suggested as a cause of potentialfalse-positive results (68) The lack of investigation in thisarea of canine diabetes is an important knowledge gapwhen comparing diabetes pathogenesis among species Inhumans with T1D b-cell destruction is largely consideredto be mediated by cellular immunity although direct evi-dence of this in humans is somewhat limited due to diffi-culties in studying these mechanisms in living subjects (77)Indirect evidence for the cellular immune response in-cludes the dominance of T lymphocytes particularly CD8+

(cytotoxic) T cells within insulitis and observations thattherapies modulating T-cell frequency and function (egregulatory T cells and T effector memory cells) possessthe ability to preserve C-peptide production in those withrecent-onset disease (7879) In dogs it is unclear based onlimited documentation of insulitis (36) whether T cells in-filtrate the canine islets and immunomodulatory therapyhas not been reported Additional evidence of cellular im-mune dysfunction in human T1D includes b-cell hyper-expression of MHC class I which may increase theirsusceptibility to killing by cytotoxic T cells (78) and iden-tification of peripheral T cells having reactivities withknown b-cell molecules (80) b-Cell destruction is also pre-dominantly mediated by autoreactive T cells in the NODmouse (14) and the mechanisms have been far better elu-cidated Similar to humans upregulation of MHC class I onNOD b-cells increases their susceptibility to T-cellndashmediatedkilling (2) Additionally the MHC class II haplotype foundin NOD mice is involved in the lack of immunologicaltolerance that is a feature of this disease (2) Multiple im-munomodulatory methods are known to prevent or reversediabetes in this species (3)

The innate immune system also plays an important rolein diabetes in the NOD mouse with macrophages identifiedas early infiltrators in islets that secrete cytokines that aretoxic to b-cells and recruit dendritic cells (2) These den-dritic cells have impaired maturation and tolerogenic func-tion (55) Natural killer (NK) cells are present in NODmouse insulitis lesions (2) and are reduced in number andfunction within peripheral blood (255) but the role of NKcells in potentiating or protecting against disease is unclear(81) In humans NK cells are present in insulitis in additionto T and B lymphocytes and a small subset of patients hasNK cellndashdominated insulitis (81) The role of the innateimmune system in diabetes has received little attention indogs Diabetic dogs have higher serum CXCL8 and MCP-1(82) and leukocytes that produce more proinflammatorycytokines in response to stimulation with lipopolysaccha-ride lipotechoic acid and peptidoglycan than control dogs(83) It is unknown whether these changes represent acause or consequence of the disease but they are suggestiveof an inflammatory state

CONCLUSIONS AND FUTURE DIRECTIONS

The limited success in identifying therapeutic strategies fordisease prevention and reversal in T1D highlight the needfor alternative animal models for comparative and trans-lational research Dogs with naturally occurring diabeteshave the potential to fill this role based on similarities tohumans in metabolic characteristics genetics therapeuticneeds and suspected autoimmunity as components of theirdisease In particular studying b-cell biology in defined dogbreeds that are highly susceptible or resistant to developingdiabetes might provide important insights into pathwaysand mechanisms that might be exploited therapeuticallyIt is plausible that each species discussed herein resideson a continuum with respect to the severity and prevalenceof autoimmunity with NOD mice at one end of the spec-trum (strongest autoimmune component) dogs at the op-posite end (weakest autoimmune component) and humanssomewhere in between

Despite similarities to human disease canine diabetesremains a relatively unexplored area of research particu-larly with respect to the contributions of autoimmunityand genetics and more basic investigations into diseasephenotype and metabolic characteristics Complicating thesestudies also is the apparent heterogeneity of the diabeticdog population with multiple possible etiologies of b-celldestruction including exocrine pancreatic disease Addition-ally concurrent diseases causing insulin resistance (eghyperadrenocorticism) may cause or contribute to the dis-ease in some cases although a canine equivalent to humantype 2 diabetes does not seem to occur We suspect thatautoimmunity is a component of disease in a proportion (orpossibly certain breeds) of diabetic dogs Given that exten-sive islet destruction is already present at symptomatic on-set of disease earlier disease detection may be necessary inorder to identify serological markers of autoimmunity insu-litis or b-cell loss Future studies in this area should be


performed using community diabetic dogs rather thanbreeding diabetic dogs for research colonies due to bothethical considerations as well as the potential benefits ofthe dogs living in a similar environment to their humancounterparts An exploration of canine diabetes as an al-ternative disease model represents a logical next step in thequest for meaningful progress in the diabetes field

