Effect of IL-15 on infection of PBMC by HHV-6. PBMC were PHA-activated, infected with HHV-6 for 2 hours, and cultured in the absence (A) or presence of 10 ng/mL (B) or 50 ng/mL (C) recombinant IL-15 (rIL-15). On day 7 postinfection, cells were harvested and tested for cell surface expression of HHV-6 antigen by flow cytometry. Results are presented as overlay histograms, with the black histograms representing cells stained with anti–HHV-6 MoAb, whereas the white histograms represent cells stained with an irrelevant MoAb. (D) depicts the results obtained when HHV-6–infected cells, treated or not with IL-15, were analyzed for HHV-6 DNA content. Genomic DNA was hybridized with the ³²P-labeled HHV-6 pZVH14 probe.