Mammary tumor virus antigen expression in inbred mouse strains of European origin established in Japan.

Expression of the mammary tumor virus (MTV) antigen in the milk from inbred mouse strains maintained in Japanese laboratories was investigated by means of the immunodiffusion test (ID) and the results were compared with the incidence of mammary tumors in breeding females of identical strains. Japanese strains tested were classified into two groups. The DD/Tbr, DDD and KF strains were derived from "dd" stock mice, and they showed equally high incidences of MTV antigen expression in the milk, though each strain developed mammary tumors with different incidences; 71%, 14% and 22%, respectively. Other strains originated from Swiss albino mice. The incidence of MTV antigen expression in the milk of SHN and SLN strains was the same as that of mammary tumors at an early age.