Fc gammaRIIb inhibits both B cell receptor- and CD19-induced Ca2+ mobilization in Fc gammaR-transfected human B cells

International Immunology
G KonczG Sarmay

Abstract

Fc gammaRIIb (CD32) controls antibody production by down-regulating cell activation, when co-clustered with B cell antigen receptors (BCR) in vivo, via immune complexes consisting of secreted IgG and antigen. Fc gammaRIIb-BCR co-ligation in vitro was shown to inhibit the Ca2+ influx from the extracellular space, the mechanism of which is not fully understood. Human B cells express Fc gammaRIIb1 and Fc gammaRIIb2, differing only in a 19 amino acid long insert in the cytoplasmic tail of the former. To elucidate whether Fc gammaRIIb1 and Fc gammaRIIb2 isoforms show any difference in the down-regulation of B cells, we have studied the effect of co-clustering of BCR and Fc gammaRIIb1 or Fc gammaRIIb2 on the Ca2+ signaling in a Burkitt's lymphoma cell line, ST486, transfected with the two isoforms respectively. We have shown here, for the first time, that co-aggregation of BCR and Fc gammaRIIb may also inhibit Ca2+ release from the endoplasmic reticulum pool of human B cells. Both isoforms mediated this inhibition and the inhibitory effect depended on the ratio of BCR to Fc gammaRIIb cross-linking. In contrast to Fc gammaRIIb, the CD21/CD19 complex was shown to up-regulate B cell response by lowering the activation threshold. We have...Continue Reading

Citations

Mar 22, 2000·Journal of Immunological Methods·R Nezlin
May 16, 2000·Immunology·C H NielsenR G Leslie

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