Evidence of CD1d pathway of lipid antigen presentation in mouse primary lung epithelial cells and its up-regulation upon Mycobacterium bovis BCG infection

SARS-CoV-2 infection induces thymic atrophy mediated by IFN-γ in hACE2 transgenic mice

Pathogenic infections cause thymic atrophy, perturb thymic T-cell development, and alter immunological response. Previous studies reported dysregulated T-cell function and lymphopenia in coronavirus disease-19 (COVID-19). However, immunopathological changes in the thymus associated with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection have not been elucidated. Here, we report that SARS-CoV-2 infects thymocytes, and induces CD4+CD8+ (double positive; DP) T-cell apoptosis leading to thymic atrophy and loss of peripheral TCR repertoire in K18-hACE2 transgenic mice. Infected thymus led to increased CD44+CD25- T-cells, indicating an early arrest in the T-cell maturation pathway. Thymic atrophy was notably higher in male hACE2-Tg mice than in females and involved an upregulated de-novo synthesis pathway of thymic glucocorticoid. Further, IFN-γ was crucial for thymic atrophy, as anti-IFN-γ -antibody neutralization blunted thymic involution. Therapeutic use of Remdesivir also rescued thymic atrophy. While the Omicron variant and its sub-lineage BA.5 variant caused marginal thymic atrophy, the delta variant of SARS-CoV-2 exhibited severe thymic atrophy characterized by severely depleted DP T-cells. Recently characterized broadly SARS-CoV-2 neutralizing monoclonal antibody P4A2 was able to rescue thymic atrophy and restore the thymic maturation pathway of T-cells. Together, we report SARS-CoV-2-associated thymic atrophy resulting from impaired T-cell maturation pathway which may contribute to dyregulated T cell response during COVID-19.

Evaluation of Ayush-64 (a Polyherbal Formulation) and Its Ingredients in the Syrian Hamster Model for SARS-CoV-2 Infection Reveals the Preventative Potential of Alstonia scholaris

In the current study, we evaluated the efficacy of Ayush-64 (A64), a polyherbal formulation containing Alstonia scholaris (L.) R. Br. (A. scholaris), Caesalpinia crista L. (C. crista), Picrorhiza kurroa Royle ex Benth (P. kurroa), and Swertia chirata (Roxb.) H. Karst. (S. chirata) against COVID-19 in a Syrian hamster infection model. Preventative use of A64 resulted in the late-phase recovery of body weight loss in severe acquired respiratory syndrome coronavirus-2 (SARS-CoV-2)-infected hamsters, suppression of pro-inflammatory cytokines, and blunted pulmonary pathology. In addition, we also investigated the efficacy of individual ingredients of A64, viz., A. scholaris, C. crista, P. kurroa, and S. chirata, in the hamster model. The hamster challenge data showed robust anti-viral and immunomodulatory potential in A. scholaris, followed by P. kurroa. However, C. crista and S. chirata of A64 showed prominent immunomodulatory potential without limiting the lung viral load. In order to better understand the immunomodulatory potential of these herbal extracts, we used an in vitro assay of helper T cell differentiation and found that A. scholaris mediated a more profound suppression of Th1, Th2, and Th17 cell differentiation as compared to A64 and other ingredients. Taken together, our animal study data identifies the ameliorative potential of A64 in mitigating coronavirus disease-19 (COVID-19) pulmonary pathology. A. scholaris, a constituent extract of A64, showed relatively higher anti-viral and immunomodulatory potential against COVID-19. The present study warrants further investigations to identify the active pharmaceutical ingredients of A. scholaris for further studies.

Omicron sub-lineage BA.5 infection results in attenuated pathology in hACE2 transgenic mice

A recently emerged sub-lineage of Omicron, BA.5, together with BA.4, caused a fifth wave of coronavirus disease (COVID-19) in South Africa and subsequently emerged as a predominant strain globally due to its high transmissibility. The lethality of BA.5 infection has not been studied in an acute hACE2 transgenic (hACE2.Tg) mouse model. Here, we investigated tissue-tropism and immuno-pathology induced by BA.5 infection in hACE2.Tg mice. Our data show that intranasal infection of BA.5 in hACE2.Tg mice resulted in attenuated pulmonary infection and pathology with diminished COVID-19-induced clinical and pathological manifestations. BA.5, similar to Omicron (B.1.1.529), infection led to attenuated production of inflammatory cytokines, anti-viral response and effector T cell response as compared to the ancestral strain of SARS-CoV-2, Wuhan-Hu-1. We show that mice recovered from B.1.1.529 infection showed robust protection against BA.5 infection associated with reduced lung viral load and pathology. Together, our data provide insights as to why BA.5 infection escapes previous SARS-CoV-2 exposure induced-T cell immunity but may result in milder immuno-pathology and alleviated chances of re-infectivity in Omicron-recovered individuals.

