Characterization of ‘h‐2k, d‐like structures’ on mm2 × 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 β 2 ‐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 C57BL/6 lymph node cells with a mixture of anti‐H‐2.2, 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‐2K b and D b 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‐2 k ). One is the same as or cross‐reactive with an ‘H‐2‐like’ alloantigen of normal C57BL/6 lymph node cells (H‐2 d ) 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).