Acknowledgments The authors sincerely thank Dr Martha Campbell-Thompson (University of Florida) for providing the human islet image shown in Fig1B The authors also thank Dr Peter Inrsquot Veld (Brussels Free University) for graciouslyproviding the human islet image shown in Fig 2CFunding The notions conveyed in this perspective were supported by JDRF theAmerican Diabetes Association and the National Institutes of Health (AI42288) JAKwas supported by the Robert and Janice McNair Foundation (DRCndashP30DK079638)the Diabetes Research Center at Baylor College of Medicine and the NationalInstitutes of Health (1R01AG040110) The UK Canine Diabetes Register and Archivehas been supported by the Kennel Club Charitable Trust Petsavers the EuropeanCommission (FP7-LUPA and GA-201370) and MSD Animal Health LJD wassupported by the Wellcome Trust Veterinary Postdoctoral Fellowship (WT096398MA)Duality of Interest No potential conflicts of interest relevant to this articlewere reported

References1 DIAMOND Project Group Incidence and trends of childhood type 1 diabetesworldwide 1990-1999 Diabet Med 200623857ndash8662 Jayasimhan A Mansour KP Slattery RM Advances in our understanding of thepathophysiology of type 1 diabetes lessons from the NOD mouse Clin Sci (Lond)20141261ndash183 Roep BO Atkinson M von Herrath M Satisfaction (not) guaranteed re-evaluating the use of animal models of type 1 diabetes Nat Rev Immunol20044989ndash9974 Catchpole B Ristic JM Fleeman LM Davison LJ Canine diabetes mellitus canold dogs teach us new tricks Diabetologia 2005481948ndash19565 Dabelea D Mayer-Davis EJ Saydah S et al SEARCH for Diabetes in YouthStudy Prevalence of type 1 and type 2 diabetes among children and adolescentsfrom 2001 to 2009 JAMA 20143111778ndash17866 Guptill L Glickman L Glickman N Time trends and risk factors for diabetesmellitus in dogs analysis of veterinary medical data base records (1970-1999) Vet J2003165240ndash2477 Nelson RW Reusch CE Animal models of disease classification and etiology ofdiabetes in dogs and cats J Endocrinol 2014222T1ndashT98 Davison LJ Herrtage ME Catchpole B Study of 253 dogs in the UnitedKingdom with diabetes mellitus Vet Rec 2005156467ndash4719 Fall T Hamlin HH Hedhammar A Kaumlmpe O Egenvall A Diabetes mellitus in apopulation of 180000 insured dogs incidence survival and breed distribution J VetIntern Med 2007211209ndash121610 Hess RS Saunders HM Van Winkle TJ Ward CR Concurrent disorders in dogswith diabetes mellitus 221 cases (1993-1998) J Am Vet Med Assoc 20002171166ndash117311 Hume DZ Drobatz KJ Hess RS Outcome of dogs with diabetic ketoacidosis127 dogs (1993-2003) J Vet Intern Med 200620547ndash55512 Tuomilehto J The emerging global epidemic of type 1 diabetes Curr Diab Rep201313795ndash80413 Makino S Kunimoto K Muraoka Y Mizushima Y Katagiri K Tochino YBreeding of a non-obese diabetic strain of mice Jikken Dobutsu 1980291ndash1314 Mathews CE Utility of murine models for the study of spontaneous autoimmunetype 1 diabetes Pediatr Diabetes 20056165ndash17715 Watson PJ Archer J Roulois AJ Scase TJ Herrtage ME Observational study of14 cases of chronic pancreatitis in dogs Vet Rec 2010167968ndash976