CD1-mediated immune responses in mucosal tissues: molecular mechanisms underlying lipid antigen presentation system

The cluster of differentiation 1 (CD1) molecule differs from major histocompatibility complex class I and II because it presents glycolipid/lipid antigens. Moreover, the CD1-restricted T cells that recognize these self and foreign antigens participate in both innate and adaptive immune responses. CD1s are constitutively expressed by professional and nonprofessional antigen-presenting cells in mucosal tissues, namely, the skin, lung, and intestine. This suggests that CD1-reactive T cells are involved in the immune responses of these tissues. Indeed, evidence suggests that these cells play important roles in diverse diseases, such as inflammation, autoimmune disease, and infection. Recent studies elucidating the molecular mechanisms by which CD1 presents lipid antigens suggest that defects in these mechanisms could contribute to the activities of CD1-reactive T cells. Thus, improving our understanding of these mechanisms could lead to new and effective therapeutic approaches to CD1-associated diseases. In this review, we discuss the CD1-mediated antigen presentation system and its roles in mucosal tissue immunity.

Pharmacological potential of Withania somnifera (L.) Dunal and Tinospora cordifolia (Willd.) Miers on the experimental models of COVID-19, T cell differentiation, and neutrophil functions

Cytokine release syndrome (CRS) due to severe acute respiratory coronavirus-2 (SARS-CoV-2) infection leads to life-threatening pneumonia which has been associated with coronavirus disease (COVID-19) pathologies. Centuries-old Asian traditional medicines such as Withania somnifera (L.) Dunal (WS) and Tinospora cordifolia (Willd.) Miers (TC) possess potent immunomodulatory effects and were used by the AYUSH ministry, in India during the COVID-19 pandemic. In the present study, we investigated WS and TC's anti-viral and immunomodulatory efficacy at the human equivalent doses using suitable in vitro and in vivo models. While both WS and TC showed immuno-modulatory potential, WS showed robust protection against loss in body weight, viral load, and pulmonary pathology in the hamster model of SARS-CoV2. In vitro pretreatment of mice and human neutrophils with WS and TC had no adverse effect on PMA, calcium ionophore, and TRLM-induced ROS generation, phagocytosis, bactericidal activity, and NETs formation. Interestingly, WS significantly suppressed the pro-inflammatory cytokines-induced Th1, Th2, and Th17 differentiation. We also used hACE2 transgenic mice to further investigate the efficacy of WS against acute SARS-CoV2 infection. Prophylactic treatment of WS in the hACE2 mice model showed significant protection against body weight loss, inflammation, and the lung viral load. The results obtained indicate that WS promoted the immunosuppressive environment in the hamster and hACE2 transgenic mice models and limited the worsening of the disease by reducing inflammation, suggesting that WS might be useful against other acute viral infections. The present study thus provides pre-clinical efficacy data to demonstrate a robust protective effect of WS against COVID-19 through its broader immunomodulatory activity.

Prophylactic treatment of Glycyrrhiza glabra mitigates COVID-19 pathology through inhibition of pro-inflammatory cytokines in the hamster model and NETosis

Severe coronavirus disease (COVID-19) is accompanied by acute respiratory distress syndrome and pulmonary pathology, and is presented mostly with an inflammatory cytokine release, a dysregulated immune response, a skewed neutrophil/lymphocyte ratio, and a hypercoagulable state. Though vaccinations have proved effective in reducing the COVID-19-related mortality, the limitation of the use of vaccine against immunocompromised individuals, those with comorbidity, and emerging variants remains a concern. In the current study, we investigate for the first time the efficacy of the Glycyrrhiza glabra (GG) extract, a potent immunomodulator, against SARS-CoV-2 infection in hamsters. Prophylactic treatment with GG showed protection against loss in body weight and a 35%–40% decrease in lung viral load along with reduced lung pathology in the hamster model. Remarkably, GG reduced the mRNA expression of pro-inflammatory cytokines and plasminogen activator inhibitor-1 (PAI-1). In vitro, GG acted as a potent immunomodulator by reducing Th2 and Th17 differentiation and IL-4 and IL-17A cytokine production. In addition, GG also showed robust potential to suppress ROS, mtROS, and NET generation in a concentration-dependent manner in both human polymorphonuclear neutrophils (PMNs) and murine bone marrow-derived neutrophils (BMDNs). Taken together, we provide evidence for the protective efficacy of GG against COVID-19 and its putative mechanistic insight through its immunomodulatory properties. Our study provides the proof of concept for GG efficacy against SARS-CoV-2 using a hamster model and opens the path for further studies aimed at identifying the active ingredients of GG and its efficacy in COVID-19 clinical cases.

