October 12, 2004. IMMUNITY ADAPTIVEINNATE CELL MEDIATEDHUMORAL ANTIBODIES EFFECTOR SYSTEMS Fc...
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Transcript of October 12, 2004. IMMUNITY ADAPTIVEINNATE CELL MEDIATEDHUMORAL ANTIBODIES EFFECTOR SYSTEMS Fc...
October 12, 2004
IMMUNITY
ADAPTIVE INNATE
CELL MEDIATED HUMORALANTIBODIES
EFFECTOR SYSTEMSFc ReceptorsComplement
RECEPTORSEFFECTORS
CellsMolecules
ANTIGENS
Innate immunity
Adaptive immunity
Immunologic memory
First response to infection
Triggered by persisting infection
Protects against subsequent infection
Functions of innate immunity
Initial response to infection
Frequently is sufficient to eliminate the infection
Effector mechanisms of innate immunity are often used to eliminate pathogens in adaptive immune
response
Innate immunity stimulates adaptive immune response and influences the nature of the adaptive response
Receptors recognize pathogen associated molecular patterns (PAMP)
Nucleic acids unique to microbes (e.g. double stranded RNA or unmethylated CpG DNA)
Features of proteins found in microbes (e.g. N-formylmethionine)
Complex lipids and carbohydrates synthesized by microbes but not mammalian cellsLPS in gram-negative bacteria
Teichoic acids in gram-positive bacteriaMannose-rich oligosaccharides found in microbial
glycoproteinsHas evolved to recognize microbial proteins often essential
for their survival
Receptors of the Innate immune responseSpecificity inherited in genome
Expressed by all cells of a particular type- not clonally distributed
Trigger immediate response
Recognize a broad class of pathogens
c
Function
Recognize pathogen
Attract effector cells
Induce effector molecules
Contribute to innate immunity
Influence the nature of the subsequent adaptive immune response
Trigger inflammation
Overview of the events during inflammation
The recruitment of leukocytes and extravasation of several plasma proteins to a site of infection with activation of the leukocytes and proteins eliminating the infectious agents
Epithelium
Barriers to infectionMechanical
Chemical Cells
Infection
Epithelial barriers to infection
Mechanical: Tight junction of epithelial cells form a physical barrier
EpitheliumInfection
Epithelial barriers to infectionChemical
Antibacterial peptides (defensins)
Enzymes (e.g. lysozyme, pepsin)
Low pH
EpitheliumInfection
Epithelial barriers to infection
CellsMast cells
Intraepithelial T lymphocyes
B-1 B cells
EpitheliumInfection
CD5 B cell binds capsular polysaccharide
CD 5 cell secretes IgM anti-
polysaccharide antibody
IgM
Phagocytes
Neutrophils
Produced and lost in large number every day
Abundant in bloodNot present in healthy tissue but recruited to
site of infection
Short-lived (6 hours) and pus contains dead and dying neutrophils
Contain granules with anti-bacterial proteins and peptides
Can eliminate pathogens by phagocytosis
Phagocytes
Macrophages
Circulating precursors are called monocytes
Longer lived than neutrophils
Can divide at the site of infection
PhagocytesWhen pathogens cross the epithelial barrierthey are recognized by phagocytes in the
subepithelial connective tissues
Trapping,engulfment and destruction by phagocytosis
Phagocytes
When pathogens cross the epithelial barrierthey are recognized by phagocytes in the
subepithelial connective tissues
Trapping,engulfment and destruction by phagocytosis
Induction of co-stimulatory molecules
Cytokine secretion by phagocyte
Antigen uptake, processing and presentation
Neutrophils and monocytes are recruited from blood to sites of infection
Resident tissue macrophages that recognize microbes secrete cytokines and chemokines that act on endothelial cells to produce adhesion molecules and attract circulating neutrophils and macrophages
Neutrophils and macrophages have receptors that recognize microbes and stimulate their phagocytosis and killing
Receptors that directly bind microbes
Mannose receptors
Scavenger receptors
Integrins
Pathogen Associated Molecular Patterns
Not clonal
Neutrophils and macrophages have receptors that recognize microbes and stimulate their phagocytosis and killing
Receptors for opsonins
FcRs
CR1, 3 and 4(recognize cleavage products of C3)
Triggering these receptors both stimulates phagocytosis and activates the phagocytes
Neutrophils and macrophages have receptors Toll-like receptors
TLR-5:flagellin
Activation through these receptors triggers cytokine production and expression of co-stimulatory
molecules
TLR-2: zymosan from yeast,bacterial lipoproteins andlipteichoic acid and peptidoglycan on Gram-positive bacteriaTLR-4: LPS on Gram-negative bacteria; viral proteins