16 American Diabetes Association Diagnosis and classification of diabetes mel-litus Diabetes Care 201437(Suppl 1)S81ndashS9017 Oram RA Thomas NM Jones SE Weedon MN Hattersley AT Analysis ofdiabetes incidence against type 1 diabetes genetic risk score in 150000 showsautoimmune diabetes presents as often between 30-60 years as before 30 years(Abstract) Diabetes 201665 (Suppl 1)A41318 Sears KW Drobatz KJ Hess RS Use of lispro insulin for treatment of diabeticketoacidosis in dogs J Vet Emerg Crit Care (San Antonio) 201222211ndash21819 Walsh ES Drobatz KJ Hess RS Use of intravenous insulin aspart for treatmentof naturally occurring diabetic ketoacidosis in dogs J Vet Emerg Crit Care (SanAntonio) 201626101ndash10720 Mathews CE Xue S Posgai A et al Acute versus progressive onset of diabetesin NOD mice potential implications for therapeutic interventions in type 1 diabetesDiabetes2015643885ndash389021 Atkinson MA Evaluating preclinical efficacy Sci Transl Med 2011396cm2222 Gan MJ Albanese-OrsquoNeill A Haller MJ Type 1 diabetes current concepts inepidemiology pathophysiology clinical care and research Curr Probl Pediatr Ado-lesc Health Care 201242269ndash29123 Grant CW Duclos SK Moran-Paul CM et al Development of standardizedinsulin treatment protocols for spontaneous rodent models of type 1 diabetes CompMed 201262381ndash39024 Harano Y Takamitsu N Keisuke K Yukio S Makino S Evaluation of ketosis anda role of insulin-antagonistic hormones in NOD mouse In Insulitis and Type 1 Di-abetes Lessons From the NOD Mouse Tarui S Yoshihiro T Eds Academic PressJapan Inc 1986 p 233ndash23825 Montgomery TM Nelson RW Feldman EC Robertson K Polonsky KS Basaland glucagon-stimulated plasma C-peptide concentrations in healthy dogs dogswith diabetes mellitus and dogs with hyperadrenocorticism J Vet Intern Med 199610116ndash12226 Fall T Holm B Karlsson A Ahlgren KM Kaumlmpe O von Euler H Glucagonstimulation test for estimating endogenous insulin secretion in dogs Vet Rec 2008163266ndash27027 Jones AG Hattersley AT The clinical utility of C-peptide measurement in thecare of patients with diabetes Diabet Med 201330803ndash81728 Rees DA Alcolado JC Animal models of diabetes mellitus Diabet Med 200522359ndash37029 Shields EJ Lam CJ Cox AR et al Extreme beta-cell deficiency in pancreata ofdogs with canine diabetes PLoS One 201510e012980930 Steiner DJ Kim A Miller K Hara M Pancreatic islet plasticity interspeciescomparison of islet architecture and composition Islets 20102135ndash14531 Brissova M Fowler MJ Nicholson WE et al Assessment of human pancreaticislet architecture and composition by laser scanning confocal microscopy J Histo-chem Cytochem 2005531087ndash109732 Hawkins KL Summers BA Kuhajda FP Smith CA Immunocytochemistry ofnormal pancreatic islets and spontaneous islet cell tumors in dogs Vet Pathol 198724170ndash17933 Wieczorek G Pospischil A Perentes E A comparative immunohistochemicalstudy of pancreatic islets in laboratory animals (rats dogs minipigs nonhumanprimates) Exp Toxicol Pathol 199850151ndash17234 Wang X Zielinski MC Misawa R et al Quantitative analysis of pancreaticpolypeptide cell distribution in the human pancreas PLoS One 20138e5550135 Gepts W Toussaint D Spontaneous diabetes in dogs and cats A pathologicalstudy Diabetologia 19673249ndash26536 Alejandro R Feldman EC Shienvold FL Mintz DH Advances in canine diabetesmellitus research etiopathology and results of islet transplantation J Am Vet MedAssoc 19881931050ndash105537 Ahlgren KM Fall T Landegren N et al Lack of evidence for a role of isletautoimmunity in the aetiology of canine diabetes mellitus PLoS One 20149e10547338 Jouvion G Abadie J Bach JM et al Lymphocytic insulitis in a juvenile dog withdiabetes mellitus Endocr Pathol 200617283ndash29039 Campbell-Thompson ML Atkinson MA Butler AE et al The diagnosis of in-sulitis in human type 1 diabetes Diabetologia 2013562541ndash2543


