Innate Immunity -M261 Spring 2005May 6, 2005 Kathleen A. Kelly
Reading:
Immunobiology (6th Edition) Janeway, Travers, Walpert & Capra Chapter 2 (p. 37-100), and Chapter 6 (p. 209-212)
Fundamental Immunology (5th Edition) Lippincott, Williams & Wilkins Chapter 17 (p.497-517)
Janeway, CA, et al. Innate Immune Recognition. Annu. Rev. Immunol. 20:197-252, 2002
Innate Immunity -M261 Spring 2004Kathleen A. Kelly
Innate immunity predates development of adaptive immunity
Does not produce protective immunity● No memory response● Prerequisite for developing adaptive immunity
Non-antigen-specific immunity● Found in plants, invertebrates and vertebrates
Innate Immunity1. Provides a barrier to prevent the spread of
infection● Mechanical (tight junctions, movement)● Chemical (fatty acids, enzymes, pH, antimicrobial
peptides)● Microbiological (normal flora)
● Mucosal surfaceso Nasopharyngeal, Oral, Respiratory, Intestinal tractUrogenital tract
● Skin (epithelial cells)o Wounds, burns, insect bites
Innate Immunity2. Identifies and eliminates pathogens
● Non-adaptive recognition systems● Activates molecules that target the microbe and aid
in it’s identification.o These factors may be expressed at the surface or
within cells, released from immune cells or are secreted and present within circulatory system
Innate Immunity3. Initiates an inflammatory response
● Reaction to injury or infectiono Trauma to tissues or cellso Presence of foreign matter (self vs. non-self)o Infectious agents (viruses, bacteria, fungi)
● Delivers effector molecules & immune cells to the site of infection
● Componentso Leukocytes & secreted factorso Blood vesselso Plasma proteins
Innate Immunity4. Provides signals to activate and regulate the
type of adaptive immune response generated● Stimulation of co-stimulatory molecules
o B7 family (CD80/86, PD-L, ICOSL)o TNFR family (OX40L)
● Induction of a cytokine/chemokine responseo Cytokines: IL-12, IL-23, IL-4o Chemokines: CXCR1, CXCR2, CCL20
• a variety and depends on stimulus
The Phases of Immunity
Identification of Microbes
Recognition● Receptors – Pattern Recognition Receptors
(PRRs)o Fixed in the genome, ie gene
rearrangement is not needed
● Distributiono Non-clonal, ie all cells of a class are
identical
Differentiation● Pathogen vs. Commensal
Identification of MicrobesPRR
● Recognize conserved molecular patterns on microbes called microbe associated molecular patterns (MAMPs) which are not present on the host
o Not limited to pathogens● Identify a class of microbes
o LPS, LTA, peptidoglycan, lipoarabinomannan, dsRNA, mannans, b-glycans
● MAMPs are often essential for microbe survivalAction Time
● Immediate activation of effectors● Delays need for adaptive immunity
Pattern Recognition Receptors (PRRs)
Three broad classes of PRRs based on expression profile, localization, function● 1) PRRs that signal an infection
o Include the Toll Receptor Family
o Expressed external or internally
o Activation of “pro-inflammatory” signaling pathways NFB and MAP kinase signaling pathways
• Antimicrobial peptides (Defensins) / lysozyme,• Inflammatory cytokines (TNF, IL-8, IL-1)
o Regulate activation of adaptive immune response• co-stimulatory molecules
● 2) Phagocytic (endocytic) PRRso Expressed on the surface of phagocytic cells
(MQs, PMNs, DCs)
o Mediate uptake of microbe into phagocytes
● 3) Secreted PRRso Secreted by MQs, epithelial cells, liver
o Activate C’, opsonize microbial cells, function as accessory proteins for MAMP recognition
Pattern Recognition Receptors (PRRs)
Toll-like Receptor Family
Curr. Opin. Hematology 9:2-10, 2002
PPR receptor● Found both on the
surface and within cells
● First discovered in Drosophila
● Currently 13 receptors
o 1-9 mouse & human
o 10 human
o 11-13 mouse
Toll-like Receptor family
Intracellular PRRs:Present in the Cytosol of Host Cells
1. Protein kinase receptor (PKR)● Activated upon binding to dsRNA (viruses)
o Blocks viral & cellular protein synthesis (eIF2)
o Activates NFB, MAP kinase STATs & IRF signaling pathways
o Induces apoptosis & IFN production of infected cells
2. 2’-5’ Oligoadenylate Synthase & RNaseL ● Family of IFN-inducible enzymes
o dsRNA activates OAS
o RNaseL degrades viral and host RNA
o Induces apoptosis
Intracellular PRRs:Present in the Cytosol of Host Cells
3. NOD proteins or nucleotide-binding oligomerization domain● Recognize intracellular peptidoglycan-derived
MAMPs and transduce signals ● three distinct functional domains
o carboxy-terminal ligand-recognition domain (LRD)
o centrally located NOD
o amino-terminal effector-binding domain (EBD) CARD domains in mammals Interacts and activates RIP2 inducing NFB and MAP-
kinase pathways
Structure of NOD Proteins
Inohara N, & Nunez G. Nat Rev Immunol. 2003 3:371
NOD Proteins
Inohara N, & Nunez G. Nat Rev Immunol. 2003 3:371
Phagocytic (endocytic) PRRsBind Carbohydrates 1. Macrophage Mannose Receptor (C-type lectin)
● Type 1 transmembrane receptor● Recognizes patterns of mannose residues in a certain spatial
orientation unique to microbes (CRD)● Only found on macrophages (not monocytes or PMNs)
2. Glucan Receptor (Dectin-1)● Type 2 transmembrane receptor● Recognizes -1,3 & -1,6 linked glycans● Present on all phagocytes
Phagocytic (endocytic) PRRs: Cont.
