Characterization of three novel monoclonal anti-OKa.

Anti-Ok(a) was first described by Morel and Hamilton in 1979. The Ok(a) antigen has a very high incidence, and only eight probands that are Ok(a-) have been found; all are of Japanese heritage. In this study,we describe the generation and characterization of three novel monoclonal antibodies (Mabs), MIMA-25, MIMA-144, and MIMA-149. The reactivity of these three Mabs was compared with the original human polyclonal anti-Ok(a). Mice were immunized with transfected HEK cells to induce an immune response, and the spleen B lymphocytes were fused with mouse myeloma X63-Ag8.653 cells to form antibody-secreting hybridomas. The resulting Mabs were tested serologically, by flow cytometry, and by immunoblotting. The specificity of each antibody was determined after excluding specificities to common antigens in the Rh, Kell, Duffy, Kidd, MNS, Lewis, Lutheran, P1, Colton, Diego, Xga, and Dombrock blood group systems. In each case only the Ok(a-)RBC sample was nonreactive. The Mabs and the original human anti-Ok(a) each have a unique pattern of reactivity when tested with enzyme-treated cells; however, none were reactive by immunoblotting. We have generated three novel anti-Ok(a) Mabs: MIMA-144 is an indirectly agglutinating IgG2b antibody, and MIMA-25 and MIMA-149 are directly agglutinating antibodies (IgM and IgA, respectively), underscoring their usefulness as typing reagents for the clinical laboratory.