IL-17 superfamily cytokines modulate normal germinal center B cell migration

The germinal center (GC) is a dynamic structure formed by proliferating B cells in the follicles of secondary lymphoid organs during T cell-dependent antibody responses to exogenous antigens. GC is composed by a dark zone, enriched in proliferating centroblasts (CBs), and a light zone where CBs migrate and transform into centrocytes (CCs), a minority of which is selected to survive, undergoes Ig class-switch recombination, and differentiates into memory B cells or long-lived plasma cells. CBs express CXCR4 and are attracted to the dark zone by stromal cell-derived CXCL12, whereas CCs express CXCR5 and are recruited to the light zone along a gradient of CXCL13 produced by follicular dendritic cells (FDCs). Therefore, CXCL12 and CXCL13 play crucial roles in the regulation of GC B cell trafficking. Among the numerous molecules involved in GC formation, IL-17A represents a recent addition. Its involvement has been demonstrated in mouse models of human autoimmune or infectious diseases. IL-17A belongs to the IL-17 cytokine superfamily, together with 5 additional structurally related cytokines. We have recently demonstrated that IL-17A renders freshly isolated tonsil GC B cells competent to migrate to CXCL12 and CXCL13 through a NF-kBp65-dependentmechanism. Here, we review the role of IL-17A on GC cells and discuss, for the first time, common effects of the cognate cytokines IL-25 and IL-17B on GC B cell function.