The cell-mediated immune reactivity (CMI) of mice to contact chemicals such as picryl chloride (PCI) is influenced by thymus-derived suppressor T lymphocytes (1,2). The development of these suppressor T lymphocytes is stimulated by the intravenous administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS). Zembala and Asherson have further demonstrated that a specific suppressor factor(s) can be detected in the supernates of cultured suppressor T cells. This factor suppresses the transfer of contact sensitivity (CS) to PCl (1,2). In experiments reported elsewhere (3), we have shown that the PCl suppressor supernates of Zembala and Asherson can also suppress the development of contact sensitivity to PCl. The immunochemical analysis of suppressor factor (SF) operative in the CS response to PCl has revealed many similar properties (3) to other suppressive moieties functioning to limit the plaque-forming cell (PFC) response to dinitrophenylated-keyhole limpet hemocyanin (DNP-KLH) as well as the strict antigen specificity of each respective suppressive factor, suggested that there might be a common origin of these substances. Indeed, in each case these respective factors were found to bear determinants controlled by the H-2 gene complex (4,5).

Recently, in selected systems, the I-J subregion has been found to code for the Ia determinants present on suppressor cells (6) and suppressor factors (4,5). In accord with these findings, we report that antigen-specific SF which limit the CS response to PCl bear I-J determinants, implying that analogous suppressive regulatory mechanisms in CMI as well as antibody responses may be determined by genes of one subregion of the H-2 complex.

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