Despite its relatively poor efficacy, Bacillus Calmette-Guérin (BCG) has been used as a tuberculosis (TB) vaccine since its development in 1921. BCG induces robust T helper 1 (Th1) immune responses but, for many individuals, this is not sufficient for host resistance against Mycobacterium tuberculosis (M. tb) infection. Here we provide evidence that early secreted antigenic target protein 6 (ESAT-6), expressed by the virulent M. tb strain H37Rv but not by BCG, promotes vaccine-enhancing Th17 cell responses. These activities of ESAT-6 were dependent on TLR-2/MyD88 signalling and involved IL-6 and TGF-β production by dendritic cells. Thus, animals that were previously infected with H37Rv or recombinant BCG containing the RD1 region (BCG::RD1) exhibited improved protection upon re-challenge with virulent H37Rv compared with mice previously infected with BCG or RD1-deficient H37Rv (H37RvΔRD1). However, TLR-2 knockout (TLR-2-/-) animals neither showed Th17 responses nor exhibited improved protection in response to immunization with H37Rv. Furthermore, H37Rv and BCG::RD1 infection had little effect on the expression of the anti-inflammatory microRNA-146a (miR146a) in dendritic cells (DCs), whereas BCG and H37RvΔRD1 profoundly induced its expression in DCs. Consistent with these findings, ESAT-6 had no effect on miR146a expression in uninfected DCs, but dramatically inhibited its upregulation in BCG-infected or LPS-treated DCs. Collectively, our findings indicate that, in addition to Th1 immunity induced by BCG, RD1/ESAT-6-induced Th17 immune responses are essential for optimal vaccine efficacy.

Background: Modulation of host miRNAs coincides with increased pathogenicity in various infectious diseases.Results: miR-99b is up-regulated in M. tuberculosis-infected dendritic cells, which inhibits production of proinflammatory cytokines.Conclusion: Our findings unfold a novel immune evasion strategy of M. tuberculosis by modulating miRNAs.Significance: Our study opens up the possibility to design vaccines and immunotherapies for tuberculosis by targeting specific miRNAs.

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malaria infection triggers pro-inflammatory responses in humans that are detrimental to host health. Parasite-induced enhancement in cytokine levels correlate with malariaassociated pathologies. Here we show that parasite tyrosyl-tRnA synthetase (PfTyrRs), a housekeeping protein translation enzyme, induces pro-inflammatory responses from host immune cells. PfTyrRs exits from the parasite cytoplasm into the infected red blood cell (iRBC) cytoplasm, from where it is released into the extracellular medium on iRBC lysis. using its ELR peptide motif, PfTyrRs specifically binds to and internalizes into host macrophages, leading to enhanced secretion of the pro-inflammatory cytokines TnF-α and IL-6. PfTyrRs-macrophage interaction also augments expression of adherence-linked host endothelial receptors ICAm-1 and VCAm-1. our description of PfTyrRs as a parasite-secreted protein that triggers proinflammatory host responses, along with its atomic resolution crystal structure in complex with tyrosyl-adenylate, provides a novel platform for targeting PfTyrRs in anti-parasitic strategies.

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