Intervention of T-cells in transportation of mouse mammary tumor virus (milk factor) to mammary gland cells in vivo.

Using BALB/c nu/nu, BALB/c nu/nufC3H (BALB/c nu/nu mice raised by C3H/HeN foster mother), BALB/c thymus-engrafted BALB/c nu/nufC3H, BALB/c nu/+, and BALB/c nu/+fC3H mice, we examined what kinds of cells are carriers of blood-borne mouse mammary tumor virus (B-MMTV). A radioimmunoassay and an immunoperoxidase assay revealed the presence of MMTV-gp52 antigen in the mammary glands of all BALB/c nu/+fC3H and BALB/c thymus-engrafted BALB/c nu/nufC3H mice (more than 60 days old) but only of some BALB/c nu/nufC3H mice (more than 120 days old): those that possessed a significant number of functional T-cells. BALB/c nu/+ mice did not show the antigen expression at any age. Transfer experiments of cells or plasma from young (less than 12 weeks) BALB/c nu/nufC3H to BALB/c +/+ virgins revealed that cells besides T-cells can also become carriers of B-MMTV. This was confirmed by Southern blotting analyses; exogenous provirus DNA sequences were found in B-cells as well as T-cells of BALB/c nu/+fC3H mice. However, when young BALB/c nu/nu mice were inoculated with BALB/c nu/nufC3H blood, they did not show the MMTV-gp52 antigen expression. Transfer experiments of purified T-cells, B-cells, natural killer cells, and macrophages from BALB/c fC3H mice to BALB/c nu/nu mice revealed that only T-cells have the ability to transfer viral activity to the mammary glands. These results suggest that B-MMTV is carried from the gastrointestinal tract to the mammary glands by lymphoid cells such as T-cells and B-cells, then transferred to the mammary gland cells by the T-cells.