Immunity & infection
Clostridium difficile infection (CDI) is a leading cause of infectious diarrhea, with approximately 25% of patients relapsing after treatment. C.difficile pathogenicity requires the activities of its toxins, TcdA and TcdB, but the T cell-mediated response to these toxins remains uncharacterized. We enrolled a cohort of patients with newly acquired CDI, a cohort with relapsing CDI, and healthy volunteers with no history of CDI. Toxin-specific CD4+ T cell responses were measured using a whole blood flow cytometry assay that measures induced co-expression of CD25 and OX40 following 44h incubation with antigen. In patients with recurring CDI, CD4+ T cell responses to TcdB, but not TcdA, were significantly higher than for healthy controls and newly acquired CDI. In both patient cohorts, TcdB-specific CD4+ T cells were functionally heterogeneous; with a 1:1 ratio of Tregs to T effectors, and T effectors containing Th1, Th2 and Th17 cells at a 1.5:1:3 ratio. Interestingly, TcdB-specific Th1 and Th17 cells were significantly reduced in recurring, compared to newly acquired, CDI. Analysis of sorted TcdB-specific CD4+ T cells confirmed antigen specificity and polarization towards Th17 cells, important for intestinal anti-pathogen immunity. Levels of anti-TcdA/TcdB IgG antibodies were not different between patients and controls. This is the first investigation of T cell immunity to C. difficile toxins, and identifies anti-TcdB CD4+ T cells as a marker of active disease. Analysing toxin-specific CD4+ T cell responses has the potential to predict relapse and provides insight into how CD4+ T cell memory develops in response to a prevalent bacterial pathogen.