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Dr C G Lopez
Ex Transfusion Medicine Unit
University Malaya Medical Centre
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Innate Non SpecificImmune Response
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Innate immune defensesNon-specific
This system does not confer long-lastingimmunity against a pathogen.
The innate immune system is the dominant
system of host defense
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Innate immune defensesInvolves the following:
phagocytic cells (neutrophils, monocytes,
and macrophages)cells that release inflammatory mediators
(basophils, mast cells, and eosinophils)
natural killer cells (NK cells)
complement proteins
cytokines
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anatomical barriers
mechanical removal
bacterial antagonism
phagocytosis
pattern-recognition receptors,
antigen-nonspecific defense chemicals,
complement pathways
Innate immune defenses
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Innate ImmunityDesigned to recognize molecules ( PAMPS) shared by groups
of related microbes. Pathogen-Associated Molecular Patterns
( PAMPS ) include
- LPS from the gram-negative cell wall,
- peptidoglycan and lipotechoic acids from the gram-positive cell wall
- bacterial and viral unmethylated DNA
- bacterial flagellin,
the amino acid N-formylmethionine found in bacterial proteins,
double-stranded and single-stranded RNA from viruses
glucans from fungal cell walls.
unique molecules displayed on stressed, injured, infected, or
transformed human cells also act as PAMPS.
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Response triggered when
microbes are identified by pattern
recognition receptors common to broadgroups of microorganisms
damaged, injured or stressed cells send outalarm signals, many of which (but not all) arerecognized by the same receptors as thosethat recognize pathogens.
Innate Response
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Response
njured or infected cells release eicosanoids
and cytokinesrostaglandins inflammation ( redness andswelling )
eicosanoids)
ytokines
eucotrenes attract WBC s to site of
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Tcells
B cells
Eosinophils
Killercells
Neutrophils
MACROPHAG
E
PLASMACELLS
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NeutrophilsMost abundant type of leukocytes in body
Highly effective in killing most bacteria and fungi.
PMNs contain many cytotoxic compounds that are non-specific needs to be regulated
PMN turnover regulated by apoptosis, a process of cell
death and safe removal by macrophages.
Apoptosis is accelerated following phagocytosis ofbacteria, a process that appears important for the
resolution of infection and inflammation.
neutrophils which have receptors for C3b
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Specific ImmuneResponse
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Cluster of genes MHC
or HLA region
encode HLA antigens ,
complement
components
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MHC Class l AntigensClass I molecules expressed by almost all the cells
of the body .Surface heterodimers that primarily present
peptides derived from the cytosol (viral bacteria,pollen, self peptides) to circulating CD8+ T cells.
Act as ligands for killer immunoglobulin receptors
(KIR), which regulate the cytotoxic activity ofnatural killer (NK) cells.
Epitopes that are part of class I histocompatibilitymolecules bind to CD8+ T cells
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Class II moleculesClass II molecules - Only specialized antigen-
presenting cells express these i.e dendriticcells phagocytic cells like macrophages and Bcells
alpha-beta heterodimer presents primarily
exogenously derived peptides (bacteria andchemical toxins) to circulating CD4+ T cells.
Epitopes that are part of class II
histocompatibility molecules bound to CD4+
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On almost all nucleated
cells and platelets
Soluble HLA antigens
found in plasma
B activated T
lymphocytes, dendritic
lymphocytes, macrophages
Alpha chainencoded by class 1
genes
Encoded by gene on
Chr 15 . May beconcerned with trans
membrane signaling
Alpha and beta
chains encoded
by class ll genes
CLASS I and II
HLA Antigens
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Stimulation through CD28 in addition to
the TCR provides a potent co-stimulatory
signal to T cells for the production of
various interleukins (IL-2 and IL-6 in
particular).
CD28
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Cytotoxic T cell Class 1Pathway
CD8+ T cells bind epitopes
part of class I
histocompatibility molecules ).
Almost all the cells of the
body express class I
molecules.
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Pathway
CD4+ T cells
bind epitopes
part of class ll
histocompatibility
molecules
The alpha-beta
heterodimer presents
primarily exogenously
derived peptides
(bacteria and
chemical toxins)to
circulating CD4+ T
cells.
