Despite the development of insulitis (Fig 2, A), characterized by infiltration of CD4+ and CD8+ T cells into the β-cell–containing islets of Langerhans, and generalized upregulated expression of MHC class I as a result of inflammatory conditions, mice reconstituted with WAS KO bone marrow did not have overt diabetes (Fig 2, B). This evidence concerns the gene CD4 and diabetes mellitus.