CD4 and infection: In vitro, GC Tfh cells are more susceptible to infection with HIV‐1 than non‐GC Tfh cells or CXCR5− extrafollicular CD4+ T cells,170, 171 and in vivo they have been shown to constitute the major CD4 T‐cell compartment for virus replication in both HIV‐1 172, 173 and SIV174, 175 infections.