Detection, isolation, and biochemical characterization of an acidic protein from the effusion fluid of patients with pancreatic cancer

Fractions containing immune complexes were isolated from effusion fluids from patients with pancreatic adenocarcinoma by ammonium sulfate precipitation, gel filtration chromatography, affinity chromatography, and preparative isoelectric focusing. The focused proteins were pooled into two fractions. The more basic fraction (pI>6.5) contained IgG. The acidic fraction (pI<3.5), after further purification by CM-Sephadex ion exchange chromatography contained an acid protein with a pI of 2.6. SDS-PAGE analysis of the acid protein under non-reducing conditions demonstrated a molecular weight of 68,000 daltons, while under reducing conditions, bound subunits with molecular weights of 40,000, 18,000 and 13,000 daltons, respectively were seen. On crossed immunoelectrophoresis, the acid protein migrated into the B-2-α region. This acid protein was detected by analytical IEF in 13 of 18 effusion fluids from patients with pancreatic cancer and 1 of 12 control effusion fluids. This protein did not react with antisera to Pancreatic Oncofetal Antigen, Carcinoembryonic Antigen, Human Alpha Fetoprotein, Alpha-1-Acid Glycoprotein, Beta-2-Microglobulin, and antiserum to normal human serum components. A goat antiserum to the acid protein identified it in 13 of 18 effusion fluids from patients with pancreatic cancer and 2 of 12 control effusion fluids. This acidic protein may serve as a tumor marker for pancreatic cancer.