We previously reported that IBD patients have increased flagellin-specific CD4+ T cells compared with healthy control subjects but reduced Th17 cell proportions within these responses,8 paralleling observations for TcdB-specific CD4+ T cells in recurrent CDI patients.6 Notably, this was not the case for responses to Pediacel,6 indicating the gut antigen-specific nature of the relative reduction in Th17 cells. Here, CD4 is linked to inflammatory bowel disease.