Resistance to infection by Leishmania major has been associated with the development of a Th1 type response that is dependent on the presence of interleukin 12 (IL-12). In this work the involvement of this cytokine in the response to infection by L. braziliensis, a less virulent species in the mouse model, was evaluated. Our results show that while interferon (IFN-γ) deficient (-/-) mice inoculated L. braziliensis develop severe uncontrolled lesions, chronic lesions that remained under control up to 12 weeks of infection were observed in IL-12p40-/- mice. IL 12p40-/- mice had fewer parasites in their lesions than IFN-γ-/- mice. Lymph node cells from IL-12p40-/- were capable of producing low but consistent levels of IFN-γ suggestive of its involvement in parasite control. Furthermore, as opposed to previous reports on L. major-infected animals, no switch to a Th2 response was observed in IL-12p40-/- infected with L. braziliensis. Key words: cutaneous leishmaniasis- Leishmania braziliensis- interleukin 12 The great majority of studies related to the immune response in cutaneous leishmaniasis using the murine model have been carried out using Leishmania major as the prototype species. These studies have established that resistance to infection by this parasite is associated with the development of Leishmania-specific Th1 cells while susceptibility and disease progression is related t
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