The H7N9 influenza A virus infection results in lethal inflammation in the mammalian host via the NLRP3-caspase-1 inflammasome

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.

Neutralization of Zika virus by germline-like human monoclonal antibodies targeting cryptic epitopes on envelope domain III

The Zika virus (ZIKV), a flavivirus transmitted by Aedes mosquitoes, has emerged as a global public health concern. Pre-existing cross-reactive antibodies against other flaviviruses could modulate immune responses to ZIKV infection by antibody-dependent enhancement, highlighting the importance of understanding the immunogenicity of the ZIKV envelope protein. In this study, we identified a panel of human monoclonal antibodies (mAbs) that target domain III (DIII) of the ZIKV envelope protein from a very large phage-display naive antibody library. These germline-like antibodies, sharing 98%-100% hoLogy with their corresponding germline IGHV genes, bound ZIKV DIII specifically with high affinities. One mAb, m301, broadly neutralized the currently circulating ZIKV strains and showed a synergistic effect with another mAb, m302, in neutralizing ZIKV in vitro and in a mouse model of ZIKV infection. Interestingly, epitope mapping and competitive binding studies suggest that m301 and m302 bind adjacent regions of the DIII C-C' loop, which represents a recently identified cryptic epitope that is intermittently exposed in an uncharacterized virus conformation. This study extended our understanding of antigenic epitopes of ZIKV antibodies and has direct implications for the design of ZIKV vaccines.

A broadly neutralizing germline-like human monoclonal antibody against dengue virus envelope domain III

Dengue is the most widespread vector-borne viral disease caused by dengue virus (DENV) for which there are no safe, effective drugs approved for clinical use. Here, by using sequential antigen panning of a yeast antibody library derived from healthy donors against the DENV envelop protein domain III (DIII) combined with depletion by an entry defective DIII mutant, we identified a cross-reactive human monoclonal antibody (mAb), m366.6, which bound with high affinity to DENV DIII from all four DENV serotypes. Immunogenetic analysis indicated that m366.6 is a germline-like mAb with very few somatic mutations from the closest VH and Vλ germline genes. Importantly, we demonstrated that it potently neutralized DENV both in vitro and in the mouse models of DENV infection without detectable antibody-dependent enhancement (ADE) effect. The epitope of m366.6 was mapped to the highly conserved regions on DIII, which may guide the design of effective dengue vaccine immunogens. Furthermore, as the first germline-like mAb derived from a naïve antibody library that could neutralize all four DENV serotypes, the m366.6 can be a tool for exploring mechanisms of DENV infection, and is a promising therapeutic candidate.

High persistence rate of hepatitis B virus in a hydrodynamic injection-based transfection model in C3H/HeN mice

AIM

To optimize the viral persistence rate in a hydrodynamic injection (HI) based hepatitis B virus (HBV) transfection mouse model.

METHODS

(1) 5-6-wk-old male C3H/HeN and C57BL/6 mice were hydrodynamically injected with 10 μg endotoxin-free pAAV/HBV1.2 plasmid DNA via the tail vein. Hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg) and HBV DNA, both in the serum and liver, were detected at different time points post HI by ELISA, immunohistochemical staining or quantitative polymerase chain reaction (PCR); (2) male C3H/HeN and C57BL/6 mice, either hydrodynamically injected mice at 10 wk post HI or naïve mice, were all immunized subcutaneously with 5 μg HBsAg formulated in complete Freund's adjuvant three times at a 2-wk interval. Two weeks after the final immunization, splenocytes were isolated for T cell function analysis by ELISPOT assay; and (3) five weeks post HI, C3H/HeN mice were intragastrically administered 0.1 mg/kg entecavir once a day for 14 d, or were intraperitoneally injected with 1 mg/kg interferon (IFN)-α twice a week for 2 wk, or were treated with PBS as controls. The sera were collected and assayed for HBV DNA on days 0, 7 and 14 after drug treatment.

