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The avian origin influenza A virus (IAV) H7N9 has caused a considerable number of human infections associated with high rates of death since its emergence in 2013. As a vital component of the host innate immune system, the nucleotide-binding domain leucine-rich repeat containing receptor, pyrin domain containing 3 (NLRP3) inflammasome plays a critical role against H1N1 viral infection. However, the function of NLRP3 inflammasome in host immunological responses to the lethal H7N9 virus is still obscure. Here, we demonstrated that mice deficient for NLRP3 inflammasome components, including NLRP3, caspase-1, and Apoptosis-associated speck-like protein containing a CARD (ASC), were less susceptible to H7N9 viral challenge than wild type (WT) controls. Inflammasome deficiency in these animals led to significantly milder mortality and less pulmonary inflammation compared with WT mice. Furthermore, IL-1 receptor deficient mice also exhibited a higher survival rate than WT controls. Thus, our study reveals that the NLRP3 inflammasome is deleterious for the host during H7N9 infection in mice, which is due to an overwhelming inflammatory response via caspase-1 activation and associated IL-1 signal. Therefore, fine-tuning the activity of NLRP3 inflammasome or IL-1 signaling may be beneficial for the host to control H7N9 associated lethal pathogenesis.

Background Human leukocyte antigen (HLA)‐DP is much less studied than other HLA class II antigens, that is, HLA‐DR and HLA‐DQ, etc. However, the accumulating data have suggested the important roles of DP‐restricted responses in the context of cancer, allergy, and infectious disease. Lack of animal models expressing these genes as authentic cis‐haplotypes blocks our understanding for the role of HLA‐DP haplotypes in immunity. Methods To explore the potential cis‐acting control elements involved in the transcriptional regulation of the HLA‐DPA1/DPB1 gene, we performed the expression analysis using bacterial artificial chromosome (BAC)‐based transgenic humanized mice in the C57BL/6 background, which carried the entire HLA‐DP401 gene locus. We further developed a mouse model of Staphylococcus aureus pneumonia in HLA‐DP401 humanized transgenic mice, and performed the analysis on the expression pattern of HLA‐DP401 and immunological responses in the model. Results In this study, we screened and identified a BAC clone spanning the entire HLA‐DP gene locus. DNA from this clone was analyzed for integrity by pulsed‐field gel electrophoresis and then microinjected into fertilized mouse oocytes to produce transgenic founder animals. Nine sets of PCR primers for regional markers with an average distance of 15 kb between each primer were used to confirm the integrity of the transgene in the five transgenic lines carrying the HLA‐DPA1/DPB1 gene. Transgene copy numbers were determined by real‐time PCR analysis. HLA‐DP401 gene expression was analyzed at the mRNA and protein level. Although infection with S aureus Newman did not alter the percentage of immune cells in the spleen and thymus from the HLA‐DP401‐H2‐Aβ1 humanized mice. Increased expression of HLA‐DP401 was observed in the thymus of the humanized mice infected by S aureus. Conclusions We generated several BAC transgenic mice, and analyzed the expression of HLA‐DPA1/DPB1 in those mice. A model of S aureus‐induced pneumonia in the HLA‐DP401‐H2‐Aβ1−/− humanized mice was further developed, and S aureus infection upregulated the HLA‐DP401 expression in thymus of those humanized mice. These findings demonstrate the potential of those HLA‐DPA1/DPB1 transgenic humanized mice for developing animal models of infectious diseases and MHC‐associated immunological diseases.

T cells play a critical role in coronavirus diseases. How they do so in COVID-19 may be revealed by analyzing the epigenetic chromatin accessibility of cis- and trans-regulatory elements and creating transcriptomic immune profiles. We performed single-cell assay for transposase-accessible chromatin (scATAC) and single-cell RNA (scRNA) sequencing (seq) on the peripheral blood mononuclear cells (PBMCs) of severely ill/critical patients (SCPs) infected with COVID-19, moderate patients (MPs), and healthy volunteer controls (HCs). About 76,570 and 107,862 single cells were used, respectively, for analyzing the characteristics of chromatin accessibility and transcriptomic immune profiles by the application of scATAC-seq (nine cases) and scRNA-seq (15 cases). The scATAC-seq detected 28,535 different peaks in the three groups; among these peaks, 41.6 and 10.7% were located in the promoter and enhancer regions, respectively. Compared to HCs, among the peak-located genes in the total T cells and its subsets, CD4+ T and CD8+ T cells, from SCPs and MPs were enriched with inflammatory pathways, such as mitogen-activated protein kinase (MAPK) signaling pathway and tumor necrosis factor (TNF) signaling pathway. The motifs of TBX21 were less accessible in the CD4+ T cells of SCPs compared with those in MPs. Furthermore, the scRNA-seq showed that the proportion of T cells, especially the CD4+ T cells, was decreased in SCPs and MPs compared with those in HCs. Transcriptomic results revealed that histone-related genes, and inflammatory genes, such as NFKBIA, S100A9, and PIK3R1, were highly expressed in the total T cells, CD4+ T and CD8+ T cells, both in the cases of SCPs and MPs. In the CD4+ T cells, decreased T helper-1 (Th1) cells were observed in SCPs and MPs. In the CD8+T cells, activation markers, such as CD69 and HLA class II genes (HLA-DRA, HLA-DRB1, and HLA-DRB5), were significantly upregulated in SCPs. An integrated analysis of the data from scATAC-seq and scRNA-seq showed some consistency between the approaches. Cumulatively, we have generated a landscape of chromatin epigenetic status and transcriptomic immune profiles of T cells in patients with COVID-19. This has provided a deeper dissection of the characteristics of the T cells involved at a higher resolution than from previously obtained data merely by the scRNA-seq analysis. Our data led us to suggest that the T-cell inflammatory states accompanied with defective functions in the CD4+ T cells of SCPs may be the key factors for determining the pathogenesis of and recovery from COVID-19.

Reporter genes are widely applied in biotechnology and biomedical research owning to their easy observation and lack of toxicity. Taking advantage of the reporter genes in conjunction with imaging technologies, a large number of reporter mouse models have been generated. Reporter mouse models provide systems that enable the studies of live cell imaging, cell lineage tracing, immunological research and cancers etc. in vivo. In this review, we describe the types of different reporter genes and reporter mouse models including, random reporter strains, Cre reporter strains and ROSA 26 reporter strains. Collectively, these reporter mouse models have broadened scientific inquires and provided potential strategies for generation of novel reporter animal models with enhanced capabilities.