intravascular fibrin deposits, hepatic infarcts and

Intravascular Fibrin Deposits, Hepatic Infarctsand Thrombocytopenia in Parent/F, MouseChimeras With Host-Versus-Graft Syndrome

Richard C. Hard Jr, MD and W. J. S. Still, MD

Host-versus-graft (HVG) disease is the fatal result of the allogenic reaction whichoccurs in parental strain mice perinatally inoculated with F1 hybrid spleen cells.The principal manifestations of the syndrome in RFMA(T6 x RFM )F1 mice arethrombocytopenia, intestinal hemorrhage, hepatic necrosis, lymphoproliferative dis-orders and renal disease due to immune complexes. The discovery of intravascularfibrin deposits in the present studies establishes disseminated intravascular coagu-lation (DIC) as an intermediary mechanism of HVG disease. It is suggested thatthe characteristic declines in blood platelet levels, intestinal hemorrhages andhepatic infarcts are triggered principally by immune complexes. Cellular infiltratesof the liver, granulocytosis and hypergammaglobulinemia are other abnormalitieswhich are regularly found in HVG mice and which are also thought to predisposeto DIC. (Am J Pathol 79:131-146, 1975)

Hosr-vERsus-GRA1r (HVG) syndrome is a lethal disease com-plex which occurs in parental strain mice perinatallv inoculated withF1 hvbrid spleen cells. Billingham and Brent 1 were probably the firstto observe some features of HVG disease when thev noted "gross spleno-megalv" and "conspicuouslv hypertrophied lymph nodes" in 5 of 15 Amice neonatallv inoculated with (C57 X A) F1 hybrid spleen cells. Workin this laboratorv has shown that, in addition to massive lymphospleno-megalv, C3H and RFMI mice perinatally inoculated with F1 hybridspleen cells develop thrombocytopenia, intestinal hemorrhage, thymicatrophv, renal disease due to immune complexes, and diffuse and focalhepatic necrosis.24 Strong support for the hypothesis that the directionof the reaction was principallv host versus graft was provided by ex-periments which showed that suppression of host immunologic reac-tivitv prevented the disease.2Although F1 hybrid versus parent reactions have been reported,5"

From the Department of Pathology, Medical College of Virginia, V?irginia Common-wealth University, Richmond, Va.

Supported bv Grants AI-10136, CA-16112 and HL-09622 from the National Insti-tutes of Health, US Public Health Service and by the Louis and Marguerite Privat Me-morial Fund.

Accepted for publication December 12, 1974.Address reprint requests to Dr. Richard C. Hard Jr, Department of Pathology-, NIedical

College of Virginia, MCV Station, Richmond, VA 23298.

131

132 HARD AND STILL American Journalof Pathology

the pathologic changes observed in HVG syndrome must be regarded asexceptional results according to the rules of transplantation in inbredmice.7 The parental strain host should either reject or become tolerantof the semiallogenic F1 hybrid cells. In neither case should there bedisease. To explain how HVG syndrome could occur, it was postulatedthat premature exposure of the immune response system to subtolero-genic doses of histoincompatible F1 hybrid cells resulted in a chronicallogenic reaction manifested by the observed lymphoproliferative dis-order and antibody-antigen complexes.3The work reported here was undertaken primarily to investigate the

cause of the hepatic necrosis regularly found in RFM mice which hadreceived (T6 X RFM)F1 hybrid spleen cells in the perinatal period.The previous findings of fibrin thrombi in renal glomeruli 3 and throm-bocytopenia 2 indicated that disseminated intravascular coagulation(DIC) might be the cause.DIC is an abnormal state of accelerated intravascular formation of

fibrin, usually accompanied by increased fibrinolysis.8 The situation be-comes clinically significant when depletion of clotting factors results inhemorrhage. If the rate of formation of fibrin thrombi outstrips the lyticprocess, infarction may be the consequence.The plan was to evaluate histopathologic, hematologic and serum

protein changes in RFM/(T6 X RFM)F1 mice in order to determine ifthe tentative diagnosis of DIC could be substantiated, and if predispos-ing factors could be identified.

Materials and Methods

MiceAll mice used in these experiments were taken from our own conventional colony.