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NK cellsUnlike B and T cells, NK cells do not express
unique clonally distributed receptors for specific
antigens, rather they express many differentpromiscuous stimulatory and inhibitory receptors
that can be divided into at least four
the killer immunoglobulin-like receptors (KIRs)
the C-type lectin receptors
the natural cytotoxicity receptors (NCRs)
toll-like receptors (TLRs)
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(KIRs) are Killer cell immunoglobulin-like receptors forclassical MHC I (HLA-A, HLA-B, HLA-C) molecules. Some
KIRs are specific for certain HLA subtypes
Provides the first line of defense against virus infection andtumor transformation.
KIRs - interacts with MHC class I molecules
- regulate the cytotoxic activity of natural killer (NK)
cells
- distinguish the tumor and virus infected
cells from normal body cells.
.
NK cells: KIR receptors
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SpecificClonal
Receptors
Non clonalReceptors
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LargegranularKiller Cellswith no T or Bmarkers
Killer Cells haveFc receptors . Canbind Ab alreadybound to tumourtargetProbably perforin
release mechanismkills cells
NK Cells bindtumour targets
NK Cells bind targetsby unknown mechanism. Kill cells thru perforin
release mechanism
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B cells B lymphocytes are both antigen-receiving and antigen-
presenting cells.
They can come in contact with these antigens by
- encountering them in the surrounding lymph
- being presented them by macrophages or
dendritic cells.
They bind intact antigens (e.g., virus particles, proteins)with their B cell receptor (BCR).
B lymphocytes process antigen by the class II
pathway for presentation to T cells.
Macrophage with Ag
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Macrophage with Agpresentedto T helper lymphocyte
B CELL
B CELL
Activated by cytokines
More Helper T cellsMore Cytotoxic T clls( CTLs)B cells to Plasma cells
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The Complement System
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Series of proteins found in fresh, normal serum.
Categorized as a beta globulin. Found in the beta region on protein electrophoresis C3 is complement component that is found in thehighest
concentration
Characteristics ofComplement
Complement components are identified by C andtheir number: C1, C2, C3 etcComplement products resulting from the splitting of
these proteins during the activation process arefollowed by a lower case letter: C3a, C3b, C1qIf complement complexes develop that haveenzymatic activity are written with a bar above the
top: C5b678
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Cell destruction through lysis Cell destruction through opsonization (enhanced
phagocytosis) especially with C3b Chemotaxis via certain split products acting as
chemical signals to the phagocytic cells Anaphylaxis again through the split products (C5a and
C3a), which promote inflammation. C5a and C3a
can bind with mast cells and basophils leading to
the release of histamine. This is turn:
Increases vascular permeability Smooth muscle contraction to preserve blood for vital
organs Increases cellular membrane adhesion
Complement controls various biological processes
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Complement and Innate Immune Response
Complement proteins bind to
- carbohydrates on the surfaces of microbes ( C4b)
- antibodies attached to these microbes or cells
Complement protease activity activated producing acatalytic cascade that amplifies the initial signal
Cascade results in production of peptides - attract immune
cells, increase vascular permeability, and opsonize (coat)
pathogen surface marking it for destruction.
Complement can kill cells directly by disrupting their
plasma membrane
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Comprises the :-
Classical pathway
Activated by antigen-antibody complexes and may
require all nine complement proteins.
Lectin pathway
Initiated by bacterial surface sugars (mannose) through the
mannose-binding lectin (MBL) protein and subsequent interaction
with mannose-binding lectin-activated serine proteases.
After that point pathway functions identically to classical pathway.
Alternative pathway
activated by LPS.
Complement Activation
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MASP: MBL-associatedserineproteinaseMBL: mannan-
binding lectin;MCP:
Alternative Pathway
Activated by C3b bound
to surface components
of microbes
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Proteins of the Classical pathway
CIin plasma as complex of - 6 mol CIq, 2 mol CIr,
2 mol Cls
Binding ofCIq - activates CIr , Cls
Activated Cl (serine protease ) cleaves C4 into
large fragment C4b and small C4 fragment
which diffuses away
C4b binds covalently to sugar residues on cell
surface glycoproteins
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Cleaved to C2b ( C2a diffuses away ) which
binds non- covalently to the large fragment C4b
Complex C4b*2a = C3 Convertase
C2
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C3b binds to covalently to
glycoproteins on phagocytese.g.
macrophages, neutrophils which
have receptors for C3b.
