Invariant natural killer T (iNKT) cells in asthma: a novel insight into the pathogenesis of asthma and the therapeutic implication of glycolipid ligands for allergic diseases

How Infection and Vaccination Are Linked to Acute and Chronic Urticaria: A Special Focus on COVID-19

Since more than a century ago, there has been awareness of the connection between viral infections and the onset and exacerbation of urticaria. Our knowledge about the role of viral infection and vaccination in acute and chronic urticaria improved as a result of the COVID-19 pandemic but it has also highlighted knowledge gaps. Viral infections, especially respiratory tract infections like COVID-19, can trigger the onset of acute urticaria (AU) and the exacerbation of chronic urticaria (CU). Less frequently, vaccination against viruses including SARS-CoV-2 can also lead to new onset urticaria as well as worsening of CU in minority. Here, with a particular focus on COVID-19, we review what is known about the role of viral infections and vaccinations as triggers and causes of acute and chronic urticaria. We also discuss possible mechanistic pathways and outline the unmet needs in our knowledge. Although the underlying mechanisms are not clearly understood, it is believed that viral signals, medications, and stress can activate skin mast cells (MCs). Further studies are needed to fully understand the relevance of viral infections and vaccinations in acute and chronic urticaria and to better clarify causal pathways.

Mast cells: Therapeutic targets for COVID-19 and beyond

Mast cells (MCs) are innate immune cells that widely distribute throughout all tissues and express a variety of cell surface receptors. Upon activation, MCs can rapidly release a diverse array of preformed mediators residing within their secretory granules and newly synthesize a broad spectrum of inflammatory and immunomodulatory mediators. These unique features of MCs enable them to act as sentinels in response to rapid changes within their microenvironment. There is increasing evidence now that MCs play prominent roles in other pathophysiological processes besides allergic inflammation. In this review, we highlight the recent findings on the emerging roles of MCs in the pathogenesis of coronavirus disease-2019 (COVID-19) and discuss the potential of MCs as novel therapeutic targets for COVID-19 and other non-allergic inflammatory diseases.

Potential of brain mast cells for therapeutic application in the immune response to bacterial and viral infections

A wide range of microorganisms can infect the central nervous system (CNS). The immune response of the CNS provides limited protection against microbes penetrating the blood-brain barrier. This results in a neurological deficit and sometimes leads to high morbidity and mortality rates despite advanced therapies. For the last two decades, different studies have expanded our understanding of the molecular basis of human neuroinfectious diseases, especially concerning the contributions of mast cell interactions with other central nervous system compartments. Brain mast cells are multifunctional cells derived from the bone marrow and reside in the brain. Their proximity to blood vessels, their role as "first responders" their unique receptors systems and their ability to rapidly release pathogen responsive mediators enable them to exert a crucial defensive role in the host-defense system. This review describes key biological and physiological functions of mast cells, concerning their ability to recognize pathogens via various receptor systems, followed by a coordinated and selective mediator release upon specific interactions with pathogenic stimulating factors. The goal of this review is to direct attention to the possibilities for therapeutic applications of mast cells against bacterial and viral related infections. We also focus on opportunities for future research activating mast cells via adjuvants.

Tilapia head glycolipids reduce inflammation by regulating the gut microbiota in dextran sulphate sodium-induced colitis mice

In this study, we evaluated the effects of tilapia head glycolipids (TH-GLs) on male C57BL/6 mice with inflammatory bowel disease (IBD) induced by dextran sulfate sodium (DSS) and the changes in gut microbiota compared with sulfasalazine. Mice were orally treated with 3% (w/v) DSS or not for 7 days, followed by drug treatment with TH-GLs or sulfasalazine. After treatment, macroscopic colitis symptoms, intestinal epithelial barrier function, inflammatory cytokines, and gut microbiota homeostasis were assessed. Further studies showed that TH-GLs and sulfasalazine showed different influences on the gut microbiota structure. Both sulfasalazine and TH-GLs decreased the DSS-induced enrichment of Gammaproteobacteria and Enterobacteriaceae. However, TH-GLs had a selective increase in the enrichment of Akkermansia, Prevotellaceae, Oscillospira, Allobaculum, Bifidobacterium, and Coprococcus in contrast to sulfasalazine, which selectively increased the enrichment of Dorea, Turicibacter, Bacteroides, Coprobacillus, Mucispirillum, and Dehalobacterium. In addition, both TH-GLs and sulfasalazine relieved body weight loss, and increased the immune organ index, while maintaining the balance between pro-inflammatory and anti-inflammatory cytokines. The results indicate that TH-GLs alleviate DSS-induced IBD in mice by decreasing the abundance of harmful gut microbiota and enhancing the abundance of probiotic gut microbiota. Thus, the mechanism through which TH-GLs inhibit inflammation through gut microbiota is different from that of sulfasalazine. Therefore, TH-GLs stand as potential prebiotics for the treatment of colonic inflammation and related diseases.

