immunoglobulin structure and function by associate lecturer mortadha h al-hussainy faculty of...
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ImmunoglobulinStructure and Function
By
Associate Lecturer Mortadha H AL-Hussainy
Faculty of Veterinary Medicine
Kufa University
Immunogobulin, Ig
• What is Immunoglobulin?
Immunoglobulin are the critical
ingredients of humoral acquired
immune response.
• The immunoglobulins are a group of
glycoproteins present in the serum and
tissue fluids of all mammals.
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
α1 α2 β γ
+ -
albumin
globulins
Mobility
Am
oun
t of
pro
tein
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
Basic Immunoglobulin Structure
• Immunoglobulins - heterogeneous
• Myeloma proteins - homogeneous immunoglobulins
Two Forms of Immunoglobulin
Membrane-bound receptor Soluble antibody
Immunoglobulin Structure
• Variable(V) & Constant (C) Regions– VL & CL
– VH & CH
• Hinge Region
CH1
VL
CL
VH
CH2 CH3
Hinge Region
Carbohydrate
Disulfide bond
Structural Regions
• hypervariable region
• also called
Complementarity Determining Regions(CDRs),
超变区超变区(( hyper-variable region, HVRhyper-variable region, HVR)),, 又称又称互补决互补决定定区区 (complementary determining region, CD(complementary determining region, CDRR ))
IgG molecule
Used with permission from: Dr. Mike Clark, Immunology Division, Department of Pathology Cambridge University, Cambridge, England
Enzymatic Digestion Products of Immunoglobulins
Immunoglobulin Fragments: Structure/Function Relationships
• Fab– Ag binding– Valence = 1– Specificity
determined by VH and VL
Papain
Fc
Fab
• Fc ( crystallizable)– Effector functions
Domains of Immunoglobulin
Functions of the domains on Ig:
VH, VL — antigen binding sites;
CH1 ~ 3, CL — genetic markers of Ig;
CH2(IgG), CH3(IgM) — C1q binding sites;
CH2 ~ CH3(IgG) — binding to placenta;
CH3(IgG) — FcγR binding site;
CH4(IgE) — FcεR binding site.
Function of Immunoglobulins
• Recognition of antigen 识别抗原• Activation of complement 激活补体• Opsonization 调理作用• Antibody-dependent cell-mediated
cytotoxicity,ADCC 抗体依赖性细胞毒作用• Mediate hypersensitivity type I 超敏反应
Immunoglobulin Classes and Subclasses
Immunglobulin 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.γ,α,μ,δ,andεchains.
Immunoglobulin Classes of Mammals
• IgG - Gamma (γ) heavy chains
• IgM - Mu (µ) heavy chains
• IgA - Alpha (α) heavy chains
• IgD - Delta (δ) heavy chains
• IgE - Epsilon (ε) heavy chains
Five Classes of Immunoglobulin
• IgG has a family of subclass, IgG1, IgG2, IgG3,
IgG4(cattle has no)
• IgA is divided into two subclasses, IgA1 and
IgA2(sheep).
Light Chain Types of Immunoglobulin
• Kappa (κ)
• Lambda (λ)
• All light chains have protein molecular weights of approximately 23,000 but can be divided into two distinct types, namely λchain, κchain, respectively
B Cell Antigen Receptor (BCR)
Ig-αIg-β Ig-βIg-α
IgA
• Structure– Serum - monomer– Secretions (sIgA)
• Dimer (11S)• J chain• Secretory component
J ChainSecretory Piece
IgA
• Structure
• Properties– 2nd highest serum Ig– Major secretory Ig (Mucosal or Local Immunity)
• Tears, saliva, gastric and pulmonary secretions
– Does not fix complement (unless aggregated)– Binds to Fc receptors on some cells
IgD
• Structure
• Properties– 4th highest serum Ig– B cell surface Ig– Does not bind complement
IgE
• Structure• Properties
– Least common serum Ig• 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
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