Programmed necrotic cell death induced by the tumor necrosis factor alpha (TNF-α) family of cytokines is dependent on a kinase cascade consisting of receptor-interacting kinases RIP1 and RIP3. How these kinase activities cause cells to die by necrosis is not known. The mixed lineage kinase domain-like protein MLKL is a functional RIP3 substrate that binds to RIP3 through its kinase-like domain but lacks kinase activity of its own. RIP3 phosphorylates MLKL at the T357 and S358 sites. Reported here is the development of a monoclonal antibody that specifically recognizes phosphorylated MLKL in cells dying of this pathway and in human liver biopsy samples from patients suffering from drug-induced liver injury. The phosphorylated MLKL forms an oligomer that binds to phosphatidylinositol lipids and cardiolipin. This property allows MLKL to move from the cytosol to the plasma and intracellular membranes, where it directly disrupts membrane integrity, resulting in necrotic death.

Dysfunctional immune response in the COVID-19 patients is a recurrent theme impacting symptoms and mortality, yet the detailed understanding of pertinent immune cells is not complete. We applied single-cell RNA sequencing to 284 samples from 196 COVID-19 patients and controls and created a comprehensive immune landscape with 1.46 million cells. The large dataset enabled us to identify that different peripheral immune subtype changes were associated with distinct clinical features including age, sex, severity, and disease stages of COVID-19. SARS-CoV-2 RNAs were found in diverse epithelial and immune cell types, accompanied by dramatic transcriptomic changes within viral positive cells. Systemic up-regulation of S100A8/A9, mainly by megakaryocytes and monocytes in the peripheral blood, may contribute to the cytokine storms frequently observed in severe patients. Our data provide a rich resource for understanding the pathogenesis and developing effective therapeutic strategies for COVID-19.

Interleukin-17 (IL-17)-producing CD4M ore than 350 million people worldwide suffer from persistent infection with hepatitis B virus (HBV) and are at risk for developing liver cirrhosis and hepatocellular carcinoma. 1 HBV itself is noncytopathic, but immune-mediated liver damage often occurs in patients with both acute and chronic HBV infection. Such damage has conventionally been attributed to killing of infected hepatocytes by virus-specific cytotoxic CD8 ϩ T cells. [2][3][4] Increasing evidence, however, suggests that non-HBV-specific inflammatory infiltration into the liver is likely responsible for hepatic pathology in patients with chronic hepatitis B (CHB). 5,6 For example, in HBV infection activated HBV-specific CD8 ϩ T cells are often present at high levels in the livers of patients without evident liver inflammation; by contrast, nonantigen-specific lymphocytes were found to be massively infiltrated into the livers of patients with hepatic inflammation. 7 An HBV transgenic mouse model further reinforced the concept that liver inflammation initiated by virus-specific CD8 ϩ T cells is amplified by other lymphocytes. 4,8 Indeed, a large number of immune cells, including myeloid dendritic cells (mDCs), plasmacytoid dendritic cells, and FoxP3-positive regulatory T cells can

Interleukin-22 (IL-22) is known to play a key role in promoting antimicrobial immunity, inflammation, and tissue repair at barrier surfaces by binding to the receptors IL-10R2 and IL-22R1. IL-22R1 is generally thought to be expressed exclusively in epithelial cells. In this study, we identified high levels of IL-10R2 and IL-22R1 expression on hepatic stellate cells (HSCs), the predominant cell type involved in liver fibrogenesis in response to liver damage. In vitro treatment with IL-22 induced the activation of signal transducer and activator of transcription 3 (STAT3) in primary mouse and human HSCs. IL-22 administration prevented HSC apoptosis in vitro and in vivo, but surprisingly, the overexpression of IL-22 via either gene targeting (IL-22 transgenic mice) or exogenous administration of adenovirus expressing IL-22 reduced liver fibrosis and accelerated the resolution of liver fibrosis during recovery. Furthermore, IL-22 overexpression or treatment increased the number of senescence-associated β-galactosidase-positive HSCs and decreased α-smooth muscle actin expression in fibrotic livers in vivo and cultured HSCs in vitro. Deletion of STAT3 prevented IL-22-induced HSC senescence in vitro, whereas the overexpression of a constitutively activated form of STAT3 promoted HSC senescence via p53- and p21-dependent pathways. Finally, IL-22 treatment upregulated suppressor of cytokine signaling 3 expression in HSCs. Immunoprecipitation analyses revealed that SOCS3 bound p53 and subsequently increased the expression of p53 and its target genes, contributing to IL-22-mediated HSC senescence. Conclusion IL-22 induces the senescence of HSCs, which express both IL-10R2 and IL-22R1, thereby ameliorating liver fibrogenesis. The anti-fibrotic effect of IL-22 is likely mediated via the induction of HSC senescence in addition to the previously discovered hepatoprotective functions of IL-22.

The coronavirus disease 2019 (COVID-19) pandemic poses a current world-wide public health threat. However, little is known about its hallmarks compared to other infectious diseases. Here, we report the single-cell transcriptional landscape of longitudinally collected peripheral blood mononuclear cells (PBMCs) in both COVID-19- and influenza A virus (IAV)-infected patients. We observed increase of plasma cells in both COVID-19 and IAV patients and XIAP associated factor 1 (XAF1)-, tumor necrosis factor (TNF)-, and FAS-induced T cell apoptosis in COVID-19 patients. Further analyses revealed distinct signaling pathways activated in COVID-19 (STAT1 and IRF3) versus IAV (STAT3 and NFκB) patients and substantial differences in the expression of key factors. These factors include relatively increase of interleukin ( IL ) 6R and IL6ST expression in COVID-19 patients but similarly increased IL-6 concentrations compared to IAV patients, supporting the clinical observations of increased proinflammatory cytokines in COVID-19 patients. Thus, we provide the landscape of PBMCs and unveil distinct immune response pathways in COVID-19 and IAV patients.