Structure and function of immunoglobulins
- 2. Immunoglobuln A (Ig A)
- 3. IgA: It constitute only 10-15% total Ig in the serum. Molecular weight of the IgA is 385,000D. The half life IgA in serum is 6 days. It is the predominant Ig class in exocrine secretion. Two subclasses- IgA1and IgA2.
- 4. IgA: IgA1 and IgA2 both are heavily GLYCOSYLATED proteins. IgA1 is the predominant IgA subclass found in serum. Most lymphoid tissues have a IgA1 producing cells. In IgA2 the heavy chains and light chains are linked with noncovalent bonds. Both IgA1 and IgA2 can be in membrane bound form.
- 5. Functions: Provides local immunity. It function is to protect the various exposed epithelial elements of the body from invasion by pathogenic microorganisms. Secretory IgA present in breast milk protects new born during first months of life. It activates complement by alternative pathway.
- 6. Immunoglobulin M (Ig M)
- 7. IgM: It is the first antibody are found early in every antibody response,usually at low level. IgM in mammals normally accounts to about 5-10% of the serum IgS. It has a half life for 6 days in serum. The human IgM molecule is a pentamer made up of 5- chain subunits each with a pair of heavy chains(μ) and the pair of kappa(K) and lamda(λ) light chains.The μ chain have about 130 amino acid residues.
- 8. IgM: IgM have two ligand binding site but it looses its ability to participate in agglutination and many other immune reactions. The IgM has one extra chain is called J chain.This chain is 15,000D.
- 9. Functions: Activation of classical pathway. It cannot transverse blood vessels.It is restricted to the blood stream. It is a good complement activation of Ig.It is the most effective in leading to the lysis of microorganisms. It binds to the Fc receptors. It act as opsonin.
- 10. Immunoglobulin D (Ig D)
- 11. IgD: IgD is a glycoprotein produced as a monomeric antibody with two identical heavy chains and two identical light chains. It is found in very small amounts in blood serum. The molecular mass of IgD is 185kDa. The half life of IgD is 2.8 days. Its overall structure is same that of IgG. IgD molecules are relatively heat labile and extremely sensitive to proteases.
- 12. IgD: IgD does not bind complement neither can cross the placenta nor can bind the Fc receptor. The light chains have two domains- one variable and one constant. The heavy chain have four domains- one varriable and three constant region domains.
- 13. Functions: In B cells the function of IgD is to signal the B cells to be activated.Then B cells are ready to take part in the defense of the body as part of the immune system.