Spontaneous helper factor production by nonadherent rabbit lymphoid cells and its feedback regulation by adherent cells

Normal, unstimulated rabbit lymphoid cells, when depleted of adherent cells, produced soluble helper factor activity that augmented antibody formation by rabbit spleen cells primed against sheep red blood cells (SRBC). Adherent cells inhibited the production of the helper factor by nonadherent cells via a soluble product. Thus unseparated (adherent cell-containing) appendix, lymph node, and spleen cell cultures did not produce the helper factor. On the other hand, the activity of the helper factor required the presence of adherent cells in the assay cultures. Peritoneal exudate cells, predominantly esterase positive, also inhibited the production of the helper factor if they were first exposed to the helper factor-containing culture supernatant. These results imply that a helper factor may participate in the feedback regulation of its own production via an adherent cell population.