Discussion

Leishmaniasis results from the capacity of intracellular Leishmania amastigotes to subvert host cell immune functions and hijack macrophage metabolic pathways. We observed that infection of primary macrophages with virulent Leishmania amazonensis amastigotes isolated from lesions of nude mice does not trigger inflammasome activation as judged by the lack of ASC speck formation, caspase-1 activation and secretion of IL-1beta / IL-18. This absence of inflammasome activation was sustained up to 30 days post infection, and was associated with a coordinated reprogramming of the host macrophage functions at the transcription level as revealed by Affymetrix GeneChip and real time quantitative PCR technologies. More specifically, these experiments revealed a down-modulation of NF-kB activators (TLRs, signaling kinases, NF-kB members) and an up-modulation of inhibitors of this pathway (de-ubiquitinating enzymes). These modulations were associated with a decreased transcription of genes whose products define different inflammasomes (NLRP3, NLRC4, AIM2, RIG1) and pro-inflammatory cytokines (IL-1beta / IL-18). Significantly, these subversions were even maintained after LPS / ATP stimulation, resulting in a strong decrease in IL-1beta and IL-18 secretion. Our study describes a new subversion mechanism deployed by amastigotes that target transcription of key regulators of the NF-kB and inflammasome activation pathways to dampen the macrophage pro-inflammatory response and favor parasite survival.