Distinct epitopes on I^k gene products identified by monoclonal antibodies

TLDR

Monoclonal anti‑I‑k alloantibodies were generated by fusing NS1 myeloma cells with spleen cells from alloimmune A.TH mice, and competitive binding and cross‑reactivity assays were used to map nine distinct determinants of the I‑k gene products and subdivide the Ia.7 specificity. The antibodies revealed two private and one public epitope on the I‑A k molecule, four strain‑specific determinants on the I‑E/C k antigen analogous to Ia.7, and all recognized membrane antigens with expected Ia tissue distribution, precipitating a 28‑kD/35‑kD heterodimer from mouse spleen lysates.

Abstract

Abstract Analysis of reactivity of monoclonal anti‐Ia k 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 I k gene products. Competitive binding experiments indicated that 2 private epitopes (defined by H 8–109.13 and H 8–138.4 antibodies) of the I‐A k product could be separated, thereby apparently splitting the Ia.2 specificity. A public determinant of the I‐A k molecule (identified by H 8–15.9 antibody) was found expressed not only on the 1‐A products of the H‐2 b , H‐2 d , H‐2 ja , H‐2 P and H‐2 q murine haplotypes, but also on human HLA‐DR antigens. Four determinants of the I‐E/C k antigen (defined by H 7–8.26, H 10–81.10, H 10–93.2 and H 8–86.2 antibodies) had a strain distribution analogous to the Ia.7 specificity. However, competitive binding experiments, and the cross‐reactivity pattern with la‐like antigens from other species ( e.g. human HLA‐DR antigens) indicated that these antibodies detected distinct determinants on the I‐E/C k 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/C k 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 28 kD and 35 kD, from mouse spleen cell lysates.