Over‐expression of p190Rho GEF enhances B‐cell activation and germinal center formation in T‐cell‐dependent humoral immune responses

Abstract Previously, we reported induced expression of the p190 Rho guanine nucleotide exchange factor ( p190Rho GEF , ARHGEF 28 ) following CD 40 stimulation of B cells isolated from mouse spleen. We also reported that p190Rho GEF and a downstream effector molecule RhoA are required for B‐cell differentiation, especially for the induction of the plasma cell ( PC ) differentiation. This study investigates the role of p190Rho GEF in B‐cell biology in vivo , using p190Rho GEF transgenic ( TG ) mice that overexpress a wild‐type full gene in B cells. Immunization of these mice with T‐cell‐dependent antigen showed that populations of germinal center B cells and PC s were significantly increased in TG mice. Furthermore, similar results were shown in recombination activating 1 (Rag1) knockout mice that were reconstituted with B cells isolated from TG mice in combination with T cells isolated from littermate control mice. Analyses of isotype class switching and transcription factors involved in a germinal center reaction and PC differentiation also supported the findings from the cellular responses. These results suggest that p190Rho GEF may play a role in the stage of PC differentiation during T‐cell‐dependent humoral immune responses.