40 Inrsquot Veld P Insulitis in human type 1 diabetes the quest for an elusive lesionIslets 20113131ndash13841 Campbell-Thompson M Fu A Kaddis JS et al Insulitis and b-cell mass in thenatural history of type 1 diabetes Diabetes 201665719ndash73142 Keenan HA Sun JK Levine J et al Residual insulin production and pancreaticszlig-cell turnover after 50 years of diabetes Joslin Medalist Study Diabetes 2010592846ndash285343 Inrsquot Veld P Insulitis in human type 1 diabetes a comparison between patientsand animal models Semin Immunopathol 201436569ndash57944 Diana J Simoni Y Furio L et al Crosstalk between neutrophils B-1a cells andplasmacytoid dendritic cells initiates autoimmune diabetes Nat Med 20131965ndash7345 Novikova L Smirnova IV Rawal S Dotson AL Benedict SH Stehno-Bittel LVariations in rodent models of type 1 diabetes islet morphology J Diabetes Res2013201396583246 Watson PJ Herrtage ME Use of glucagon stimulation tests to assess beta-cellfunction in dogs with chronic pancreatitis J Nutr 2004134(Suppl)2081Sndash2083S47 Rodriguez-Calvo T Ekwall O Amirian N Zapardiel-Gonzalo J von Herrath MGIncreased immune cell infiltration of the exocrine pancreas a possible contribution tothe pathogenesis of type 1 diabetes Diabetes 2014633880ndash389048 Papaccio G Chieffi-Baccari G Mezzogiorno V Esposito V Extraislet infiltrationin NOD mouse pancreas observations after immunomodulation Pancreas 19938459ndash46449 Roescher N Lodde BM Vosters JL et al Temporal changes in salivary glandsof non-obese diabetic mice as a model for Sjoumlgrenrsquos syndrome Oral Dis 20121896ndash10650 Karlsson EK Lindblad-Toh K Leader of the pack gene mapping in dogs andother model organisms Nat Rev Genet 20089713ndash72551 Kennedy LJ Davison LJ Barnes A et al Identification of susceptibility andprotective major histocompatibility complex haplotypes in canine diabetes mellitusTissue Antigens 200668467ndash47652 Noble JA Valdes AM Genetics of the HLA region in the prediction of type1 diabetes Curr Diab Rep 201111533ndash54253 Noble JA Valdes AM Varney MD et al Type 1 Diabetes Genetics ConsortiumHLA class I and genetic susceptibility to type 1 diabetes results from the Type1 Diabetes Genetics Consortium Diabetes 2010592972ndash297954 Valdes AM Thomson G Type 1 Diabetes Genetics Consortium Several loci inthe HLA class III region are associated with T1D risk after adjusting for DRB1-DQB1Diabetes Obes Metab 200911(Suppl 1)46ndash5255 Driver JP Serreze DV Chen YG Mouse models for the study of autoimmunetype 1 diabetes a NOD to similarities and differences to human disease SeminImmunopathol 20113367ndash8756 Morahan G Insights into type 1 diabetes provided by genetic analyses CurrOpin Endocrinol Diabetes Obes 201219263ndash27057 Polychronakos C Li Q Understanding type 1 diabetes through geneticsadvances and prospects Nat Rev Genet 201112781ndash79258 Short AD Holder A Rothwell S et al Searching for ldquomonogenic diabetesrdquo indogs using a candidate gene approach Canine Genet Epidemiol 20141859 Short AD Catchpole B Kennedy LJ et al Analysis of candidate susceptibilitygenes in canine diabetes J Hered 200798518ndash52560 Short AD Catchpole B Kennedy LJ et al T cell cytokine gene polymorphismsin canine diabetes mellitus Vet Immunol Immunopathol 2009128137ndash14661 Short AD Saleh NM Catchpole B et al CTLA4 promoter polymorphisms areassociated with canine diabetes mellitus Tissue Antigens 201075242ndash25262 Hoenig M Dawe DL A qualitative assay for beta cell antibodies Preliminaryresults in dogs with diabetes mellitus Vet Immunol Immunopathol 199232195ndash20363 Andersson C Kolmodin M Ivarsson SA et al Better Diabetes Diagnosis StudyGroup Islet cell antibodies (ICA) identify autoimmunity in children with new onsetdiabetes mellitus negative for other islet cell antibodies Pediatr Diabetes 201415336ndash344

