Expression of K1 in THP-1, U937, and KS SLK cells blocks anti-Fas antibody–induced apoptosis. THP-1, U937, and KS SLK transfectants were incubated with 50 ng/mL CH-11, 1 μg/mL anti-HGFR antibody, or both for 24 hours. Cells were then fixed and analyzed for apoptosis by DAPI staining. (A) Apoptosis of THP-1 transfectants induced by CH-11, anti-HGFR antibody, or both. (B) Apoptosis of U937 transfectants induced by CH-11, anti-HGFR antibody, or both. (C) Apoptosis of KS SLK transfectants induced by CH-11, anti-HGFR antibody, or both. The error bars indicate standard deviation (*P < .05 for all comparisons). Similar results were obtained in 2 independent experiments.