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Immunoglobulins: Structure and Function

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Presentation on theme: "Immunoglobulins: Structure and Function"— Presentation transcript:

1 Immunoglobulins: Structure and Function

2 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 of protein

3 General Functions of Immunoglobulins
Ag binding Can result in protection Valency Effector functions Fixation of complement Binding to various cells Usually requires Ag binding

4 Basic Immunoglobulin Structure
Immunoglobulins - heterogeneous Myeloma proteins - homogeneous immunoglobulins

5 Immunoglobulin Structure
CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond Heavy & Light Chains Disulfide bonds Inter-chain Intra-chain


7 Immunoglobulins (Ig) are
glycoproteins made up of light (L) and heavy(H) polypeptide chains. The simplest antibody molecule has a Y shape and consists of four polypeptide chains:two H chains and two L chains. The four chains are linked by disulfide bonds.

8 Immunoglobulin Structure
CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond Variable & Constant Regions VL & CL VH & CH Hinge Region

9 Of the five Ig classes or isotypes
H chains are distinct for each Of the five Ig classes or isotypes and are designated γ α μδ ε for the respective classes of Ig, namely IgG IgA IgM IgD IgE.

10 Human Immunoglobulin Classes
IgG - Gamma () heavy chains IgM - Mu () heavy chains IgA - Alpha () heavy chains IgD - Delta () heavy chains IgE - Epsilon () heavy chains

11 Designated κ and λ and only one type is found in Ig.
L chains are one of two types Designated κ and λ and only one type is found in Ig.

12 Human Immunoglobulin Light Chain Types
Kappa () Lambda ()

13 L and H chains are subdivided into
variable and constant regions.The regions are composed of three-dimensionally folded, repeating segments called domains. An L chain consists of one variable (VL) and one constant (CL) domain.Most H chains consist of one variable (VH) and three constant(CH) domains.(IgG and IgA have three CH domains,whereas IgM and IgE have four.)

14 Immunoglobulin Structure
CH1 VL CL VH CH2 CH3 Hinge Region Carbohydrate Disulfide bond Domains VL & CL VH & CH1 - CH (or CH4) Oligosaccharides

15 for antigenbinding ,whereas the constant
The various regions are responsible for antigenbinding ,whereas the constant regions are responsible for various biologic functions eg, complement activation and binding to cell surface receptors.

16 and H chains have three extremely variable (“hypervariable”) amino
The variable regions of both L and H chains have three extremely variable (“hypervariable”) amino acid sequence at the amino- terminal end that form the antigen- binding site.



19 Structure of the Variable Region
Hypervariable (HVR) or complimentarity determining regions (CDR) Framework regions FR1 FR2 FR3 FR4 HVR1 HVR2 HVR3 Variability Index 25 75 50 100 Amino acid residue 150

20 Immunoglobulin Fragments: Structure/Function Relationships
Papain Fc Fab Fab Ag binding Valence = 1 Specificty determined by VH and VL Fc Effector functions

21 Immunoglobulin Fragments: Structure/Function Relationships
Ag Binding Complement Binding Site Placental Transfer Binding to Fc Receptors

22 Immunoglobulin Fragments: Structure/Function Relationships
Pepsin Fc Peptides F(ab’)2 Fab Ag binding Fc Effector functions F(ab’)2

23 IgG Structure Monomer (7S) IgG1, IgG2 and IgG4 IgG3

24 IgG Structure Properties Major serum Ig
Major Ig in extravascular spaces The only antibody to cross the placental Fixes complement Binds to Fc receptors Phagocytes - opsonization NK cells – ADCC Binds to SPA

25 IgM Structure Pentamer (19S)
composed H2L2 units plus one molecule of J chain Extra domain (CH4) C4 J Chain

26 Fixation of C1 by IgG and IgM Abs
C1r C1s C1q No activation Activation

27 IgM Structure Properties 3rd highest serum Ig
First Ig made by fetus and B cells Produced early in the primary response The most efficient Ig Fixes complement Tail Piece Agglutinating Ig Binds to Fc receptors B cell surface Ig

28 B Cell Antigen Receptor (BcR)

29 IgA Structure Serum - monomer Secretions (sIgA)
Dimer (11S), sIgA molecule consists of two H2L2 units plus one molecule each of J chain and secretory component(SC or SP) J Chain Secretory Piece

30 Origin of sIgA: The SP is a polypeptide synthesized by epithelial cells that provides for IgA passage to the mucosal surface. It also protests IgA from being degraded in the intestinal tract. Y Y Y

31 IgA Properties 2nd highest serum Ig
Major secretory Ig ( saliva, tears, respiratory, intestinal, and genital tract secretions.) Does not fix complement unless aggregated Binds to Fc receptors on some cells

32 IgD Structure Monomer Tail piece Tail Piece

33 IgD Structure Properties 4th highest serum Ig B cell surface Ig
Does not bind complement

34 IgE Structure Monomer Extra domain (CH4) C4

35 IgE Structure Properties Least common serum Ig Allergic reactions
Parasitic infections Does not fix complement

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