CD38 and infection: Both prior to and at peak infection, the frequency of CD45RA-CXCR5+ Tfh cells was significantly higher amongst CD38- CD4+ T cells compared to CD38+ CD4+ T cells (Fig 4C and 4D), and Tfh cells represented a small fraction of the total CD38+ CD4+ T cell population (average of 5.6% and 5% of total CD38+ CD4+ T cells prior to, and at peak infection, respectively, Fig 4C and 4D).