FcgammaRIIb expression on human germinal center B lymphocytes

IgG antibody can specifically suppress the antibody response to antigen. This has been explained by the hypothesis that signaling through the B cell antigen receptor is negatively modulated by the co-ligation of immunoglobulin with the receptor for IgG, FcgammaRIIb. We hypothesized that inhibitory signaling through FcgammaRIIb would be counter-productive in germinal center cells undergoing selection by affinity maturation, since these cells are thought to receive a survival/proliferative signal by interacting with antigen displayed on follicular dendritic cells. We have identified and characterized a population of B lymphocytes with low/negative FcgammaRIIb expression that are present in human tonsil. Phenotypically these cells correspond to germinal center B cells and comprise both centroblast and centrocyte populations. In examining expression at the molecular level we determined that these B cells do not express detectable mRNA for FcgammaRIIb. We examined several culture conditions to induce expression of FcgammaRIIb on germinal center cells but could not determine conditions that altered expression. We then examined the functional consequence of cross-linking membrane immunoglobulin and the receptor for IgG on human B lymphocytes. Our results cast some doubt on the value of anti-IgG as a model for antigen-antibody complexes in studying human B cell regulation.