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Preclinical mouse models that recapitulate some characteristics of coronavirus disease (COVID-19) will facilitate focused study of pathogenesis and virus–host responses. Human agniotensin-converting enzyme 2 (hACE2) serves as an entry receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to infect people via binding to envelope spike proteins. Herein we report development and characterization of a rapidly deployable COVID-19 mouse model. C57BL/6J (B6) mice expressing hACE2 in the lung were transduced by oropharyngeal delivery of the recombinant human adenovirus type 5 that expresses hACE2 (Ad5-hACE2). Mice were infected with SARS-CoV-2 at Day 4 after transduction and developed interstitial pneumonia associated with perivascular inflammation, accompanied by significantly higher viral load in lungs at Days 3, 6, and 12 after infection compared with Ad5-empty control group. SARS-CoV-2 was detected in pneumocytes in alveolar septa. Transcriptomic analysis of lungs demonstrated that the infected Ad5-hACE mice had a significant increase in IFN-dependent chemokines Cxcl9 and Cxcl10, and genes associated with effector T-cell populations including Cd3 g, Cd8a, and Gzmb. Pathway analysis showed that several Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were enriched in the data set, including cytokine–cytokine receptor interaction, the chemokine signaling pathway, the NOD-like receptor signaling pathway, the measles pathway, and the IL-17 signaling pathway. This response is correlative to clinical response in lungs of patients with COVID-19. These results demonstrate that expression of hACE2 via adenovirus delivery system sensitized the mouse to SARS-CoV-2 infection and resulted in the development of a mild COVID-19 phenotype, highlighting the immune and inflammatory host responses to SARS-CoV-2 infection. This rapidly deployable COVID-19 mouse model is useful for preclinical and pathogenesis studies of COVID-19.

In 1967, two toddlers immunized with a formalin-inactivated vaccine against respiratory syncytial virus (FIRSV) in the United States died from enhanced RSV disease (ERD), a severe form of illness resulting from aberrant priming of the antiviral immune response during vaccination. Up to 80% of immunized children subsequently exposed to wild-type virus were hospitalized. These events hampered RSV vaccine development for decades. Here, we provide a characterization of the clinical, immunopathological, and transcriptional signature of fatal human ERD, outlining evidence for safety evaluation of RSV vaccines and a framework for understanding disease enhancement for pathogens in general.

A subunit mucosal vaccine conferred protection against heterologous Klebsiella pneumoniae strains, via IL-17R signaling in lung fibroblasts.

Tissue resident memory (TRM) cells are thought to play a role in lung mucosal immunity to pathogens, but strategies to elicit TRM by mucosal vaccines have not yet been fully realized. Here, we formulated a vaccine composed of outer membrane protein (Omp) X from K. pneumoniae and LTA1 adjuvant that was administered by the intrapulmonary route. This vaccine elicited both Th1 and Th17 cells that shared transcriptional features with cells elicited by heat-killed K. pneumoniae. Antibody responses were required to prevent bacterial dissemination but dispensable for lung-specific immunity. In contrast, lung immunity required CD4(+) T cells, STAT3 expression, and IL-17R signaling in fibroblasts. Lung-specific CD4(+) T cells from OmpX+LTA1 immunized mice were observed homing to the lung and could mediate protection against infection in an adoptive transfer model. Vaccine-elicited Th17 cells showed reduced plasticity and were resistant to the immunosuppressant FK506 compared with Th1 cells, and Th17 cells conferred protection under conditions of transplant immunosuppression. These data demonstrate a novel vaccine strategy that elicits lung TRM cells and promotes serotype-independent immunity to K. pneumoniae.

