CD4 and infection: On the other hand, some virus-specific B cells migrate toward the marginal zone of the B follicles, where they interact with CD4+ T cells triggering a germinal center reaction (GCR) that leads, late during the infection, to the generation of long-lived plasma cells that maintain high levels of high-affinity Abs, which is the most desirable consequence of vaccination or infection, along with long-lived memory B cells (18).