Circulating immune complexes in sarcoidosis.

Circulating immune complexes (CIC) were detected in 100 out of 112 sera from 33 sarcoidosis patients. Five tests were used representing three different basic principles. All patients had detectable CIC at some stage of their disease. The three platelet tests detecting IgG complexes exhibited the highest positive titres in the acute cases. The ClqB-ELISA test, which detects complement fixing IgG complexes, was the test most frequently positive in the chronic cases. The presence of extra-pulmonary lesions or corticosteroid therapy did not influence the appearance or disappearance of CIC. No positive correlation was found between CIC and elevated levels of serum angiotensin-converting enzyme (ACE) and/or serum lysozyme (LZM). The evaluation of CIC in sarcoidosis requires a battery of different tests carried out at regular intervals during the follow up.