Background The goal of this study was to determine if IL-22:Fc would Acute Respiratory Distress Syndrome (ARDS). Summary background data No therapies exist for ARDS and treatment is purely supportive. Interleukin-22 (IL-22) plays an integral component in recovery of the lung from infection. IL-22:Fc is a recombinant protein with a human FC immunoglobulin that increases the half-life of IL-22. Study design ARDS was induced in C57BL/6 mice with intra-tracheal lipopolysaccharide (LPS) at a dose of 33.3 or 100 ug. In the low-dose LPS group (LDG), IL-22:FC was administered via tail vein injection at 30 minutes (n = 9) and compared to sham (n = 9). In the high-dose LPS group (HDG), IL-22:FC was administered (n = 11) then compared to sham (n = 8). Euthanasia occurred after bronchioalveolar lavage (BAL) on post-injury day 4. Results In the LDG, IL-22:FC resulted in decreased protein leak (0.15 vs. 0.25 ug/uL, p = 0.02). BAL protein in animals receiving IL-22:Fc in the HDG was not different. For the HDG, animals receiving IL-22:Fc had lower BAL cell counts (539,636 vs 3,147,556 cells/uL, p = 0.02). For the HDG, IL-6 (110.6 vs. 527.1 pg/mL, p = 0.04), TNF-α (5.87 vs. 25.41 pg/mL, p = 0.04), and G-CSF (95.14 vs. 659.6, p = 0.01) levels were lower in the BAL fluid of IL-22:Fc treated animals compared to sham. Conclusions IL-22:Fc decreases lung inflammation and lung capillary leak in ARDS. IL-22:Fc may be a novel therapy for ARDS.

Infections due to carbapenem-resistant Klebsiella pneumoniae have emerged as a global threat due to its widespread antimicrobial resistance. Transplant recipients and patients with hematologic malignancies have high mortality rate, suggesting host factors in susceptibility. We developed a model of pulmonary infection using ST258 strain C4, KPC-2 clone, which are predominant K. pneumoniae carbapenemase–producing (KPC-producing) bacteria, and demonstrated that Rag2(–/–) Il2rg(–/–) mice — but not WT C57BL/6 or Rag2(–/–) mice — were susceptible to this opportunistic infection. Using single cell RNA sequencing in infected Rag2(–/–) mice, we identified distinct clusters of Ifng(+) NK cells and Il17a(+), Il22(+), and inducible T cell costimulatory molecule–positive (ICOS(+)) group 3 innate lymphoid cells (ILCs) that were critical for host resistance. As solid organ transplantation is a risk factor, we generated a more clinically relevant model using FK506 in WT C57BL/6 mice. We further demonstrated that immunotherapy with recombinant IL-22 treatment ameliorated the ST258 pulmonary infection in both FK506-treated WT mice and Rag2(–/–) Il2rg(–/–) mice via hepatic IL-22ra1 signaling. These data support the development of host-directed immunotherapy as an adjunct treatment to new antibiotics.

The type 17 cytokine receptors are thought to play critical roles in mucosal immunity. We have shown that intestinal epithelial expression of IL–17 receptor control the development of microbiota in the terminal ileum and conditional deletion of these receptors results in overgrowth of segmented filamentous bacteria. To study the roles of these receptors in response to an attaching and effacing pathogen we challenged intestinal specific Il17ra mice and Il17rc mice with Citrobacter rodentium (C. rodentium). Conditional deletion of Il17ra and l17rc Iresulted in increased bacterial growth in the colon as well as enhanced dissemination to the liver suggesting that intestinal epithelial IL–17 receptors expression is required for control of this infection. This was supported by unbiased RNAseq analysis of the colon that showed diminished expression of Pigr, Tnfsf13 and Nox1 in the absence of Il17ra. IgA has crucial role in mucosal immunity to protect from pathogenic bacteria. PIGR binds dimeric IgA and translocation into lumen, while TNFSF13 activates induce differentiation to plasma cells following–crass switch. C. rodentium specific IgA in stool and C. rodentium specific IgA producing cells in lamina propria were reduced in Il17ra mice. These results suggested IL-17 receptor signaling regulates transcytosis of C. rodentium specific IgA as well as secretion of bacteria specific IgA. On the other hands Nox1 can produce apical hydrogen peroxide. Nox1 null mice were more sensitive for C. rodentium infection. Furthermore Nox1 was expressed by IL–17A stimulation in colonic organoid. Taken together, IL–17 receptor signaling control to produce C. rodentium specific IgA through PIGR and TNFSF13 as well as hydrogen peroxide through NOX1.

