Abstract
M-P virus infection of adult mice exerts an anti-tumour effect on certain murine carcinomas and lymphatic leukaemia (Molomut & Padnos, 1965). However, adult mice made tolerant to M-P virus by inoculation as neonates are deficient in the anti-tumour activity (Padnos, Molomut & Ferris, 1967). Attempts have been made to elucidate the mechanism of the anti-tumour activity of M-P virus and it has been suggested that the immune defence mechanisms of the host may assist in the destruction of the tumour cells. An immunological reaction need not be the only mode of anti-tumour action exerted by M-P virus however, since there is greater tumour inhibition during the early acute viraemic period than during the post-viraemic period when virus antibody levels are highest (Molomut et al. 1964; M. Padnos, N. Molomut & P. Ferris, unpublished results). Furthermore, the entire role of the reticuloendothelial system in the host reaction to neoplasias is not completely understood but is known to be very important (Old et al. 1961).