Biological Properties of B Particles From C3H and C3Hf Mouse Milk

Publisher Website
Google Scholar
Abstract
B particles were isolated from C3H and C3Hf mouse milk by ultracentrifugation in Ficoll density gradients. Quantities of B particles with the same optical density in ultraviolet light were compared for their tumorigenic activity in BALB/c mice. The high mammary-tumor-virus activity of C3H B particles was confirmed. After this preparation was diluted 10,000 times it still had tumorigenic activity. An undiluted preparation of C3Hf B particles did not induce mammary tumors before 300 days. This indicated the presence, in C3Hf mice, of another virus with the morphology of B particles and less or no carcinogenic activity. Injection of a mixture of equal amounts of B particles from both sources did not decrease the tumor incidence as compared to the C3H B particles alone, which thus excludes the possibility of an inhibitor in the C3Hf B-particle preparation. Addition of a 1000-fold higher concentration of C3Hf B particles to a threshold dose of C3H B particles greatly increased the tumor incidence.