Avidity of Aspergillus umbrosus IgG antibodies in farmer's lung disease.

Farmer's lung disease (FL), the commonest form of allergic alveolitis caused by repeated inhalation of mouldy hay, is associated with exposure to the fungus Aspergillus umbrosus among Finnish farmers. The antigen-binding avidity of A. umbrosus-specific IgG antibodies was measured in 12 FL patients in acute phases of initial and recurrent attacks and during 1 year follow up as well as in 12 healthy farmers and five healthy urban controls. The farmers' groups were further divided into two subgroups: subjects with short exposure (< 7 years) and subjects with long exposure (> 25 years). During the first acute phase FL patients with long exposure exhibited a high avidity of A. umbrosus-specific IgG antibodies that remained high during the 1 year follow up, although the A. umbrosus-specific IgG antibody titre decreased. A re-exposure to mouldy hay leading to a recurrence further enhanced the maturation of the antibody avidity, so that an even higher A. umbrosus-specific IgG avidity with a less significant increase of antibody titre occurred than during the first acute attack. Notably higher IgG antibody avidity was observed in FL patients with long exposure than in healthy farmers or in healthy controls.