The HCMV protein pp65 mediates down-regulation of HLA-DR. To examine whether pp65 directly inhibited HLA-DR expression, cells were transfected with a pCDNA3 vector, containing the pp28 or pp65 genes, respectively. The expression level of HLA-DR in cells transfected with either pCDNA3 alone (A; black line) or pCDNA3-pp28 (B; black line), or pCDNA3-pp65 (C; black line) was compared with untreated cells (gray lines). The figure shows 1 representative example of 4 experiments.