CEACAM1 and graft versus host disease: It is difficult to directly assess the relative importance of gastrointestinal radiation sensitivity versus increased GVHD in Ceacam1−/− allo-BMT recipients, as radiation-induced gut damage may both be directly manifested in intestinal pathology, yet transmural migration of bacterial superantigens is an important first step for the initiation of GVHD[1], [39], [40], and increased damage to the intestines of Ceacam1−/− mice may thus amplify the development of GVHD in these mice, and also explain in part the specifically increased large intestinal GVHD we observed.