Circulating immune complexes and rheumatoid factors in patients with farmer's lung.

Circulating IgG immune complexes (CICs), IgM rheumatoid factors (RFs), complement level (C3 and C4), and IgG antibodies to Aspergillus fumigatus, Aspergillus umbrosus, Thermoactinomyces vulgaris, and Micropolyspora faeni were analysed in the sera of 14 patients with farmer's lung (FL), 10 in the acute and four in the subacute phase of the disease. Ten spouses of FL patients served as exposed healthy controls. C3 and C4 were measured fluoronephelometrically. C3 levels were above the normal range and C4 levels near the upper limit of the normal range in both patients and controls; no statistically significant difference between patients and controls were observed. CICs were determined by enzyme immunoassays (EIA) of conglutinin-binding (KgB) and Clq-binding (ClqB). CIC levels above the normal range were detected in 12 (KgB-EIA) and nine (ClqB-EIA) of the patients and three (KgB-EIA) and six (ClqB-EIA) of the controls. No statistically significant differences were found in the mean levels between patients and controls. In contrast, RF levels in the acute phase of FL were significantly higher in the patients (P less than 0.01) than in the controls. CICs correlated positively with most microbial IgG antibodies, but negatively with RFs. RFs also correlated negatively with microbial IgG antibodies, as well as with both C3 and C4. In FL, the increased RF level may, in the absence of increased CIC and decreased complement levels, represent an immune response (IgM anti-IgG autoantibodies) induced by local mechanisms of IgG immune complexes in the lungs.