[Research progress on regulation of class II MHC expression]

Class II MHC antigens play a critical role in the induction of immune responses through presentation of processed antigen to CD4+ T lymphocytes. The absence of MHC II normal expression results in severe primary immunodeficiency diseases, such as the bare lymphocyte syndrome (BLS). Four different MHC II regulatory genes have been identified. These genes encode RFXANK, RFX5, RFXAP and CIITA. The first three are subunits of RFX, a ubiquitously expressed factor that binds to the promoters of all MHC II genes. CIITA is the master control factor for MHC II expression. The highly regulated expression pattern of CIITA ultimately dictates the cell type specificity, induction and level of MHC II expression. This review focuses on research progress on regulation of class II MHC expression in recent years.