Expression of eNOS enzyme in transfected U937 cells. Western blot with a monoclonal antibody against human endothelial NOS (eNOS) is shown. Lanes are numbered as follows: (1) M.W. markers; (2) untransfected U937 cells; (3) U937 cells transfected with the pCEP4 vector without the eNOS gene; (4) U937 cells transfected with the pCEP4 vector containing the eNOS gene; (5) human endothelial cell lysate (positive control).