Role of macrophages as modulators but not as autonomous accessory cells in the proliferative response of immune T cells to soluble antigen

The role of murine macrophages (M phi) and that of splenic dendritic cells (DC) were investigated in the antigen-specific proliferative response of memory T cells of mice primed with key-hole limpet hemocyanin (KLH) 6 weeks or more before. Peritoneal M phi, whether expressing Ia antigens or not, did not function as autonomous accessory cells (A cells). A-cell activity of the spleen adherent cell population, which comprised M phi in the majority and DC in the minority, was abolished by eliminating DC with a DC-specific monoclonal antibody and complement, and regained by the addition of a small number of DC. Though M phi did not function as autonomous A cells, they augmented the proliferative response in the presence of a small number of DC. This occurred not only in the presence of free antigen, but also when DC and/or M phi were pulsed with antigen. A culture supernatant of M phi having interleukin-1 activity was effective in enhancing the proliferation of T cells which responded to antigen-pulsed DC. On the other hand, interleukin-2 did not replace DC even in the presence of antigen-pulsed Ia+ M phi. We also investigated recently primed T cells, but no evidence was obtained in favor of the competence of M phi as autonomous A cells.