A T cell clone isolated from antigen-primed CB6/F1 mice was shown to proliferate to keyhole limpet hemocyanin (KLH) in the presence of irradiated syngeneic F1 spleen cells, as well as spleen cells from either parental strain (BALB/c and C57BL/6). The genetic restriction involved in this antigen-specific proliferation was mapped using BXD (C57BL/6 X DBA/2) recombinant inbred strains of mice to the Mls gene on chromosome one. To exclude the role of Ia antigens as the restricting determinants, monoclonal anti-Ia antibodies were used to block the in vitro proliferative response of this clone. Although anti-Iab and anti-Iad blocked the proliferation of this clone to KLH in the presence of irradiated spleen cells from either parent, this effect was shown to be dependent on Ia molecules passively absorbed by the T cell clone from the irradiated filler cells. Since the T clone expressed Thy-1.2 and Lyt-1+ differentiation markers, its helper activity was compared with other KLH carrier-specific clones in an in vitro antibody synthesis assay. The Mls-KLH-restricted T cell clone, in contrast to other carrier-specific, major histocompatibility complex (MHC)-restricted T cell clones, was unable to cooperate with trinitrophenyl (TNP)-primed B cells in the presence of TNP-KLH to generate an anti-TNP response. These experiments suggest that non-MHC determinants, such as autologous Mls gene products, may play a role in genetically restricted antigen recognition by T lymphocytes.

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