Immunological characterization of FcR gamma bearing and nonbearing B cells: functional modulation of immune complexes.
By the 1g sedimentation method using discontinuous gradients of Ficoll solution (concentrations of 6 to 14%), keyhole limpet hemocyanin (KLH)-primed spleen cells of C3H/He or DBA/2 mice were fractionated into 4 to 10 populations after IgG antibody-coated erythrocytes (EA gamma) rosetting and then treatment with anti-Thy-1.2 + complement (C). No significant difference was observed in the distribution of isotype specificities of surface immunoglobulins on B cells in each population thus fractionated, when determined by indirect immunofluorescence staining. The mixture of the 12 and 14% Ficoll fractions contained 95% of B cells bearing Fc receptor for IgG (FcR+ gamma) and 3.58% of antigen-binding cells (ABC) for KLH, while the 8% Ficoll fraction included 15% of FcR+ gamma B cells and 1.53% of ABC. Nevertheless, the FcR- gamma B-cell-enriched populations caused intensive plaque-forming cell (PFC) responses to dinitrophenol (DNP), whereas FcR+ gamma B-cell-enriched populations generated weak responses. Noteworthy is that 4 days preculture of a population containing 95% FcR+ gamma B cells resulted in the appearance of precursor activity which was ascertained by a further 4 days culture of these cells with antigen, DNP-dextran. These findings suggest that FcR gamma bearing B cells intrinsically possess precursor activity for IgM/IgG antibody-forming cells, but lose it transiently by binding immune complexes (IC). Moreover, the titer of a factor suppressing anti-DNP PFC responses (suppressive B-cell factor, SBF) was higher in the 24-hr culture supernatants of the FcR+ gamma B-cell-enriched fraction than of the FcR- gamma B-cell-enriched fraction, suggesting that SBF is produced by FcR+ gamma B cells themselves. Thus, IC seems to play an important role for the negative feedback regulation of antibody production by stimulating FcR gamma bearing B cells.
D000818:Animals; D000921:Antibody-Producing Cells / Q000276:immunology; D000936:Antigen-Antibody Complex; D000941:Antigens / Q000276:immunology; D000954:Antigens, Surface / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology*; D002469:Cell Separation; D006433:Hemocyanins; D007074:Immunoglobulin G / Q000378:metabolism; D007165:Immunosuppression Therapy; D051379:Mice; D008809:Mice, Inbred C3H; D008811:Mice, Inbred DBA; D008819:Mice, Nude; D011961:Receptors, Fc / Q000276:immunology* / Q000378:metabolism; D017452:Receptors, IgG
D000936:Antigen-Antibody Complex; D000941:Antigens; D000954:Antigens, Surface; D007074:Immunoglobulin G; D011961:Receptors, Fc; D017452:Receptors, IgG; D006433:Hemocyanins; C032808:keyhole-limpet hemocyanin