Abstract
Host resistance to Trypanosoma cruzi infection is dependent on both natural and acquired immune responses. During the early acute phase of infection in mice, natural killer (NK) cell-derived IFN-gamma is involved in controlling intracellular parasite replication, mainly through the induction of nitric oxide biosynthesis by activated macrophages. We have shown that IL-12, a powerful inducer of IFN-gamma production by NK cells, is synthesized soon after trypomastigote-macrophage interaction. The role of IL-12 in the control of T. cruzi infection in vivo was determined by treating infected mice with anti-IL-12 monoclonal antibody (mAb) and analyzing both parasitemia and mortality during the acute phase of infection. The anti-IL-12 mAb-treated mice had higher levels of parasitemia and mortality compared to control mice. Also, treatment of infected mice with mAb specific for IFN-gamma or TNF-alpha inhibited the protective effect of exogenous IL-12. On the other hand, TGF-beta and IL-10 produced by infected macrophages inhibited the induction and effects of IL-12. Therefore, while IL-12, TNF-alpha and IFN-gamma correlate with resistance to T. cruzi infection, TGF-beta and IL-10 promote susceptibility. These results provide support for a role of innate immunity in the control of T. cruzi infection. In addition to its protective role, IL-12 may also be involved in the modulation of T. cruzi-induced myocarditis, since treatment of infected mice with IL-12 or anti-IL-12 mAb leads to an enhanced or decreased inflammatory infiltrate in the heart, respectively. Understanding the role of the cytokines produced during the acute phase of T. cruzi infection and their involvement in protection and pathogenesis would be essential to devise new vaccines or therapies.
Highlights
Host resistance to Trypanosoma cruzi infection is dependent on both natural and acquired immune responses
We have suggested that IFN-γ is important in the control of acute infection when produced shortly after parasite injection and that IFN-γ may limit early parasite replication by inducing macrophage activation, through stimulation of tumor necrosis factor secretion [5] and activation of nitric oxide synthase [6,7], or by down-regulating Th2 differentiation, leading to a decrease in the levels of secreted IL10
We have shown that inhibition of IL-10 by anti-IL-10 monoclonal antibody leads to an increased T. cruzi-induced IFN-γ production in vitro [5] and in vivo [10], suggesting that this cytokine may be a potent inhibitor of IFN-γ production during T. cruzi infection in mice and that early resistance to T. cruzi infection may be mediated by the pattern of IFN-γ/IL-10 produced
Summary
Host resistance to Trypanosoma cruzi infection is dependent on both natural and acquired immune responses. In addition to its protective role, IL-12 may be involved in the modulation of T. cruzi-induced myocarditis, since treatment of infected mice with IL12 or anti-IL-12 mAb leads to an enhanced or decreased inflammatory infiltrate in the heart, respectively.
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