The conditions for cooperative interactions between nonresponder B10.S B cells and GAT-primed irradiated (C57BL/6 x SJL)F1 T cells in the response by cultures of mouse spleen cells to GAT were investigated. GAT-specific antibody responses could be elicited by soluble GAT in cultures of GAT-primed irradiated (C57BL/6 x SJL)F1 T cells with C57BL/6 B cells but not with B10.S B cells.

In contrast, when GAT was presented to the cultures on F1 macrophages or as aggregates of GAT with MBSA, GAT-specific PFC responses were observed with both B10.S or C57BL/6 B cells. Irradiated GAT-primed T cells were nevertheless essential for the development of these responses. The GAT-specific response of B10.S B cells in these cultures was inhibited by the addition of soluble GAT at culture initiation. These results indicate that genetic disparity at Ir loci is not an absolute barrier to T-B-cell cooperative interactions in the response to antigens under Ir gene control. The significance of these data for the function of Ir gene products in immunocompetent cells is discussed.

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