The role of I region gene products in macrophage induction of an antibody response. I. Ability of anti-I-J region sera to block macrophage function

Splenic macrophages required for a primary in vitro antibody response express Ia antigens coded for by genes of the I-A, I-J, I-E and I-C subregions. Experiments were performed with anti-Ia alloantisera restricted to react with determinants of a specific subregion. The splenic macrophages were treated with these sera with and without complement (C), permitting comparison within each experiment of the blocking and lytic effects of antibodies to each subregion. Only antibodies restricted to recognize products of the I-J subregion were effective blockers of macrophage-T cell interaction. Sera directed at I-A, I-E or I-C subregions had no effect unless used with C to actually delete the Ia⁺ macrophages. Anti-I-J sera and C treatment of the T-B cell population did not affect the ability of these cells to reconstitute a normal response when added to normal macrophages. To examine the possibility that anti-I-J sera treatment of macrophages resulted in antigen-specific or nonspecific suppression of the response, cells obtained at 72 hr from cultures containing anti-I-J sera blocked macrophages were co-cultured with normal spleen cells and antigen. Such co-cultured cells were not suppressive to the PFC response of normal spleen cells.