EBV lytic protein BZLF1 is detected in PBMCs. Photomicrographs of PBMCs stained for EBV BZLF1 shows virus lytic infection in B cells (patient 21, A), T cells (patient 12, B), and non-B, non-T cells (patient 26, C). BZLF1 was directly conjugated to Alexa 488. T cells were stained by using Alexa 594–conjugated anti-CD3, and B cells by using a combination of Alexa 647–conjugated anti-CD19 and anti-CD20 antibodies. BZLF1 staining of EBV-positive B95-8 (D) and EBV-negative BJAB (E) cells served as positive and negative controls, respectively, for EBV lytic infection. Arrows indicate BZLF1-positive cells. (F) B95-8 cells stimulated with butyric acid and TPA (phorbol 12-myristate 13-acetate) served as an additional control for lytic infection; cells undergoing lytic infection show a homogeneous pattern with high levels of EBV DNA (arrow), and latently infected cells show a punctate pattern (arrowheads).