RESULTS

(1) Approximately 90% (22/25) of the injected C3H/HeN mice were still HBsAg-positive at 46 wk post HI, whereas HBsAg in C57BL/6 mice were completely cleared at 24 wk. Serum levels of HBeAg in C3H/HeN mice were higher than those in C57BL/6 mice from 4 wk to 46 wk. HBV DNA levels in the hydrodynamically injected C3H/HeN mice were higher than those in the C57BL/6 mice, both in the serum (from 4 wk to 46 wk) and in the liver (detected at 8 wk and 46 wk post HI). Histology showed that hepatitis B core antigen and HBsAg were expressed longer in the liver of C3H/HeN mice than in C57BL/6; (2) HBsAg specific T cell responses after HBsAg vaccination in hydrodynamically injected C3H/HeN and C57BL/6 mice, or naive control mice were detected by ELISPOT assay. After stimulation with HBsAg, the frequencies of IFN-γ producing splenocytes in the hydrodynamically injected C3H/HeN mice were significantly lower than those in hydrodynamically injected C57BL/6 mice, control C3H/HeN and control C57BL/6 mice, which were 0, 17 ± 7, 18 ± 10, and 41 ± 10 SFCs/10(6) splenocytes, respectively, and the mean spot sizes showed the same pattern. Even just stimulated with PMA and ionomysin, T-cell responses elicited in the vaccinated control C3H/HeN were much higher than those in hydrodynamically injected C3H/HeN mice; and (3) For drug treatment experiments on the hydrodynamically injected C3H/HeN mice, serum HBV DNA levels in the entecavir treatment group declined (131.2 folds, P < 0.01) on day 7 after treatment and kept going down. In the group of IFN-α treatment, serum HBV DNA levels declined to a lowest point (6.42 folds, P < 0.05) on 7 d after treatment and then rebounded.

CONCLUSION

We have developed a novel HI-based HBV transfection model using C3H/HeN mice, which had a higher HBV persistence rate than the classic C57BL/6 mouse model.

Epigenetic Landscapes of Single-Cell Chromatin Accessibility and Transcriptomic Immune Profiles of T Cells in COVID-19 Patients

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.

Generation and expression analysis of BAC humanized mice carrying HLA-DP401 haplotype

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 Saureus-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.

Reprogramming alternative macrophage polarization by GATM-mediated endogenous creatine synthesis: A potential target for HDM-induced asthma treatment

Cellular energy metabolism plays a crucial role in the regulation of macrophage polarization and in the execution of immune functions. A recent study showed that Slc6a8-mediated creatine uptake from exogenous supplementation modulates macrophage polarization, yet little is known about the role of the de novo creatine de novobiosynthesis pathway in macrophage polarization. Here, we observed that glycine amidinotransferase (GATM), the rate-limiting enzyme for creatine synthesis, was upregulated in alternative (M2) polarized macrophages, and was dependent on the transcriptional factor STAT6, whereas GATM expression was suppressed in the classical polarized (M1) macrophage. Next, we revealed that exogenous creatine supplementation enhanced IL-4-induced M2 polarization, confirming recent work. Furthermore, we revealed that genetic ablation of GATM did not affect expression of M1 marker genes (Nos2, IL1b, IL12b) or the production of nitric oxide in both peritoneal macrophages (PMs) and bone marrow-derived macrophages (BMDMs). By contrast, expression levels of M2 markers (Arg1, Mrc1, Ccl17 and Retnla) were lower following GATM deletion. Moreover, we found that deletion of GATM in resident alveolar macrophages (AMs) significantly blocked M2 polarization but with no obvious effect on the number of cells in knockout mice. Lastly, an upregulation of GATM was found in lung tissue and bronchoalveolar lavage fluid macrophages from HDM-induced asthmatic mice. Our study uncovers a previously uncharacterized role for the de novo creatine biosynthesis enzyme GATM in M2 macrophage polarization, which may be involved in the pathogenesis of related inflammatory diseases such as an T helper 2 (Th2)-associated allergic asthma.

Characterization of genetic humanized mice with transgenic HLA DP401 or DRA but deficient in endogenous murine MHC class II genes upon Staphylococcus aureus pneumonia

BACKGROUND

Staphylococcus aureus can cause serious infections by secreting many superantigen exotoxins in "carrier" or "pathogenic" states. HLA DQ and HLA DR humanized mice have been used as a small animal model to study the role of two molecules during S. aureus infection. However, the contribution of HLA DP to S. aureus infection is unknown yet.

