[A protein related to the main core protein of the mouse mammary cancer virus in a microparticle fraction of human milk].

Virus-like density fractions (VDF) have been prepared from 6 specimens of human milk by ultracentrifugation of milk sera and recentrifugation of pellet through 35% sucrose or by separation in sucrose density gradient. Using electroblotting and enzyme-linked antibody probes, the protein with a molecular weight of 27 kD, reacting with serum against MMTV gag proteins, was identified in 5/6 of milk VDF. The absence (or very low amounts) of this protein among proteins of milk, fat globule membranes and cellular membranes of human milk has been demonstrated. Positive VDF decrease the activity of anti-p27 MMTV-specific serum and the activity of human sera reacting with p27 MMTV. A human protein immunologically related to the main gag protein of MMTV has been described; this protein seems to be an antigen causing the appearance of anti-MMTV antibodies in human sera.