Mucosal-associated invariant T (MAIT) cells are abundant in humans and recognize bacterial ligands. Here, we demonstrate that MAIT cells are also activated during human viral infections in vivo. MAIT ...cells activation was observed during infection with dengue virus, hepatitis C virus and influenza virus. This activation-driving cytokine release and Granzyme B upregulation-is TCR-independent but dependent on IL-18 in synergy with IL-12, IL-15 and/or interferon-α/β. IL-18 levels and MAIT cell activation correlate with disease severity in acute dengue infection. Furthermore, HCV treatment with interferon-α leads to specific MAIT cell activation in vivo in parallel with an enhanced therapeutic response. Moreover, TCR-independent activation of MAIT cells leads to a reduction of HCV replication in vitro mediated by IFN-γ. Together these data demonstrate MAIT cells are activated following viral infections, and suggest a potential role in both host defence and immunopathology.
MAIT cells are an unconventional T cell population that can be activated through both TCR-dependent and TCR-independent mechanisms. Here, we examined the impact of combinations of TCR-dependent and ...TCR-independent signals in human CD8+ MAIT cells. TCR-independent activation of these MAIT cells from blood and gut was maximized by extending the panel of cytokines to include TNF-superfamily member TL1A. RNA-seq experiments revealed that TCR-dependent and TCR-independent signals drive MAIT cells to exert overlapping and specific effector functions, affecting both host defense and tissue homeostasis. Although TCR triggering alone is insufficient to drive sustained activation, TCR-triggered MAIT cells showed specific enrichment of tissue-repair functions at the gene and protein levels and in in vitro assays. Altogether, these data indicate the blend of TCR-dependent and TCR-independent signaling to CD8+ MAIT cells may play a role in controlling the balance between healthy and pathological processes of tissue inflammation and repair.
Display omitted
•Activation of human MAIT cells is TCR-dependent or TCR-independent and enhanced by TL1A•TCR-dependent and TCR-independent triggering induces distinct transcriptional responses•TCR-dependent triggering of MAIT cells induces a tissue-repair program•Data integration with in vivo studies in mice indicates a shared transcriptome
Leng et al. explore the consequences of activation of human MAIT cells via their TCR and/or cytokines, including the gut-associated TNF-superfamily member TL1A. TCR triggering reveals a transcriptional program linked to tissue-repair functions seen in vivo, consistent with a homeostatic role for these cells in epithelia.
Summary The study of errors in gene translation has largely been confined to a small number of model organisms. We have examined all possible misreading errors at a defined codon in Mycobacterium ...smegmatis. Using a dual-luciferase gain of function reporter system that employs a mutated essential lysine in firefly luciferase, we accurately quantified mistranslation errors. Overall, accuracy of gene translation was comparable with Escherichia coli at <1/2000 errors/codon during exponential growth. Stationary phase was associated with a dramatic increase in misincorporation errors by Lys- tRNA CUU Lys at a subset of three codons, each with a single base changed from the AAG lysine codon. The maximum error rate detected was 0.2% with codon AUG. Treatment with streptomycin increased misreading errors at several codons associated in particular with U·U, G·U and C·U codon·anti-codon mismatches, but oxidative stress did not change translational fidelity. Our study is the first comprehensive examination of misreading errors for a defined codon in mycobacteria.
Mucosal-associated invariant T (MAIT) cells represent an innate T-cell population that can recognize ligands generated by the microbial riboflavin synthesis pathway, presented via the major ...histocompatibility complex class I-related molecule (MR1). Streptococcus pneumoniae is a major human pathogen that is also associated with commensal carriage; thus, host control at the mucosal interface is critical. The recognition of pneumococci by MAIT cells has not been defined nor have the genomics and transcriptomics of the riboflavin operon. We observed robust recognition of pneumococci by MAIT cells, using both MR1-dependent and MR1-independent pathways. The pathway used was dependent on the antigen-presenting cell. The riboflavin operon was highly conserved across a range of 571 pneumococci from 39 countries, dating back to 1916, and different versions of the riboflavin operon were also identified in related Streptococcus species. These data indicate an important functional relationship between MAIT cells and pneumococci.
Mucosal‐associated invariant T (MAIT) cells are a well‐characterized innate‐like T cell population abundant in the human liver, peripheral tissues and blood. MAIT cells serve in the first line of ...defense against infections, through engagement of their T cell receptor, which recognizes microbial metabolites presented on MR1, and through cytokine‐mediated triggering. Typically, they show a quiescent memory phenotype but can undergo rapid upregulation of effector functions including cytolysis upon stimulation. T cells profoundly change their cellular metabolism during their maturation and activation. We sought to determine how MAIT cell metabolism may facilitate both the long‐term memory phase in tissue and the transition to rapid effector function. Here, we show, by flow cytometric metabolism assays and extracellular flux analysis that, despite an effector‐memory profile, human MAIT cells are metabolically quiescent in a resting state comparable to naïve and central memory T cells. Upon stimulation, they rapidly increase uptake of glucose and show a concomitant upregulation of the effector molecules notably granzyme B, which is impaired by inhibition of glycolysis with 2‐deoxyglucose. These findings suggest that MAIT cells share some metabolic characteristics of both resting and effector T cell subsets, with a rapid transition upon triggering. Metabolic programming of this cell type may be of interest in understanding and modulating their function in infectious diseases and cancer.
Mucosal‐associated invariant T (MAIT) cells are an innate‐like T cell population abundant in humans. T cell immunometabolism has been studied before in memory cell populations showing distinct usage of metabolic pathways according to activation status. Here, we show for the first time that upon stimulation, MAIT cells engage their glycolytic pathway along with an upregulation of the effector molecule granzyme B.
