Macrophage-derived soluble factors mediate suppression induced by 2,4-dinitrophenyl-conjugated mouse IgG in hybridoma cells

Our laboratory has established that 2,4-dinitrophenyl-conjugated mouse IgG (DNP-MGG) can specifically suppress proliferation, antibody synthesis, and secretion in vivo in two anti-DNP secreting cell lines: hybridoma 35-12 and myeloma MOPC-315. In the present study an in vitro system was used to further analyze the mechanism of suppression of hybridoma 35-12 cells (HC) by DNP-MGG. It was found that DNP-MGG-induced suppression of HC requires macrophages (M phi) and occurs only in eclipsed HC which are mainly small, nonsecreting cells. The M phi-mediated suppression is DNP specific, requires no M phi-HC cell contact, and does not involve killing of eclipsed HC. M phi culture supernatant alone cannot mediate suppression, but supernatants obtained by culturing M phi with either HC or supernatant from HC culture can mediate suppression of eclipsed HC in the presence of DNP-MGG. DNP-MGG is not required for the generation of effective M phi factors, but it is required for suppression of HC in the presence of M phi factors. Indomethacin cannot reverse M phi-mediated suppression, suggesting prostaglandins may not be the M phi factors. These data suggest that M phi-derived factors which are not prostaglandins in nature may play a role in B-cell regulation and in B-cell suppression induced by tolerogenic forms of antigen.