Hypothetical model for the reprogramming of the chemotactic responsiveness of B cells promoted by BCR ligation.

This model proposes that resting B cells have a broad chemokine responsiveness potential, which should equally allow for their migration to the crypt, the T zone, and the B-cell follicle. In contrast, Ag-activated B cells have a very restricted migratory potential, which should favor their relocation to defined microanatomic sites. Our data are compatible with the hypothesis that Ag is the main force that drives the reprogramming of B-cell chemotaxis responsiveness in the course of the immune response. Upon Ag binding, B cells initiate an ordered change of their chemotactic machinery that allows them to redistribute sequentially (1) in the T zone, where the B-cell response is initiated, and (2) in the follicle, where the B-cell response is amplified and improved.