Severe cases of COVID-19 are characterized by a strong inflammatory process that may ultimately lead to organ failure and patient death. The NLRP3 inflammasome is a molecular platform that promotes inflammation via cleavage and activation of key inflammatory molecules including active caspase-1 (Casp1p20), IL-1β, and IL-18. Although participation of the inflammasome in COVID-19 has been highly speculated, the inflammasome activation and participation in the outcome of the disease are unknown. Here we demonstrate that the NLRP3 inflammasome is activated in response to SARS-CoV-2 infection and is active in COVID-19 patients. Studying moderate and severe COVID-19 patients, we found active NLRP3 inflammasome in PBMCs and tissues of postmortem patients upon autopsy. Inflammasome-derived products such as Casp1p20 and IL-18 in the sera correlated with the markers of COVID-19 severity, including IL-6 and LDH. Moreover, higher levels of IL-18 and Casp1p20 are associated with disease severity and poor clinical outcome. Our results suggest that inflammasomes participate in the pathophysiology of the disease, indicating that these platforms might be a marker of disease severity and a potential therapeutic target for COVID-19.

bThe relationship established between Leishmania infantum and the vertebrate host can lead to a self-healing infection or to the manifestation of visceral leishmaniasis, a chronic systemic infection associated with high rates of mortality. We hypothesized that regulatory cytokines, such as interleukin-27 (IL-27), play a role in susceptibility to L. infantum infection. IL-27 is a heterodimeric cytokine composed of IL-27p28 and EBi3 subunits which, when combined, bind to IL-27R, leading to STAT-1 and -3 activation, playing a role in the regulation of the immune response. We observed in this work that IL-27 regulates the Th1/Th17 profiles in a mouse model of visceral leishmaniasis (VL) caused by L. infantum. We showed here that the pathogen recognition by endosomal Toll-like receptors triggers a type I interferon (IFN) response, which acts through the type I IFN receptor and interferon regulatory factor 1 to induce IL-27 production by macrophages. Furthermore, IL-27 plays a major regulatory role in vivo, because Ebi3 ؊/؊ mice can efficiently control parasite replication despite reduced levels of IFN-␥ compared to wild-type mice. On the other hand, the absence of Ebi3 leads to exacerbated IL-17A production in the infected organs as well as in a coculture system, suggesting a direct regulatory action of IL-27 during L. infantum infection. As a consequence of exacerbated IL-17A in Ebi3 ؊/؊ mice, a greater neutrophil influx was observed in the target organs, playing a role in parasite control. Thus, this work unveiled the molecular steps of IL-27 production after L. infantum infection and demonstrated its regulatory role in the IL-17A-neutrophil axis. Visceral leishmaniasis (VL), or kala-azar, is a systemic chronic disease with high mortality rates if not treated. It is caused by the parasites Leishmania infantum and L. donovani, and it is estimated that 300,000 new cases and 20,000 deaths occur annually (http://www.who.int/mediacentre/factsheets/fs375/en/). After dermal inoculation by the sandfly vector, the parasite disseminates to the liver, spleen, bone marrow, and lymph nodes of susceptible hosts, causing symptoms such as hepatosplenomegaly, lymphadenopathy, anemia, constant fever, and immunosuppression (1). Even though it is considered one of the six most important parasitic diseases affecting humans, the immunobiology of VL is not completely understood and novel therapeutic approaches are desired.The immune response against Leishmania spp. is critically mediated by gamma interferon (IFN-␥)-producing Th1 cells, which activate macrophages to produce leishmanicidal compounds, such as nitric oxide (NO) (2). Together with IFN-␥, the inflammatory cytokine interleukin-17A (IL-17A) also mediates protection against L. infantum (3, 4). On the other hand, Th2 cytokines are involved in susceptibility to leishmaniasis (2, 5). Moreover, the regulatory cytokines IL-10, IL-21, and IL-27 are produced in the bone marrow of VL patients, suggesting their association with the disease (6).The cytokine IL-27 is a dimer composed of p28...

Background The release of neutrophil extracellular traps (NETs) is associated with inflammation, coagulopathy, and organ damage found in severe cases of COVID-19. However, the molecular mechanisms underlying the release of NETs in COVID-19 remain unclear. Objectives We aim to investigate the role of the Gasdermin-D (GSDMD) pathway on NETs release and the development of organ damage during COVID-19. Methods We performed a single-cell transcriptome analysis in public data of bronchoalveolar lavage. Then, we enrolled 63 hospitalized patients with moderate and severe COVID-19. We analyze in blood and lung tissue samples the expression of GSDMD, presence of NETs, and signaling pathways upstreaming. Furthermore, we analyzed the treatment with disulfiram in a mouse model of SARS-CoV-2 infection. Results We found that the SARS-CoV-2 virus directly activates the pore-forming protein GSDMD that triggers NET production and organ damage in COVID-19. Single-cell transcriptome analysis revealed that the expression of GSDMD and inflammasome-related genes were increased in COVID-19 patients. High expression of active GSDMD associated with NETs structures was found in the lung tissue of COVID-19 patients. Furthermore, we showed that activation of GSDMD in neutrophils requires active caspase1/4 and live SARS-CoV-2, which infects neutrophils. In a mouse model of SARS-CoV-2 infection, the treatment with disulfiram inhibited NETs release and reduced organ damage. Conclusion These results demonstrated that GSDMD-dependent NETosis plays a critical role in COVID-19 immunopathology and suggests GSDMD as a novel potential target for improving the COVID-19 therapeutic strategy.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with a hyperinflammatory state and lymphocytopenia, a hallmark that appears as both signature and prognosis of disease severity outcome. Although cytokine storm and sustained inflammatory state are commonly associated with immune cell depletion, it is still unclear whether direct SARS-CoV-2 infection of immune cells could also play a role in this scenario by harboring virus replication. We found that monocytes, as well as both B and T lymphocytes, were susceptible to SARS-CoV-2 infection in vitro, accumulating double-stranded RNA consistent with viral RNA replication and ultimately leading to expressive T cell apoptosis. In addition, flow cytometry and immunofluorescence analysis revealed that SARS-CoV-2 was frequently detected in monocytes and B lymphocytes from coronavirus disease 2019 (COVID-19) patients. The rates of SARS-CoV-2-infected monocytes in peripheral blood mononuclear cells (PBMCs) from COVID-19 patients increased over time from symptom onset, with SARS-CoV-2-positive monocytes, B cells, and CD4+ T lymphocytes also detected in post mortem lung tissue. These results indicated that SARS-CoV-2 infection of blood circulating leukocytes in COVID-19 patients might have important implications for disease pathogenesis and progression, immune dysfunction, and virus spread within the host.