Lactic dehydrogenase-immunoglobulin G kappa complex in a patient with idiopathic interstitial pneumonia.

A female patient with idiopathic interstitial pneumonia (IIP) was admitted again 40 months after the diagnosis due to progression of clinical findings and increased activity of serum lactic dehydrogenase (LDH). Analysis of LDH isoenzyme disclosed a broad band between LDH4 and LDH5. Gel filtration and immunoelectrophoresis showed that immunoglobulin (Ig) G (kappa type) bound the LDH. With prednisolone and azathioprine, her symptoms and radiological findings improved concomitant with a decrease in the serum LDH activity. The LDH-IgG kappa complex disappeared in the circulation 14 months after initiation of the therapy. We report circulating LDH-Ig complex in a patient with IIP, which may be related to the disease progression of IIP.