Evaluation of the frequency of invariant natural killer T (iNKT) cells in nasal polyps

Nasal polyps (NP) are associated with inflamed mucosa of unknown etiology. The role of T cells in nasal polyposis is unclear. Invariant natural killer T cells (iNKT) can promote Th2 responses and have been implicated in some types of asthma. As there are shared inflammatory pathways involved in asthma and NPs, we evaluated the frequency of iNKT in 17 patients with NPs, but without asthma. A median of 6% polyp cells were T lymphocytes, of which iNKT were 0 to 2.38% (mean 0.674%). In the matched group (n = 10), iNKT in NPs was significantly higher than PBMCs (1.057% vs 0.155%, P < 0.05). Relative expression of Vα24 to TCR-beta genes in polyps (n = 14) was higher than blood in matched samples (n = 4). The presence of greater proportions of iNKT in NPs than in blood suggests that iNKT may play a role in the pathogenesis of nasal polyposis.

The Role of Invariant Natural Killer T Cells in Dendritic Cell Licensing, Cross-Priming, and Memory CD8(+) T Cell Generation

New vaccination strategies focus on achieving CD8⁺ T cell (CTL) immunity rather than on induction of protective antibody responses. While the requirement of CD4⁺ T (Th) cell help in dendritic cell (DC) activation and licensing, and in CTL memory induction has been described in several disease models, CTL responses may occur in a Th cell help-independent manner. Invariant natural killer T cells (iNKT cells) can substitute for Th cell help and license DC as well. iNKT cells produce a broad spectrum of Th1 and Th2 cytokines, thereby inducing a similar set of costimulatory molecules and cytokines in DC. This form of licensing differs from Th cell help by inducing other chemokines, while Th cell-licensed DCs produce CCR5 ligands, iNKT cell-licensed DCs produce CCL17, which attracts CCR4⁺ CD8⁺ T cells for subsequent activation. It has recently been shown that iNKT cells do not only enhance immune responses against bacterial pathogens or parasites but also play a role in viral infections. The inclusion of iNKT cell ligands in influenza virus vaccines enhanced memory CTL generation and protective immunity in a mouse model. This review will focus on the role of iNKT cells in the cross-talk with cross-priming DC and memory CD8⁺ T cell formation.

Invariant NKT cells act as an adjuvant to enhance Th2 inflammatory response in an OVA-induced mouse model of asthma

Background

Invariant natural killer T cells (iNKT cells) are a unique subset of T lymphocytes and are considered to play an important role in the development of allergic bronchial asthma. Recently, iNKT cells were shown to play an immunoregulatory role in CD4⁺ and CD8⁺ T cell-mediated adaptive immune response. Allergen-specific Th2 inflammatory responses are an important part of the adaptive immune response in asthma. However, the regulatory functions of the Th2 inflammatory response in asthma have not been studied in detail.

Method

In this study, we have investigated the regulatory functions of iNKT cells on the Th2 inflammatory response in an ovalbumin (OVA)-induced murine model of asthma.

Results

Our results demonstrate that α-Galactosylceramide (α-GalCer) administration activated iNKT cells but could not induce the Th2 inflammatory response in wild-type (WT) mice. In the OVA-induced asthma model, α-GalCer administration and adoptive transfer of iNKT cells significantly augmented the Th2 inflammatory responses, including elevated inflammatory cell infiltration in the lung and bronchoalveolar lavage fluid (BALF); increased levels of IL-4, IL-5, and IL-13 in the BALF and splenocyte culture supernatant; and increased serum levels of OVA-specific IgE and IgG1. In addition, the Th2 inflammatory response was reduced, but not completely abrogated in CD1d^-/- mice immunized and challenged with OVA, compared with WT mice.

Conclusion

These results suggest that iNKT cells may serve as an adjuvant to enhance Th2 inflammatory response in an OVA-induced murine model of asthma.

