Transcript Innate Immunity

Innate Immunity -M261 Spring 2005
May 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 2004
Kathleen 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 Immunity
 1. Provides a barrier to prevent the spread of
infection
● Mechanical (tight junctions, movement)
● Chemical (fatty acids, enzymes, pH, antimicrobial
peptides)
● Microbiological (normal flora)
● Mucosal surfaces
o Nasopharyngeal, Oral, Respiratory, Intestinal tract
Urogenital tract
● Skin (epithelial cells)
o Wounds, burns, insect bites
Innate Immunity
 2. 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 Immunity
 3. Initiates an inflammatory response
● Reaction to injury or infection
o Trauma to tissues or cells
o Presence of foreign matter (self vs. non-self)
o Infectious agents (viruses, bacteria, fungi)
● Delivers effector molecules & immune cells to the
site of infection
● Components
o Leukocytes & secreted factors
o Blood vessels
o Plasma proteins
Innate Immunity
 4. 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 response
o Cytokines: IL-12, IL-23, IL-4
o 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
● Distribution
o Non-clonal, ie all cells of a class are
identical
 Differentiation
● Pathogen vs. Commensal
Identification of Microbes
 PRR
● 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 survival
 Action 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
 NFkB and MAP kinase signaling pathways
• Antimicrobial peptides (Defensins) / lysozyme,
• Inflammatory cytokines (TNFa, IL-8, IL-1)
o Regulate activation of adaptive immune response
• co-stimulatory molecules
Pattern Recognition Receptors (PRRs)
● 2) Phagocytic (endocytic) PRRs
o Expressed on the surface of phagocytic cells
 (MQs, PMNs, DCs)
o Mediate uptake of microbe into phagocytes
● 3) Secreted PRRs
o Secreted by MQs, epithelial cells, liver
o Activate C’, opsonize microbial cells, function as
accessory proteins for MAMP recognition
Toll-like Receptor Family
PPR receptor
Toll-like Receptor family
● 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
Curr. Opin. Hematology 9:2-10, 2002
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 (eIF2a)
o Activates NFkB, MAP kinase STATs & IRF signaling
pathways
o Induces apoptosis & IFNa/b 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 NFkB and MAPkinase 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) PRRs
Bind 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 b-1,3 & b-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 cells
o 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 proteases
o Precursor enzymes
 Function
● Facilitates the uptake & destruction of pathogens by phagocytes
● Induces an inflammatory responses
Activation of C’ System
b
C4b
+
C2b
C3b
+
Bb
Secreted Pattern Recognition Molecules
Activation of Complement
Opsonization of microbial cells
Primarily produced by the liver but can be produced by
phagocytes
Acute Phase Proteins
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
Collagen helix
Microbe
a-coiled helix
C-type
Lectin domain
Secreted Pattern Recognition Molecules
– Cont.
 2. Pentraxin
● Members include
o 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 effects
o 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 Patterns
of Naïve T Cells
CD62L:selectin
CCR7:chemokine receptor
Peripheral
Blood
HEV
GlyCAM-1
Lymphatic
system
ICAM-1
Peripheral
lymph
nodes
Chemokines
CCL21 / SLC
CCL19 / ELC (MIP-3b)
Lymphocyte Trafficking Patterns
of Naïve T Cells
CD62L:selectin
CCR7:chemokine receptor
Peripheral
Blood
HEV
GlyCAM-1
Lymphatic
system
ICAM-1
Peripheral
lymph
nodes
Chemokines
CCL21 / SLC
CCL19 / ELC (MIP-3b)
Lymphocyte Trafficking Patterns of
Effector/Memory T Cells
Inflammation
CXCR3: chemokine receptor
PSGL-1:selectin
a4b1:Integrin
Peripheral
lymph
nodes
Lymphatic
system
HEV
CD44
ICAM-1
Any Tissue
Chemokines
CXCL9 / MIG
CXCL10 / IP-10
CXCL11 / I-TAC
Steps in Lymphocyte Trafficking
1. Tethering 2. Triggering
3. Firm adhesion
4. Diapedesis
Blood Vessel
Lymphocyte
Chemokines
Pathogens
Stromal
cells
Endothelial
Cell
Cytokines
Macrophage
Phagocytosis
 Phagocytosis
● Definition: uptake of large particles (>0.5 mm)
● Actin-dependent, clathrin-independent
● High rate & efficiency of internalization
 Professional phagocytic cells
● Macrophages
● Neutrophils
 These cells have phagocytic receptors
o External receptors
 FcR, CR3, Mannose receptor
o 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 tissues
 Short lifespan - 12 hours
 Functions:
● 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 pathogen
 Pathogen is surrounded and then internalized
Signaling Interactions during
Phagocytosis
Ann. Rev. Immunol.
20:825-852, 2002
Killing Mechanisms
 Phagosome - membrane bounded vesicle that
becomes acidified
 Lysozome - 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
bacteria
o 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, TNFb)
NADPH Oxidase
Mitochondrial-independent
respiratory burst
P47phox & p67phox
normally resides in the
cytoplasma.
P47phox becomes
hyperhposphorylated
following 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 Burst
NADPH
+
2 O2
NADP+
2 O-
Superoxide
dismutase
H2O2
Myeloperoxidase
● Enzyme which is stored in primary granules of PMN &
MQ and uses the products of the respiratory burst.
● H2O2 + C1Chloramines
Professional APC
Regulation of Adaptive Response
Veterinary Immunology & Immunopathology 91: 1, 2003
T cells Recirculate to “Find”
Antigen-loaded Dendritic cells
Follicular
Area
Afferent
lymphatics
HEV
Paracortical
Area
Germinal
Center
Efferent
lymphatics
Mucosal Immunity –
Reading Assignment
May 10, Spring 2004
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 Th3type TGF-beta-secreting regulatory cells. Microbes & Infection 3:947954, 2001.