Mycobacterium tuberculosis persistence in various adipose depots of infected mice and the effect of anti-tubercular therapy

The adipocytes are one of the non-professional phagocytes postulated to be a haven for Mycobacterium tuberculosis during persistence in the human host. The adipocyte - M. tuberculosis interaction data available to date are ex vivo. The present study was primarily aimed to investigate M. tuberculosis infection of adipocytes in course of infection of mouse model. Using primary murine adipocytes, the study first confirmed the infection and immunomodulation of natural adipocytes by M. tuberculosis. The bacilli could be isolated form visceral, subcutaneous, peri renal and mesenteric adipose depots of immunocompetent mice infected with M. tuberculosis intravenously. The bacilli could be isolated from adipocytes and the stromal vascular fraction, even though the numbers were significantly higher in the latter. The bacterial burden in the adipose depots was comparable to those in lungs in the early phase of infection. But with time, the burden in the adipose depots was either decreased or kept under control, despite the increasing burden in the lungs. Infected mice treated with standard anti tubercular drugs, despite effective elimination of bacterial loads in the lungs, continued to harbour M. tuberculosis in adipose depots at loads similar to untreated mice in the late infection phase.