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SummaryTumour necrosis factor (TNF)-a is crucial for resistance to Trypanosoma cruzi acute infection, but there is scant information on its role during the chronic phase. To address this issue, we analysed whether a short treatment with a TNF-a blocker affected the course and characteristics of chronic disease in a rat experimental model of T. cruzi infection. An anti-TNF-a agent (infliximab) was administered during the chronic phase for a period of 4 weeks (3 mg/kg/week), while control infected rats were inoculated with saline physiological solution. Search for parasites yielded non-successful results in all infected groups, irrespective of treatment. Nevertheless, the presence of T. cruzi kDNA in heart tissue was detected in infected and infected plus treated animals. Because infliximab might induce changes in the anti-parasite cytokine response, circulating levels of interleukin (IL)-10, interferon-gamma and nitric oxide were evaluated. An increase in IL-10 levels was observed only in the infected group treated with the anti-TNF-a blocker compared to the remaining groups (P < 0·05). A clear attenuation of histological damage associated with a diminution of cardiac TNF-a mRNA expression was observed in the infected and treated animals compared to the infected and non-treated group. Blocking of TNF-a during a relatively short period in chronically infected rats did not lead to evident parasite reactivation but reduced myocarditis severity significantly, indicating a role of this cytokine in the pathogenesis of chronic myocardial damage.

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Specific anti-OVA IgE was detected in sensitized animals by the PCA (passive cutaneous anaphylaxis) method. In 5 regions of the cecal appendix we observed a significant increase in the number of macrophages in sensitized animals (G2) versus the control group (G1). The observed sensitization-mediated increase in cells is probably related to enhanced recruitment of monocytes from peripheral blood towards the appendix. This process could be induced by chemical mediators, and demonstrates macrophage participation in local immune response during sensitization phenomena.