Question

How can your body make so many different antibodies (proteins) from just a select set of genes?

Answer 1

The ability to produce billions of antibodies in humans is a result of one of the following:

1. the presence of billions of complete antibody genes in B cells.
2. Both B and T cells contain antibody genes.
3. the production of variable regions of light and heavy antibody genes caused by DNA rearrangement
4. a single gene coding for an antibody can produce antibody capable of taking up different 3D structures with the ability to combine with any antigen.

An antibody is a Y shaped molecule with an identical light and heavy chain

The variable region has about 110-130 amino acid residues in both the light and heavy chains and this is the region that binds to the antigen. The constant or 'C - terminal end' region contains more or less similar residues for the same class of antibodies (5 classes - IgM, IgG, IgA, IgD and IgE). The immune system creates billions of different antibodies with a small number of genes by bringing about rearrangements in the DNA segments during B cell development. This process happens even before the antibody is exposed to an antigen. Mutations are also a source of producing a wide range of antibodies. When a stem cell changes to become a B cell, DNA segments for both heavy and light chains are combined at random. Thus each B cell gets a functional gene that codes for one heavy and one light chain of an antibody. Thus antibody specificity depends on the different combinations of gene fragments used in that B cell.

It is estimated that over 15,000,000 different combinations are possible thus contributing to antibody diversity. Apart from this, imprecise recombinations and mutations add to this number.