64 Holder AL Kennedy LJ Ollier WE Catchpole B Breed differences in devel-opment of anti-insulin antibodies in diabetic dogs and investigation of the role of dogleukocyte antigen (DLA) genes Vet Immunol Immunopathol 2015167130ndash13865 Davison LJ Walding B Herrtage ME Catchpole B Anti-insulin antibodies indiabetic dogs before and after treatment with different insulin preparations J VetIntern Med 2008221317ndash132566 Davison LJ Herrtage ME Catchpole B Autoantibodies to recombinant canineproinsulin in canine diabetic patients Res Vet Sci 20119158ndash6367 Davison LJ Weenink SM Christie MR Herrtage ME Catchpole B Autoanti-bodies to GAD65 and IA-2 in canine diabetes mellitus Vet Immunol Immunopathol200812683ndash9068 Kim JH Furrow E Ritt MG et al Anti-insulin immune responses are detectablein dogs with spontaneous diabetes PLoS One 201611e015239769 Pietropaolo M Towns R Eisenbarth GS Humoral autoimmunity in type 1 di-abetes prediction significance and detection of distinct disease subtypes ColdSpring Harb Perspect Med 2012 2 pii a01283170 Wenzlau JM Juhl K Yu L et al The cation efflux transporter ZnT8 (Slc30A8) isa major autoantigen in human type 1 diabetes Proc Natl Acad Sci U S A 200710417040ndash1704571 Bingley PJ Gale EA European Nicotinamide Diabetes Intervention Trial (ENDIT)Group Progression to type 1 diabetes in islet cell antibody-positive relatives in theEuropean Nicotinamide Diabetes Intervention Trial the role of additional immunegenetic and metabolic markers of risk Diabetologia 200649881ndash89072 Bingley PJ Bonifacio E Williams AJ Genovese S Bottazzo GF Gale EA Pre-diction of IDDM in the general population strategies based on combinations ofautoantibody markers Diabetes 1997461701ndash171073 Bonifacio E Atkinson M Eisenbarth G et al International Workshop on LessonsFrom Animal Models for Human Type 1 Diabetes identification of insulin but notglutamic acid decarboxylase or IA-2 as specific autoantigens of humoral autoim-munity in nonobese diabetic mice Diabetes 2001502451ndash245874 Wong FS Wen L Tang M et al Investigation of the role of B-cells in type1 diabetes in the NOD mouse Diabetes 2004532581ndash258775 Hinman RM Cambier JC Role of B lymphocytes in the pathogenesis of type1 diabetes Curr Diab Rep 20141454376 Sai P Debray-Sachs M Jondet A Gepts W Assan R Anti-beta-cell immunity ininsulinopenic diabetic dogs Diabetes 198433135ndash14077 Di Lorenzo TP Peakman M Roep BO Translational mini-review series on type1 diabetes systematic analysis of T cell epitopes in autoimmune diabetes Clin ExpImmunol 20071481ndash1678 Roep BO Peakman M Diabetogenic T lymphocytes in human type 1 diabetesCurr Opin Immunol 201123746ndash75379 Marek-Trzonkowska N Myśliwec M Siebert J Trzonkowski P Clinical appli-cation of regulatory T cells in type 1 diabetes Pediatr Diabetes 201314322ndash33280 Seyfert-Margolis V Gisler TD Asare AL et al Analysis of T-cell assays tomeasure autoimmune responses in subjects with type 1 diabetes results of ablinded controlled study Diabetes 2006552588ndash259481 Grieco FA Vendrame F Spagnuolo I Dotta F Innate immunity and the path-ogenesis of type 1 diabetes Semin Immunopathol 20113357ndash6682 OrsquoNeill S Drobatz K Satyaraj E Hess R Evaluation of cytokines and hormonesin dogs before and after treatment of diabetic ketoacidosis and in uncomplicateddiabetes mellitus Vet Immunol Immunopathol 2012148276ndash28383 DeClue AE Nickell J Chang CH Honaker A Upregulation of proinflammatorycytokine production in response to bacterial pathogen-associated molecular patternsin dogs with diabetes mellitus undergoing insulin therapy J Diabetes Sci Technol20126496ndash50284 Koulmanda M Bhasin M Awdeh Z et al The role of TNF-a in mice with type1- and 2- diabetes PLoS One 20127e3325485 Hess RS Kass PH Ward CR Breed distribution of dogs with diabetes mellitusadmitted to a tertiary care facility J Am Vet Med Assoc 20002161414ndash1417


