Mammary Tumor Virus Activity in Red Blood Cells of BALB/c f. C3H Mice2

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Abstract
The noduligenic test for mammary tumor virus (MTV) was used in investigations designed to ascertain which fraction of blood carries MTV activity in female BALB/c f. C3H mice of various ages and physiological states. Electron microscopic examination of red blood cells (RBC) and bone marrow cells, fluorocarbon extraction of blood, and potassium tartrate isopycnic density gradient centrifugation of whole blood and RBC from BALB/c f. C3H mice were also carriftl out to determine whether bloodborne MTV activity is associated with the presence of B particles. Biologically detectable MTV activity was always associated with the RBC fraction of blood. No such activity was associated with white blood cells (burfy coat) of 5-week-old females, or with plasma from donors of various physiological states except at lactation. Electron microscopically visible MTV particles (types A and B) were not observed in mature RBC, in bone marrow cells, or in pellets following fluorocarbon extraction of hemolyzed whole blood. The characteristic band for B particles was also absent after density gradient centrifugation of whole blood and of RBC from mice of the BALB/c f. C3H strain. Nodules in the mammary tissues of test mice inoculated with RBC from BALB/c f. C3H donors contained abundant A and B particles. The significance of these findings has been discussed and the suggestion was made that blood-borne MTV activity in BALB/c f. C3H mice may not be associated with B particles.