Isoenzyme specificities of immunoglobulins isolated from lactate dehydrogenase-immunoglobulin complexes.

Lactate dehydrogenase (L-lactate: NAD oxidoreductase, EC 1.1.1.27, LD) specific immunoglobulins were isolated from LD-immunoglobulin complexes in sera from 11 patients and the isoenzyme specificity of the immunoglobulins was studied by sandwich electroimmunofixation (SEIF). The immunoglobulins differed in isoenzyme specificity, depending on the heavy and/or light chains. IgA kappa recombined with LD2 and LD3, and was thought to be the antibody to common structures (H2M) in LD2 (H3M) and LD3 (H2M2). IgA kappa in a IgA/G kappa lambda case recombined with LD3-5, so that the IgA kappa might be an antibody to M2 dimer in the isoenzymes. IgA lambda recombined only with LD3, and was thought to recognize the H2M2 structure of LD3. As IgG kappa and/or lambda recombined with all LD isoenzymes of LD1-5, the immunoglobulins might react with common structures in H and M subunits. IgG lambda recombined with LD2-5, particularly with LD5, so that the IgG lambda was thought to be an antibody to the M subunit in LD2-5. From the above findings and the tetrameric structure of the LD molecule, 18 types of antibodies to different antigenic determinants on LD molecules can be theoretically derived. Each of the present 11 cases of immunoglobulin corresponded to one of the 18 types, respectively. A formula which can theoretically determine the percent LD activity recombined with immunoglobulins is described.