Serum prostate-specific acid phosphatase: development and validation of a specific radioimmunoassay

We describe radioimmunoassay for human prostatic acid phosphatase [orthophosphoric-monoester phospho-hydrolase (acid optimum), EC 3.1.3.2] in serum, with use of monospecific antisera raised in rabbits against highly purified acid phosphatase from human prostates. The antiserum did not cross react with partly purified acid phosphatases from human spleen, erythrocytes, or synovial tissues. 125I-labeled acid phosphatase was prepared by a Chloramine T method, and the bound and free antigen was separated in the assay by use of anti-rabbit gamma-globulin raised in sheep. Uniform low nonspecific binding of the [125I]acid phosphatase was achieved by using acid-phosphatase-free serum to prepare standard curves and diluted samples of serum with high acid phosphatase activities. Concentrations of immunoreactive acid phosphatase in the serum of healthy men ranged from less than 1 to 10 microgram/liter and for 12 patients with advanced prostatic carcinoma between 100 and 500 microgram/liter. The concentrations of the enzyme in sera of patients with benign prostatic hyperplasia were very similar to those in sera of the reference group.