The RFM/Al (+) (RFM) mice were descendents of outbred RFM/Up mice,9 inturn derived from RF mice. They have been maintained by brother-sister matingsfor more than 20 generations since their acquisition from Dr. Robert Allen, for-merly of Oak Ridge National Laboratory. Mice of this subline now accept skingrafts permanently from other members of the same subline. Our T.T. (T.) mice,homozygous for the characteristic chromosome markers, have been similarly inbredsince receipt of these Harwell-derived mice from Dr. John Trentin of Baylor Uni-versity. The (Te X RFM) F1 hybrids were always formed by mating T. femaleswith RFM males. F1 hybrids accept T6 and RFM skin grafts indefinitely. RFMhosts reject (T, x RFM) F1 hybrid skin between 12 and 16 days after grafting.

Formation of Chimeras

All experimental chimeras were formed by the neonatal inoculation of RFMmice with (T. x RFM)F1 hybrid spleen cells in dosages of 5 x 106 intravenouslyand 10 x 106 intraperitoneally. At 7 days, a booster dose of 100 x 106 F1 hybrid

Vol. 79, No. 1 DIC IN HVG SYNDROME 133April 1975

spleen cells was given intraperitoneally. Control animals were RFM littermateswhich had received isogenic RFM spleen cells on the same schedules, or were un-treated.

L;ght MicroscopyPieces of lver and kidney, together with whole spleens, lymph nodes, thymi and

femurs were fixed in buffered formalin. Sections of all tissues were routinely stainedwith hematoxylin and eosin. Liver, kidney and some spleens were also stained forfibri with phosphotungstic acid-hematoxyhn (PTAH).

Elnctron MIcros_opyPieces of liver and kddney were fixed in either 1% osmium tetroxide for 1 hour

or in 4% buffered guarayde for 2 hours, both in the cold. Ghtaraldehyde-fixed material was p d i 1% osmium te de for 1 hour. All material waseventally embeded in Maraglas/DER. Sections were studied in a Siemens El-miskop IA at 60 kV.

HanhTotal white blood cell counts were done using a hemocytometer. Wright-stained

blood films were studied for differential white cell comts, quantitative estimationof platelets and morplogic appearances of red blood cels. Blood for these stud-ies was obtained frm the roorbital plexus. The presence of fecal occult bloodwas detected by the phenolphthalin method 10

Serum and Urinary Prein StudiesAll serum studies were done on individual samples of blood drawn from the

hearts of mice anethetized with sodium pentobarbitaL Total serum proteins weredetermined by the method of Lowry et aLt" Electphoretc separations were doneon cellulose acetate stips at pH 8.6 in 0.075 M barbital buffer. Tracings of thePonceau-S-stained strips were made with a Beckman Model R-11O densitometer.Albumen concentrations were calculated from the percentage of the area under thealbumen peak and the total serum protein concentration. Immunoglobuin concen-trations were determined by radial immuIoiffusion,12 using agar plates and mu-rine immunoglolin standards from Meloy Laboratories. Urinary proteins wereroughly quantitated with Ames' Labstix@.

SacsThe powerful Mann-Whitney U test13 was used for analyses of white blood cel

and neutrophil coumts becuse of the great differcs in experimental and controlvariances. Analyses of data on serum immunoglobulin were done with the one-sided t test after logarithmic transformation of the values.

ResultsNine experimental RFM/(T6 X RFM)Fl mice and 7 littermate con-

trols matched for age were bled and sacrificed when the HVG miceappeared moribund at ages ranging from 31 to 52 days. Because no dif-ferences were noted between injected and uninjected controls, theywere considered together.


Clinical Course

Experimental mice appeared healthy and gained weight normallyuntil 5 days or less prior to death. Signs of imminent death includedslowed growth or slight loss of weight, lethargy, ruffled fur and de-creased body temperature. Facial puffiness and ascites were observedin some cases.

Gross Pathology

Anasarca was noted in 4 of the 9 experimental mice. Three patternsof hepatic necrosis were observed. The lesions appeared as small yel-lowish white foci with red borders located at the liver edges, or as dif-fusely congested and hemorrhagic areas, or as yellowish green discolora-tion of one or more lobes. The kidneys were usually pale. As describedpreviously,2 lymph nodes and spleen were greatly enlarged, and thethymus was shrunken. Splenic infarcts were noted in 2 cases. Lymphnodes were sometimes hemorrhagic, indicating internal hemorrhage.Areas of white consolidation were noted in the lungs of 2 experimentalmice.

