Suppression of mitogen-induced peripheral B cell differentiation by soluble Fc gamma receptors released from lymphocytes.

Soluble receptors for FcIgG released from unstimulated human peripheral blood lymphocytes were isolated by affinity chromatography on Sepharose 4B-IgG. This material was shown to interfere with the differentiation of peripheral blood B cells into Ig-secreting cells in cultures stimulated with pokeweek or Nocardia opaca extracts. Neither cell viability nor [3H]thymidine incorporation were altered, but the number of Ig-containing cells and that of Ig-secreting cells were decreased. These effects were dose-related. They were found to be associated with Fc IgG-binding soluble material, since absorption on Sepharose 4B-IgG but not on pepsin-digested F(ab')2 fragments removed the inhibitory activity. This suppressor factor, released by unstimulated lymphocytes, may represent a human analogue of murine immunoglobulin-binding factor (IBF) produced by alloactivated T cells.