Mouse mammary tumour virus-related antigens in core-like density fractions from large samples of women's milk

Abstract

Specimens of human milk (500 ml) were processed applying methods useful for isolating oncornavirus cores from mouse milk. Treatment with Triton X 100 and diethyl ether as well as banding in sucrose density gradients were included in the preparation procedure. Out of 28 women investigated, five exhibited mouse mammary tumour virus (MuMTV)-related antigens in fractions of density 1.26–1.28 g/ml. By means of a sensitive radioimmunodiffusion (RID) test, these antigens were shown to be identical to at least two main antigenic constituents of MuMTV-B particles and intracytoplasmic A particles (iAp) of mouse mammary tumours. They were precipitated by rabbit antisera against MuMTV-B particles, iAp, and isolated iAp polypeptides (Ap 37, Ap 14). The antigens were reproducibly detected in 22 out of 23 core-like density fractions prepared from the milk of the five positive women between the 5th and 28th week after delivery. By indirect immunofluorescence technique, a rabbit hyperimmune serum against antigen-positive human milk fractions was seen to react with clusters of iAp within mouse mammary tumour cells. There were no immunological cross-reactions with Mason-Pfizer monkey virus main core antigen p 27 and Mason-Pfizer-like viruses replicating in a cell line of human origin (HEp- 2). All women found positive for MuMTV-antigens in their milk, possessed the previously described serum antibody which reacts with murine iAp and inner constituents of B particles. Antigenpositive human milk fractions absorbed the antibody from autologous and homologous sera. Thus, in summary, the presence is indicated of an antigen-antibody system in man that is closely related to MuMTV.