Cxcr4 desensitization is an essential regulatory mechanism controlling the extra-follicular B cell response.

The signaling axis formed by the chemokine CXCL12 and its receptor CXCR4 plays an important role in B cell development and activation and is finely regulated by a process termed desensitization. Mutations leading to a truncation of the C-terminus tail of CXCR4 and thus to a defective desensitization have been reported in two diseases, a rare immunodeficiency called the WHIM syndrome and a B cell plasmacytoma called Waldenstrom s Macroglobulinemia (WM). How CXCR4 desensitization may impact B cell activation in the context of a T-independent extra-follicular response is still unknown. Here using a unique mouse model bearing an orthologous gain of function mutation of Cxcr4 we report that Cxcr4 desensitization is an essential gatekeeper controlling B lymphocyte entry into cycle, plasma cell differentiation, migration and maturation upon Myd88-dependent signaling. Altogether, our results support an essential role for Cxcr4 desensitization in limiting the depth and width of the B cell extra-follicular response and PC development.