Invariant natural killer T-cell neutralization is a possible novel therapy for human eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a recently recognized inflammatory disorder that needs a potential therapeutic strategy. We earlier showed that iNKT cell-deficient mice are protected from allergen-induced EoE. Therefore, we now tested the hypothesis that iNKT cells are induced in the human EoE and is a novel possible target for the treatment of human EoE. Accordingly, we examine number of iNKT cells and eosinophils and expression of iNKT-associated cell surface receptors and chemokines by performing immunofluorescence, qPCR and ELISA in the esophageal biopsies and blood samples of normal subjects (comparison control) and EoE patients. Herein, we show that iNKT cell number, their receptor subcomponents Vα24 and Vβ11 expression, and associated chemokine CXCL16 levels (or expression) are induced significantly in EoE patients compared with normal individuals. In addition, we show that CXCL16 levels (or expression) correlate with the mRNA levels of Vα24 receptor but not well with esophageal eosinophilia in human EoE. Of note, we show that in vivo activation of iNKT cells is sufficient to induce EoE in mice. Furthermore, we show that anti-mCD1d- and anti-hVα24Jα18-neutralizing antibody treatment protects allergen-induced experimental EoE. Taken together, we have shown first time that iNKT cells have a critical pathogenic role in human and experimental EoE. iNKT cell neutralization by humanized anti-CD1d and anti-Vα24Jα18 antibodies might be a novel and potential therapy for human EoE.

Allergy and risk of acute lymphoblastic leukemia among children: a nationwide case control study in Greece

BACKGROUND

Several reports point to inverse associations between allergies and ALL; yet, no study has explored this link using both self-reported-data on allergic history and biomarkers of atopic sensitization.

METHODS

Clinical information for the variables of interest was available for 252 out of 292 cases of childhood (0-14 years) ALL, newly diagnosed across Greece over a 4.5 year period as well as for 294 hospital controls. Allergen-specific-IgEs, as markers of allergic predisposition, against 24 most prevalent respiratory and food allergens, were determined, using an enzyme immunoassay procedure for 199 children with ALL and 113 controls. Cases were compared with controls through frequency distributions and unconditional multiple logistic regression models to estimate odds ratios (ORs) and 95% confidence-intervals (CIs) regarding associations of allergy with childhood ALL.

RESULTS

Self-reported-allergic history overall (OR: 0.49, 95% CI: 0.34-0.72) and practically each one of its main components (respiratory, food, any other clinical allergy) were strongly and inversely associated with ALL. Likewise, the serum IgE inverse association was of the same magnitude (OR: 0.43, 95% CI: 0.22-0.84) mainly contributed by food IgE (OR: 0.39, 95% CI: 0.18-0.83).

CONCLUSION

Beyond the already established inverse association of allergic history with childhood ALL, a same magnitude association is evident when serologic markers of allergic predisposition are used as an alternative measure of allergy. Further research with more appropriate study designs is needed to better understand possible associations between prior allergy and childhood ALL risk.

Kynurenines in the CNS: recent advances and new questions

Various pathologies of the central nervous system (CNS) are accompanied by alterations in tryptophan metabolism. The main metabolic route of tryptophan degradation is the kynurenine pathway; its metabolites are responsible for a broad spectrum of effects, including the endogenous regulation of neuronal excitability and the initiation of immune tolerance. This Review highlights the involvement of the kynurenine system in the pathology of neurodegenerative disorders, pain syndromes and autoimmune diseases through a detailed discussion of its potential implications in Huntington's disease, migraine and multiple sclerosis. The most effective preclinical drug candidates are discussed and attention is paid to currently under-investigated roles of the kynurenine pathway in the CNS, where modulation of kynurenine metabolism might be of therapeutic value.

Natural killer T cells regulate the development of asthma

Studies in mice, monkeys and humans suggest that invariant natural killer (iNK) T cells play a very important role in the pathogenesis of asthma, a heterogeneous disease associated with airway inflammation and airway hyper-reactivity. The requirement for iNK T cells in multiple mouse models of asthma is novel and surprising, challenging the prevailing dogma that CD4(+) T cells responding to environmental allergens are the key cell type in asthma. In this article, we examine the recent studies of iNK T cells and asthma, and discuss how different subsets of NK T cells function in different forms of asthma, including forms that are independent of adaptive immunity and Th2 cells. Together, these studies suggest that iNK T cells, which can interact with many other cell types including Th2 cells, eosinophils and neutrophils, provide a unifying pathogenic mechanism for many distinct forms of asthma.

