In CD4+ T cell-mediated colitis in Rag1-deficient mice, administration of B. vulgatus or a cathepsin S inhibitor LY3000328 had similar effects in attenuating weight loss, improving histological scores, and reducing numbers of CD3+CD4+ T cells and MHC-IIhiCD11c+ dendritic cells, providing additional support for this hypothesis. Here, CD4 is linked to colitis.