Determinants of the immune response in visceral leishmaniasis: Evidence for predominance of endogenous interleukin 4 over interferon-γ production

Accumulating evidence points toward an antagonism between Th 1 and Th 2 focused immune responses decisive for the outcome of parasitic infections with leishmaniae. Interferon-γ (IFN-γ) and interleukin 4 (IL4), the principal cytokines involved in these pathways, as well as IgE and the IgG subclasses differentially modulated by these cytokines, were therefore assessed in 18 Brazilian patients with visceral leishmaniasis. The results are compared to those of a local control group. IL4 was detected in all patient sera but in only one control. Low concentrations of IFN-γ where detectable in 50% of the Brazilian controls but in only two patients. While group medians of mitogen-induced in vitro synthesis of IL4 and IFN-γ were similar, release of these lymphokines correlated inversely in patients (Spearman's ϱ = −0.84). Elevations of serum IgE complement the lymphokine data to indicate prominent TH 2 type responses in clinical infections with Leishmania donovani.