Research Notes REGRESSION OF ROUS SARCOMAS IN TWO LINES OF CHICKENS*'1

ABSTRACT A genetic difference between two lines of chickens in the incidence of regres-sion of Rous sarcomas was found. PODXIRY SCIENCE 52: 799-800,1973 Rubin (1962) suggested that the rarity of metastases in older birds, the immunity of recovered birds to reinfection and tu-mor regression were dependent upon the same immunological mechanism. Gyles et al. (1968) suggested that tumor regres-sion in chickens was influenced by a single gene exhibiting partial dominance, or by a very few genes, and also by the strength of the inoculum. Freire et al. (1953) ob-served that the incidence of regression in chickens may be influenced by host age at inoculation. This is a report on the incidence of re-gression of wing-web tumors in two lines of chickens when challenged with highly purified preparations of Rous sarcoma virus (Crittenden et al., 1971). MATERIALS AND METHODS Stock—Two lines of chickens were used; a highly inbred line of White Leghorns (line 6) obtained from the United State