3. Scavenger Receptors● Recognize charged ligands
o Polyanionic ligands (ds-RNA, LPS, LTA)o Acetylated low-density lipoproteins (LDL)
● Found on all phagocytes● MARCO (macrophage receptor with collagenous
struction)o binds bacterial cell walls but not yeast
● Phagocytose apoptotic cellso new factor MFG-E8 (released from activated
macrophages and binds to apoptotic cells via phosphatidylserine)
Secreted PRRs activate the Complement (C’) System
Complement system is activated by innate immunity Recognition by Complement receptors (CR)
o CR1, CR2, CR3, CR4, C5a, C3a
Comprised of plasma proteins that when activated forms a triggered enzyme cascade
● Zymogens – activated by the cleavage of other proteaseso Precursor enzymes
Function● Facilitates the uptake & destruction of pathogens by phagocytes● Induces an inflammatory responses
b
C4b+
C2b
C3b+
Bb
Activation of C’ System
Secreted Pattern Recognition Molecules
Acute Phase Proteins
Activation of ComplementOpsonization of microbial cellsPrimarily produced by the liver but can be produced by phagocytes
Secreted Pattern Recognition Molecules
1. Collectins● Recognizes microbial carbohydrates (CRD domain)● Effector function mediated by collagenous domain ● Mannan-binding lectin (MBL)
o Recognizes patterns of mannose & fucose residues in a certain spatial orientation unique to microbes
o Initiates the lectin pathway of C’ cleaving C2 & C4
o Can function as an opsonin Binds a receptor on phagocytes (C1qRp)
● Surfactant proteins (SP-A / SP-D)o lung
Collectins
• Structure is conserved and similar to other proteins with similar function:
o Some Complement proteins & Mannose Binding Protein
o Binds to bacteria, fungi & viruses
• Function by binding microbes and are important for mediating phagocytosis of alveolar macrophages
Microbe
C-type Lectin domain
Collagen helix
-coiled helix
Secreted Pattern Recognition Molecules – Cont.2. Pentraxin
● Members includeo Serum amyloid protein (SAP)
o C-reactive protein (CRP)● Recognize phosphorylcholines on microbes ● Functions as an opsonins ● Binds to C1q & activate classical C’ pathway
Secreted Pattern Recognition Molecules – Cont.
3. Lipid Transferases● LPS binding protein (LBP)
o Opsonin● Bactericidal permeability increasing protein (BPI)
o Bactericidal protein 4. Peptidoglycan recognition proteins (PGRS)
● Recognizes peptidoglycans in evolutionarily distant organisms● 4 human PGRS● Function is unknown
o One has bactericidal effectso Triggers a serine protease cascade in insects
? Complement cascade ?
