EBI2 mediates B cell segregation between the outer and centre follicle.
B cell follicles are specialized microenvironments that support events necessary for humoral immunity. After antigen encounter, activated B cells initially seek T-cell help at the follicle-T-zone boundary and then move to interfollicular and T-zone distal (outer) regions of the follicle. Subsequently, some cells move to the follicle centre, become germinal centre B cells and undergo antibody affinity maturation. Although germinal centres within follicles were described in 1885 (ref. 12), the molecular cues mediating segregation of B cells between the outer and centre follicle have remained undefined. Here we present a role for the orphan G-protein-coupled receptor, Epstein-Barr virus induced molecule-2 (EBI2, also known as GPR183), in this process. EBI2 is expressed in mature B cells and increases in expression early after activation, before being downregulated in germinal centre B cells. EBI2 deficiency in mice led to a reduction in the early antibody response to a T-dependent antigen. EBI2-deficient B cells failed to move to the outer follicle at day 2 of activation, and instead were found in the follicle centre, whereas EBI2 overexpression was sufficient to promote B cell localization to the outer follicle. In mixed bone marrow chimaeras, EBI2-deficient B cells phenocopied germinal centre B cells in preferentially localizing to the follicle centre. When downregulation of EBI2 in wild-type B cells was antagonized, participation in the germinal centre reaction was impaired. These studies identify an important role for EBI2 in promoting B cell localization in the outer follicle, and show that differential expression of this receptor helps position B cells appropriately for mounting T-dependent antibody responses.