The Fc receptor for IgG (Fc gamma RII; CD32) on human neonatal B lymphocytes

B cells express an Fe receptor fur IgG (Fc gamma RII; CD32) which is involv ed in feedback inhibition of anti-body production. Engagement of Fc gamma R II during ligation of the antigen receptor provides an inhibitory signal. F c gamma RII exists as several isoforms, with Fc gamma RIIb (which carries a n immunoreceptor tyrosine-based inhibition motif; ITIM) being predominant f orm on adult B cells. The inhibitory role of Fc gamma RIIb map be unhelpful to the infant, since primary exposure to infectious agents is likely to be in thy presence of maternal IBG. We hypothesized that neonatal D cells wou ld be loss susceptible to feedback inhibition by antibody, either through t he expression of activation-competent Fc gamma RII isoforms (Fc gamma RIIa and Fc gamma RIIc) or through reduced expression of the inhibitory Fc gamma RIIb isoforms. Cord and adult B cells were examined for expression of Fc g amma RII isoforms using monoclonal antibodies and RT-PCR. In vitro assays w ere performed to assess susceptibility of cord and adult cells to Fc gamma RII-mediated suppression. Although there is no phenotypic difference in Fc gamma RII expression (Fc gamma RIIb predominating on both adult and cord B cells), Fc gamma RIIb is expressed at lower levels on cord cells. This quan titative difference in Fc gamma RIIb expression map explain tile reduced su sceptibility of cord B cells to anti body-mediated inhibition observed in t hese experiments (C) American Society for Histocompatibility and Immunogene tics, 2001. Published by Elsevier Science Inc.