Development of an infectivity assay for mouse mammary-tumor virus

SUMMARY-The detection of soluble mammary-tumor virus (MTV) anti-gen by gel microimmunodiFJusion was used as the basis of an assay For MTV. The detectability of anfigen in the third lactation milks of mice inoc-ulated with serial dilutions of MTV preparations was reliably predictive of eventual tumorigenesis; 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 couldbe calculated. In comparison with tumor development, the assay time wasshort (3-31/2 months).-J Nat Cancer Inst 43: 1289-1296,1969. THE DETECTION, by gel immunoprecipitation, of antigens related to murine mammary-tumor virus (MTV) has been demonstrated by Lezhneva (1), Blair (2), and Blair and Weiss (3). This antigen is thought to be the intact virion. Now