Genetic Restriction Elements Used To Recognize the KLH by Various T Cell

T h e T cell receptor for antigen is similar to that o f B cells (Ig) in that there are a very large number o f specificities and this reper to i re of specificities is clonally distributed. What appears unique about T cell recognit ion is the ability o f T cells to recognize foreign ant igen only in association with a p roduc t of the MHC (1, 2), whereas antibodies, in most cases, require only antigen. Recent serological and biochemical analyses have shown that the T cell receptor exists on the cell surface as a disulfide-linked mul t imer o f two subunits, a and/3 (3-7). These peptide chains are genera ted in a manner similar to Ig in that they are encoded by several sets o f gene segments: variable (V); diversity (D), at least in the case of beta chains; and jo ining (J) regions. These segments rear range dur ing the maturat ion o f an individual cell to p roduce a recep tor combination unique to that cell lineage (8-13). T h e rest o f the T cell receptor protein consists o f a constant (C) region that is itself encoded by three or four separate exons (1416). T h e V regions o f the T cell receptor conserve certain residues that are present in both VH and VL (17-19). This suggests that their overall s t ructure is similar to that of Ig. Some differences have also been no ted (17, 20), whose exact significance remains controversial. T h e T cell receptor , like Ig, expresses antigenic determinants of V and C regions. T h e antigenic determinants o f the T cell recep tor V regions can be considered as equivalent to the idiotypes of Ig molecules, phenotypic markers of V region genes. T cell idiotypes were identified with antisera or mAbs f rom syngeneic, allogeneic, or xenogeneic animals immunized with T cell clones (37). One such antiidiotypic ant ibody has been used to select o ther T cells, which