Expression of early fetal antigens on transformed mouse cells.

We have used immunoprecipitation of radioactivity from labeled cell membrane preparations to study further the association between the histocompatibility-2 (H-2) peptides and a tumor-associated embryonic antigen (Ag I) on the surface of L-cells. Since earlier studies had shown that Ag I and H-2 co-cap on L-cells, the present study was initiated to test the hypothesis that Ag I presents an altered H-2 peptide expressed on transformed cells. Indeed, sodium dodecyl sulfate-gel electrophoresis of Ag I shows two major peaks at approximately 110,000 and 40,000 daltons, the latter co-migrating with the major H-2 peptide. However, further analysis using sequential immunoprecipitation indicates that the molecules reacting with antisera to H-2 and to Ag I are separate entities, precipitating independently of one another. This has led us to postulate that Ag I and H-2 participate in a unique kind of association in the cell membrane, that is, that the bonds between them which allow them to co-cap may be in the lipid bilayer itself, and that these bonds are distrupted upon solubilization of the membrane.