CD4 and infection: In uninfected animals, there were 1941±371 CD4+ T cells/mm2 (Fig 3B), but as early as 6 days PI, lung CD4+ T cells had decreased significantly (1056±364 cells/mm2, p<0.05, non-parametric Mann-Whitney U test) and reached a nadir at 10 days PI (777±400 cells/mm2, p<0.05, Fig 3D) and remained depleted through 12 weeks post infection (899±280 cells/mm2, p<0.01, Fig 3E and 3F).