See also: Special Feature on MAIT cells
Mucosal‐associated invariant T (MAIT) cells are an abundant human T‐cell subset with antimicrobial properties. They can respond to bacteria presented via antigen‐presenting cells (APCs) such as ...macrophages, which present bacterially derived ligands from the riboflavin synthesis pathway on MR1. Moreover, MAIT cells are also highly responsive to cytokines which enhance and even substitute for T‐cell receptor‐mediated signaling. The mechanisms leading to an efficient presentation of bacteria to MAIT cells by APCs have not been fully elucidated. Here, we showed that the monocytic cell line THP‐1 and B cells activated MAIT cells differentially in response to Escherichia coli. THP‐1 cells were generally more potent in inducing IFNγ and IFNγ/TNF production by MAIT cells. Furthermore, THP‐1, but not B, cells produced TNF upon bacterial stimulation, which in turn supported IFNγ production by MAIT cells. Finally, we addressed the role of antibody‐dependent opsonization of bacteria in the activation of MAIT cells using in vitro models. We found that opsonization had a substantial impact on downstream MAIT cell activation by monocytes. This was associated with enhanced activation of monocytes and increased TNF release. Importantly, this TNF acted in concert with other cytokines to drive MAIT cell activation. These data indicate both a significant interaction between adaptive and innate immunity in the response to bacteria, and an important role for TNF in MAIT cell triggering.
Binding of IgG antibodies to the bacterial surface results in an enhanced activation of MAIT cells. IgG‐mediated improvement of MAIT cell functions was accompanied with an elevated production of TNF by monocytes. This TNF acted in concert with MR1 and other cytokines to drive MAIT cell activation.
Human type-2 CD8
T cells are a cell population with potentially important roles in allergic disease. We investigated this in the context of severe asthma with persistent airway eosinophilia-a ...phenotype associated with high exacerbation risk and responsiveness to type-2 cytokine-targeted therapies. In two independent cohorts we show that, in contrast to Th2 cells, type-2 cytokine-secreting CD8
CRTH2
(Tc2) cells are enriched in blood and airways in severe eosinophilic asthma. Concentrations of prostaglandin D
(PGD
) and cysteinyl leukotriene E
(LTE
) are also increased in the airways of the same group of patients. In vitro PGD
and LTE
function synergistically to trigger Tc2 cell recruitment and activation in a TCR-independent manner. These lipids regulate diverse genes in Tc2 cells inducing type-2 cytokines and many other pro-inflammatory cytokines and chemokines, which could contribute to eosinophilia. These findings are consistent with an important innate-like role for human Tc2 cells in severe eosinophilic asthma and suggest a potential target for therapeutic intervention in this and other diseases.
Human mucosal associated invariant T (MAIT) cells are an important T cell population present in circulation as well as immune privileged sites such as the liver and the gut. They are characterised by ...a semi-invariant T cell receptor (TCR) and high surface expression levels of CD161 and IL-18Rα, and restriction by the MHC class I-related protein (MR1). Studies have described a broad range of MAIT cell effector functions, including MR1-mediated antibacterial responses and TCR- independent, cytokine-mediated proinflammatory and antiviral properties. How human MAIT cells integrate these signals to exert their effector functions in the gut and in autoimmune and immune-mediated diseases such as inflammatory bowel diseases (IBD) has not been fully described. In this study, an in vitro approach was used to probe MAIT cell activation, and the roles of the TCR, IL-12/-15/-18, TL1A and type I interferons (IFNs). MAIT cells were shown here to achieve certain effector and antimicrobial functions - measured by IFN-γ / tumour necrosis factor-α release and granzyme B expression - with specific innate cytokine signals. These features were reproduced in gut-derived CD8+ MAIT cells and CD161-expressing CD4+ T cells, whose phenotypes and effector functions may not only be mediated by exogenous TCR/cytokine signals, but also tuned by the gut microenvironment and various cues from IBD. Furthermore, while TCR triggering was insufficient to drive full activation, gene expression signatures of TCR-triggered MAIT cells showed specific enrichment of tissue-repair functions, and genome-wide comparison of functional responses to TCR-dependent and -independent signals defined novel functions of MAIT cells relevant not only to host defence but also tissue homeostasis. Overall, these findings indicate the importance of both TCR and inflammatory cytokine signals in promoting effector functions of human CD161-expressing T cells. Further in vitro and in vivo investigations on these gut-derived innate-like CD161+ T cells will be useful to understand their tissue-specific and signal-specific effector functions, as well as their role in various diseases.
Human MAIT Cell Activation In Vitro Hagel, Joachim P; Garner, Lucy C; Bilton, Matthew ...
Methods in molecular biology,
2020, Letnik:
2098
Journal Article, Book Chapter
Odprti dostop
Mucosal-associated invariant T (MAIT) cells are an abundant innate-like T cell subset in humans, enriched in mucosal tissues and the liver. MAIT cells express a semi-invariant T cell receptor (TCR) ...and recognize microbial-derived riboflavin metabolites presented on the MHC Class I-like molecule MR1. In addition to activation via the TCR, MAIT cells can also be activated in response to cytokines such as IL-12 and IL-18, in contrast to conventional T cells. Here we describe TCR-dependent and -independent methods for MAIT cell activation. The TCR-dependent approaches include stimulation with microbead- or plate-bound anti-CD3/anti-CD28 antibodies, and with 5-OP-RU or paraformaldehyde (PFA)-fixed E. coli in the presence of antigen-presenting cells (APCs). The latter method includes a combination of TCR- and cytokine-mediated stimulation. The TCR-independent methods include direct stimulation with the recombinant cytokines IL-12 and IL-18, and indirect stimulation with TLR-4/TLR-8 agonists or influenza A virus in the presence of APCs. Finally, we outline a protocol to analyze activated MAIT cells using flow cytometry.
PDF
