Identification and isolation of the T-cell receptor was accomplished by producing large numbers of monoclonal antibodies to various T-cell clones and then screening the antibodies to find one that was clone specific, or clonotypic. This approach assumes that, since the T-cell receptor is specific for both an antigen and an MHC molecule, there should be significant structural differences in the receptor from clone to clone; each T-cell clone should have an antigenic marker similar to the idiotype markers that characterize monoclonal antibodies. Using this approach, researchers in the early 1980s isolated the receptor and found that it was a het-erodimer consisting of a and (3 chains.
When antisera were prepared using a(3 heterodimers isolated from membranes of various T-cell clones, some antis-era bound to a (3 heterodimers from all the clones, whereas other antisera were clone specific. This finding suggested that the amino acid sequences of the TCR a and (3 chains, like those of the immunoglobulin heavy and light chains, have constant and variable regions. Later, a second type of TCR heterodimer consisting of 8 and 7 chains was identified. In human and mouse, the majority of T cells express the a (3 heterodimer; the remaining T cells express the 78 heterodimer. As described below, the exact proportion of T cells expressing a (3 or 78 TCRs differs by organ and species, but a (3 T cells normally predominate.
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