Pathophysiological Roles of Mucosal-Associated Invariant T Cells in the Context of Gut Microbiota-Liver Axis

Mucosal-associated invariant T cells in cancer: dual roles, complex interactions and therapeutic potential

Mucosal-associated invariant T (MAIT) cells play diverse roles in cancer, infectious diseases, and immunotherapy. This review explores their intricate involvement in cancer, from early detection to their dual functions in promoting inflammation and mediating anti-tumor responses. Within the solid tumor microenvironment (TME), MAIT cells can acquire an 'exhausted' state and secrete tumor-promoting cytokines. On the other hand, MAIT cells are highly cytotoxic, and there is evidence that they may have an anti-tumor immune response. The frequency of MAIT cells and their subsets has also been shown to have prognostic value in several cancer types. Recent innovative approaches, such as programming MAIT cells with chimeric antigen receptors (CARs), provide a novel and exciting approach to utilizing these cells in cell-based cancer immunotherapy. Because MAIT cells have a restricted T cell receptor (TCR) and recognize a common antigen, this also mitigates potential graft-versus-host disease (GVHD) and opens the possibility of using allogeneic MAIT cells as off-the-shelf cell therapies in cancer. Additionally, we outline the interactions of MAIT cells with the microbiome and their critical role in infectious diseases and how this may impact the tumor responses of these cells. Understanding these complex roles can lead to novel therapeutic strategies harnessing the targeting capabilities of MAIT cells.

Trimethylamine-N-oxide (TMAO) and basic fibroblast growth factor (bFGF) are possibly involved in corticosteroid resistance in adult patients with immune thrombocytopenia

PURPOSE

Immune thrombocytopenia (ITP) is an autoimmune disease characterized by accelerated platelet clearance. Gut dysbiosis was associated with its pathogenesis, but the underlying mechanisms have not been fully elucidated. Patients with ITP exhibit varying degrees of responsiveness to corticosteroid treatment. Therefore, prognostic indexes for corticosteroid responsiveness in ITP could offer valuable guidance for clinical practices.

METHODS

The present study examined the signature of six types of gut-microbiota metabolites and forty-eight types of cytokines, chemokines, and growth factors and their clinical significance in patients with ITP.

RESULTS

Both patients with good and poor corticosteroid responsiveness exhibited significantly elevated/suppressed secretion of twenty-two cyto(chemo)kins/growth factors in comparison to healthy controls. Additionally, patients with ITP demonstrated a significant decrease in plasma levels of trimethylamine-N-oxide (TMAO), which was found to be negatively correlated to circulating platelet counts, and positively correlated with Interleukin (IL)-1β and IL-18. Notably, patients who exhibited poor response to corticosteroid treatment displayed elevated levels of TMAO and basic fibroblast growth factor (bFGF) in comparison to responders. Additionally, we found that the amalgamation of TMAO, bFGF and interleukin (IL)-13 could serve as a valuable prognostic tool for predicting CS responsiveness.

CONCLUSION

Patients with ITP were characterized overall by an imbalanced secretion of cyto(cheo)kins/growth factors and inadequate levels of TMAO. The varying degrees of responsiveness to corticosteroid treatment can be attributed to different profiles of basic FGF and TMAO that might be related to overburdened oxidative stress and inflammasome overactivation, and ultimately mediate corticosteroid resistance.

Aging unconventionally: γδ T cells, iNKT cells, and MAIT cells in aging

Unconventional T cells include γδ T cells, invariant Natural Killer T cells (iNKT) cells and Mucosal Associated Invariant T (MAIT) cells, which are distinguished from conventional T cells by their recognition of non-peptide ligands presented by non-polymorphic antigen presenting molecules and rapid effector functions that are pre-programmed during their development. Here we review current knowledge of the effect of age on unconventional T cells, from early life to old age, in both mice and humans. We then discuss the role of unconventional T cells in age-associated diseases and infections, highlighting the similarities between members of the unconventional T cell family in the context of aging.

