Characterization of Micropolyspora faeni antigens by human antibodies and immunoblot analysis

IgG, IgM and IgA antibody responses against Micropolyspora faeni (Mf) antigens were studied by means of immunoblotting experiments using 70 sera derived from three groups of farmers, namely patients with extrinsic allergic alveolitis (EAA) due to thermophilic actinomycetes (n = 25), patients without EAA but with hay exposure (n = 14), and patients suspected to have EAA (n = 31), and 27 sera from two groups of control persons (healthy laboratory workers, n = 13; healthy farmers, n = 14). Patients with EAA showed IgG, IgM and IgA antibody responses mainly against the antigens with molecular weights (MW) of 11, 12, 25, 35 and 60 kD ("major antigens"), and in addition, but less often, against six antigens with MW in the range of 15 to 62.5 kD ("minor antigens"). The other two groups of patients and also the exposed control persons showed very similar results; however, the antibody response in healthy farmers was substantially weaker in comparison to the three groups of patients and was almost limited to the major antigens with MW 11, 25 and 60 kD. Although patients with proven EAA had higher amounts of antibodies, there was no correlation between this antibody response and the onset of disease. The results indicate the necessity of including at least the major antigens with MW of 11, 25 and 60 kD in all extracts used for in vitro diagnosis of Mf-induced EAA.