Characterization of immunoglobulin A kappa autoantibodies to human lactate dehydrogenase isoenzyme-3.

We have purified with a cumulative recovery of 48% from the serum of a patient the immunoglobulin A kappa subunit of the lactate dehydrogenase-immunoglobulin A kappa (LD-IgA kappa) complex. It appears that the pI range of the complex is 5.4-5.8. The Ig part of the complex showed a monoclonal character, and the complex exhibited a 1:2 molar ratio of the Ig to the LD isoenzyme. From reconstitution experiments by two different methods we concluded that LD-3 is essential for restoring the original complex. Additional studies showed a recombination of the IgA kappa with both autologous and homologous LD-3, and a binding of LD-3 at the Fab region of the Ig. The estimated value of the affinity constant (Keq) was 2.1 X 10(9) liters/mol. Analysis of the specific LD-3-binding IgA kappa concentrations in the sera of five cases revealed a broad range of the individual immune response. Our first quantitative data on the lymphocyte subpopulations revealed a significantly increased OKT4/OKT8 ratio due to a reduction in the absolute number of T suppressor cells.