Differential antigen presentation in tumor immunity.

The tumor S1509a elicits a cell-mediated immune response in immune A/J mice but leads to the generation of suppressor T cells (Ts) in nonimmune mice. Previous studies have shown that I-A+ antigen-presenting cells (APC) present S1509a tumor antigen and thereby activate immune T cells. Recent studies with polyoma-induced tumors reveal similar findings. Administration of anti-I-A antibodies not only prevents effective T cell activation by I-A+ APC bearing S1509a tumor antigen but also induces Ts after a tumor challenge. Ts, which inhibit S1509a tumor immunity, may be activated by tumor antigen presented on I-J+ APC. Examination of the immunologic effects of cyclophosphamide and UV radiation supports this hypothesis.