Visceral Leishmaniasis in mice devoid of tumor necrosis factor and response to treatment
Tumor necrosis factor (TNF)-deficient mice were challenged with Leishmania donovani to characterize TNF in the response of visceral intracellular infection to antileishmanial chemotherapy. In wild-type controls (i) liver infection peaked at week 2 and resolved, (ii) discrete liver granulomas developed at weeks 2 to 4 and involuted, and (iii) leishmanicidal responses to antimony (Sb), amphotericin B (AmB), and miltefosine were intact. In TNF knockout (KO) mice (i) initial liver infection was unrestrained, plateaued, and then declined somewhat by week 6, (ii) an absent early granulomatous reaction abruptly accelerated with striking tissue inflammation, widespread hepatic necrosis, and 100% mortality by week 10, and (iii) while the initial response to AmB and miltefosine was intact, killing induced by Sb therapy was reduced by >50%. Although initial AmB treatment during weeks 2 to 3 killed 98% of liver parasites, 75% of AmB-treated KO mice subsequently relapsed and died by week 12; however, additional maintenance AmB preserved long-term survival. These results for a model of visceral infection indicate that endogenous TNF is required early on to control intracellular L. donovani, support granuloma development, and mediate optimal initial effects of Sb and prevent relapse after ordinarily curative AmB treatment. A compensatory, TNF-independent antileishmanial mechanism developed in TNF KO mice; however, its effect was uncontrolled fatal inflammation. Chemotherapeutic elimination of the parasite stimulus reversed the hyperinflammatory response and preserved survival.