Inhibition of IRF-4 by FKBP52 specifically reduces CIITA-PIII activity in B cells and abolishes HLA-DR expression in primary B lymphocytes. (A) CD19⁺-enriched B cells were transfected with EGFP with either addition of empty expression vector (i,iii) or addition of FKBP52 (ii,iv), respectively. (v-vi) Transfections without EGFP but solely with empty expression vector (v) or FKBP52 (vi). FACS analysis was performed after 18 hours of transfection, and in all plots cells are gated for CD19 expression and lymphocyte-specific cell scatter pattern. Cells were stained as described in “Materials and methods” and expression of CD19, EGFP, and HLA-DR is indicated on the axes. (B-C) Transient transfection of CIITA-PIII reporter plasmids pGL3 basic, PIIIfl, and PIII mut-Ets were performed in (B) Raji and Ramos B cells, and (C) Jurkat T cells, THP-1, and U937 monocytic cell lines. Five and 10 μg FKBP52 expression plasmid was added to the B cells (PIIIfl+), panel B, lanes 3 and 4, respectively, and 10 μg FKBP52 expression plasmid was added to the Jurkat T cells (PIIIfl+), THP-1, and U937 monocytic cell lines (PIIIfl+) panel C, lane 3. 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 withRenilla luciferase activity values and represent the means of 3 experiments.