METHODS

In this study, we have produced HLA DP401 and HLA DRA0101 humanized mice by microinjection of C57BL/6J zygotes. Neo-floxed IAβ+/- mice were crossbred with Ella-Cre and further crossbred with HLA DP401 or HLA-DRA0101 humanized mice. After several rounds of traditional crossbreeding, we finally obtained HLA DP401-IAβ-/- and HLA DRA-IAβ-/- humanized mice, in which human DP401 or DRA0101 molecule was introduced into IAβ-/- mice deficient in endogenous murine MHC class II molecules. A transnasal infection murine model of S. aureus pneumonia was induced in the humanized mice by administering 2 × 108  CFU of S. aureus Newman dropwise into the nasal cavity. The immune responses and histopathology changes were further assessed in lungs in these infected mice.

RESULTS

We evaluated the local and systemic effects of S. aureus delivered intranasally in HLA DP401-IAβ-/- and HLA DRA-IAβ-/- transgenic mice. S. aureus Newman infection significantly increased the mRNA level of IL 12p40 in lungs in humanized mice. An increase in IFN-γ and IL-6 protein was observed in HLA DRA-IAβ-/- mice. We observed a declining trend in the percentage of F4/80+ macrophages in lungs in HLA DP401-IAβ-/- mice and a decreasing ratio of CD4+ to CD8+ T cells in lungs in IAβ-/- mice and HLA DP401-IAβ-/- mice. A decreasing ratio of Vβ3+ to Vβ8+ T cells was also found in the lymph node of IAβ-/- mice and HLA DP401-IAβ-/- mice. S. aureus Newman infection resulted in a weaker pathological injury in lungs in IAβ-/- genetic background mice.

CONCLUSION

These humanized mice will be an invaluable mouse model to resolve the pathological mechanism of S. aureus pneumonia and study what role DP molecule plays in S. aureus infection.

Comparative transcriptome analyses of immune responses to LPS in peripheral blood mononuclear cells from the giant panda, human, mouse, and monkey

Gram-negative bacteria are major pathogens that can cause illnesses in giant pandas. Lipopolysaccharides (LPS), components of Gram-negative bacteria, can activate immune responses in mammals (i.e., humans and mice) through recognition by toll-like receptors (TLRs). However, the giant pandas' immune response to LPS stimulation and the differences between the giant panda and other mammals are not fully known. In this study, we administrated peripheral blood mononuclear cells (PBMCs) from giant pandas, humans, C57BL/6 mice, and rhesus monkeys by LPS treatment at 6 h followed by RNA sequencing (RNA-seq), respectively, with control of non-stimulation. KEGG analyses of differentially expressed genes (DEGs) pathways indicated that LPS could activate the classic signaling pathway of NF-κB in PBMCs from those four tested species. Thus, similar to the other three species, NF-κB is an LPS-responsive regulator of innate immune responses in giant pandas. Furthermore, the expression patterns of adapter genes, inflammatory cytokine genes, chemokines, interferon genes, cytokine genes related to cell growth and development, costimulatory molecules, Th1/Th2 cytokine genes, Th17 cytokine genes, Th9, and Th22 cytokine genes were compared among giant pandas and three other species. Our data indicated that in addition to the similar expression patterns of certain genes among giant pandas and other species, the unique expression pattern response to LPS in giant pandas was also discovered. Furthermore, Th9, Th17, and Th22 cells might be involved in the response to LPS in giant pandas at this tested time point. This study reveals that LPS-induced immune responses have different sensitivities and response timelines in giant pandas compared with other mammals. This study facilitates further understanding of the role of the TLR signaling pathway and the immune system in giant pandas, which might be helpful for disease prevention and protection.

Genetic mutation of Tas2r104/Tas2r105/Tas2r114 cluster leads to a loss of taste perception to denatonium benzoate and cucurbitacin B

BACKGROUND

Bitter taste receptors (Tas2rs) are generally considered to sense various bitter compounds to escape the intake of toxic substances. Bitter taste receptors have been found to widely express in extraoral tissues and have important physiological functions outside the gustatory system in vivo.

METHODS

To investigate the physiological functions of the bitter taste receptor cluster Tas2r106/Tas2r104/Tas2r105/Tas2r114 in lingual and extraoral tissues, multiple Tas2rs mutant mice and Gnat3 were produced using CRISPR/Cas9 gene-editing technique. A mixture containing Cas9 and sgRNA mRNAs for Tas2rs and Gnat3 gene was microinjected into the cytoplasm of the zygotes. Then, T7EN1 assays and sequencing were used to screen genetic mutation at the target sites in founder mice. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunostaining were used to study the expression level of taste signaling cascade and bitter taste receptor in taste buds. Perception to taste substance was also studied using two-bottle preference tests.

