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The clonal selection theory proposes that antigen selects lymphocytes for activation from a population of cells precommitted to produce specific antibody. Implicit in this theory is that antibody-forming cells are monospecific and express cell-surface receptors capable of binding foreign antigens.
Interaction of antigen with these side chains induced the cell to synthesize additional antibody molecules. This proposal seemed untenable once Karl Landsteiner demonstrated that the immune system could produce antibodies to a vast array of antigens; for over 50 years theories of antibody formation postulated that antigen instructed cells to synthesize antibodies complementary to the antigen. The introduction of the clonal selection theory of antibody formation by Macfarlane Burnet in the 1950s revived the idea that antibody-forming cells express cell-surface receptors by which they bind antigen. In 1961, Göran Möller provided the first evidence that antibody-forming cells had antibody (immunoglobulin) on their surface. The antigenbinding specificity of these immunoglobulin molecules was shown to be identical to the antibody that cells will produce when activated. Initially, many immunologists thought that the T lymphocyte receptor would also be an immunoglobulin molecule. However, studies by several laboratories in the early 1980s using a combination of monoclonal antibodies and molecular genetic techniques showed that the receptor consists of two polypeptide chains. The antigen-specific receptors on both T and B lymphocytes are associated with other trans-membrane molecules involved in the transduction of activation signals into the cell.
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