Inhalation challenge and skin testing in farmer's lung.

An immunologic basis for episodes of farmer's lung is shown by the response of susceptible individuals to inhalation challenge with extracts of Micropolyspora faeni, the main sensitizing agent in moldy hay dust. However, if the complement-fixing capacity of the farmer's serum for M. faeni antigen is used as a quantitative assessment of sensitivity, it does not predict whether an individual will respond to inhalation challenge. A positive immediate skin test to M. faeni antigens was observed in all cases with over 40 CH50 consuming units of antibody per milliliter of serum. A similar correlation was seen between complement consumption and precipitins.