Intracytoplasmic type A particles from mammary tumours and leukaemias of strain ICRC mice

Abstract

Summary.-The ovarian-hormone-induced leukaemias of strain ICRC mice, with an abundance of intracytoplasmic type A particles in primary as well as transplanted lesions, were used to study morphological, biophysical, immunological and structural characteristics of type A particles. Mammary tumours of strains ICRC and C3H(Jax) were also used as sources for type A particles. The purified virions banded at the density of 1-20 g/ml in 12 60% linear sucrose-density gradient when subjected to spinning at 113,000 g for 4 h. The SDS-polyacrylamide-gel electrophoresis of type A particles from mammary tumours and leukaemias reproducibly resolved at least 8 polypeptides, 2 of these 54,000 and 24,000 dalton proteins, showing variable expression. Type A particles and B particles, despite the fact that each had a distinct polypeptide pattern, showed common antigens with different electrophoretic mobilities. Proteins of 24,000, 18,000 and 12,000 daltons from B particles were found to be antigenically related to those from type A particles. The bioassay studies carried out with purified A particles showed that 2/7 males of strain ICRC and 1/6 females of strain DBA-MTI developed leukaemias, as against none in the controls, when inoculated between the ages of 1-7 days. Spleen tumour and cervical tumour were seen in one female each of strain DBA-MTI.

Integration of type B retroviral DNA in virus-induced primary murine thymic lymphomas

“…Particles released by the DBA/2 lymphoma cell line induced a low level of mammary tumors but were not tested under experimental conditions which would have assessed their leukemogenicity (37). A second report (25) that concentrated preparations of intracytoplasmic A particles (prepared from either an in vivo serially transplanted leukemic cell line or from mammary tumors) could induce leukemia was not conclusive. The incidence was low (12%), the latent period was long (300 to 400 days), and extracts of the leukemias induced mammary tumors and not leukemia.…”