Immunologic cross-reactions among thermophilic actinomycetes associated with hypersensitivity pneumonitis.

Antibodies produced in rabbits against Micropolyspora faeni, Thermoactinomyces vulgaris, T. sacchari, Thermoactinomyces candidus, and Saccharomonospora viridis were tested against antigens derived from many strains of thermophilic actinomycetes for precipitating antibodies by immunodiffusion test. It was found that immune sera reacted strongly against antigens from strains belonging to the same species and weakly against antigens from different species of thermophilic actinomycetes. However, sera from farmer's lung patients showed cross-reactivity against antigens from different species. This may be because the patient is sensitized to multiple species of thermophilic actinomycetes present in the environment and developed antibodies against most of them.