The innate immune response relies upon pattern recognition receptors (PRRs) to identify the presence of microorganisms and generate an effective response for infection control. The PRRs family is constituted by Toll-like receptors (TLRs) receptors RIG-I-like (RLRs) and Nod-like receptors (NLRs). The NLRs are responsible for the recognition of intracellular pathogens, which can induce activation of caspase-1 by the aggregation of a molecular platform known as inflammasome. Coxiella burnetii is a Gram-negative intracellular bacterium and the causative agent of Q fever, an atypical pneumonia that can result in endocarditis or hepatitis. C. burnetii is highly adapted to evade immune responses and to subvert cellular functions for the establishment of its replicative phagolysosomal vacuole. Importantly, the expression of the Coxiella type IVsecretion system (Dot / Icm) is essential for subversion of host cells. The Dot/Icm system of Coxiella is homolog to the similar to the complex of Legionella pneumophila. Coxiella also express several effectorproteins that are injected into the cytoplasm through the Dot / Icm and must have essential roles in subversion of the normal host cell functions. Previous investigations undertaken by our group revealed that Coxiella is able to inhibit the activation of caspase-1 and secretion of mature IL-1b in response to flagellin-independent activation of inflammasome by L. pneumophila. IWe thus aimed to find an effector of Coxiella that interferes with caspase-1 activation, by performing a screening with a library of flagellin-deficient L. pneumophila mutants adoptively expressing effectors of Coxiella secreted by Dot/Icm system. Surprisingly, we identified a mutant that upon expression of Coxiella secreted effector CBU1823 is not able to activate caspase-1 in macrophages. Herein, we aim to investigate the mechanisms involved in inhibition of activation of caspase-1 by C. burnetii and the effector protein encoded by CBU1823. The development of this proposal will contribute to the elucidation of the processes by which C. burnetii and its effector CBU1823 inhibit the activation of caspase-1 thus contributing to the understanding of this important pathway of the immune response. Additionally, the investigation of the mechanisms by which CBU1823 inhibits the inflammasome can help to identify possible targets for the development of therapy for various inflammatory rheumatic diseases characterized by constitutive activation of caspase-1.
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