CD4 and influenza: We found that specifically targeting the recall and expansion of memory antigen-specific CD4+ T cells induced an increase in GC Tfh and HA-specific GC B cells early compared to mice that lacked antigen-specific memory CD4+ T cell during primary influenza infection, indicating that our findings concur with previous studies that targeting CD4+ T cells is a successful strategy to enhance the GC reaction [43,47,110–112].