CD4 and infection: As expected, a substantial proportion of TFH cells (ICOS+Bcl6+) formed by 7.5 days post infection (~30% of CD4+ T cells) while only few follicular regulatory T cells (TFR, Foxp3+Bcl6+) were generated by this time point, representing ~7% of Foxp3+ T cells and ~0.5-1% of all CD4+ T cells (Supplementary Figure 3A).