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

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.

CDT of Clostridioides difficile Induces MLC-Dependent Intestinal Barrier Dysfunction in HT-29/B6 Epithelial Cell Monolayers

“…Furthermore, as a consequence of these mutual toxin effects, one has to take into account the facilitated access of toxins to the mucosal subepithelial immune cells, as a result of which intestinal inflammatory processes are intensified along the leaky gut concept. It has been argued that such effects on mucosal immune cells in C. difficile infection lead to a more severe disease outcome [ 35 , 36 ]. Furthermore, it may be reasonable to conclude that the combined cytotoxicity of the different toxins in CDT-positive strains induces cell death in the epithelial cell layer such as apoptosis, necrosis, necroptosis, or autophagy.…”

Pathogenicity and virulence of Clostridioides difficile

“…CDT also induces inflammation via the Toll-like receptor 2-dependent pathway, and suppresses the protective host eosinophil response [ 121 ]. Recent evidence has also implicated CDT in the activation of cytotoxic responses in human mucosal-associated invariant T-cells, leading to further aggravation of the pro-inflammatory response [ 122 ]. Collectively, these studies suggest CDT is an important virulence factor in C. difficile pathogenesis, particularly in hypervirulent strains.…”

Die Kämpfe únd schláchten—the struggles and battles of innate-like effector T lymphocytes with microbes

“…Similarly, studies of C. difficile pathology indicate that these bacteria potently activate MAIT cells in a combined TCR- and cytokine-dependent manner inducing a pathological cytokine storm. The resultant runaway inflammation perhaps enables C. difficile to overcome cellular barriers to potentiate C. difficile –induced antibiotic-associated colitis ( 138 ). In a similar vein, gastric H. pylori infections elicit a hyperactive MAIT cell response, promoting an increased recruitment of inflammatory immune cells to the gastric mucosa exacerbating H. pylori gastritis ( 145 ).…”