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Virus-induced cell death is a key contributor to COVID-19 pathology. Cell death induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is well studied in myeloid cells but less in its primary host cell type, angiotensin-converting enzyme 2 (ACE2)–expressing human airway epithelia (HAE). SARS-CoV-2 induces apoptosis, necroptosis, and pyroptosis in HAE organotypic cultures. Single-cell and limiting-dilution analysis revealed that necroptosis is the primary cell death event in infected cells, whereas uninfected bystanders undergo apoptosis, and pyroptosis occurs later during infection. Mechanistically, necroptosis is induced by viral Z-RNA binding to Z-DNA–binding protein 1 (ZBP1) in HAE and lung tissues from patients with COVID-19. The Delta (B.1.617.2) variant, which causes more severe disease than Omicron (B1.1.529) in humans, is associated with orders of magnitude–greater Z-RNA/ZBP1 interactions, necroptosis, and disease severity in animal models. Thus, Delta induces robust ZBP1-mediated necroptosis and more disease severity. Editor's summary: SARS-CoV-2 infection triggers multiple cell death pathways that contribute to disease severity. Here, Liang et al. characterized cell death mechanisms in angiotensin-converting enzyme 2 (ACE2)–expressing cells and primary human airway epithelial (HAE) cell cultures during SARS-CoV-2 infection and in autopsied lungs from patients with COVID-19. Necroptosis was the primary form of cell death and was induced by viral Z-RNA binding to Z-DNA binding protein-1 (ZBP-1). Infected and bystander cells underwent apoptosis, but limiting dilution analysis showed that apoptosis was a bystander effect. The Delta variant induced much greater Z-RNA/ZBP-1 interactions and necroptosis compared with Omicron, thus suggesting a mechanism associated with greater disease severity (see related Focus by Wong and Perlman). —Christiana N. Fogg [ABSTRACT FROM AUTHOR]

As a hallmark of immunological aging, low-grade, chronic inflammation with accumulation of effector memory T cells contributes to increased susceptibility to many aging-related diseases. While the proinflammatory state of aged T cells indicates a dysregulation of immune homeostasis, whether and how aging drives regulatory T cell (Treg) aging and alters Treg function are not fully understood owing to a lack of specific aging markers. Here, by a combination of cellular, molecular, and bioinformatic approaches, we discovered that Tregs senesce more severely than conventional T (Tconv) cells during aging. We found that Tregs from aged mice were less efficient than young Tregs in suppressing Tconv cell function in an inflammatory bowel disease model and in preventing Tconv cell aging in an irradiation-induced aging model. Furthermore, we revealed that DDB1- and CUL4-associated factor 1 (DCAF1) was downregulated in aged Tregs and was critical to restrain Treg aging via reactive oxygen species (ROS) regulated by glutathione-5-transferase P (GSTP1). Importantly, interfering with GSTP1 and ROS pathways reinvigorated the proliferation and function of aged Tregs. Therefore, our studies uncover an important role of the DCAF1/GSTP1/ROS axis in Treg senescence, which leads to uncontrolled inflammation and immunological aging., Introduction Immunological aging is associated with declined immunity (immunosenescence) and chronic nonspecific inflammation (inflammaging) (1), contributing to age-associated morbidities and mortalities, including infection, cancer, and autoimmunity, which are detrimental to [...]

While most NOD‐like receptors (NLRs) are predominately expressed by innate immune cells, NLRC3, an inhibitory NLR of immune signaling, exhibits the highest expression in lymphocytes. The role of NLRC3 or any NLRs in B lymphocytes is completely unknown. Gammaherpesviruses, including human Epstein–Barr virus (EBV) and murine gammaherpesvirus 68 (MHV‐68), establish latent infection in B lymphocytes, which requires elevated NF‐κB. This study shows that during latent EBV infection of human B cells, viral‐encoded latent membrane protein 1 (LMP1) decreases NLRC3 transcript. LMP1‐induced‐NF‐κB activation suppresses the promoter activity of NLRC3 via p65 binding to the promoter. Conversely, NLRC3 inhibits NF‐κB activation by promoting the degradation of LMP1 in a proteasome‐dependent manner. In vivo, MHV‐68 infection reduces Nlrc3 transcripts in splenocytes, and Nlrc3‐deficient mice show greater viral latency than controls. These results reveal a bidirectional regulatory circuit in B lymphocytes, where viral latent protein LMP1 reduces NLRC3 expression, while NLRC3 disrupts gammaherpesvirus latency, which is an important step for tumorigenesis. [ABSTRACT FROM AUTHOR]

Author(s): Song Zhang [1, 2]; Motoki Takaku [3]; Liyun Zou [1, 2]; Ai-di Gu [1, 2]; Wei-chun Chou [1, 2, 4]; Ge Zhang [1, 2, 5]; Bing Wu [1, 2]; [...]

