IFNγ blockade in Mycobacterium tuberculosis infected macaques alters the granuloma environment but not bacterial control

Abstract

Abstract IFNγ is considered the primary mediator of adaptive immunity to Mycobacterium tuberculosis (Mtb) infection. In mice, control of Mtb requires IFNγ. In humans, IFNγ is critical for resistance to infection with non-tuberculous mycobacteria (NTM), but its relative requirement for control of pulmonary tuberculosis (TB) is less clear. Here we block IFNγR1 signaling in macaques at different times following Mtb infection. IFNγ blockade from day 45 to 49 post-infection rapidly reduced 18 FDG-PET/CT scores and broadly enhanced anti-viral-like inflammatory responses. Strikingly, IFNγR1 blockade for the first three months of infection had no impact on bacterial loads despite suppression of bioactive IFNγ in granulomas and changes to host immune responses and granuloma structure. We find individuals from Mtb endemic regions with anti-IFNγ neutralizing autoantibodies who develop NTM disease and not TB despite evidence of previous exposure to Mtb. Lastly, we show that mice over-estimate the importance IFNγ in host resistance to TB due to a species-specific induction of iNOS by IFNγ. Thus, while IFNγ has immunoregulatory effects in granulomas, normal resistance to TB in macaques and humans likely requires little IFNγR1 signaling during infection, indicating that the major mechanisms of adaptive immunity to Mtb infection remain unknown.