Western blot analysis of B-cell lines and transiently transfected Cos cells with the MoAbs 15F9 and 4E11 shows LMP2A expression in protein extracts from Cos cells transiently transfected with the LMP2A open reading frame (lanes 4). By contrast, no specific bands are detected in an EBV-negative B-cell lymphoma line, BJAB (lanes 1); an EBV-positive lymphoblastoid cell line, X50/7 (lanes 2); Cos cells transfected with the vector only (lanes 3); or Cos cells transfected with the LMP2B gene (lanes 5). A weak band is seen in BJAB cells (lane 1), probably representing cross-reactivity with a nonviral cellular protein.