2.0 What are Antibodies
2.1 Antibodies, protein molecules produced by specialized cells (B Lymphocytes, spleen, lymph glands and blood) in the body, are a basic constituent of animal and human diseases fighting immune systems, that bind to antigens thus effectively neutralizing and destroying them. Antibodies are symmetrical molecules made up of four polypeptide chains containing two identical glycosylated heavy chains and two identical non-glycosylated light chains. The basic unit structure is folded in such a manner to form on its surface two identical regions consisting of heavy and light chain called Fab (antigen binding sites) and a third region called Fc which determines the biological properties. Based on physiochemical and antigenic differences. Five classes of antibodies or immunoglobulins have been recognized: lgG, lgA, lgM, lgD, and lgE. lgG is the major immunoglobulin component of serum making up 75% of the total. When molecules of antibody and antigen are brought together in solution, they interact with each other by forming a link between the antigen binging site on the Fab fragment of the immunoglobulin and the particular chemical groupings which make up the antigenic determining site on the antigen molecule.
2.2 Antigen- Antibody Reactions
Antigen–antibody reactions play an important role in the diagnosis of disease and the in the identification of microorganisms. The key antigen-antibody reactions are agglutination, precipitation, complement fixation. Radio immunoassays and immunoassays using enzyme–linked antibody or antigen are presently used in diagnostic test.
2.3 Monoclonal Antibodies, Polyclonal Antibodies and Single Domain Antibodies
Monoclonal Antibodies (mAbs) are antibodies secreted by a clone of cells. The most popular method of obtaining a clone of such secretors is b fusing a myeloma cell (an immortal B cell preferably a non-secretor) with B cells from the spleen. The resultant hybrids are cloned and each clone produces antibody all of which have the same binding specificity and affinity.
Because they are more specific and sensitive than other antibodies, they can used in diagnostics kits to detect the presence of viruses, bacteria, parasites, chemicals ad biologicals.
Monoclonal antibodies are the reagents of choice when
1) The antigen is difficult to purify (as in the case of lymphocyte markers)
2) The antigen is proteinaceous in nature and
3) There are risks involved in handling the serum (as is the case of anti-blood group sera obtained from professional donors)
The technology to produce mAbs was developed in 1975 by Cesar Milsterin. This was achieved by fusion of myeloma cells with lymphocytes from spleen of mice immunized with particular antigen. The hybridoma so developed has the ability to multiply indefinitely and to produce an antibody of predetermined specificity.
Polyclonal Anti bodies (pAbs) are a mixture of many antibodies with varying affinities and specificities. The cost of development of pAb may be small but its requirement fro purified antigen for its production increases its actual production cost. Back