Detection of virus antigens in Swiss albino mice infected by milk-borne mouse mammary tumour virus: the effect of age, sex and reproductive status. II. Radioimmunoassay of two virus components, gp47 and p28 in serum and organ extracts.

Extracts of various organs, mammary tumours and sera from milk-borne MMTV infected Swiss albino mice of different age, sex and physiological conditions were tested by radioimmunoassay for the presence of gp47, the main envelope polypeptide, and p28, the main core protein of the virus. Except in brain, ovaries and testes, both antigens were found in all organs of old animals and of females after the onset of their first pregnancy. Antigens were not present in organs of weanlings or in whole foetuses. Higher values were found in mammary glands, mammary tumours, epididymis and seminal vesicles. These organs also harboured a greater amount of gp47 than p28. The serum generally contained gp47 but rarely p28. This indicates that gp47 is not virion-bound in blood. Pregnancy, lactation and especially the presence of mammary tumours increased the concentration of gp47 in serum. The results do not allow localization of target organs of MMTV infection in the interval between ingestion of the virus by the suckling mouse and the first pregnancy. Moreover, results obtained with one group of mice devoid of exogenous virus show that, as endogenous MMTV genome expresses p28, it might account for part of the p28 detected exogenous MMTV-infected mice.