Post on 06-Apr-2018
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Immunoglobulin Structure and Function
, PhDMD
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Immunogobulin, Ig
What isImmunoglobulin?
Immunoglobulins are the critical
ingredients of humoral acquiredimmune response.
The immunoglobulins are a group of
glycoproteins present in the serum and
tissue fluids of all mammals.
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Immunoglobulins:Structure and
Function Definition: Glycoprotein molecules that are
produced by plasma cells in response to an
immunogen and which function as antibodies
Immune serum
Ag adsorbed serum
1 2
+ -
albumin
globulins
Mobility
Amount
ofprotein
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General Functions of
Immunoglobulins
Effector functions
Fixation of complement
Binding to mast cells , macrophages, NK cell
(Usually require Ag binding)
Ag binding
Can result in protection
Valence
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Basic Immunoglobulin Structure
Immunoglobulins - heterogeneous
Myeloma proteins - homogeneous
immunoglobulins
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Two Forms ofImmunoglobulin
Membrane-boundreceptor Soluble antibody
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Immunoglobulin Structure
Variable(V) &
Constant (C)
Regions
VL & CL
VH & CH
Hinge Region
CH1
VL
CL
VH
CH2
CH3
Hinge Region
Carbohydrate
Disulfide bond
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Structural Regions
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hypervariable
region
also called
Complementarity
Determining
Regions(CDRs),
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Immunoglobulin Fragments:
Structure/Function Relationships
Fab
Ag binding
Valence = 1
Specificity
determined by VH
and VL
Papain
Fc
Fab
Fc ( crystallizable)
Effector functions
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DomainsofImmunoglobulin
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Function ofImmunoglobulins
Recognition of antigen
Activation of complement
Opsonization
Antibody-dependent cell-mediated
cytotoxicity,ADCC
Mediate hypersensitivity type I
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Immunoglobulin Classes and
SubclassesImmunglobulin molecules are divided into
distinct classes and subclasses in terms of
the differences in amino acid sequence of
constant region of heavy chain,
i.e.,,,,andchains.
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Immunoglobulin Classes ofMammals
IgG - Gamma () heavy chains
IgM - Mu () heavy chains
IgA - Alpha () heavy chains IgD - Delta () heavy chains
IgE - Epsilon () heavy chains
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Five Classes ofImmunoglobulin
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IgG has a family of subclass, IgG1, IgG2, IgG3,
IgG4(cattle has no)
IgA is divided into two subclasses, IgA1 and
IgA2(sheep).
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Light Chain Types ofImmunoglobulin
Kappa ()
Lambda ()
All light chains have protein molecularweights of approximately 23,000 but can
be divided into two distinct types, namely
chain, chain, respectively
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IgA
Structure
Serum - monomer
Secretions (sIgA)
Dimer (11S)
J chain
Secretory component
JChainSecretory Piece
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IgA
Structure
Properties
2nd highest serumIg Major secretory Ig (Mucosal orLocal Immunity)
Tears, saliva, gastric and pulmonary secretions
Does not fix complement (unless aggregated)
Binds to Fc receptors on some cells
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IgD
Structure
Properties
4th highest serumIg B cell surface Ig
Does not bind complement
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IgE
Structure
Properties
Least common serumIg Binds to basophils and mast cells (Does not
require Ag binding)
Allergic reactions
Parasitic infections (Helminths) Binds to Fc receptor on eosinophils
Does not fix complement