To explore whether B cells contribute to colitis severity, we transferred various ratios of spleen-derived naive B cells with CD45RBhigh T cells into severe combined immune deficient mice to induce colitis.<h4>Results</h4>Our analysis identified a distinct subset of naive (MS4A1+CD27-IGHD+TCL1A+) B cells that are significantly enriched and present a more matured phenotype in inflamed compared to non-inflamed biopsies from UC patients. The gene discussed is CD27; the disease is colitis.