The suppression activity of Fc gamma receptors is not related to their T-cell origin

Soluble receptors for Fc IgG (FcγR) were obtained by short incubation of various cell types in serum-free medium, and isolated by affinity chromatography on human IgG. The suppressive activity of this material was investigated in cultures of human peripheral blood lymphocytes (PBL) stimulated by extracts of Nocardia opaca as polyclonal activator. Addition of PBL-FcγR, at the third day of the culture, resulted in a marked decrease of the number of Ig-secreting cells, determined by a reverse hemolytic plaque assay, without diminution of Ig-containing cell numbers. FcγR, however, did not inhibit plaque-forming cells when added immediately or 3 hr before the assay. FcγR prepared from T-enriched or T-depleted unstimulated PBL, as well as FcγR released from neutrophils or from murine T-cell hybridoma displayed similar suppressive activities. The results indicate that the suppressive properties of soluble FcγR are associated with their capacity to bind the Fc part of IgG but not related to their T-cell origin.