Notably, there was no difference in the levels of anti-TcdB or anti-TcdBCROPS (the C-terminal combined repetitive oligopeptides domain of TcdB, a target of neutralizing antibodies)16 IgG or IgA between IBD patients and control subjects (Figure 1D), further confirming that TcdB-specific CD4+ T cells are more relevant than antibodies in defining normal vs pathologic immunity to TcdB.6 However, similar to our findings for anti-flagellin antibodies in these cohorts,8 anti-TcdB IgA levels were decreased in UC compared with CD patients. Here, CD4 is linked to inflammatory bowel disease.