Inflammatory Response
Inflammatory Response
Leukocyte Adhesion
Naïve and Memory T Cells Travel in Different Paths
Naïve (have not seen their antigen) T cells travel in the blood and lymphatics
Memory T cells (have been activated by their antigen) can also travel through tissues
Lymphocyte Trafficking Patternsof Naïve T Cells
PeripheralBlood
Peripherallymphnodes
Lymphaticsystem
HEVGlyCAM-1
CD62L:selectin
ChemokinesCCL21 / SLCCCL19 / ELC (MIP-3)
CCR7:chemokine receptor
ICAM-1
Lymphocyte Trafficking Patternsof Naïve T Cells
PeripheralBlood
Peripherallymphnodes
Lymphaticsystem
HEVGlyCAM-1
CD62L:selectin
ChemokinesCCL21 / SLCCCL19 / ELC (MIP-3)
CCR7:chemokine receptor
ICAM-1
Lymphocyte Trafficking Patterns of Effector/Memory T Cells
Lymphaticsystem
Any TissuePeripherallymphnodes
Inflammation
PSGL-1:selectin41:Integrin
CXCR3: chemokine receptor
ChemokinesCXCL9 / MIGCXCL10 / IP-10CXCL11 / I-TAC
HEVCD44ICAM-1
Endothelial Cell
1. Tethering 3. Firm adhesion2. Triggering 4. Diapedesis
Lymphocyte
PathogensMacrophage
Cytokines
Chemokines
Stromal cells
Blood Vessel
Steps in Lymphocyte Trafficking
PhagocytosisPhagocytosis
● Definition: uptake of large particles (>0.5 m)● Actin-dependent, clathrin-independent● High rate & efficiency of internalization
Professional phagocytic cells● Macrophages● Neutrophils
These cells have phagocytic receptorso External receptors
FcR, CR3, Mannose receptoro Internal receptors
TLRs
Macrophages(MQ)
Blood - Called monocytes (1-6% WBC)Tissues - Called macrophages
● mature form of monocytes● normally found in tissues such as gastrointestinal
tract, lung, liver and spleen
Functions:● Phagocytose and kills after bactericidal mechanisms
are activated (T cells)● Produce cytokines/chemokines (initiates inflammation)● Is an antigen presenting cell (co-stim. Molecules)
Neutrophils(PMN)
Present in blood (55-60% of WBC)Not normally present in tissuesShort lifespan - 12 hoursFunctions:
● First at the site of infection/injury
Ingest and kill microbes after bactericidal mechanisms are activated (binding to pathogen)
Phagocytosis (MQ & PMN)
Active process initiated by binding to pathogenPathogen is surrounded and then internalized
Signaling Interactions during Phagocytosis
Ann. Rev. Immunol. 20:825-852, 2002
Killing MechanismsPhagosome - membrane bounded vesicle that
becomes acidifiedLysozome - granules that contain products that
damage or kill pathogens● Enzymes
o Lysozyme - dissolves cell walls of some bacteria
o Acid hydrolases - digests bacteria● Proteins
o Lactoferrin - binds Fe++ needed for bacterial growth
o Vitamin B12-binding protein● Peptides
o Defensins and cationic proteins - direct antimicrobials
Killing Mechanisms - cont.Respiratory Burst
● Activated following phagocytosis● Stimulated by PRR● Requires increased oxygen consumption ● Produces substances that are directly toxic to the
bacteriao Oxygen-derived products
O2-, H2O2 & Myeloperoxidase
o Nitrogen-derived products NO (nitrogen oxide) Produced by inducible NO synthase (iNOS) enzyme Enzyme is induced by cytokines (LT, TNF)
NADPH Oxidase Mitochondrial-independent respiratory burst
P47phox & p67phoxnormally resides in the cytoplasma.
P47phox becomes hyperhposphorylatedfollowing phagocytosis and binds to p67phox.
These components move to the membrane and bind the NADPH complex resulting in an active complex.
Enzyme Reactions of Respiratory Burst
Respiratory BurstNADPH NADP+ Superoxide
+ dismutase
2 O2 2 O- H2O2
Myeloperoxidase
● Enzyme which is stored in primary granules of PMN & MQ and uses the products of the respiratory burst.
● H2O2 + C1-Chloramines
Professional APC
Regulation of Adaptive Response
Veterinary Immunology & Immunopathology 91: 1, 2003
T cells Recirculate to “Find” Antigen-loaded Dendritic cells
GerminalCenter
EfferentlymphaticsAfferent
lymphatics
ParacorticalArea
FollicularArea
HEV
Mucosal Immunity – Reading Assignment
Immunobiology (6th Edition) Janeway, Travers, Walpert and Capra Chapter 10 (p. 432-445).
Neutra, MR et al Antigen sampling across epithelial barriers and induction of mucosal immune responses. Annu. Rev. Immunol. 14:275-300, 1996
Wright, JR. Immunoregulatory Functions of Surfactant Proteins. Nature Review Immunol. 5:58-68, 2005.
Cheroutre, H. Start at the beginning: new perspectives on the biology of mucosal T cells. Annu. Rev. Immunol. 22:217-46, 2004.
Weiner, H. Oral tolerance: immune mechanism and the generation of Th3-type TGF-beta-secreting regulatory cells. Microbes & Infection 3:947-954, 2001.
May 10, Spring 2004