Question

Compare and contrast the Instructional Theory and Clonal Selection Theory explaining specificity of the immune response.

Answer 1

Instructional theories postulated that antigens play a central role in determining antibody specificity. Conversely, Selective theories stated that an antigen reacts with an already-existing antibody.

Instructional theory:

According to the instructional theories, a particular antigen would serve as a template around which antibody would fold. The antibody molecule would thereby assume a configuration complementary to that of the antigen template.

The instructional theories were formally disproved later, by which time information was emerging about the structure of DNA, RNA, and protein that would offer new insights into the vexing problem of how an individual could make antibodies against almost anything.

Clonal selection theory:

According to the clonal-selection theory, an individual lymphocyte expresses membrane receptors that are specific for a distinct antigen. This unique receptor specificity is determined before the lymphocyte is exposed to the antigen.

Binding of antigen to its specific receptor activates the cell, causing it to proliferate into a clone of cells that have the same immunologic specificity as the parent cell. The clonal-selection theory has been further refined and is now accepted as the underlying paradigm of modern immunology.

B cells were discovered approximately fifteen years after Burnett's Clonal Selection Theory, proving that antibodies all pre-exist and that the repertoire is independent of the antigenic universe.