TLR-9: unmethylated CpG
Neutrophils and macrophages have receptors Seven-transmembrane -helical or G
protein-coupled receptors
Peptides containing N-formylmethionyl residues
Activation induces migration of cells from bloodthrough endothelium and production of microbicidal
substances
Receptors of this class recognize
Chemokines such as IL-8
C5a
Neutrophils and macrophages have receptors for cytokines such as IFN-, the major macrophage-activating cytokine
Macrophage Possessses Many Receptors
LPS receptor (CD14)
Mannose receptor
Scavenger receptors
Fc receptors
CD11b/CD18
Engulfment
Cytokine Secretion
Activation
TLRTLR
Antigen presentation
Deliver additional effectors molecules and cells to site of infectionProvide a physical barrier to prevent the spread of infectionPromote the repair of injured tissues
Role of inflammation in combating infection
Combined local effects increase inflmmatory response
1. Increase in vascular diameter lead to increased local blood volume--
heat and redness from reduced velocity of blood flow
2. Decreased blood flow allows leukocytes to better interact with the vascular endothelium
Extravasation:
Selectins recognize certain leukocyte glycoproteins causing
lymphocytes to roll. ICAM-1 on endothelium interacts with
LFA-1 (a.k.a. CD11a;Cd18) and CR3 (Mac-1) so that leukocytes
attach firmly to the endothelium, to cross the vascular endothelial wall and enter site of infection
3. Increase in vascular permebility leads to local accumulation of fluid-
swelling and pain--
accumulation of Igs, C’ and other blood protein in the tissue.
Combined local effects increase inflmmatory response
4. Mediators induce expression of adhesion molecules on the endothelium neutrophils and monocytes are recruited to the site5. Migration of leukocytes through tissues under the influence of chemoattractant molecules. Direct migration along a gradient of the chemokine that increases as get nearer the site of infection. Chemokines appear to bind to proteoglycan molecules so that they can remain cell associated to create the gradient.
CC chemokines promote the migration of monocytes: MCP-1, MIP-1β, RANTES
CXC chemokines promote migration of : neutrophils -8IL
An increase in vascular permeability leads to local accumulation of fluid
Swelling (edema)
Pain
Accumulation of Igs, complement and other blood proteins in tissue
Entry of fluid into blood at site of infection is prevented
TNF-
Local clots in small vessels are produced.
Fluid in tissue carries pathogen, either directly or within a phagocytic cell, via lymph to regional lymph nodes where an adaptive immune response is elicited
Sepsis
TNF-s released by macrophages
Infection spread to the blood stream
Septic shock requires signaling through TLR-4 (recognizes LPS) and mice (or humans) defective in TLR-4 do not experience septic shock
Vasodilation occurs with increased vascular permeability leading to shock
Mice defective in TLR-4 are highly sensitive to LPS containing pathogens.
TNF-, IL-1 and IL-6 are endogenous pyrogens which elicit acute-phase proteins
virus
IFN-, -IFNβ
Inhibit protein synthesis and DNA - replication in virus infected cells
Increase MHC class I expression and antigen presentation in all cells
- Activate NK cells to kill virus infected cells
Natural Killer Cells
Function against intracellular pathogens such as viruses
Tumor immunity
Activated by IFN-, IFN-β or IL-12
Must be able to distinguish infected from uninfected cells
Summary - Features of Innate Immunity
Triggered by germline encoded receptors of limited diversity
No lasting immunity or memory
Elicit cytokine release by phagocytes
Induced production of acute-phase proteinsElevate body temperature
Induce inflammation
NK cells are able to recognize infected or altered cells
B-1 B cells provide pathogen specific Abs of limited diversity in the absence of T-cell help
Properties of substances that elicit an adaptive immune response
Immunogen: Substance which is capable of eliciting a humoral or cell mediated immune response
B cells + antigen --> effector B cells (plasma cells) + memory B cells; Abs produced
T cells + antigen --> effector T cells (e.g. CTLs) + memory T cells
Antigen: a substance which reacts with an antibody or T-cell receptor
All immunogens are antigens but not all antigens are immunogens
Haptens: small molecules that are antigens (that is can react with Ab or TcR) but which cannot by themselves elicit an immune response
Hapten
(Dinitrophenol) Carrier
(BSA)
Haptens must be linked to a carrier to elicit an immune response. Abs are formed to both the hapten and carrier.
