Influence of Host Age on Leukaemogenesis and Virus Proliferation after Infection with a Murine Leukaemia Virus

Abstract

WITH few exceptions, the virus induced thymic lymphomas in mice are strongly dependent on age^1–4. Early passages of virus were leukaemogenic only for mice less than 2 days old. After repeated passage of the virus, however, the age specificity diminished and leukaemia could be induced in older mice. Even in these systems, host susceptibility still decreases with advancing age as measured by the increasing latent period between virus inoculation and the development of leukaemia. Despite repeated reports of optimum susceptibility in young animals, there is at present little information available about the cause or mechanism of this phenomenon. The elucidation of its mechanism has been complicated by the fact that both susceptibility to virus infections (for example, ref. 5) and susceptibility to tumour cell transplantation^6–8 have been shown to be enhanced in younger animals. The virus induced thymic lymphomas are convenient for resolving this problem, for the development of viraemia in these systems is separated by some 40–70 days from the first appearance of tumour cells^9–13. It was possible therefore, with this system, to determine the influence of host age on virus proliferation independently of the development of leukaemia.