Mice lacking the MHC class II transactivator (CIITA) show tissue-specific impairment of MHC class II expression

textabstractCIITA activates the expression of multiple genes involved in antigen presentation and it is believed to be required for both constitutive and IFNγ-inducible expression of these genes. To understand the role of CIITA in vivo, we have used gene targeting to generate mice that lack CIITA. CIITA-deficient (-/-) mice do not express conventional MHC class II molecules on the surface of splenic B cells and dendritic cells. In addition, macrophages resident in the peritoneal cavity do not express MHC class II molecules upon IFNγ stimulation nor do somatic tissues of mice injected with IFNγ, in contrast with wild-type mice. The levels of li and H-2M gene transcripts are substantially decreased but not absent in CIITA (-/-) mice. The transcription of nonconventional MHC class II genes is, however, not affected by CIITA deficiency. A subset of thymic epithelial cells express MHC class II molecules. Nonetheless, very few mature CD4 T cells are present in the periphery of CIITA (-/-) mice despite MHC class II expression in the thymus. Consequently, CIITA (-/-) mice are impaired in T-dependent antigen responses and MHC class II-mediated allogeneic reponses