Golden Syrian hamster as a model to study cardiovascular complications associated with SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 infection in the Golden Syrian hamster causes lung pathology that resembles human coronavirus disease (COVID-19). However, extra-pulmonary pathologies associated with SARS-CoV-2 infection and post COVID sequelae remain to be understood. Here we show, using a hamster model, that the early phase of SARS-CoV-2 infection leads to an acute inflammatory response and lung pathologies, while the late phase of infection causes cardiovascular complications (CVC) characterized by ventricular wall thickening associated with increased ventricular mass/ body mass ratio and interstitial coronary fibrosis. Molecular profiling further substantiated our findings of CVC, as SARS-CoV-2-infected hamsters showed elevated levels of serum cardiac Troponin-I (cTnI), cholesterol, low-density lipoprotein and long-chain fatty acid triglycerides. Serum metabolomics profiling of SARS-CoV-2-infected hamsters identified N-acetylneuraminate, a functional metabolite found to be associated with CVC, as a metabolic marker was found to be common between SARS-CoV-2-infected hamsters and COVID-19 patients. Together, we propose hamsters as a suitable animal model to study post-COVID sequelae associated with CVC which could be extended to therapeutic interventions.

Effect of Prophylactic Use of Intranasal Oil Formulations in the Hamster Model of COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection initiates with viral entry in the upper respiratory tract, leading to coronavirus disease 2019 (COVID-19). Severe COVID-19 is characterized by pulmonary pathologies associated with respiratory failure. Thus, therapeutics aimed at inhibiting the entry of the virus or its internalization in the upper respiratory tract are of interest. Herein, we report the prophylactic application of two intranasal formulations provided by the National Medicinal Plant Board (NMPB), Anu oil and til tailya, in the hamster model of SARS-CoV-2 infection. Prophylactic intra-nasal instillation of these oil formulations exhibited reduced viral load in lungs and resulted in reduced body weight loss and lung-pneumonitis. In line with reduced viral load, histopathological analysis revealed a reduction in lung pathology in the Anu oil group as compared to the control infected group. However, the til tailya group did not show a significant reduction in lung pathology. Furthermore, molecular analysis using mRNA expression profiling indicated reduced expression of pro-inflammatory cytokine genes, including Th1 and Th17 cytokines for both the intranasal formulations as a result of decreased viral load. Together, the prophylactic intranasal application of Anu oil seems to be useful in limiting both viral load and severity in SARS-CoV2 infection in the hamster model.

High-salt diet mediates interplay between NK cells and gut microbiota to induce potent tumor immunity

High-salt diet (HSD) modulates effector and regulatory T cell functions and promotes tissue inflammation in autoimmune diseases. However, effects of HSD and its association with gut microbiota in tumor immunity remain undefined. Here, we report that HSD induces natural killer (NK) cell–mediated tumor immunity by inhibiting PD-1 expression while enhancing IFNγ and serum hippurate. Salt enhanced tumor immunity when combined with a suboptimal dose of anti-PD1 antibody. While HSD-induced tumor immunity was blunted upon gut microbiota depletion, fecal microbiota transplantation (FMT) from HSD mice restored the tumor immunity associated with NK cell functions. HSD increased the abundance of Bifidobacterium and caused increased gut permeability leading to intratumor localization of Bifidobacterium, which enhanced NK cell functions and tumor regression. Intratumoral injections of Bifidobacterium activated NK cells, which inhibited tumor growth. These results indicate that HSD modulates gut microbiome that induces NK cell–dependent tumor immunity with a potential translational perspective.

Mast cells modulate early responses to Mycobacterium bovis Bacillus Calmette-Guerin by phagocytosis and formation of extracellular traps

The early interactions between the vaccine Mycobacterium bovis Bacillus Calmette Guerin (BCG) and host peripheral innate immune cells like Mast cells (MCs) may pave the way for generating appropriate protective innate and adaptive immune responses. Mice on administration of BCG by intratracheal instillation showed a massive increase in MC numbers in the infected lung. In vitro co-culture of BCG and rodent Rat Basophilic Leukaemia (RBL-2H3) MCs led to significant killing of BCG. RBL-2H3 MCs were able to phagocytose BCG, take up BCG-derived antigens by macropinocytosis, generate Reactive Oxygen Species (ROS) and degranulate. Further, a few MCs died and released MC extracellular traps (MCETs) having DNA, histones and tryptase to trap BCG. This study highlights the multi-pronged effector responses of MCs on encountering BCG. These responses or their evasion may lead to success or failure of BCG vaccine to provide long term immunity to infections.

Regulation of Immune Responses by Nonhematopoietic Cells in Asthma

Nonhematopoietic cells are emerging as important contributors to many inflammatory diseases, including allergic asthma. Recent advances have led to a deeper understanding of how these cells interact with traditional immune cells, thereby modulating their activities in both homeostasis and disease. In addition to their well-established roles in gas exchange and barrier function, lung epithelial cells express an armament of innate sensors that can be triggered by various inhaled environmental agents, leading to the production of proinflammatory molecules. Advances in cell lineage tracing and single-cell RNA sequencing have expanded our knowledge of rare, but immunologically important nonhematopoietic cell populations. In parallel with these advances, novel reverse genetic approaches are revealing how individual genes in different lung-resident nonhematopoietic cell populations contribute to the initiation and maintenance of asthma. This knowledge is already revealing new pathways that can be selectively targeted to treat distinct forms of asthma.