Qualitative and quantitative evaluation of bird-specific IgG antibodies

Abstract

Background: Exposure to organic dust produced by birds often gives rise to an immune response, e.g. IgG antibodies, but intense exposure can lead to high concentrations of IgG antibodies and the development of allergic alveolitis, often known as ‘bird fancier’s lung’. The aim of this study was to establish the distribution of bird-specific IgG antibodies in exposed and nonexposed individuals and compare a nonquantitative and quantitative method in evaluating raised levels of IgG antibodies.

Methods: Sera were collected in Sweden and South Africa and levels of IgG antibodies specific to pigeon, budgerigar and parrot antigens were quantified using the UniCAP system. Results were compared to the precipitation in gel assay. The IgG antibody values of symptomatic patients without precipitating antibodies (non-PP group; n = 51) and patients with precipitating antibodies (PP group; n = 34) were analyzed and compared to nonexposed asymptomatic blood donors (BD group; n = 73) and environmentally exposed pigeon breeders (n = 11).

Results: The IgG antibody response of the analyzed groups in Sweden and South Africa did not vary significantly from each other. IgG antibody responses were the strongest to pigeon antigens with clear increased IgG antibody levels in the PP group [geometric mean (GM) 603 mg/l] compared to the non-PP (GM 6.9 mg/l) and BD group (GM 5.0 mg/l). Threshold values, calculated as the GM value from the BD group plus 3 standard deviations (99% confidence interval), were 9.8, 10.8 and 10.0 mg/l for pigeons, budgerigars and parrots, respectively. Comparison of the two methods resulted in a good concordance with a level of agreement of 94.1% (kappa statistic = 0.83).

Conclusions: The UniCAP system for the detection of bird-specific IgG antibodies is a highly reproducible, generally available, quantitative method for routine diagnostic testing and monitoring of exposed subjects with a very high level of agreement to the precipitating gel assay.