Appearance of Virus Particles in BALB/c Mammary Nodule Outgrowth Lines Transplanted Into BALB/c f. C3H and (C3Hf ) × BALB/c) F₁ Mice

Summary

The time virus particles appeared in 2 BALB/c mammary nodule outgrowth lines (D1 and D2) transplanted into mammary tumor virus (MTV)-positive BALB/c f. C3H and nodule-inducing virus (NIV)-positive (C3Hf × BALB/c)F₁ mice was determined by electron microscopy. Whereas MTV was detected within 8–11 weeks after the D1 and D2 nodule outgrowth lines were transplanted into BALB/c f. C3H mice, NIV appeared 44 weeks after the D1 nodule outgrowths were transplanted into (C3Hf × BALB/c)F₁ mice. The different times of appearance of MTV and NIV may reflect an important difference between the 2 viruses. Whether this difference in viral activity is directly correlated with the oncogenic capacity of these 2 viruses remains unknown. D1 nodule outgrowths also were transplanted into (C3Hf × BALB/c)F₁ mice that experienced prolonged hormone stimulation by pituitary isografts. Prolonged hormone stimulation reduced the time NIV particles became visible in D1 nodule outgrowths from 44 to 26 weeks. The appearance of virus particles representing NIV was correlated with the length of hormone stimulation and the age of the NIV-positive host.