Lack of Resistance of Adult Mice to Erythrocyte-borne Bittner Virus

Abstract

BITTNER virus, the classical mouse mammary tumour virus (MTV), can be detected in bioassays of various organs and tissues of infected mice including mammary tissues and erythrocytes^1–3. We have shown that the final result of the administration of MTV-carrying RBC or of mammary tissue extracts to young hosts is identical: namely, the production in test mice which are free from MTV of mammary nodules and tumours containing electron microscopically visible B particles. The MTV in these two tissues differ, however, in several respects^2,3. MTV activity in mammary tissues (M-MTV) is itself associated with B particles, but such particles do not seem to be associated with RBC which bear MTV activity (R-MTV). Resistance to tumorigenesis of adult animals following oncogenic viral administration is well known⁴. Several investigators have demonstrated that adult mice are more resistant than young ones to mammary tumour development after administration of MTV^5,6. We have recently suggested that this resistance in adult mice of the BALB/c strain is systemically mediated⁷. Dux and Mühlbock⁸, however, have proposed that both host age and tissue age are involved in the resistance of older mice to MTV. R-MTV has been shown to precede the appearance of M-MTV in naturally infected mice³, and so it was thought possible that a failure in R-MTV production which followed administration of M-MTV to adult mice might account for the low incidence of mammary nodules and tumours. We have now compared the effects of administration of the two forms of MTV to mice of different ages.