CD4 and infection: Comparable frequencies of CD4+ T cells were present between the two strains at both day 14 and day 21 post-infection (Fig. 5a,b; Gating strategy in Supplementary Fig. 2), Interestingly while equivalent frequencies of pulmonary CD4+CD44+ T cells were measured in both strains 14 days and 21 days post-infection (Fig. 5c), the MFI of cell surface CD44 expression gated on CD4+ T cells was lower in p55∆NS mice compared to WT mice, significantly so (p < 0.05) at day 14 post-infection (Fig. 5d,e).