Collectively, this data indicates that IECs and ISCs can assume one of four antigen-presenting phenotypes, that polarization towards MHCII- rather than or CD1d-mediated antigen presentation by IECs/ISCs is a feature of primary antibody deficiency in mice, and that ISCs focused on lipid antigen presentation may be central to maintaining immune homeostasis in the small bowel. The gene discussed is CD1D; the disease is agammaglobulinemia.