Suppression of polyclonal B cell activation by IgG-binding factors. Requirement for T cells.

IgG-binding factors (IgG-BF) prepared from cell-free supernatant of human peripheral blood mononuclear cells interfere with the polyclonal activation of peripheral B cells by decreasing the numbers of IgG-containing cells and Ig plaque-forming cells. Using Nocardia opaca delipidated cell mitogen (NDCM), a T helper cell-independent polyclonal B cell activator, it was found that the suppressive effect of IgG-BF was no longer demonstrable after removal of T cells. In pokeweed mitogen-stimulated cultures, the suppression by IgG-BF required the presence of radiosensitive T cells. Selective depletion of OKT4+ or OKT8+ subsets in NDCM-stimulated cultures showed that IgG-BF required the presence of OKT4+ lymphocytes to induce suppression. It is concluded that the effect of human IgG-BF was mediated by one or several subsets of T cells.