obesity is associated with insulin resistance this doesnot progress to overt diabetes unless other predisposingfactors are present (4) A variety of causes of insulin re-sistance diabetes have been suggested which primarily in-volve hormonal antagonism of insulin activity related tothe diestrus period (progesterone associated) exogenous orendogenous excess of glucocorticoids or the presence ofacromegaly (4) Some studies report a female predominance(689) whereas others have not demonstrated a sex pre-dilection (1011) This discrepancy may be due to geo-graphic location of the study population as dogs inEurope are more likely to remain sexually intact (and atrisk for diestrus diabetes) than dogs in the US There isno strong sex predilection in human T1D but geographicvariation exists with Finland Sardinia and Sweden havingthe highest incidence of childhood-onset T1D (12) In theNOD mouse however a clear association with sex existswith 60ndash90 of females and 10ndash65 of males developingthe disorder (1314)

Most diabetic dogs suffer from insulin deficiency di-abetes with the underlying cause of the pancreatic b-cellloss or destruction most likely a result of an inflammatoryprocess in the exocrine or endocrine tissues and autoimmu-nity suspected in some cases (4) Pancreatitis may be di-agnosed concurrently with diabetes in some cases (15) Therole of autoimmunity is currently less clear than in humanT1D and the NOD mouse in which an immune-mediatedpathogenesis is well established (1416) The majority ofdogs are middle-aged to older (5ndash7 years) at diagnosis(681011) although a relatively uncommon juvenile orcongenital form of insulin deficiency diabetes has been re-ported in some breeds (4) This contrasts with the juvenileonset that is more common than adult-onset disease inpeople (16) though there is an emerging realization thatT1D onset occurs more frequently in adults than once be-lieved (17) It also parallels the late (postsexual maturation)onset of disease in the NOD mouse at 10ndash26 weeks of age(1314)

