LMP1 expression in BJAB-tTA-LMP1 Burkitt lymphoma cells is associated with multinuclearity. Original magnification ×640, Zeiss AxioImager Z1 microscope. (A) LMP1-suppressed transfectants at day 7 still reveal uniform Burkitt cell morphology with only a few binucleated or large mononuclear cells (arrows) (Pappenheim staining). (B) Immunostaining with anti-LMP1 monoclonal antibody CS.1-4 confirms successful LMP1 suppression through tetracycline. (C) LMP1-expressing transfectants at day 7 contain multiple RS-like giant cells. Arrow points to a satellite nucleus (Pappenheim staining). (D) Strong LMP1 expression is confirmed with anti-LMP1 monoclonal antibody CS.1-4. (E) LMP1 induced accumulation of multinuclear cells. BJAB-tTA-LMP1 cells were induced for the expression of LMP1 for 21 days by removal of tetracycline. Samples from LMP1-induced and LMP1-suppressed cells at days 1, 7, 14, and 21 were cytocentrifuged and counted for the presence of multinucleated cells. For each time point, 200 cells were counted in 15 independent experiments. LMP1-induced formation of RS-like giant cells is evident. *P < .05; **P < .0001.