RESULTS

We successfully produced several Tas2rs and Gnat3 mutant mice using the CRISPR/Cas9 technique. Immunostaining results showed that the expression of GNAT3 and PLCB2 was not altered in Tas2rs mutant mice. But qRT-PCR results revealed the changed expression profile of mTas2rs gene in taste buds of these mutant mice. With two-bottle preference tests, these mutant mice eliminate responses to cycloheximide due to genetic mutation of Tas2r105. In addition, these mutant mice showed a loss of taste perception to quinine dihydrochloride, denatonium benzoate, and cucurbitacin B (CuB). Gnat3-mediated taste receptor and its signal pathway contribute to CuB perception.

CONCLUSIONS

These findings implied that these mutant mice would be a valuable means to understand the biological functions of TAS2Rs in extraoral tissues and investigate bitter compound-induced responses mediated by these TAS2Rs in many extraoral tissues.

Codelivery of SARS-CoV-2 Prefusion-Spike Protein with CBLB502 by a Dual-Chambered Ferritin Nanocarrier Potentiates Systemic and Mucosal Immunity

Thousands of breakthrough infections are confirmed after intramuscular (i.m.) injection of the approved vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Two major factors might contribute to breakthrough infections. One is the emergence of mutant variants of SARS-CoV-2, and the other is that i.m. injection has an inefficient ability to activate mucosal immunity in the upper respiratory tract. Here, we devised a dual-chambered nanocarrier that can codeliver the adjuvant CBLB502 with prefusion-spike (pre-S) onto a ferritin nanoparticle. This vaccine enabled enhanced systemic and local mucosal immunity in the upper and lower respiratory tract. Further, codelivery of CBLB502 with pre-S induced a Th1/Th2-balanced immunoglobulin G response. Moreover, the codelivery nanoparticle showed a Th1-biased cellular immune response as the release of splenic INF-γ was significantly heightened while the level of IL-4 was elevated to a moderate extent. In general, the developed dual-chambered nanoparticle can trigger multifaceted immune responses and shows great potential for mucosal vaccine development.

Human liver chimeric mouse model based on diphtheria toxin-induced liver injury

AIM

To establish an inducible liver injury mouse model and transplant human hepatocytes to obtain liver-humanized mice.

METHODS

We crossed three mouse strains, including albumin (Alb)-cre transgenic mice, inducible diphtheria toxin receptor (DTR) transgenic mice and severe combined immune deficient (SCID)-beige mice, to create Alb-cre/DTR/SCID-beige (ADSB) mice, which coincidentally harbor Alb-cre and DTR transgenes and are immunodeficient. As the Cre expression is driven by the liver-specific promoter Alb (encoding ALB), the DTR stop signal flanked by two loxP sites can be deleted in the ADSB mice, resulting in DTR expression in the liver. ADSB mice aged 8-10 wk were injected intraperitoneally (i.p.) with diphtheria toxin (DT) and liver damage was assessed by serum alanine aminotransferase (ALT) level. Two days later, mouse livers were sampled for histological analysis, and human hepatocytes were transplanted into the livers on the same day. A human ALB enzyme-linked immunosorbent assay was performed 7, 14, 21 and 28 d after transplantation. Human CD68 immunohistochemistry was performed 30 and 90 d after transplantation.

RESULTS

We crossed Alb-cre with DTR and SCID-beige mice to obtain ADSB mice. These mice were found to have liver damage 4 d after i.p. injection of 2.5 ng/g bodyweight DT. Bodyweight began to decrease on day 2, increased on day 7, and was lowest on day 4 (range, 10.5%-13.4%). Serum ALT activity began to increase on day 2 and reached a peak value of 289.7 ± 16.2 IU/mL on day 4, then returned to background values on day 7. After transplantation of human liver cells, peripheral blood human ALB level was 1580 ± 454.8 ng/mL (range, 750.2-3064.9 ng/mL) after 28 d and Kupffer cells were present in the liver at 30 d in ADSB mice.

CONCLUSION

Human hepatocytes were successfully repopulated in the livers of ADSB mice. The inducible mouse model of humanized liver in ADSB mice may have functional applications, such as hepatocyte transplantation, hepatic regeneration and drug metabolism.