Development of an Infectivity Assay for Mouse Mammary-Tumor Virus2

Abstract

The detection of soluble mammary-tumor virus (MTV) antigen by gel microimmunodiffusion was used as the basis of an assay for MTV. The detectability of antigen in the third lactation milks of mice inoculated with serial dilutions of MTV preparations was reliably predictive of eventual tumorigencsis; 85% of antigen-positive mice developed tumors after 18 months of observation; antigen-negative mice did not develop tumors. The dose-response regression of the assay was characteristic of other virus dilution assays, and definite 50% infective endpoints could be calculated. In comparison with tumor development, the assay time was short (3–3½ months).