On the role of I-A antigens in lectin- and antigen-induced interleukin 2 production.

The role of I-A molecules in lectin- and antigen-induced interleukin 2 (IL2) production has been analyzed using monoclonal antibodies. Both lectin- and antigen [plus major histocompatibility complex (MHC)]-induced IL2 production were profoundly inhibited by monoclonal anti-I-A antibodies, whereas monoclonal anti-D and anti-K antibodies had no effect. The anti-I-A-mediated inhibition of lectin-induced IL2 production was fully overcome by addition of interleukin 1 (IL 1), while no reconstitution was observed in antigen (plus MHC)-specific induction. Anti-I-A antibodies were also found to inhibit the T cell-independent induction of IL 1 production. I-A antigens appear, therefore, to play two distinct roles in the induction of IL 2 production: (a) I-A molecules are directly involved in mediating activation signals to the macrophages at the level of IL 1 production; (b) I-A epitopes act as restricting elements in specific antigen recognition by T helper cells at the level of IL 2 production, a requirement which is overcome by lectin.