REGULATION OF MHC CLASS-II EXPRESSION BY INTERFERON-GAMMA MEDIATED BYTHE TRANSACTIVATOR GENE CIITA

Major histocompatibility complex (MHC) class II genes are expressed co nstitutively in only a few cell types, but they can be induced in the majority of them, in particular by interferon-gamma (IFN-gamma). The M HC class II transactivator gene CIITA is defective in a form of primar y MHC class II deficiency. Here it is shown that CIITA expression is c ontrolled and induced by IFN-gamma. A functional CI ITA gene is necess ary for class II induction, and transfection of CIITA is sufficient to activate expression of MHC class II genes in class II-negative cells in the absence of IFN-gamma. CIITA is therefore a general regulator of both inducible and constitutive MHC class II expression.