Precipitin (F.L.H.) Test in Farmer's Lung

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Abstract
Agar-gel precipitin tests were performed on the sera of 327 United Kingdom farmers, who had given a history of exposure to mouldy hay, with extracts of mouldy hay, Thermopolyspora polyspora, Micromonospora vulgar is, Mucor sp., and Aspergillus fumigatus. Positive reactions in the immunoelectrophoretic test to "farmer''s lung hay" (F.L.H.) antigens were obtained in 89% of 205 subjects regarded as having farmer''s lung, and, of these, 87% were due to the F.L.H. antigens derived from T. polyspora. These sera gave reactions to all 3 of the main F.L.H. antigens (A,B, and C) in 42% of cases, to 2 in 31%, and to 1 in 14%. The wider the range of the serological reaction, the greater was the frequency of reactions to the other extracts, the more frequent and severe were the attacks, the higher the degree of clinical sensitivity to the dust of mouldy hay, and the higher the proportion of males, presumably because they were more heavily exposed. F.L.H. reactions (T. polyspora type) were obtained with the sera of Icelandic patients with farmer''s lung. In 16 patients with farmer''s lung due to other vegetable dusts only 50% gave F.L.H. reactions. In 122 farmers, who had been exposed to mouldy hay and were not suffering from farmer''s lung, F.L.H. reactions were obtained in 18% of 28 apparently unaffected farmers, in 15% of 61 with asthma and bronchitis, and in 21% of 33 with other lung disease, these reactions being much weaker in intensity than in the farmer''s lung patients. In tests on the sera of subjects who had not been exposed to mouldy hay, some having been exposed to other vegetable dusts, no F.L.H. reactions were obtained against extracts of mouldy hay in tests on 304 sera, and no reactions (except in 5 bagasse workers) were obtained against an extract of T. polyspora in tests on 302 sera. Trichloracetic acid frac-tionation of T. polyspora extract gave a precipitate containing the A and B antigens and a supernatant containing the C antigen. Both fractions provoked systemic and pulmonary reactions in affected subjects in inhalation tests. The mode of onset of the farmer''s lung was insidious in 49% (group I), insidious and later typical in 9% (group II), typical in 32% (group III), and insidious and/or typical and later rapid in 10% (group IV). The latter group had many of the clinical and serolo-gical features of the other groups.