Differential Expression of the Inhibitory IgG Fc Receptor FcγRIIB on Germinal Center Cells: Implications for Selection of High-Affinity B Cells

Abstract

The murine low-affinity receptor for IgG, FcγRIIB, mediates inhibition of B cell receptor-triggered events in primary B cells. We investigated the expression of FcγRIIB on germinal center (GC) cells to better understand its role in memory B cell development. Immunohistological analyses demonstrated differential regulation of FcγRIIB on GC cells. Its levels are markedly down-regulated on GC B cells and up-regulated on follicular dendritic cells (FDC) at all times during the GC response. Analyses of surface expression of FcγRIIB by flow cytometry and FcγRIIB mRNA levels by RT-PCR analysis confirmed that this FcR is down-regulated in GC B cells. In mice lacking FcγRIIB, the development of the secondary FDC reticulum in GCs is substantially delayed, although the overall kinetics of the GC response are unaltered. These findings have direct implications for models proposed to account for the selection of high-affinity B cells in the GC and suggest a role for FcγRIIB in promoting the maturation of the FDC reticulum.