Non-H-2 antigens on fibroblasts and an embryocarcinoma cell line react with xenoantisera against H-2 antigens.

The murine embryocarcinoma cell line F9 lacks the classical transplantation antigens. However, rabbit anti-H-2 antigen sera, recognizing "backbone structures" of H-2 K and D antigens, react with three types of molecules manufactured by F9 cells. A 49,000- and a 25,000-dalton chain are glycoproteins located on the cell surface. The third component with an apparent molecular weight of 15,000, and the 25,000-dalton chain seem to be unrelated to the 49,000-dalton glycoprotein. The 25,000- and 15,000-dalton components are not manufactured by splenocytes, thymocytes, hepatocytes, or various lymphoma, mastocytoma, and plasmacytoma cell lines. However, fibroblasts derived from both embryos and adult animals synthesize 25,000- and 15,000-dalton molecules reactive with the rabbit anti-H-2 antigen sera. The 49,000-, 25,000-, and 15,000-dalton molecules are not recognized by a syngeneic anti-F9 cell serum.