Six2+ cap mesenchyme cells, also called nephrons progenitor cells (NPC), are precursors of all epithelial cell types of the nephron, the filtering unit of the kidney. Current evidence indicates that perinatal “old” NPC have a greater tendency to exit the progenitor niche and differentiate into nascent nephrons than their embryonic “young” counterpart. Understanding the underpinnings of NPC aging may offer insights to rejuvenate old NPC and expand the progenitor pool. Here, we compared the chromatin landscape of young and old NPC and found common features reflecting their shared lineage but also intrinsic differences in chromatin accessibility and enhancer landscape supporting the view that old NPC are epigenetically poised for differentiation. Annotation of open chromatin regions and active enhancers uncovered the transcription factor Bach2 as a potential link between the pro-renewal MAPK/AP1 and pro-differentiation Six2/b-catenin pathways that might be of critical importance in regulation of NPC fate. Our data provide the first glimpse of the dynamic chromatin landscape of NPC and serve as a platform for future studies of the impact of genetic or environmental perturbations on the epigenome of NPC.Summary statementHilliard et al. investigated the chromatin landscape of native Six2+ nephron progenitors across their lifespan. They identified age-dependent changes in accessible chromatin and regulatory regions supporting the view that old nephron progenitors are epigenetically poised for differentiation.

Th17 cells producing cytokines, IL-17A and IL-22 are important key player in host defense. We have reported that intestinal epithelial expression of IL-17 receptors in gut epithelial cells control the development of microbiota. To study the roles of these receptors in response to an attaching and effacing pathogen we challenged Citobacter rodenium (C. rodentium) to intestinal epithelial specific IL-17RA or IL-22RA1 KO mice. Conditional deletion of Il17ra or Il22ra1 resulted in increased bacterial growth in the colon as well as enhanced dissemination to the spleen. It suggested both cytokine receptors are required for control of this infection. In addition this was supported by unbiased RNAseq analysis of the colonic epithelium that showed diminished expression of Pigr, Duox2 and Duoxa2 in the absence of IL-17RA signaling and reduced Bcl3 expression in the absence of IL-22ra1 expression. To elucidate whether production from epithelial cells effect bacteria killing we cultured crypt and stimulated IL-17A. It resulted in increasing Pigr, Duoxa2 and Duox2 were associated with increasing bacteria killing. Pigr binds dimeric IgA and translocation into lumen from lamina propria, while Duox2 and Duoxa2 make complex and produce hydrogen peroxide into lumen from apical epithelial cell membrane. These result suggested mucosal immunity to C. rodentium requires both IL-17RA and IL-22ra1 signaling and that IL-17RA regulates transcytosis of C. rodentium specific IgA as well as luminal hydrogen peroxide concentrations to control bacterial growth. In contrast, Il-22Ra1 regulates epithelial Bcl3 expression, which restrains TNFα and NF-κB signaling in the colonic epithelium.

SUMMARY Interleukin (IL)-17 signaling to the intestinal epithelium regulates the intestinal microbiome. Given the reported links between intestinal dysbiosis, bacterial translocation, and liver disease, we hypothesize that intestinal IL-17R signaling plays a critical role in mitigating hepatic inflammation. To test this, we study intestinal epithelium-specific IL-17RA-deficient mice in an immune-driven hepatitis model. At the naive state, these mice exhibit microbiome dysbiosis and increased translocation of bacterial products (CpG DNA), which drives liver IL-18 production. Upon disease induction, absence of enteric IL-17RA signaling exacerbates hepatitis and hepatocyte cell death. IL-18 is necessary for disease exacerbation and is associated with increased activated hepatic lymphocytes based on Ifng and Fasl expression. Thus, intestinal IL-17R regulates translocation of TLR9 ligands and constrains susceptibility to hepatitis. These data connect enteric Th17 signaling and the microbiome in hepatitis, with broader implications on the effects of impaired intestinal immunity and subsequent release of microbial products observed in other extra-intestinal pathologies., In Brief Castillo-dela Cruz et al. describe a unique protective role of intestinal IL-17RA in hepatitis. Disruption of intestinal IL-17RA signaling results in microbiome dysbiosis and translocation of bacterial products, specifically unmethylated CpG DNA, to the liver. This promotes IL-18 production and subsequent lymphocyte activation and cell death to exacerbate liver inflammation., Graphic Abstract