| Summary: | The MHC-restricted TCR consists of a 90-kD heterodimeric glycoprotein composed of an a and a (3 chain that are encoded by somatically rearranging gene segments (for review, see references 1-3). Receptor diversity and antigen/MHC specificity are generated by rearrangement ofthe known variable elements (variable [V], diversity [D], and joining [,J] segments), as well as by the addition of N-region nucleotides. While the a/(3 receptor confers both antigen recognition and MHC restriction (4, 5), no general rules for the relative contribution of specific variable elements to antigen or MHC specificity have emerged. Early work demonstrated that the same Va and V(3 gene segments can encode a receptor with specificity for antigen plus a class II MHC gene product or with specificity for a class I alloantigen (6). The same V/3 domain has been shown to participate in a TCR specific for cytochrome c/1-Ek as well as in a TCR reactive to hen eggwhite lysozyme/I-Ab (7). On the other hand, surveys of sperm whale myoglobin-reactive T cells (8) and ofcytochrome c-reactive T cells (9, 10) have been consistent with the idea that the Va gene segment encodes a TCR's antigen specificity while the Vo domain confers its MHC specificity. However
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