25.19 : 抗原受容体の多様性

Antigen receptors are multiprotein complexes on the B and T cell membranes that recognize specific antigens.

A B cell antigen receptor, or BCR, is a membrane-bound antibody molecule comprising a pair of heavy and light chains. In contrast, a T cell receptor or TCR primarily includes alpha and beta chains.

Both these receptors can recognize and bind to diverse antigens even before exposure. This diversity is achieved through somatic recombination.

Here, the germline genes encoding for BCR and TCR undergo recombination during the lymphocyte maturation.

During recombination, the variable or V, diversity or D, and joining or J segments of each gene are randomly selected and joined together to form a single mRNA molecule, which is later translated into a functional receptor.

These permutations produce billions of receptor chains, which are expressed as BCRs and TCRs. This enables the lymphocytes to recognize an array of antigens and mount an efficient immune response.

As a result, each lymphocyte is uniquely immunocompetent with a BCR or TCR, which remains inactive unless it encounters the corresponding antigen.