Complexes of Lactate Dehydrogenase Isoenzymes with Immunoglobulin G and Complement 3 in a Patient with Rheumatoid Arthritis

Abstract

Complexes of lactate dehydrogenase with immunoglobulin (LDH-Ig) were detected in a case of RA. Circulating immune complex (CIC) and LDH activity were high in the serum of the patient.
By immunofixation, binding immunoglobulins were identified with IgG (κ) and IgG (λ). IgG (λ) disappeared soon, and only IgG (κ) existed for about 4 months. The two peaks of LDH activity were shown between 4S and 7S (Peak-S), 7S and 19S (Peak-F) by gel filtration on Sephadex G-200. By solid phase anti-C3 enzymelinked immunosorbent assay (ELISA), CIC level was high in Peak-F and low in Peak-S. In the sample of Peak-F fraction, LDH activity was high in the plates coated with anti-C3, anti IgG and anti κ antibody.
In conclusion, this is a first report that LDH-IgG binds with Complement and forms immune complexes. LDH activity was not affected by binding to IgG-C3.