Similar to humans the reference range for normal bloodglucose in dogs is 81ndash118 mgdL (45ndash66 mmolL) (Table1) Clinical signs of symptomatic diabetes in all three speciesare similar (polyuria polydipsia polyphagia and weightloss) (41316) Canine diabetes is classically diagnosedwhen hyperglycemia (typically250 mgdL [139 mmolL])(1819) and glucosuria are identified in the presence ofclinical signs (Table 1) This is similar to NOD mice inwhich a diagnosis is typically made when blood glucoseis 250 mgdL (139 mmolL) on two consecutive readings(Table 1) (20) however no single diagnostic criterion exists(21) Diabetes in people can be diagnosed using specificcriteria for hemoglobin A1C or plasma glucose (16) (Table1) and thus may be more likely to be recognized prior tothe onset of symptoms As glucosuria in dogs does notusually develop until blood glucose is between 180 and220 mgdL (10 and 122 mmolL) (7) dogs that mayhave early or subclinical diabetes are often not identifiedKetoacidosis may be present at diagnosis or may develop

during therapy (4) This is comparable to human T1D inwhich diabetic ketoacidosis remains a somewhat commonfeature of clinical presentation (22) The NOD mouse de-velops ketosis without insulin therapy (132324) butthrough evaluation for ketoacidosis in the literature thiscomplication appears rare (24)

Few reports exist describing b-cell function in dogs Inthe majority of diabetic dogs baseline fasting C-peptide wassimilar to or lower than healthy control canines whereasthe insulin and C-peptide response to glucagon stimulationwas blunted indicating insulin deficiency (2526) Theseresults parallel findings in human T1D in which there isinsulin deficiency assessed using C-peptide as a marker ofb-cell function (27) and lifelong insulin therapy is requiredat diagnosis (22) Although the NOD mice can survive forseveral weeks without insulin therapy after diabetes onset(23) insulin therapy markedly prolongs survival (13) Inaddition to the NOD mouse several other rodent modelsare used to study autoimmune diabetes most notably theBioBreeding (BB) rat (142328) Although an in-depth de-scription of the BB rat is beyond the scope of this Perspec-tive important characteristics are summarized in Table 1

PANCREATIC ISLET PATHOLOGY

Islet ArchitectureThe basic islet characteristics for each of the three speciesare summarized in Table 2 Canine islets have on average78 b-cells 11 a-cells 11 d-cells (29) and 4 pan-creatic polypeptide (PP) cells (30) In comparison humanislets have fewer b-cells and more a-cells averaging 50b-cells 40 a-cells 10 d-cells and rare PP cells (3031)NOD mice fall somewhere in between with an average of60ndash80 b-cells 15ndash20 a-cells 10 d-cells and 1PP cells in their islets (30) Islet endocrine cell distributionis strikingly different between humans and mice In miceb-cells are located in the center of the islet and a- andd-cells on the periphery (Fig 1A) whereas in humans en-docrine cells are generally distributed throughout theislets without a distinct central and peripheral zone(Fig 1B) (3031) Canine islets do not have a distinct zonaldistribution with b-cells commonly located in the centerof the islet but also in the periphery a-cells located in ei-ther the center or periphery and d-cells having a randomdistribution (Fig 1C) (293233) In humans and dogs thedistribution of cell types varies with the region of the pan-creas (3334) Both species have a PP cellndashdominant regionthat is located in the uncinate process of the head of thepancreas in humans (34) and in the right limb of the pan-creas in dogs which is analogous to the head of the humanpancreas (33)

Pancreatic Histopathology in T1DThe histopathological characteristics reported in thepancreata of diabetic dogs have been variable Histori-cally studies reported a slight to marked decrease in isletnumber and mild to marked reduction in b-cells withnormal to proportionately decreased numbers of a- and


Table


ofT1D

inhum

ansdogsNOD

miceand

BB

rats

Hum

anDog

NOD

mouse

BBrat

Genetic

susceptibility+

++

+

Presence

ofautoantibodies

++2

++

Insulitis+

+2+

+

Disease

heterogeneity+

+mdash

mdash


Outbredinbred

InbredInbred

Sex

predilectionmdash

mdash+(fem

ale)mdash

Diagnosis

a)Hem

oglobinA1C

$65

(48mmolm

ol)b)Fasting

plasmaglucose

126

mgdL

(70mmolL)

c)2-hplasm

aglucose

$200

mgdL

(111mmolL)

duringan


testd)R

andomplasm

aglucose

$200

mgdL

(111mmolL)

with

classicsym

ptoms

Con

firmdiagnosis

byab

orcwith

repeattesting

Presence

ofhyperglycem

ia(typically

250

mgdL


andclinicalsigns

(normal

fastingreference

range81

ndash118mgdL

[45ndash66

mmolL])

