Characterization of "H-2K,D-like structures" on MM2 X mouse L cell hybrids. I. "H-2K,D-like" alloantigen encoded by the D region and/or to the right of the D region of the H-2 gene complex.

It was found that anti-MM2 serum, which had been prepared by immunizing C3H/He mice with syngeneic MM2 mouse mammary ascites tumor, detected molecules of 44-46,000 and 12,000 daltons on EL4 leukemic cells and on C57BL/6 lymph node cells, as well as on somatic cell hybrids between the MM2 and mouse L cells. Experiments with a known rabbit anti-mouse beta2-microglobulin serum showed that the two molecules detected by anti-MM2 serum were hydrophobically associated with each other in membrane extracts; thus, the antigen detected by anti-MM2 serum was structurally similar to H-2K and D antigens. Preclearing of lysates from C57BL6 lymph node cells with a mixture of anti-H-22, anti-H-2.33, and anti-H-2.28 sera did not remove the "H-2-like" antigen, indicating that the antigen was distinct from the H-2Kb and Db molecules. Neither C3H/He nor B10.BR lymph node cells expressed the "H-2-like" antigen, but B10.A(4R) and B10.AM lymph node cells did possess the antigen. Absorption of anti-MM2 serum with EL4 cells abolished the capacity of the absorbed serum to precipitate the "H-2-like" antigen activity on C57BL/6 lymph node cell extracts and reduced the "H-2-like" radioactive peaks of the hybrid cells. These results indicate that there are at least two components being recognized by the anti-MM2 serum in hybrid cells between MM2 tumor and mouse L cells, both of which had originated in the C3H/He mouse (H-2k). One is the same as or cross-reactive with an "H-2-like" alloantigen of normal C57BL/6 lymph node cells (H-2d) and the other is another "H-2-like" antigen. Experiments with recombinant mice show that the "H-2-like" alloantigen on lymph node cells is coded for by the D region and/or to the right of the D region of the major histocompatibility complex (MHC).