Evidence for circulating immune complexes in erythema nodosum and early sarcoidosis.

Twenty-two patients were investigated during acute attacks of erythema nodosum with a series of tests for circulating immune complexes. Nineteen had bilateral hilar lymphadenopathy and were considered to have sarcoidosis. Evidence of circulating immune complexes was found in 18, out of 22 patients (including 15 out of the 19 cases of sarcoidosis). The most frequent abnormality was the detection of elevated levels of C3 breakdown products (C3i), which were found in 14 out of 18 tests. The test results returned gradually to normal as symptoms subsided in 20-40 days, but 2 patients still showed abnormalities at 40 days despite the disappearance of symptoms. It is concluded that free immune complexes appear in the circulation during the early stages of acute sarcoidosis and gradually disappear as symptoms subside.