Non-canonical NLRP3 inflammasome activation and IL-1β signaling are necessary to L. amazonensis control mediated by P2X7 receptor and leukotriene B4.

Leishmaniasis is a neglected tropical disease affecting millions of individuals worldwide. P2X7 receptor has been linked to the elimination of Leishmania amazonensis. Biological responses evoked by P2X7 receptor activation have been well-documented, including apoptosis, phagocytosis, cytokine release, such as IL-1 beta. It was demonstrated that NLRP3 inflammasome activation and IL-1 beta signaling participated in resistance against L. amazonensis. Furthermore, our group has shown that L. amazonensis elimination through P2X7 receptor activation depended on leukotriene B-4 (LTB4) production and release. Therefore, we investigated whether L. amazonensis elimination by P2X7 receptor and LTB4 involved NLRP3 inflammasome activation and IL-1 beta signaling. We showed that macrophages from NLRP3(-/-), ASC(-/-), Casp-1/11(-/-), gp91(phox-/- ,) and IL-1R(-/-) mice treated with ATP or LTB4 did not decrease parasitic load as was observed in WT mice. When ASC(-/-) macrophages were treated with exogenous IL-1 beta, parasite killing was noted, however, we did not see parasitic load reduction in IL-1R(-/-) macrophages. Similarly, macrophages from P2X7 receptor-deficient mice treated with IL-1 beta also showed decreased parasitic load. In addition, when we infected Casp-11(-/-) macrophages, neither ATP nor LTB4 were able to reduce parasitic load, and Casp-11(-/-) mice were more susceptible to L. amazonensis infection than were WT mice. Furthermore, P2X7(-/-) L. amazonensis-infected mice locally treated with exogenous LTB4 showed resistance to infection, characterized by lower parasite load and smaller lesions compared to untreated P2X7(-/-) mice. A similar observation was noted when infected P2X7(-/-) mice were treated with IL-1 beta, i.e., lower parasite load and smaller lesions compared to P2X7(-/-) mice. These data suggested that L. amazonensis elimination mediated by P2X7 receptor and LTB4 was dependent on non-canonical NLRP3 inflammasome activation, ROS production, and IL-1 beta signaling. Author summary Leishmania spp. is a protozoan parasite that infects human and causes several diseases. Leishmania amazonensis causes cutaneous leishmaniasis (CL) and mucocutaneous leishmaniasis (MCL). Leishmania parasites preferentially infect macrophages. In macrophages, several mechanisms have been described as controlling L. amazonensis infection. Here, we showed that P2X7 receptor and LTB4 eliminated L. amazonensis in macrophages by a pathway dependent on non-canonical NLRP3 inflammasome activation and IL-1 beta signaling.