Histopathology of the Liver

Light Microscopy

The infarcts seen in 8 of the 9 cases of HVG syndrome varied in sizefrom small subcapsular foci (Figures 1 and 2) up to large confluentareas involving whole lobes, and in age from fresh to approximately3 days. Fibrin deposits (Figure 1) and platelet-fibrin thrombi were seenin the sinusoids or veins of all 9 experimental animals, but never inarterioles. The cellular infiltrates (Figure 2) were usually perivascularin location and were composed of lymphoid cells, plasma cells, and otherunidentifiable mononuclear cells, as well as mature and immature poly-morphonuclear (PMN) cells. There was a rough correlation betweenthe numbers and size of the infiltrates and the extensiveness of the in-farctive process.

Electron Microscopy

Thin layers of fibrin were found lining the walls of small vessels (Fig-ure 3). Some of this fibrin showed cross striations at approximately220-A intervals; most did not. Previous studies have shown that suchcross striations are not necessary for the recognition of fibrin in tissues.'4


Histopathology of the Kidney

Light Microscopy

As described previously 3 the glomeruli of HVCG mice were largerthan those of controls and were composed of capillarv loops thickenedby eosinophilic material. By immunofluorescent studies,3 immunoglobu-lin deposits have been visualized in the granular pattern typical of im-mune complexes. Studv of sections stained with PTAH revealed fibrinin glomerular capillaries but not in arterioles. The absence of fibrinthrombi from arteries and arterioles mav explain the absence of renalcortical necrosis in all cases of HVG seen to date.

Electron Microscopy

Previous studies have shown electron-dense deposits on both sides ofthe basement membrane. An occasional subendothelial deposit showed"finger print" configurations considered to be characteristic of systemiclupus erythematosus.3 In the present studv, fibrin, usuallv identifiablein this situation bv its characteristic cross striations, could be seen inthe glomerular capillaries, at times plugging some of them (Figure 4).Subepithelial deposits consisting at least partlv of striated fibrin werealso present (Figures 5 and 6).

Histopathology of Other Organs

Hvperplasia of unidentified stem cells in the red pulp was the prin-cipal reason for splenomegalvT. There was marked depletion of lympho-cvtes in the periarteriolar, thlvmic-dependent areas in all cases, as pre-Viously described.'316 Additionallv, germinal centers were unidentifiablein 7 of 9 cases. Fibrin deposits were not seen in either infarcted orintact spleens. Lymph nodes had one or more germinal centers in thecortex usuallv with abundant lvmphocytes. The subcortical, thvmic de-pendent areas and the medullarv cords were markedlv enlarged byhvperplasia of reticular cells, and infiltration of large numbers of plasmacells and PMNrNs. The degree of lvmphocvtic depletion in these twoinner areas varied from moderate to severe. Mfultinucleate giant cellswere found in the nodes, especiallv those around the thvmus. The cor-tex of the thvmus was severelv depleted of thvmocvtes in all cases ofHVG disease. Nfegakarvocvtic hvperplasia was the most consistent find-ing in studies of femoral marrow. Development of platelets appeared toproceed normally, both bv light and electron microscopic evaluations.MIveloid hvperplasia correlated fairly well with the granulocytosis seenin studies of peripheral blood (see below). The two pulmonarv lesionsnoted grossly were due to severe necrotizing pneumonitis.


Hematology

Sequential studies revealed progressively severe thrombocytopeniain all HVG mice. Eight of the 9 experimental animals had an estimated90% depletion of their platelets and strongly positive (3+) tests forfecal blood (Table 1). The ninth case had an estimated 75% decreaseand no detectable intestinal blood loss. Increased bleeding from theorbit at the time of sampling and poor clot retraction were correlatesof this important hematologic finding.

