(a) Presence of apoptotic bodies in HF cells after 1 week of cocultivation. The EBV-positive BL41/95 (A through C) and -negative BL41 (D through F) were labeled for 48 hours with BrdU before irradiation and cultivation with HF cells. DNA from the lymphomas was detected with antibodies against BrdU (A and D). Cells were double-stained with human serum against EBV nuclear antigens (EBNA; B and E). (C) and (F) show Hoechst 33258, anti-EBNA, and anti-BrdU stainings in the same picture. Size bar = 5 μm. (b) Fibroblasts pulsed with BrdU before being cultivated with irradiated BL41/95 cells. Nuclei of fibroblastic origin were detected with antibodies against BrdU. Cells were double-stained with human serum against EBNAs. The picture shows overlapping signals of EBNA, BrdU, and Hoechst 33258 staining in fibroblast nuclei. Size bar = 8 μm.