Autoimmunity and mast cell-related diseases

Allergy and autoimmunity are complex inflammatory processes caused by dysregulation of the immune system. There are select situations in which allergy and autoimmunity coexist pathologically. Traditionally considered unrelated, recent evidence suggests unexpected roles for allergic mediators in several autoimmune diseases. This review presents updated evidence for allergic mediators in several autoimmune diseases, as well as autoimmune phenomena in mast cell-related conditions. We will describe the concomitant manifestation of these conditions in patients and in animal models. The involvement of the main effectors of the immune system - mast cells, T lymphocytes, antibodies and cytokines - in both conditions is also discussed.

CD1d presentation of glycolipids

The CD1 family of antigen-presenting molecules consists of five members, CD1a to e. Of these molecules CD1d has been the subject of much interest over the past 10 years following the discovery that this molecule presents antigens to a group of T cells known as invariant natural killer T cells (iNKT). iNKT cells carry an invariant T cell receptor which contains homologous gene segments in mouse and man. iNKT cells are positively selected in the thymus in the same manner as major histocompatibility complex restricted T cells, except iNKT cells require CD1d to be presented by thymocytes rather than epithelial cells. Once in peripheral organs, iNKT cells appear to play multiple roles in host defence against pathogens and cancer. If the numbers of iNKT cells are not correctly regulated it can result in autoimmune disorders, such as diabetes. The ligands for iNKT cells have been the subject of much research but identifying physiologically relevant candidate ligands for positive selection or activation has proved technically very challenging. This is largely due to the fact that the ligands for iNKT cells are lipids. The lipid ligands for thymic selection and some of those involved in peripheral activation are self-derived. Glycosphingolipids are suggested to be the class of lipid for iNKT cell thymic development. For peripheral activation it appears multiple classes of self-derived lipids may play a role, in addition to pathogen-derived lipids. This review will cover essential background to iNKT cell and CD1d biology with emphasis on the candidate iNKT cell ligands proposed to date.

House dust mite extract induces interleukin-9 expression in human eosinophils

BACKGROUND

Eosinophils play a pivotal role in allergic inflammation. Recent evidence suggests that they not only function as terminal effector cells but have potential to interact with allergen and initiate immune responses. We investigated cytokine production from eosinophils through direct interaction with a major allergen, house dust mite (HDM) .

METHODS

Purified eosinophils from HDM-sensitized or non-sensitized donors were cultured with HDM extract or lipopolysaccharide (LPS) for 18 or 40 h. A panel of cytokine gene expression in eosinophils was examined by means of real-time RT-PCR. Released cytokines in the culture supernatants were assessed with a specific ELISA. In some experiments, HDM was pretreated with protease inhibitors, then added to the culture. Cytokines tested for gene expression were interleukin (IL)-2, 4, 6, 7, 8, 9, 10, 11, 12, 13, 16,17, 18, TGF-beta1 and GM-CSF,.

RESULTS

LPS induced small enhancement of GM-CSF gene expression at 18 h. At 40 h, HDM induced about 60-fold enhancement of IL-9 gene expression. IL-9 protein was also detected in the culture supernatants at 60 h. Those reactions were observed regardless of HDM sensitization status of the donors. HDM-induced IL-9 expression was completely inhibited with a serine protease inhibitor, AEBSF, not with a cysteine protease inhibitor, E-64.

CONCLUSIONS

Accumulated eosinophils in the airways in asthma may directly react with HDM and produce IL-9 to further promote Th2-type immune responses. Protease-activated receptor 2, a ligand for serine proteases, which contained in HDM, may be involved in the reaction.

The autoimmune origin of atherosclerosis

Atherosclerosis is a chronic inflammatory disease. Many studies and observations suggest that it could be caused by an immune reaction against autoantigens at the endothelial level, the most relevant of which are oxidized LDL and heat shock proteins (HSP) 60/65. Endothelial dysfunction plays a fundamental role. The first antigen is related to the increased leakage and oxidation of LDL; the second to cellular reaction to stress. Experimental and clinical observations confirm the pathogenetic role of these antigens. Both innate and adaptive immunity and impaired regulatory mechanisms of the autoimmune reaction are involved. Different triggering factors are examined: infectious agents, smoking, air pollution, diabetes and hypercholesterolemia. Analogies and differences between systemic atherosclerosis and transplant-related coronary atherosclerosis help to understand their respective nature. Immune mechanisms might be responsible for the passage from stable plaque to unstable and rupture-prone plaque. Finally, prospects of treatment and prevention are linked to the induction of tolerance to responsible antigens, activation of immune regulatory response and the use of immunomodulatory drugs.