Total white blood cell counts of experimental mice ranged from 13,050to 211,150/cu mm and were elevated (P < .005) above control valuesof 3,950 to 11,100/cu mm. Absolute and relative granulocytosis waspresent in every case of HVG disease, usually with a marked left shift(Table 1). The range of counts of neutrophils was from 5,900 to 175,250/cu mm for HVG mice and from 350 to 1,100/cu mm for controls (P <.005). Because of absence of leukemic changes in the bone marrow, thediagnosis of leukemoid response was made even in the cases with veryhigh counts and immature forms including myelocytes in the blood. Asnoted by another worker,17 it can be extremely difficult to distinguishbetween leukemoid responses and leukemia in RFM mice. Plasma cellswere observed occasionally in peripheral blood. Anemia (HVG hemo-globin 7.7 g/dl versus 14.2 g/dl for controls), increased polychro-masia, anisocytosis, poikilocytosis and occasional nucleated red bloodcells were all seen, but fragmented red cells (helmet cells) were not.

Serum and Urinary Protein StudiesMarked hyperglobulinemia was detected in all HVG mice, both by

electrophoresis and quantitative analyses of immunoglobulins. The mostspectacular differences were seen in IgG1 levels where values for ex-perimental mice ranged from 530 to 1,670 mg/dl, while control valuesvaried only from 15 to 47 mg/dl (Table 1). The IgG1, IgA and IgMvalues seen in experimental mice were significantly greater (P < .01)than control values. Differences between HVG and control IgG2 valueswere significant at the P < .02 level. Marked hypoalbuminemia waspresent in the 4 HVG mice with anasarca.

Urinary protein loss averaged 216 mg/dl in experimental mice andundoubtedly reflected the glomerular damage. Only one control lost asmuch as 30 mg protein/dl of urine.

DiscussionThe pathognomonic finding of intravascular fibrin deposits 18 in this

study of RFM/(T6 X RFM)F1 mice has clearly shown that dissemi-

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nated intravascular coagulation is a major complication of host-versus-graft disease. These microthrombi were the most obvious causes of theobserved hepatic and splenic infarcts. The marked thrombocytopeniamost likely reflected increased consumption of platelets, probably ac-companied by consumption of plasma clotting factors as well. Lowplatelet levels with hemorrhage are among the cardinal signs of acuteDIC.18A brief survey of factors reported 19 to predispose to DIC shows that

several are present in parent/F1 mice with HVG disease. Stasis of bloodhas been thought to promote thrombosis since Virchow's time. It ispossible that the normally sluggish, poorly oxygenated hepatic bloodflow was further impeded by the innumerable perivascular infiltratesand intrasinusoidal foci of extramedullary hemopoiesis. The resultanthypoxia and acidosis 20 of the liver could induce DIC by activation ofboth intrinsic and extrinsic clotting mechanisms 21 and by impairedclearance of activated plasma procoagulants.22Immune complexes have been recognized as promotors of DIC, and

are emerging as factors of major importance in the pathogenesis ofHVG disease. Their presence in parent/F1 mice was established by thepathognomonic23 finding of subepithelial, granular deposits of immuno-globulins in the renal glomeruli.3 McKay24 suggested that the early effectsof immune complexes on coagulation might be a clinically inapparent,increased rate of consumption of clotting factors. If clearance of acti-vated clotting factors by the reticuloendothelial system were impaired,acute DIC would be superimposed with sudden appearance of fibrinthrombi and thrombocytopenia and hemorrhage. Indications that thisprogression from chronic to acute DIC occurred in HVG mice wereprovided by observations of progressive declines in platelet levels priorto the acute terminal episode. Henson 25 revealed the mechanism bywhich antigen-antibody complexes interact with the clotting systemwhen he demonstrated platelet aggregation and lysis following expo-sure to complexes coupled with complement. Activation of the intrinsicclotting system would presumably have followed.The renal component of HVG syndrome may also have contributed

in a more indirect way to chronic DIC. The abnormal platelet aggrega-tion observed in some cases of chronic active renal disease has beenattributed to an upset in the equilibrium between plasma proteins en-hancing or inhibiting platelet function following loss of inhibitors inthe urine.26 Proteinaceous inhibitors of platelet aggregation have beenfound in the urine of patients with active glomerular disease.26The roles of granulocytes in pathogenesis of DIC and HVG are poorly


