Clostridioides difficile Toxin CDT Induces Cytotoxic Responses in Human Mucosal-Associated Invariant T (MAIT) Cells.

Isabel Marquardt,Meina Neumann-Schaal,Jessica Scheibel,Dunja Bruder,Ralf Gerhard,Lothar Jänsch,Julia Danielle Hofmann,Josefine Jakob,Frank Klawonn

doi:10.3389/fmicb.2021.752549

Abstract

Clostridioides difficile is the major cause of antibiotic-associated colitis (CDAC) with increasing prevalence in morbidity and mortality. Severity of CDAC has been attributed to hypervirulent C. difficile strains, which in addition to toxin A and B (TcdA, TcdB) produce the binary toxin C. difficile transferase (CDT). However, the link between these toxins and host immune responses as potential drivers of immunopathology are still incompletely understood. Here, we provide first experimental evidence that C. difficile toxins efficiently activate human mucosal-associated invariant T (MAIT) cells. Among the tested toxins, CDT and more specifically, the substrate binding and pore-forming subunit CDTb provoked significant MAIT cell activation resulting in selective MAIT cell degranulation of the lytic granule components perforin and granzyme B. CDT-induced MAIT cell responses required accessory immune cells, and we suggest monocytes as a potential CDT target cell population. Within the peripheral blood mononuclear cell fraction, we found increased IL-18 levels following CDT stimulation and MAIT cell response was indeed partly dependent on this cytokine. Surprisingly, CDT-induced MAIT cell activation was found to be partially MR1-dependent, although bacterial-derived metabolite antigens were absent. However, the role of antigen presentation in this process was not analyzed here and needs to be validated in future studies. Thus, MR1-dependent induction of MAIT cell cytotoxicity might be instrumental for hypervirulent C. difficile to overcome cellular barriers and may contribute to pathophysiology of CDAC.

Highlights

Clostridioides difficile infections (CDI) are the major cause of antibiotic-associated colitis and an emerging threat for hospitalized patients
Data obtained in frame of this study suggest that mucosal-associated invariant T (MAIT) cell cytotoxicity might contribute to clearance of toxemia or to pronounced immunopathology observed in C. difficileassociated colitis (CDAC) that is caused by hypervirulent C. difficile
We previously demonstrated that hypervirulent C. difficile bacteria, which express the toxins TcdA, TcdB and C. difficile transferase (CDT), exhibit superior capacities than less toxigenic TcdA/B+ RT012 to activate human MAIT cells (Bernal et al, 2018)

Summary

Introduction

Clostridioides difficile infections (CDI) are the major cause of antibiotic-associated colitis and an emerging threat for hospitalized patients. In contrast to monomeric TcdA and TcdB, CDT consists of two subunits, the substrate binding component CDTb and the enzymatic component CDTa that ADP-ribosylates actin and thereby inactivates host cell actin polymerization, leading to increase of cell surface protrusion (Gülke et al, 2001). These toxin-induced modulations of host cell organization facilitate successful C. difficile colonization at the intestinal epithelium (Schwan et al, 2009, 2014; Kasendra et al, 2014; Cowardin et al, 2016a; Buccigrossi et al, 2019). We demonstrated previously that compared to less toxigenic strains, hypervirulent C. difficile trigger superior responses in human mucosal-associated invariant T (MAIT) cells (Bernal et al, 2018)

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