Reactivity with
Antiserum
against
Aminobenzene
o -aminobenzoic acid
m -aminobenzoic acid
p -aminobenzoic acid
Aminobenzene
(aniline)
o - aminobenzoic
acid
m -aminobenzoic
acid
p -aminobenzoic
acid
Small ligands often bind in a deep Ab pocket. There is a tight fit so Ab binding can distinguish structurally related but different haptens.
Epitope or antigenic
determinant is the part
of the immunogen that binds
Ab or the T C R
Abs are designed to interact with the surface of soluble antigens.
Essentially the whole surface of a globular protein can antigenic
B-cell epitopes
May be amino acids located next to each other in sequence (sequential determinant)
Or may be amino acids that are not next to each other in linear sequence but fold into proximity (non-sequential or conformational)
inject
antiserum
antibodies of differentspecificityaffinityisotype
{heterogeneity
anti-
anti-anti-anti-
TCR
MHC
Antigen presenting cell
T cell
EpitopeAgretope
T-Cell EpitopesT cells do not recognize soluble native Ag but instead recognize Ag that has been processed and is presented in association with MHC molecules
Cross reactivity
1. shared epitopes e.g.DNP BSA and DNP- globulin
2. structurally similar epitopes . . e g BSA and HSA
Reaction with other than immunizing Ag
Antigenic determinants on Abs
1. isotypic
constant region determinants that distinguish each
H and L chain class and subclass
2. allotypic
structurally different alleles of the same gene
3. idiotypic
structures unique to a variable region; may be
associated with Ag binding site
NEVER!!
genesgenes
genes
leu
leu
val
val
ANTIBODIES
aa191
or
offspring
For Abs there is allelic exclusion: the products of only one allele are present within one antibody
Isotype : separate constant region
gene. Everyone (who is normal)
has all of the genes for the
different isotypes
Allotype : multiple alleles exist in
the population for a particular
gene.
ForeignnessMust be recognized as "non-self" by the immune system
In general the greater the degree of foreignness, the stronger the response
What determines if something is effective in eliciting an immune response?
SizeBest immunogens usually at least 100,000 daltons
Most (but not all) substances smaller than 5000-10000 Da are poor immunogens
What determines if something is effective in eliciting an immune response?
Composition and Heterogeneity
Are processed and presented
Both the humoral and the cell-mediated immune response are aided by interaction with T cells. Antigen presenting cells present processed Ag in the context of MHC molecules to activate T cells
Molecules that cannot be degraded (e.g. D-amino acids) are poor immunogens
Treatment to increase uptake by antigen presenting cells improves immunogenicity
cross-linking
aggregation
attachment to insoluble matrices
What determines if something is effective in eliciting an immune response?
GenotypeMHC molecules which function in Ag presentation
B-cell and T-cell receptor genes
Genes that encode proteins involved in immune regulation
Route of injection and doseToo little or too much can induce "tolerance"
Boosters further expand B and T cells (memory)
Administration route determines which immune organs and cell populations will respond
Intravenous--> spleen
Subcutaneous--> lymph nodes
AdjuvantsEnhance immunogenicity of Ag
Prolong Ag persistence
Enhance co-stimulatory signalInduce granuloma formation
Nonspecifically stimulate lymphocyte proliferation
Granuloma: Nodule of inflammatory tissue composed of clusters of Activated macrophages and T lymphocytes often with associatedNecrosis and fibrosis.
AlumAluminum potassium sulfate
Causes precipitation
Results in Ag persistance
Increased size improves phagocytosis
Local chronic inflammatory response (granuloma -macrophage rich mass of cells)
Freund's AdjuvantIncomplete: Ag in aqueous solution, mineral oil, and emulsifying agent
Ag is slowly released
Complete: also contains heat-killed Mycobacteria
a muramyl dipeptide of the mycobacterial cell wall activates MΦ
Both result in granuloma formation