Altered Frequency, Activation, and Clinical Relevance of Circulating Innate and Innate-Like Lymphocytes in Patients With Alcoholic Liver Cirrhosis

Alcoholic liver cirrhosis (ALC) is caused by chronic alcohol overconsumption and might be linked to dysregulated immune responses in the gut-liver axis. However, there is a lack of comprehensive research on levels and functions of innate lymphocytes including mucosal-associated invariant T (MAIT) cells, NKT cells, and NK (NK) cells in ALC patients. Thus, the aim of this study was to examine the levels and function of these cells, evaluate their clinical relevance, and explore their immunologic roles in the pathogenesis of ALC. Peripheral blood samples from ALC patients (n = 31) and healthy controls (HCs, n = 31) were collected. MAIT cells, NKT cells, NK cells, cytokines, CD69, PD-1, and lymphocyte-activation gene 3 (LAG-3) levels were measured by flow cytometry. Percentages and numbers of circulating MAIT cells, NKT cells, and NK cells were significantly reduced in ALC patients than in HCs. MAIT cell exhibited increased production of IL-17 and expression levels of CD69, PD-1, and LAG-3. NKT cells displayed decreased production of IFN-γ and IL-4. NK cells showed elevated CD69 expression. Absolute MAIT cell levels were positively correlated with lymphocyte count but negatively correlated with C-reactive protein. In addition, NKT cell levels were negatively correlated with hemoglobin levels. Furthermore, log-transformed absolute MAIT cell levels were negatively correlated with the Age, Bilirubin, INR, and Creatinine score. This study demonstrates that circulating MAIT cells, NKT cells, and NK cells are numerically deficient in ALC patients, and the degree of cytokine production and activation status also changed. Besides, some of their deficiencies are related to several clinical parameters. These findings provide important information about immune responses of ALC patients.

Microbiome-Based Metabolic Therapeutic Approaches in Alcoholic Liver Disease

Alcohol consumption is a global healthcare problem. Chronic alcohol consumption generates a wide spectrum of hepatic lesions, the most characteristic of which are steatosis, hepatitis, fibrosis, and cirrhosis. Alcoholic liver diseases (ALD) refer to liver damage and metabolomic changes caused by excessive alcohol intake. ALD present several clinical stages of severity found in liver metabolisms. With increased alcohol consumption, the gut microbiome promotes a leaky gut, metabolic dysfunction, oxidative stress, liver inflammation, and hepatocellular injury. Much attention has focused on ALD, such as alcoholic fatty liver (AFL), alcoholic steatohepatitis (ASH), alcoholic cirrhosis (AC), hepatocellular carcinoma (HCC), a partnership that reflects the metabolomic significance. Here, we report on the global function of inflammation, inhibition, oxidative stress, and reactive oxygen species (ROS) mechanisms in the liver biology framework. In this tutorial review, we hypothetically revisit therapeutic gut microbiota-derived alcoholic oxidative stress, liver inflammation, inflammatory cytokines, and metabolic regulation. We summarize the perspective of microbial therapy of genes, gut microbes, and metabolic role in ALD. The end stage is liver transplantation or death. This review may inspire a summary of the gut microbial genes, critical inflammatory molecules, oxidative stress, and metabolic routes, which will offer future promising therapeutic compounds in ALD.

Recent Trends of Microbiota-Based Microbial Metabolites Metabolism in Liver Disease

The gut microbiome and microbial metabolomic influences on liver diseases and their diagnosis, prognosis, and treatment are still controversial. Research studies have provocatively claimed that the gut microbiome, metabolomics understanding, and microbial metabolite screening are key approaches to understanding liver cancer and liver diseases. An advance of logical innovations in metabolomics profiling, the metabolome inclusion, challenges, and the reproducibility of the investigations at every stage are devoted to this domain to link the common molecules across multiple liver diseases, such as fatty liver, hepatitis, and cirrhosis. These molecules are not immediately recognizable because of the huge underlying and synthetic variety present inside the liver cellular metabolome. This review focuses on microenvironmental metabolic stimuli in the gut-liver axis. Microbial small-molecule profiling (i.e., semiquantitative monitoring, metabolic discrimination, target profiling, and untargeted profiling) in biological fluids has been incompletely addressed. Here, we have reviewed the differential expression of the metabolome of short-chain fatty acids (SCFAs), tryptophan, one-carbon metabolism and bile acid, and the gut microbiota effects are summarized and discussed. We further present proof-of-evidence for gut microbiota-based metabolomics that manipulates the host's gut or liver microbes, mechanosensitive metabolite reactions and potential metabolic pathways. We conclude with a forward-looking perspective on future attention to the “dark matter” of the gut microbiota and microbial metabolomics.

