Radioimmunoassay for protein p28 of murine mammary tumor virus in organs and serum of mice and search for related antigens in human sera and breast cancer extracts

The main protein of the core of murine mammary tumor virus, with a molecular weight of 28,000 (p28), was solubilized by deoxycholate treatment of the virus and purified by Ultrogel ACA-54 filtration and hydroxyapatite chromatography. This protein was used as labeled antigen in a highly specific and reproducible radioimmunoassay. Organ extracts of uninfected C57BL mice did not contain p28, but organ extracts of infected RIII mice did contain the antigen. Despite the high content in the mammary gland, the level of p28 in the other organs was identical in male and female mice. Sera of uninfected mice and the majority of the sera of infected mice did not contain the antigen. The investigation included 338 human sera (50, normal; 157, breast cancer; 77, polycystic disease; 32, benign mastopathy; 12, fibroadenoma; 10, at risk of developing breast cancer). None contained an antigen related to p28. Eight of 24 extracts of human breast cancer gave results that appeared weakly positive, possibly as a result of proteolysis. Extracts of healthy breast tissue and the serum from the breast arterial and venous blood of corresponding patients were negative.