Studies on human blood lymphocytes with iC3b (type 3) complement receptors. II. Characterization of subsets which regulate pokeweed mitogen-induced lymphocyte proliferation and immunoglobulin synthesis.

Human blood lymphocytes that express Type 3 complement receptors (CR3) can be divided into a major subset with high density Fc receptors for IgG (FcR) identified with the monoclonal antibody Leu 11 and two minor subsets which display either CD8 (Leu 2) or CD4 (Leu 3) markers. We isolated CR3+ lymphocyte subsets and examined them for regulatory effects on pokeweed mitogen (PWM) stimulated cells. The FCR CR3+ cell suppressed PWM-induced proliferation and Ig production. Pretreatment of these lymphocytes with immune complexes was required to suppress proliferation, but not IgG production. The CR3+ Leu 2+ FCR- subset also had suppressive activity, but this effect was not observed unless the CR3+ Leu 3+ enriched subset was removed. In fact, the CR3+ Leu 3+ enriched subset enhanced IgG synthesis. Brief exposure of CR3+ lymphocytes to recombinant interleukin 2, recombinant alpha-interferon, but not gamma-interferon, markedly enhanced the inhibitory effect. Time course studies and a comparison of inhibition of Ig synthesis with natural killer cell activity suggested that CR3+ lymphocytes act shortly after lymphocytes are exposed to PWM and that Ig production was regulated by suppression rather than cytotoxicity. These CR3+ lymphocyte subsets may have broad antigen non-specific effects on immunoglobulin synthesis.