Indirect immunofluorescent detection of antibodies against thermophilic actinomycetes in patients with hypersensitivity pneumonitis.

With slide culture preparations of Micropolyspora faeni, Thermoactinomyces candidus, and Thermoactinomyces vulgaris used as antigens, 59 sera from patients with hypersensitivity pneumonitis and 23 sera from normal controls were studied for the presence of specific antibodies by indirect immunofluorescence and immunodiffusion methods. Of the 82 sera, 31 showed precipitins to M. faeni, five to T. candidus, and four to T. vulgaris. A group of 19 sera positive to Aspergillus antigens showed questionable reactions to thermophilic actinomycetes. The 23 sera from normal individuals were negative for specific antibodies when tested by immunodiffusion. In indirect immunofluorescence studies, we found that IgG antibodies in high titers are present only in the precipitin-positive sera whereas other antibody classes either are negative or failed to show consistent differences in titers of the positive, questionable, and control groups. The titer of IgG antibodies varied from 0 to 1:20 in the normal control group, 0 to 1:40 to 1:640 in the precipitin-positive group.