1. Immunoglobulins structure and classification
Plasma Proteins
Immunoglobulins structure and classification

2. Immunoglobulin (Ig) / antibody(Ab):
Glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodies, mostly associated with γ fraction.
But γ-globulin and Ig are not synonymous.
Ig is a functional term
γ-globulin is physical term.
Amount of protein
Mobility
albumin
globulins + -

3. Immunoglobulins Ag
NH2
NH2
Antibodies produced by B cells in response to antigen stimulation of the organism
React specifically with antigenic determinants
Structure:
consist of a minimum of 4 polypeptide chains - 2 heavy (H) a 2 light (L) linked by disulfide bridges
COOH
COOH

4. The molecule consists of two light (L) chains and two heavy (H) chains
The molecule consists of two light (L) chains and two heavy (H) chains. Each light chain consists of a variable (VL) and a constant (CL) region. Each heavy chain consists of a variable region (VH) and a constant region that is divided into three domains (CH1, CH2, and CH3). The CH2 domain contains the complement-binding site and the CH3 domain contains a site that attaches to receptors on neutrophils and macrophages (Fc receptors).The antigen-binding site is formed by the hypervariable regions of both the light and heavy chains, which are located in the variable regions of these chains. The light and heavy chains are linked by disulfide bonds, and the heavy chains are also linked to each other by disulfide bonds.
Immunoglobulins
IgG
NH2

5. Complement Binding Site Binding to Fc Receptors
Functions of the domains on Ig
Ag Binding
Complement Binding Site
Placental Transfer
Binding to Fc Receptors

6. Fc receptor
Fc receptor: protein found on the surface of certain cells (including natural killer cells, macrophages, neutrophils, and mast cells).
Fc receptors bind to antibodies that are attached to infected cells or invading pathogens.
Their activity stimulates phagocytic or cytotoxic cells to destroy microbes, or infected cells by antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity.

7. THE CONSTANT REGIONS DETERMINE CLASS-SPECIFIC EFFECTOR FUNCTIONS
The constant regions of the immunoglobulin molecules, particularly the CH2 and CH3 (and CH4 of IgM and IgE), which constitute the Fc fragment, are responsible for the class-specific effector functions of the different immunoglobulin molecules. eg, complement fixation or transplacental passage.
Some immunoglobulins such as immune IgG exist only in the basic tetrameric structure, while others such as IgA and IgM can exist as higher order polymers of two, three (IgA), or five (IgM) tetrameric units. The L chains and H chains are synthesized as separate molecules and are subsequently assembled within the B cell or plasma cell into mature immunoglobulin molecules, all of which are glycoproteins.

8. Antigenic determinant or epitope:
The structure recognized by an antibody
Concept: Epitopes can bind in pockets or grooves or on extended surfaces in the binding site of antibodies.

9. BOTH LIGHT & HEAVY CHAINS ARE PRODUCTS
OF MULTIPLE GENES
Each immunoglobulin light chain is the product of at least three separate structural genes: a variable region (VL) gene, a joining region (J) gene (bearing no relationship to the J chain of IgA or IgM), and a constant region (CL) gene. Each heavy chain is the product of at least four different genes: a variable region (VH) gene, a diversity region (D) gene, a joining region (J) gene, and a constant region (CH) gene. Thus, the “one gene, one protein” concept is not valid. The molecular mechanisms responsible for the generation of the single immunoglobulin

10. Immunoglobulin Classes and Subclasses
In terms of the differences in amino acid sequence of constant region of heavy chain, immunglobulin molecules are divided into 5 classes:
IgG, IgA, IgM, IgD and IgE
Heavy chain:
5 types: γ,α,μ,δ and ε.
Light chains
2 types: κ and λ.

11. Immunoglobulin Classes of Mammals
IgG - γ heavy chains
IgM - µ heavy chains
pentamer
IgA - α heavy chains
dimer
IgD - δ heavy chains
IgE - ε heavy chains
monomer
dimer
pentamer

13.   IgG
IgG1, IgG2, IgG4
IgG3
It is the most abundant class in serum, constitutes about 80% of the total serum Ig.
4 subclasses, IgG1, IgG2, IgG3, and IgG4.
All IgG's are monomers. The subclasses differ in the number of disulfide bonds and length of the hinge region.

14. Two Forms of Ig 1. Membrane Ig, mIg
It confers antigenic specificity on B cells.
mIg
2. Secreted Ig, SIg
It can circulate in the blood and serve as the effectors of humoral immunity by searching out and neutralizing antigens or marking them for elimination.
SIg

15. IgA Structure Serum - monomer Secretions (sIgA) Dimer J chain
Secretory component
J Chain
Secretory Piece

16.   IgM
Structure
The largest Ig composed of 5 Y-shaped units held together by a J polypeptide chain.
1. Pentamer
2. Extra domain (CH4)
3. J chain

17. IgD
Structure
Monomer
Tail piece
Tail Piece

18. IgD Properties 4th highest serum Ig, its role in serum uncertain.
B cell surface Ig.
Does not bind complement.

19. IgE
Structure
Monomer
Extra domain (CH4)
CH4