Class-specific antibodies during follow up of patients with farmer's lung.

Sequential serum samples of 13 patients with acute farmer's lung (FL) taken during a follow-up of 18-36 months, were tested for antibodies of immunoglobulin G (IgG), IgA, IgM and IgE classes against Thermoactinomyces vulgaris and Micropolyspora faeni, and compared with contemporary lung function parameters. In the acute phase, antibodies of several Ig classes were present, those of IgG and IgA being most common. At the end of the follow-up, the mean values of all antibody titres were lower than in the acute phase, and antibodies were now mostly of one or two Ig classes only. The reduction in antibody levels was most often detectable in IgG and IgA antibodies against T. vulgaris. Antibody titres correlated inversely with tested lung function parameters, especially IgA antibodies with pulmonary diffusing capacity. Our results show that a follow-up of levels of class-specific antibodies, especially of IgG and IgA gives valuable information on causative microbes and on temporal changes of the exposure.