CD4 and infection: We hypothesize that restrictions in target cell availability within follicular centers limits the quantity of infectious virus that is produced and retained within the GC of SM, and reduces the risk of infection of resident GC immune cells such as CD4+ follicular helper T cells, which are critical for the development of immunologic memory [14], [47], [48], [49], [50], [51], macrophages, and other cells that traffic through the GC.