CXCR5-deficient mice develop functional germinal centers in the splenic T cell zone

The chemokine receptor CXCR5 is thought to be essential for the migration o f B cells into the network Df follicular dendritic cells in the spleen. How ever, as shown here, B cells and follicular dendritic cells do co-localize, albeit aberrantly, even in the absence of CXCR5. In mice lacking CXCR5 bot h cell types are found in a broad ring around the sinuses of the marginal z ones. Upon immunization with the T cell-dependent antigen 2-phenyl-oxazolon e, ectopic germinal centers develop in the periarteriolar lymphocyte sheath . A network of follicular dendritic cells forms in the vicinity of the cent ral arteriole within which the antigen-activated B cells proliferate. The a nalysis of the expressed V gene repertoire revealed that during B cell prol iferation, hypermutation is activated and V region genes accumulate somatic mutations. The pattern of somatic mutations suggests that affinity selecti on may occur. This analysis confirms that in CXCR5-deficient mice, the orga nization of splenic primary follicles is severely impaired. However, within the T cell zone a micro-environment is built up, which provides all requir ements needed for the affinity maturation to take place.