Erratum: Corrigendum: Antimicrobial activity of mucosal-associated invariant T cells

Immune Monitoring of Human Mucosal-Associated Invariant T Cells by Quantitative Proteomics

Molecular phenotypes of mucosal-associated invariant T (MAIT) cells are correlating with individual susceptibilities and outcomes in human diseases. Quantitative proteome strategies can examine such variations in the functional and druggable inventory of MAIT cells comprehensively, but protocols for the support of translational and clinical studies are still rare. Here, we describe a protocol in which MR1-restricted MAIT cells were isolated from blood donations by FACS and are then characterized by quantitative proteomics (iTRAQ-LC-MS/MS) to complement information about their unique effector phenotype and to investigate donor-/patient- or disease-specific variations in protein networks with high precision.

Clostridioides difficile Activates Human Mucosal-Associated Invariant T Cells

Clostridioides difficile infection (CDI) causes severe inflammatory responses at the intestinal mucosa but the immunological mechanisms underlying CDI-related immunopathology are still incompletely characterized. Here we identified for the first time that both, non-toxigenic strains as well as the hypervirulent ribotypes RT027 and RT023 of Clostridioides difficile (formerly Clostridium difficile), induced an effector phenotype in mucosal-associated invariant T (MAIT) cells. MAIT cells can directly respond to bacterial infections by recognizing MR1-presented metabolites derived from the riboflavin synthesis pathway constituting a novel class of antigens. We confirmed functional riboflavin synthesis of C. difficile and found fixed bacteria capable of activating primary human MAIT cells in a dose-dependent manner. C. difficile-activated MAIT cells showed an increased and MR1-dependent expression of CD69, proinflammatory IFNγ, and the lytic granule components granzyme B and perforin. Effector protein expression was accompanied by the release of lytic granules, which, in contrast to other effector functions, was mainly induced by IL-12 and IL-18. Notably, this study revealed hypervirulent C. difficile strains to be most competent in provoking MAIT cell responses suggesting MAIT cell activation to be instrumental for the immunopathology observed in C. difficile-associated colitis. In conclusion, we provide first evidence for a link between C. difficile metabolism and innate T cell-mediated immunity in humans.