C3b coats particles e.g bacteria
before they are phagocytosed -
acts as opsonin
binds to C5 to form C3/ C5
Convertase
C3a diffuses into
plasma can bind tobasophils, mast cells
which release
vasoactive contents
histamine - acts as
anaphylotoxin )
Cleaved by C3 Convertase (called C4b* 2a before ) to
C3 Most abundant protein - 1.3 mg/ml
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C5
Cleavage of C5 by C3/C5 Convertase produces
set of complement proteins for membrane attack
called Membrane Attack Complex
C5a released into surrounding fluid acts as
anaphylatoxin ( like C3a ) and chemotactic
attractant for neutrophils
C5b serves as anchor for assembly of single
molecule each ofC6, C7, C8.
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Resulting complex C5b *6*7*8 guides C9
polymerisationAs many as 18 molecules of C9 form a
channel into the bi lipid layer of the cell
membrane allowing passage of ions andsmall molecules
Water enters cell by osmosis and cell lysis
Note: Membrane Attack Complex by another C5
convertase produced by theAlternate Pathway
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Contains 74 amino acids
Induces release ofgranular enzymes fromphagocytic cells production in neutrophils ofsuperoxide
anionvasodilatation increased vascular permeability induction ofthymocyte apoptosis duringsepsis
Excessive production of C5a by activationin sepsis can lead to an unregulated pro-inflammatory response, ultimately
resulting in tissue damage and multi-
C5a anaphylatoxin
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The Alternate ( Properdin ) Pathway
Does not require specific antibody to recognise potential
pathogens.
6 plasma proteins perform A, (C3), B (C3 proactivator ),
D, H, I, performcontinuous surveillance function
Activated by
- Organisms - bacteria, fungi, certain viruses
- virus infected cells- variety of polysaccharides & lipopolysaccharides
- human RBC lacking Decay Accelerating Factor
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The Alternate ( Properdin ) Pathway
C3b continuously generated in circulation in small
amounts formed from intervention with activators e.g cell
walls of bacteria, fungi, ect also endotoxins
C3b + Factor B ( C3 Proactivator ) forms complex
Complex C3bBbP ( activated Factor B )
Activates large numbers ofC3 molecules
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MASP: MBL-associatedserineproteinaseMBL: mannan-
binding lectin;MCP:
Alternative Pathway
Activated by C3b bound
to surface components of
microbes ( opsonised )
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Proteins of the MBL ( Mannose Binding Lectin )
Pathway
MBL made in liver in response to Macrophage
cytokines
MBL cascade initiated by MBL binding topathogen surface ( microbial carbohydrates)
MBL and 2 serum proteases C4 & C2 function
like CI to form C3 convertase
C3b combines with C5 & C6 to form C5
convertase
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All pathways converge at level of C3leading to
the cleavage products, C3a and C5a
terminal membrane attack complex,
C5b-9, which forms pores in the
membranes of bacteria and cells,ultimately causing their lysis.
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Summary of Effector Functions of Complement
Opsonization by C3b targets foreign particles for
phagocytosis
Chemotaxis by C5 a attracts phagocytic cells to site
of damage aided by increased permeability of the
capillary beds mediated by C3a and C5a
Assists in catabolism of Ag/Ab complexes and
elimination from body Deficiency of C2 associatedwith Lupus Erythematosis an auto immune disease
Lysis of antibody coated cells
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Immunoglobulins
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Each
antibodymoleculehas specificAg binding
site
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Macrophagereceptors bind
here
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Immunoglobin Molecule and Complement
CIq largest six globed structure
fused by shafts to single base
Serves as recognition unit that
binds to Fc region of Immunoglobin
moleculeto Ch2 domain - if IgG
to Ch 4 domain - if IgM
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IgGless efficient at complement binding thanIgM
Two IgG molecules with FcR binding sites
must be in close proximity for CIq to attach andactivate the full complement cascade
IgM has 5 Fc sites. One molecule of IgM is
capable of CIq binding to activate the full
complement cascade
Immunoglobin Molecules and Complement
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CI
Two IgG
moleculesrequiredto bind CIq
One IgMmoleculeable to spandistancebetween cellsand bind CIq
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IgM antibodies able to
span the distance and
bring about direct
agglutination
IgG antibodies unable to span
the distance cells are
sensitized but agglutination
not seen