Nitric oxide inhibits the accumulation of CD4+CD44hiTbet+CD69lo T cells in mycobacterial infection

Animals lacking the inducible nitric oxide synthase gene (nos2-/-) are less susceptible to Mycobacterium avium strain 25291 and lack nitric oxide-mediated immunomodulation of CD4+ T cells. Here we show that the absence of nos2 results in increased accumulation of neutrophils and both CD4+ and CD8+ T cells within the M. avium containing granuloma. Examination of the T-cell phenotype in M. avium infected mice demonstrated that CD4+CD44hi effector T cells expressing the Th1 transcriptional regulator T-bet (T-bet+) were specifically reduced by the presence of nitric oxide. Importantly, the T-bet+ effector population could be separated into CD69hi and CD69lo populations, with the CD69lo population only able to accumulate during chronic infection within infected nos2-/- mice. Transcriptomic comparison between CD4+CD44hiCD69hi and CD4+CD44hiCD69lo populations revealed that CD4+CD44hiCD69lo cells had higher expression of the integrin itgb1/itga4 (VLA-4, CD49d/CD29). Inhibition of Nos2 activity allowed increased accumulation of the CD4+CD44hiT-bet+CD69lo population in WT mice as well as increased expression of VLA-4. These data support the hypothesis that effector T cells in mycobacterial granulomata are not a uniform effector population but exist in distinct subsets with differential susceptibility to the regulatory effects of nitric oxide.