Quantification of Human MAIT Cell-Mediated Cellular Cytotoxicity and Antimicrobial Activity

MAIT cell activation and recruitment in inflammation and tissue damage in acute appendicitis

Mucosal-associated invariant T (MAIT) cells are antimicrobial T cells abundant in the gut, but mechanisms for their migration into tissues during inflammation are poorly understood. Here, we used acute pediatric appendicitis (APA), a model of acute intestinal inflammation, to examine these migration mechanisms. MAIT cells were lower in numbers in circulation of patients with APA but were enriched in the inflamed appendix with increased production of proinflammatory cytokines. Using the patient-derived appendix organoid (PDAO) model, we found that circulating MAIT cells treated with inflammatory cytokines elevated in APA up-regulated chemokine receptors, including CCR1, CCR3, and CCR4. They exhibited enhanced infiltration of Escherichia coli-pulsed PDAO in a CCR1-, CCR2-, and CCR4-dependent manner. Close interactions of MAIT cells with infected organoids led to the PDAO structural destruction and death. These findings reveal a previously unidentified mechanism of MAIT cell tissue homing, their participation in tissue damage in APA, and their intricate relationship with mucosal tissues during acute intestinal inflammation in humans.

Culture, expansion, and flow-cytometry-based functional analysis of pteropid bat MR1-restricted unconventional T cells

Bats harbor viruses of global public health significance. Understanding bat immune systems may provide intervention strategies to prevent zoonotic disease transmission and identify therapeutic targets. This protocol describes how to culture and expand pteropid bat unconventional T cells, restricted by the MHC-I-related protein 1 (MR1), an MHC-I-like protein. Using multicolor flow-cytometry-based techniques, we examine pteropid MR1T cell functionality, including proliferative capacity, cytotoxicity, and cytokine production. This protocol can be adapted to aid immunological research in other bat species.

For complete details on the use and execution of this protocol, please refer to Leeansyah et al. (2020b)

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Studies into bat immune systems are hampered by the lack of specific protocols

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Protocol describes culture and expansion of pteropid bat MR1-restricted T cells

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Performs antigen-specific stimulations of pteropid bat MR1-restricted T cells

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Flow-cytometry-based analyses of proliferation, cytotoxicity, and cytokine production

Human MAIT cell cytolytic effector proteins synergize to overcome carbapenem resistance in Escherichia coli

Mucosa-associated invariant T (MAIT) cells are abundant antimicrobial T cells in humans and recognize antigens derived from the microbial riboflavin biosynthetic pathway presented by the MHC-Ib-related protein (MR1). However, the mechanisms responsible for MAIT cell antimicrobial activity are not fully understood, and the efficacy of these mechanisms against antibiotic resistant bacteria has not been explored. Here, we show that MAIT cells mediate MR1-restricted antimicrobial activity against Escherichia coli clinical strains in a manner dependent on the activity of cytolytic proteins but independent of production of pro-inflammatory cytokines or induction of apoptosis in infected cells. The combined action of the pore-forming antimicrobial protein granulysin and the serine protease granzyme B released in response to T cell receptor (TCR)-mediated recognition of MR1-presented antigen is essential to mediate control against both cell-associated and free-living, extracellular forms of E. coli. Furthermore, MAIT cell-mediated bacterial control extends to multidrug-resistant E. coli primary clinical isolates additionally resistant to carbapenems, a class of last resort antibiotics. Notably, high levels of granulysin and granzyme B in the MAIT cell secretomes directly damage bacterial cells by increasing their permeability, rendering initially resistant E. coli susceptible to the bactericidal activity of carbapenems. These findings define the role of cytolytic effector proteins in MAIT cell-mediated antimicrobial activity and indicate that granulysin and granzyme B synergize to restore carbapenem bactericidal activity and overcome carbapenem resistance in E. coli.

Mucosa-associated invariant T (MAIT) cells are abundant antimicrobial T cells in humans that recognize bacterial metabolites. This study shows that MAIT cells exert potent antimicrobial activity against both cell-associated and extracellular forms of Escherichia coli, including strains that are resistant to the last resort antibiotics carbapenems.