Impact of gut microbiome on skin health: gut-skin axis observed through the lenses of therapeutics and skin diseases

The human intestine hosts diverse microbial communities that play a significant role in maintaining gut-skin homeostasis. When the relationship between gut microbiome and the immune system is impaired, subsequent effects can be triggered on the skin, potentially promoting the development of skin diseases. The mechanisms through which the gut microbiome affects skin health are still unclear. Enhancing our understanding on the connection between skin and gut microbiome is needed to find novel ways to treat human skin disorders. In this review, we systematically evaluate current data regarding microbial ecology of healthy skin and gut, diet, pre- and probiotics, and antibiotics, on gut microbiome and their effects on skin health. We discuss potential mechanisms of the gut-skin axis and the link between the gut and skin-associated diseases, such as psoriasis, atopic dermatitis, acne vulgaris, rosacea, alopecia areata, and hidradenitis suppurativa. This review will increase our understanding of the impacts of gut microbiome on skin conditions to aid in finding new medications for skin-associated diseases.

T Cell Subsets and Natural Killer Cells in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a condition characterized by hepatic accumulation of excess lipids. T cells are commonly classified into various subsets based on their surface markers including T cell receptors, type of antigen presentation and pathophysiological functions. Several studies have implicated various T cell subsets and natural killer (NK) cells in the progression of NAFLD. While NK cells are mainly components of the innate hepatic immune system, the majority of T cell subsets can be part of both the adaptive and innate systems. Several studies have reported that various stages of NAFLD are accompanied by the accumulation of distinct T cell subsets and NK cells with different functions and phenotypes observed usually resulting in proinflammatory effects. More importantly, the overall stimulation of the intrahepatic T cell subsets is directly influenced by the homeostasis of the gut microbiota. Similarly, NK cells have been found to accumulate in the liver in response to pathogens and tumors. In this review, we discussed the nature and pathophysiological roles of T cell subsets including γδ T cells, NKT cells, Mucosal-associated invariant T (MAIT) cells as well as NK cells in NAFLD.

Gut microbiome and metabolic response in non-alcoholic fatty liver disease

Fatty liver disease (FLD) is one of the largest burdens to human health worldwide and is associated with gut microbiome and metabolite stability. Engineered liver tissues have shown promise in restoring liver functions in non-alcoholic FLD (NAFLD), hepatitis and cirrhosis. Fatty liver, largely noted in obesity and hepatic cancer, is highly fatal and has led to a global increase in death rates. It is associated with complex metabolic reprogramming too. A standard approach to therapy in the newly diagnosed setting includes surgery or identification of biomarkers/ metabolites for therapeutic purposes, which ultimately focus on improvement of liver health in patients. As such there are no standard procedures for patient care, but depending on the severity, systemic therapy with either genomic, proteomic or metabolomic profiling form potential options. Better comparisons and study of underlying mechanisms in gut microbiome-based metabolic functions in obesity are urgently required. Today, an emerging field, focusing on metabolomic approaches and metabolic phenotyping, involved in high-throughput identification of metabolome in obesity and gut disorders, is involved in biomarker and metabolite identification. There are supporting technologies and approaches in NAFLD that throw light on the metabolites and gut microbiome, and also on the understanding of the risk factors of obesity along with liver cancer metabolic reaction networks. We discuss the current state of NAFLD metabolites, gut micro-environmental changes, and the further challenges in digital metabolomics profiling. Innovative clinical trial designs, with biomarker-enrichment strategies that are required to improve the outcome of NAFLD in patients are also discussed.