CXCR5 and infection: The accumulation of TFH (CD4+ PD1+ CXCR5+) and GC B (CD19+ Fas+ GL7+) cells was decreased in old mice relative to adult mice at days 4 and 6, although nearly equivalent levels of TFH and GC B cells were present at 8 days post infection (Fig 2A and 2C).