Identification of regulatory regions that are involved in B cell-specific activation of CIITA-PIII. (A) Schematic representation of the CIITA-PIII-derived reporter plasmids PIIIfl, PIII-151, and PIII-mut-Ets. Indicated are the 2 E-boxes, Site-C comprising the EICE, ARE-1, ARE-2, and the 5′-UTR. (B) Transient transfections of reporter plasmids pGL3 basic, PIIIfl, and PIII-151, which harbor a deletion as depicted in panel A, were performed in Raji B cells and Jurkat T cells. Transient transfection of reporter plasmids pGL3 basic, PIIIfl, and PIII-mut-Ets were performed in Raji and Ramos B cells (C), Jurkat T cells (D), and THP-1 and U937 monocytic cell lines (E). B and T cells were harvested after 48 hours and monocytic cells after 24 hours and analyzed for luciferase activity. Luciferase activity values were normalized with Renilla luciferase activity values and represent the means of 3 experiments. Error bars indicate SEM.