The inflammasomes are innate immune system receptors and sensors that regulate the activation of caspase-1 and induce inflammation in response to infectious microbes and molecules derived from host proteins. They have been implicated in a host of inflammatory disorders. Recent developments have greatly enhanced our understanding of the molecular mechanisms by which different inflammasomes are activated. Additionally, increasing evidence in mouse models, supported by human data, strongly implicates an involvement of the inflammasome in the initiation or progression of diseases with a high impact on public health, such as metabolic disorders and neurodegenerative diseases. Finally, recent developments pointing toward promising therapeutics that target inflammasome activity in inflammatory diseases have been reported. This review will focus on these three areas of inflammasome research., Inflammation is a protective immune response mounted by the evolutionarily conserved innate immune system in response to harmful stimuli, such as pathogens, dead cells or irritants, and is tightly regulated [...]

Angiotensin-converting enzyme 2 (ACE2), part of the renin-angiotensin system (RAS), serves as an entry point for SARS-CoV-2, leading to viral proliferation in permissive cell types. Using mouse lines in which the Ace2 locus has been humanized by syntenic replacement, we show that regulation of basal and interferon induced ACE2 expression, relative expression levels of different ACE2 transcripts, and sexual dimorphism in ACE2 expression are unique to each species, differ between tissues, and are determined by both intragenic and upstream promoter elements. Our results indicate that the higher levels of expression of ACE2 observed in the lungs of mice relative to humans may reflect the fact that the mouse promoter drives expression of ACE2 in populous airway club cells while the human promoter drives expression in alveolar type 2 (AT2) cells. In contrast to transgenic mice in which human ACE2 is expressed in ciliated cells under the control of the human FOXJ1 promoter, mice expressing ACE2 in club cells under the control of the endogenous Ace2 promoter show a robust immune response after infection with SARS-CoV-2, leading to rapid clearance of the virus. This supports a model in which differential expression of ACE2 determines which cell types in the lung are infected, and this in turn modulates the host response and outcome of COVID-19. Author summary: SARS-CoV-2, the virus responsible for COVID-19, infects the human respiratory tract by binding to angiotensin-converting enzyme 2 (ACE2), a protein on the outer surface of cells that is exposed to the air we inhale. Differences in the structure of ACE2 between mouse and man prevent the virus from infecting cells lining the airways of the mouse, limiting the usefulness of wildtype mice as a model system for studying COVID-19. To circumvent this problem, we have created two mouse lines in which the chromosomal segment that encodes the mouse ACE2 protein has been replaced with the equivalent segment of human DNA. In the first of these lines, expression of human ACE2 is regulated by the mouse upstream promoter, while in the second line it is regulated by the human upstream promoter. Using these mice, we show both qualitative and quantitative differences between ACE2 expression driven by the mouse and human promoters that are likely to impact disease progression in the two species. Mice expressing the full-length human ACE2 gene under the control of its own promoter should provide a useful model system for understanding the complex pathological processes and immune responses associated with COVID-19 in humans. [ABSTRACT FROM AUTHOR]

The inflammasome regulates the release of caspase activation-dependent cytokines, including interleukin (IL)-1β, IL-18 and high-mobility group box 1 (HMGB1) (1-5). By studying HMGB1 release mechanisms, here we identify a role for double-stranded RNA-dependent protein kinase (PKR, also known as EIF2AK2) in inflammasome activation. Exposure of macrophages to inflammasome agonists induced PKR autophosphorylation. PKR inactivation by genetic deletion or pharmacological inhibition severely impaired inflammasome activation in response to double-stranded RNA, ATP, monosodium urate, adjuvant aluminium, rotenone, live Escherichia coli, anthrax lethal toxin, DNA transfection and Salmonella typhimurium infection. PKR deficiency significantly inhibited the secretion of IL-1β, IL-18 and HMGB1 in E. coli-induced peritonitis. PKR physically interacts with several inflammasome components, including NOD-like receptor (NLR) family pyrin domain-containing 3 (NLRP3), NLRP1, NLR family CARD domain-containing protein 4 (NLRC4), absent in melanoma 2 (AIM2), and broadly regulates inflammasome activation. PKR autophosphorylation in a cell-free system with recombinant NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC, also known as PYCARD) and pro-caspase-1 reconstitutes inflammasome activity. These results show a crucial role for PKR in inflammasome activation, and indicate that it should be possible to pharmacologically target this molecule to treat inflammation., HMGB1, a ubiquitous nuclear and cytosolic protein, is released into the extracellular space during sterile inflammation and infection (6). Immunocompetent cells secrete HMGB1 after stimulation with microbial products and other [...]