Blood

glucose250

mgdL

(139mmolL)

ontw

oconsecutive

readings

Glucosuria

(4+)incom

binationwith

bloodglucose

250

mgdL

(139mmolL)

Ketoacidosis

common

++

+

Insulinrequired

atonset

++

++

Thistable

doesnotinclude

congenitalb-cellde

ficiencyorinsulin

resistancediabetes


induced)Atthe

timeofthis

writingthere

isno

publishedstandard

rangefor

caninesThe

rangereported

hereis

fromthe

Endocrinology

Section

Diagnostic

Center

forPopulation

andAnim

alHealthM

ichiganState

University

LansingMI
















GENETICS











IMMUNOPATHOGENESIS














Fox Terrier Bulldog

Keeshond Great Dane






Shih Tzu

Boston Terrier

Irish Setter

Doberman Pinscher

Dalmatian

Basset Hound

Labrador Retriever

English Setter

Beagle




















Table


ofT1D

inhum

ansdogsNOD

miceand

BB

rats

Hum

anDog

NOD

mouse

BBrat

Genetic

susceptibility+

++

+

Presence

ofautoantibodies

++2

++

Insulitis+

+2+

+

Disease

heterogeneity+

+mdash

mdash


Outbredinbred

InbredInbred

Sex

predilectionmdash

mdash+(fem

ale)mdash

Diagnosis

a)Hem

oglobinA1C

$65

(48mmolm

ol)b)Fasting

plasmaglucose

126

mgdL

(70mmolL)

c)2-hplasm

aglucose

$200

mgdL

(111mmolL)

duringan


testd)R

andomplasm

aglucose

$200

mgdL

(111mmolL)

with

classicsym

ptoms

Con

firmdiagnosis

byab

orcwith

repeattesting

Presence

ofhyperglycem

ia(typically

250

mgdL


andclinicalsigns

(normal

fastingreference

range81

ndash118mgdL

[45ndash66

mmolL])

Blood

glucose250

mgdL

(139mmolL)

ontw

oconsecutive

readings

Glucosuria

(4+)incom

binationwith

bloodglucose

250

mgdL

(139mmolL)

Ketoacidosis

common

++

+

Insulinrequired

atonset

++

++

Thistable

doesnotinclude

congenitalb-cellde

ficiencyorinsulin

resistancediabetes


induced)Atthe

timeofthis

writingthere

isno

publishedstandard

rangefor

caninesThe

rangereported

hereis

fromthe

Endocrinology

Section

Diagnostic

Center

forPopulation

andAnim

alHealthM

ichiganState

University

LansingMI
















GENETICS











IMMUNOPATHOGENESIS














Fox Terrier Bulldog

Keeshond Great Dane






Shih Tzu

Boston Terrier

Irish Setter

Doberman Pinscher

Dalmatian

Basset Hound

Labrador Retriever

English Setter

Beagle


































GENETICS











IMMUNOPATHOGENESIS














Fox Terrier Bulldog

Keeshond Great Dane






Shih Tzu

Boston Terrier

Irish Setter

Doberman Pinscher

Dalmatian

Basset Hound

Labrador Retriever

English Setter

Beagle



























IMMUNOPATHOGENESIS














Fox Terrier Bulldog

Keeshond Great Dane






Shih Tzu

Boston Terrier

Irish Setter

Doberman Pinscher

Dalmatian

Basset Hound

Labrador Retriever

English Setter

Beagle




















comparative pathogenesis of autoimmune diabetes in …

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