Soluble MUC16 has a lower affinity for mesothelin. (A) A431-Meso+ cells were incubated with purified MUC16 (50,000 U/ml). After 1 h, the amount of MUC16 on the cell surface was measured using the VK-8 antibody and a FITC labeled secondary. (B) Binding of A431-Meso+ cells to MUC16 from peritoneal fluid was measured by flow cytometry. The cells were cultured in the peritoneal fluid from patient #15 that contains (84,000 U of CA125/ml). MUC16 binding was detected using the VK-8 and the FITC-labeled secondary antibodies. (C) The A431-Meso+ cells were labeled with MN and a FITC-conjugated secondary. Mesothelin expression was measured by flow cytometry.