Definition of antibody
The antibody is also called immunoglobulin (Ig). Immunoglobulin is a glycoprotein that is made in response to an antigen and can recognize and bind to the antigen that caused its production. It protects us from microbial infection. They are gamma globulin and synthesized by plasma cells. They constitute 25-30 % of total serum proteins. Antibodies are present in serum, tissue fluids, and mucosal surfaces and on the surface of B-cells where they act as antigen receptors.
Structure of immunoglobulin
- Composed of 4 polypeptide chains- 2 identical light chains (25 kDa each) and 2 identical heavy chains (50-73 kDa each)
- Linked by disulfide bonds
- Light chains similar in all immunoglobulins
- Light chains occur in 2 varieties:-kappa (k) and lambda( λ )
- Kappa chains are more frequently found.
- Heavy chains:- gamma, alpha, mu, delta and epsilon.
- One Ig contains one type of light chain and one type of heavy chain.
- Fc (Fragment Crystallizable ) -fixes complement
- Fab( Fragment, antigen-binding) binds antigen.
- Fab terminal has amino and Fc terminal have-COOH group.
- L and H chain consists of 2 parts-
V (variable) region at amino terminal & C (constant) region at carboxyl terminal.
- Hypervariable region: binds epitope also called complement determining region (CDR).
- Look at the above structure of the antibody.
Types of antibody
Based on the structure and antigenic nature of heavy chains the immunoglobulins are classified into 5 classes.
Ig G- (gamma)
Ig A- (alpha)
Ig M- (mu)
Ig D- (delta)
Ig E – (epsilon)
Properties of antibodies
Properties of Antibodies
Keynote: All antibodies are immunoglobulins but not all immunoglobulins are antibodies e.g. cryoglobulin is immunoglobulin but not antibody.
Further Readings
- Basic Clinical immunology. Editors: Fudenberg, Stites, Caldwell, Weils.6. Basic Clinical immunology. Editors: Fudenberg, Stites, Caldwell, Weils.
- Immunology. Editors: David Male, Jonathan Brostoff, David B. Roth & Ivan Roitt, 7th ed 2006, Publisher Elsevier.
- Ivan Roitt, Jonathan Brostoff and David Male, iMMUNOLOGY, 3rd Ed. 1993.
- Ivan Roitt; Essential Immunology, 8th Ed., 1994, Blackwell Scientific Publication, London.
- Janis Kuby, Barbara A. Osborne, Textbook of Immunology, 3rd Ed, 1992