The differential action of neonatal thymectomy in mice infected with murine sarcoma virus‐harvey (msv‐h)

Intact C3H/Bi and BALB/c mice infected with Murine Sarcoma Virus‐Harvey (MSV‐H) at 3–16 days developed either „early”︁ erythroblastic splenomegaly with concomitant severe anaemia and sarcomas at sites related to the route of inoculation or, after a perceptible delay, „late”︁ lymphocytic leukaemia. These effects were dependent on the dilution of the virus and the age of the recipients. Neonatal thymectomy both accelerated the erythroblastosis and increased the tumour incidence in older 14–16 day recipients but prevented (or indefinitely postponed) the lymphocytic leukaemia. This differential action of neonatal thymectomy is discussed in the light of current immunological theory. A virus causing only lymphocytic leukaemia was separated by passage from the plasma of leukaemic intact or non‐leukaemic thymectomized mice. Thus, in these experiments, MSV‐H behaved as a complex of two viruses, one causing the early changes and a second, always present in higher concentration but slower acting, responsible for the late changes.