Activation of human B cells and inhibition of their terminal differentiation by monoclonal anti-mu antibodies.
Anti-mu antibody preparations have been found to exert both positive and negative effects on B cell activation and differentiation. To explore these paradoxical influences of IgM cross-linkage on human B cells, three gamma 1 kappa murine monoclonal antibodies specific for human mu-chains (DA4.4, AB6.4, 145.8) were examined for their comparative effects on activation of B cells and inhibition of terminal plasma cell differentiation. All three antibodies appeared equally efficient in immunoprecipitation of surface IgM molecules; however, fluorescence-activated cell sorter analysis revealed that the DA4.4 and AB6.4 antibodies saturated the B cell surface IgM at slightly lower concentrations than did the 145.8 antibody. When the affinity-purified antibodies were added in varying concentrations to cultures of small resting B cells, all three antibodies induced B cell enlargement and DNA synthesis, but with varying degrees of efficiency (DA4.4 greater than AB6.4 much greater than 145.8). In striking contrast, large B cells isolated either by FACS or density gradient separation were unresponsive. The anti-mu-induced proliferative response of small B cells required relatively high B cell densities, but not T cells or the Fc portion of the antibody molecules. The maximal proliferative response was obtained during the third day of culture, and the response curve suggested that anti-mu induced only one round of B cell replication. All three antibodies were capable of completely inhibiting T cell factor-induced differentiation of large B cells into IgM plasma cells; both F(ab')2 fragments and intact anti-mu antibodies were effective in final concentrations as low as 1 microgram/ml. Significant suppression of IgG and IgA plasma cell differentiation was also achieved, but required higher concentrations of the anti-mu antibodies. For each antibody, there was a close correlation between the efficiency of inducing small B cell proliferation and of inhibiting large B cell differentiation into plasma cells. The results show that the B cell response to cross-linkage of cell surface IgM varies according to the differentiation stage. We postulate that the mature resting B cell represents the only stage in the life history of the B cell during which surface Ig cross-linkage leads to a positive signal, negative signals being the rule at other stages in B cell replication and differentiation.
D000328:Adult; D000911:Antibodies, Monoclonal / Q000502:physiology*; D000937:Antigen-Antibody Reactions; D001402:B-Lymphocytes / Q000145:classification / Q000166:cytology / Q000276:immunology*; D001667:Binding, Competitive; D002454:Cell Differentiation; D003593:Cytoplasm / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000502:physiology; D007074:Immunoglobulin G / Q000502:physiology; D007143:Immunoglobulin Heavy Chains / Q000276:immunology*; D007075:Immunoglobulin M / Q000502:physiology; D007148:Immunoglobulin mu-Chains / Q000276:immunology*; D008213:Lymphocyte Activation; D011947:Receptors, Antigen, B-Cell / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology; D013997:Time Factors
D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007075:Immunoglobulin M; D007148:Immunoglobulin mu-Chains; D011947:Receptors, Antigen, B-Cell