understood. That granuloevtes are important in the initiation of DICwas shown some vears ago bv Thomas and Good2 when thev demon-strated that intravascular coagulation associated with endotoxin injec-tions could be prevented if the experimental animals were first madeneutropenic bv treatment with nitrogen mustard. Possible mechanismsfor the exacerbation of DIC in HVG mice with neutrophilia includeactivation of thrombin in association with platelets and antigen-anti-bodv-complement complexes, and increased platelet aggregation withincreased release of vasoactive amines and nucleotides.28 It is interestingto note that there is an increased incidence of DIC in patients withvarious types of mvelogenous leukemia,"9 a disease to which mice ofthe RFM strain are predisposed.30The elevated gamma globulin levels seen in the HVG mice may have

been important contributors in DIC. Bang et al noted that increasedconcentrations of 7S globulin could enhance platelet aggregation.The results presented here support the thesis that acute DIC with

intestinal hemorrhage and hepatic infarction was the cause of death inRFMI/(T6 X RFMI )F1 mice. It is likelv that these terminal events werepreceded by a chronic, clinically inapparent state of DIC until the com-pensatorv replacement of clotting factors and fibrinolvtic activity couldno longer keep pace.

Although one intermediary mechanism of HVG disease mav haveBeen discovered, the causes of some other pathologic findings havenot. It is not clear why the liver is the main target of the DIC processin RFMI/(T6 X RFMl)F1 mice. The widespread and often massive he-patic infarcts appeared out of proportion to the size of the fibrin micro-thrombi. This morphologic discrepancy might be attributed to very ac-tive fibrinolysis. Superimposition of another, as vet unknown process oragent is not ruled out. Focal areas of hepatic necrosis have also beenseen in C3H/ ( C3H X T6 ) F1 mice with HVG disease, but intestinal hem-orrhage appears to be the principal sign in DIC in this chimeric system.Differences that mav be important in the pathogenesis of large infarctsin RFM/ (T6 X RFMI)F1 mice include higher numbers of blood granu-locytes, higher immunoglobulin levels and increased numbers of peri-vascular infiltrates. Focal and sometimes confluent areas of hepaticnecrosis have been observed in NZB mice 31 which are genetically pre-disposed to autoimmune diseases, and in mice suffering from graft-versus-host (CGVH) disease.3' The focal areas of bland necrosis observedin mice thymectomized as newborns were thought to be due to murinehepatitis virus.33 Clinically, hepatic infarcts and intravascular fibrin de-posits are seen in eclampsia.8 Because eclampsia, like HVG disease, fol-


lows exposure of the host to foreign cells, parent/F1 chimeras may proveto be experimental models for further etiologic studies of this diseaseof pregnancy.

It is apparent that immune complexes are another intermediarymechanism of HVG disease. They are the most likely cause of the renalmanifestations of HVG syndrome and probably trigger the observedDIC. There is little known about the basic causes of relentlessly pro-gressive formation of immune complexes. However, comparison of threeexperimental models in which immune complexes are seen reveals somesimilarities that may be significant. Immunopathologic studies of NZBmice and some of their F, hybrids, and mice with GVH and HVG dis-eases have shown that they all exhibit increased immunologic reactivityin the early stages.15'34'35 Later, depletion of lymphocytes 15,16,31,35 wasaccompanied by defects in cell-mediated immunity.3547 Identification ofthe antigenic component of the antigen-antibody complexes involved inHVG syndrome may help to understand why they are formed. Prelimi-nary studies 38 have failed to detect antibodies either to cells bearingT6 histocompatibility antigens or to nucleoproteins. Fudenberg39 haspostulated that immune complex diseases are due to abnormal responsesto viral antigens in cases of genetic or acquired T cell deficiency. Im-mune complex disease can be exacerbated in NZB mice by viral infec-tions.40 Chronic GVH reactions have been shown to activate endogenousoncorna viruses.4' The role of infectious agents in HVG disease is notyet known. Because the nature and sequence of the aberrant immuno-logic responses are similar in the three models, it is tempting to specu-late that the basic cellular defects that lead to immune complex forma-tion might also be similar-genetically determined in the case of NZBmice and induced in GVH and HVG diseases. It remains to be seen ifDIC as a consequence of immune complexes is also causally related tothe hepatic necrosis seen in NZB and GVH mice.

