Characterisation of mammary tumour virus of strain ICRC mouse.

The mouse mammary tumour virus (MuMTV) isolated and purified from the milk of strain ICRC mice, susceptible to spontaneous development of mammary cancer and leukemia, was investigated for its morphological, biophysical, immunological and structural characters.The purified virions banded at the density of 1.17 g/ml in 0–55% linear sucrose gradient and contain mature B type particles along with few C type particles when studied under the electron microscope. The polyacrylamide gel electrophoresis of strain ICRC MuMTV reproducibly resolved at least ten polypeptides. The mol. wt of the three major polypeptides are 49,000 (p 49), 34,000 (p 34) and 24,000 (p 24). Two of these polypeptides p 49 and p 34 have been characterised as glycoproteins on the basis of staining with periodic acid Schiff's reagent. High titers of MuMTV antigens were noted in the milk plasma of strain ICRC mice. The anti MTV-S serum could detect common antigens in disrupted virions of strains ICRC and C3H(Jax) by immunodiffusion test.Strain ICRC was a high cancer strain in the earlier generations of inbreeding (the average tumour incidence in the breeders of first ten generations was 81.3%) however, the tumour incidence in the 45th generation has gone down considerably. The parameters studied in the present investigations have indicated that the MuMTV of strain ICRC exhibit characters comparable to those of high cancer strain C3H(Jax), in spite of a significant decrease in the mammary tumour incidence.