Overall, in this study, we took a broad look at the role of B cells in ileitis and uncovered disparate areas where they influence the disease in positive or adverse ways, from the protective role conferred locally by IgA production and secretion into the lumen, to their role in TLS formation, and, finally, in their unexpected role for B cell production of LTα3 in protection against a systemic manifestation of disease. The gene discussed is CD79A; the disease is Crohn ileitis.