References1. Billingham RE, Brent L: Quantitative studies on tissue transplantation im-

munity. IV. Induction of tolerance in newborn mice and studies on the phe-nomenon of runt disease. R Soc Lond Philosoph Trans (Series B) 242:439-477, 1958

2. Hard RC Jr, Kullgren B: Etiology, pathogenesis, and prevention of a fatalhost-versus-graft syndrome in parent/F1 mouse chimeras. Am J Pathol 59:203-224, 1970

3. Hard RC Jr, Moncure CW, Still WJS: Renal lesions with organized depositsand lipid as part of the host versus graft syndrome in parent/F1 mouse chi-meras. Lab Invest 28:468-476, 1973


4. Hard RC Jr: Hepatic lesions in parent/F1 mouse chimeras with host versusgraft syndrome. Am J Pathol 74:84a-85a, 1974 (Abstr)

5. Celada F, Welshons WJ: Demonstration of F1 hybrid anti-parent immuno-logical reaction. Proc Natl Acad Sci USA 48:326-331, 1962

6. Ramseier H, Lindenmann J: Similarity of cellular recognition structures forhistocompatibilty antigens and of oombining sites of corresponding alloanti-bodies. Eur J Immunol 2:109-114, 1972

7. Snell GD, Stimpfling JN: Genetics of tissue transplantation. Biology of theLaboratory Mouse. Edited by EL Green. New York, McGraw-Hill Book Co,1966, pp 458-459

8. McKay DG: Disseminated Intravascular Coagulation: An IntermediaryMechanism of Disease. New York, Harper & Row, Publishers, Inc, 1964

9. Popp DM, Amos DB: An H-2 analysis of strain RFM/Un mice. Transplant3:501-508, 1965

10. Gettler AO, Kave S: The phenolphthalin test for the detection of "occult"blood. Am J Clin Pathol (Tech Section) 13:77-79, 1943

11. Lowry OH, Rosebrough NJ, Farr AL, Randall RJ: Protein measurementwith the Folin phenol reagent. J Biol Chem 193:265-275, 1951

12. Fahey JL, McKelvey EM: Quantitative deternination of serum immuno-globulins in antibody-agar plates. J Immunol 94:84-90, 1965

13. Siegel S: Non-Parametric Statistics for the Behavioral Sciences. New York,McGraw-Hill Book Co, 1956, pp 116-127

14. Still VJS, Boult EH: Electron microscopic appearance of fibrin in thin sec-tions. Nature 179:868-869, 1957

15. Hard RC Jr: Immunodeficiency and depletion of thymic dependent lympho-cytes in host versus graft disease. Proc Soc Exp Biol Med 146:30-36, 1974

16. Hard RC Jr: Correlation of immunological functions with splenic histopa-thology during the predlinical stages of host-versus-graft syndrome in parent-F1mouse chimeras. Transplant 17:613-623, 1974

17. Clapp NK: An Atlas of RF Mouse Pathology: Disease, Descriptions andIncidences. Springfield, Va, National Technical Information Service, 1973

18. Merskey C, Johnston AJ, Kleiner GJ, Whol H: The defibrination syndrome:Clinical features and laboratory diagnosis. Br J Haematol 13:528-549, 1967

19. MIcKay DG: Tissue damage in disseminated intravascular coagulation:Mechanisms of localization of thrombi in the microcirculation. Thromb DiathHaemorrh (Suppl 36):67-81, 1969

20. Broersma RJ, Bullemer GD, Mammen EF: Blood coagulation changes inhemorrhagic shock and acidosis. Thromb Diath Haemmorrh (Suppl 36):171-176, 1969

21. Pechet L, Groth CG, Daloze PM: Changes in coagulation and fibrinolvsisafter orthotopic canine liver homotransplantation. J Lab Clin Med 73:91-102, 1969

22. Deykin D: The role of the liver in serum-induced hypercoagulability. J ClinInvest 45:256-263, 1966

23. Cochrane CG, Koffler D: Immune complex disease in experimental animalsand man. Adv Immunol 16:185-264, 1973

24. McKay DG: Diseases of hypersensitivity. Arch Intern Med 116:83-94, 196525. Henson PM: Mechanisms of release of constituents from rabbit platelets by


antigen-antibody complexes and complement. I. Lytic and non-lytic reac-tions. J Immunol 105:476-489, 1970

26. Bang NU, Heidenreich RO, Trygstad CW: Plasma protein requirementsfor human platelet aggregation. Ann NY Acad Sci 201:280-299, 1972

