Some C3H substrains are characterized by a high incidence of mammary tumors caused by a virus transmitted through the mother's milk. C3H substrains that originated from neonate mice foster nursed onto or ova transferred into virus-free females have dramatically lower mammary tumor incidence.
The Jackson Laboratory maintains four C3H substrains. Two of these, C3HeB/FeJ and C3H/HeSnJ, are free of milk-transmitted virus and have low mammary tumor incidence. The other two substrains, C3H/HeJ and C3H/OuJ, carry the milk-transmitted mammary tumor virus (MuMTV) and develop mammary tumors.
The substrains C3H/HeJ and C3H/OuJ have been separated since 1952. A mutation occurred in C3H/HeJ between 1960 and 1968 at the Lps (lipopolysaccharide response) locus such that C3H/HeJ is endotoxin resistant. An increased latency and reduced incidence in mammary tumors also has been reported in C3H/HeJ and may be related to the Lps mutation (Outzen, H.J., et al., JNCI 75:917, 1985).