Only T alpha or T gamma cells can be triggered by IgG or IgA to suppress the production of the matching Ig class.

A short exposure of human peripheral blood mononuclear cells (PBMC) to heat-aggregated IgG (or IgA) was found to inhibit pokeweed mitogen (PWM)-induced human B cell differentiation into IgG (or IgA)-producing cells. The present study was designed to investigate the nature of the cells inducible by aggregated (Agg)-IgG or Agg-IgA into isotype-specific suppressors. When T cell-enriched suspensions were exposed to Agg-IgG or Agg-IgA, then thoroughly washed, and cultured with autologous nonrosetting cells in the presence of PWM, a selective suppression of the generation of cells synthesizing and secreting IgG or IgA, respectively, was observed. Conversely, no inhibition was induced by T-depleted PBMC treated in exactly the same way. Unlike Agg-IgG, Agg-F(ab')2 fragments did not trigger suppression. Finally, in vitro X-irradiation of T cells pretreated with Agg-IgG or Agg-IgA abrogated their suppressive activity. It is concluded that among cells bearing Fc gamma or Fc alpha receptors, only T cells were inducible into suppressor cells by the binding of the matching immunoglobulin class.