SPECIFICATION AND QUANTITATION OF CIRCULATING IMMUNE-COMPLEXES IN THESERUM OF PATIENTS WITH ACTIVE PULMONARY SARCOIDOSIS

Background - Circulating immune complexes can be elevated in serum sam ples of patients with sarcoidosis and are associated with disease acti vity, but their diagnostic significance is not understood. Methods - T he different classes of circulating immune complexes containing immuno globulin A, G, or M, and the content of complement in circulating immu ne complexes (polyethylene glycol precipitation) as well as levels of complement binding circulating immune complexes (complement binding as say) were determined in 19 patients with active, untreated pulmonary s arcoidosis. The results were compared with other parameters in the ser um (soluble interleukin 2 receptor, angiotensin converting enzyme, imm unoglobulin A, G, and M) and the bronchoalveolar lavage fluid (lymphoc ytes, helper cells, suppressor cells, activated T cells), and with rad iological stage and functional parameters (FEV(1), vital capacity, tot al lung capacity, transfer coefficient (Kco), and the alveolar-arteria l oxygen difference during exercise). Results - In all patients circul ating immune complexes could be detected by polyethylene glycol precip itation and were similar to control subjects. The content of C1q in ci rculating immune complexes was higher than in controls, yet in all but one of the cases was still within normal limits. In contrast, elevate d levels of complement binding circulating immune complexes were found in 67% of the patients. No correlation was seen between circulating i mmune complexes and any of the other parameters in the serum, bronchoa lveolar lavage fluid, or lung function values. No differences were fou nd between radiological type I and II presentations of sarcoidosis. Co nclusions - The complement binding assay showed a much higher sensitiv ity for the detection of circulating immune complexes in active pulmon ary sarcoidosis than the polyethylene glycol precipitation method. As there was no correlation between levels of circulating immune complexe s and other parameters of the disease they are probably not useful for the assessment of disease activity.