27. Thomas L, Good RA: Studies on the generalized Shwartzman reaction. I.General observations concerning the phenomenon. J Exp Med 96:605-624,1952

28. Henson PM: Mechanisms of release of constituents from rabbit platelets byantigen-antibody complexes and complement. II. Interaction of platelets withneutrophils. J Immunol 105:490-501, 1970

29. Didisheim P, Bowie EJ, Owen CA Jr: Intravascular coagulation-fibrinolysis(ICF) syndrome and malignancy: historical review and report of two caseswith metastatic carcinoid and with acute myelomonocytic leukemia. ThrombDiath Haemmorrh (Suppl 36) :215-231, 1969

30. Upton AC, Jenkins VK, Walburg HE Jr, Tyndall RL, Conklin JW, Wald N:Observations on viral, chemical and radiation-induced myeloid and lymphoidleukemias in RF mice. Natl Cancer Inst Monogr 22:329-347, 1966

31. Howie JB, Helyer BJ: The immunology and pathology of NZB mice. AdvImmunol 9:215-266, 1968

32. van Bekkum DW, de Vries MJ: Radiation Chimeras. New York, AcademicPress, Inc, 1967, pp 150-152

33. East J, Parrott DVM, Chesterman FC, Pomerance A: The appearance ofa hepatotrophic virus in mice thymectomized at birth. J Exp Med 118:1069-1082, 1963

34. Evans MM, Williamson WG, Irvine WJ: The appearance of immunologicalcompetence at an early age in New Zealand black mice. Clin Exp Immunol3:375-383, 1968

35. Elkins WL: Cellular immunology and the pathogenesis of graft versus hostreactions. Prog Allergy 15:78-186, 1971

36. Teague PO, Yunis EJ, Rodey G, Fish AJ, Stutman 0, Good RA: Autoim-mune phenomena and renal disease in mice: Role of thymectomy, ageing,and involution of immunologic capacity. Lab Invest 22:121-130, 1970

37. Hard RC Jr: Apparent lack of T cells in parent/F1 mouse chimeras withhost versus graft disease. Fed Proc 33:645, 1974 (Abstr)

38. Hard RC Jr, Still WJS: Unpublished data39. Fudenberg HH: Genetically determined immune deficiency as the predis-

posing cause of "autoimmunity" and lymphoid neoplasia. Am J Med 51:295-298, 1971

40. Tonietti G, Oldstone MBA, Dixon FJ: The effect of induced chronic viralinfections on the immunologic diseases of New Zealand mice. J Exp Med132:89-109, 1970

41. Hirsch MS, Black PH, Tracy GS, Leibowitz S, Schwartz RS: Leukemiavirus activation in chronic allogenic disease. Proc Natl Acad Sci USA 67:1914-1917, 1970

AcknowledgmentsWe thank Dr. Edward F. Meydrech for statistical analyses, Susan Dennison for ex-

pert technical assistance, and Dr. Lyman Fisher for critical review of the manuscript.

Fig 1-The subcapsular hepatic infarct seen at the left is associated with a fibrin deposit(arrow) in a small vein. Within the sinusoids of the necrotic area are entrapped degenerat-ing red cells, leukocytes and probably hemopoietic cells. The parenchymal cells seenin the right third of the photomicrograph appear shrunken but still viable amidst dilated,congested sinusoids (PTAH, x 300). Fig 2-The subcapsular infarct of the liver seenat the left is associated with two infiltrates at its interior border and one in a nearby portalarea (upper right). These infiltrates are comprised predominately of mononuclear cells andsome polyrnorphonuclear cells. Additionally, there are numerous foci of extramedullaryhemopoiesis in the dilated sinusoids (PTAH, x 25).

Fig 3-Liver sinusoidal vessel lined by fibrin (F) and containing two platelets (x 8500).

Fig 4-Glomerular capillary plugged by fibrin, most of which, at higher magnification,was found to be striated. Note the fusion of epithelial cell foot processes (x 12,000).

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Fig 5-This glomerular capillary is plugged by platelets and amorphous material. Twosubepithelial deposits are present (arrows) and the epithelial cell foot processes are fused(X 14,500). Fig 6-Higher magnification of previous figure. At this power, striatedfibrin is seen on both sides of the basement membrane (arrows) (X 32,000).

intravascular fibrin deposits, hepatic infarcts and

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