Cross-reactions between mouse Ia and human HLA-D/DR antigens analyzed with monoclonal alloantibodies.

Two mouse monoclonal anti-I-E/Ck alloantibodies (H7-8.26 and H10-81.10) directed against 2 distinct determinants of the specificity Ia-7 and 1 anti-I-Ak alloantibody (H8-15.9) directed against a public determinant common to the I-A subregion products of the H-2k, H-2b, H-2d, H-2q, and H-2ja haplotypes identified cross-reactive determinants on lymphoid cells from various mammalian species, including rat, dog, pig, cow, hamster, and guinea pig. In man, these antibodies detected nonpolymorphic determinants of DR antigens on B cell-enriched peripheral blood lymphocytes from 50 unrelated individuals. These cross-reactive DR determinants were also detected on lymphoblastoid B cell lines, on PHA-activated peripheral T lymphocytes, and on allospecific cytolytic T cell clones, but not on various DR-negative human T leukemia cell lines. Two chains of 29,000 and 35,000 daltons m.w., corresponding to DR antigens, were precipitated by H7-8.26 and H8-15.9 antibodies from radiolabeled membrane extracts of Raji cells. Competitive binding experiments indicated that the 3 mouse anti-Iak antibodies identified 3 distinct cross-reactive determinants on human cells. The results indicate that: a) The cross-reactivity described between mouse I-E/C gene products (Ia-7) and human DR antigen(s) involves, in fact, several distinct and topologically distant determinants. b) At least 1 determinant cross-reacting with DR can be identified on I-Ak gene products. c) The intriguing genetic problem of mouse MHC allotypic determinant(s) being nonpolymorphic in man cannot be simply explained by the deletion of an I-E alpha chain in some strains of mice.

Distinct epitopes of Ik gene products identified by monoclonal antibodies.

Analysis of reactivity of monoclonal anti-Iak alloantibodies, obtained by fusion between NS 1 myeloma and spleen cells from alloimmune A. TH mice, permitted the identification of 9 distinct determinants of the Ik gene products. Competitive binding experiments indicated that 2 private epitopes (defined by H8-109.13 and H8-138.4 antibodies) of the I-Ak product could be separated, thereby apparently splitting the Ia.2 specificity. A public determinant of the I-Ak molecule (identified by H8-15.9 antibody) was found expressed not only on the I-A products of the H-2b, H-2d, H-2ja, H-2p and H-2q murine haplotypes, but also on human HLA-DR antigens. Four determinants of the I-E/Ck antigen (defined by H7-8.26, H10-81.10, H10-93.2 and H8-86.2 antibodies) had a strain distribution analogues to the Ia.7 specificity. However, competitive binding experiments, and the cross-reactivity pattern with Ia-like antigens from other species (e.g. human HLA-DR antigens) indicated that these antibodies detected distinct determinants on the I-E/Ck molecule, thereby subdividing the broad Ia. 7 specificity. Two other determinants (defined by H9-14.8 and H9-15.4 antibodies) had a strain distribution that did not permit a precise assignment to a given Ia antigen, even though preliminary data suggested that they could detect separate determinants on the I-E/Ck product. All these monoclonal antibodies identified membrane antigens with the expected Ia tissue distribution pattern, and most of them could precipitate a molecule containing two chains of 28kD and 35kD, from mouse spleen cell lysates.