Studies of Parotid-Tumor Agent in Cultures of Leukemic Tissues of Mice

Abstract

Attempts to detect a presumptive leukemia-inducing or leukemia-accelerating agent in leukemic tissues of the mouse in short-term cultures have been unsuccessful, since no agent was found in a variety of leukemias, including 3 from the induced passage A series of Gross. However, parotid-tumor agent (PTA) was isolated from 2 of the 3 leukemias from the Gross series. One of the positive lines subsequently converted to negative during serial transplantation. This added to the evidence that association of leukemias with PTA is largely coincidental. Continuous cultures (P388 D₁) derived from a DBA/2 lymphoma initially gave no evidence of carrying PTA, but were susceptible to infection with PTA. Ten serial passages of PTA through P388 D₁ were completed without evident decline of tumor-inducing activity. Thymic epithelial tumors and a variety of other tumors and lesions associated only rarely with the agent before passage through P388 D₁ cultures were observed more frequently after such passage. The tumors associated with PTA form a histologically distinctive group. “Carrier” cultures of P388 D₁ infected with PTA were maintained continuously for 9 months in high-serum medium. Continued presence of the agent was demonstrated by persistent tumor-inducing activity of these cultures. No completely resistant strain of mouse was found among 12 tested with PTA. Mice up to 14 days of age were found susceptible to induction of parotid tumors by PTA of high activity. Resistance of certain entire litters to PTA appeared to be correlated with maternal immunity. Tissue-culture preparations of PTA induced tumors in all litters and in nearly 100 percent of mice born of uninfected mothers.