Mesothelin binds to native MUC16. (A) Meso-Fc binding to MUC16 samples from the ascites of patient #2 (100 U of CA125; lane 1) and from OVCAR-3 cells (500 U of CA125; lane 2) is shown (left panel). A control blot (right panel) with MUC16 from patient #2 (100 U of CA125; lane 1) and OVCAR-3 (500 U of CA125; lane 2) and meso-Fc (Lane 3) was overlaid with secondary antibody only. (B) For comparison, MUC16 from OVCAR-3 (100 U of CA125) was detected by VK-8 antibody. Note that since only 100 U (CA125) of OVCAR-3-derived MUC16 was loaded the banding pattern is identical to that of lane 1 of (A).