Author's Response to Reviews Quantifying Serum Antibody in Bird Fanciers'

24 Background 25 Detecting serum antibody against inhaled antigens is an important diagnostic adjunct for 26 hypersensitivity pneumonitis (HP). We sought to validate a quantitative fluorimetric 27 assay testing serum from bird fanciers. 28 Methods 29 Antibody activity was assessed in bird fanciers and control subjects using various avian 30 antigens and serological methods, and the titer was compared with symptoms of HP. 31 Results 32 IgG antibody against pigeon serum antigens, quantified by fluorimetry, provided a good 33 discriminator of disease. Levels below 10mg/L were insignificant, and increasing titers 34 were associated with disease. The assay was unaffected by total IgG, autoantibodies and 35 antibody to dietary hen’s egg antigens. Antigens from pigeon serum seem sufficient to 36 recognize immune sensitivity to most common pet avian species. Decreasing antibody 37 titers confirmed antigen avoidance. 38 Conclusions 39 Increasing antibody titer reflected the likelihood of HP, and decreasing titers confirmed 40 antigen avoidance. Quantifying antibody was rapid and the increased sensitivity will 41 improve the rate of false-negative reporting and obviate the need for invasive diagnostic 42 procedures. Automated fluorimetry provides a method for the international 43 standardization of HP serology thereby improving quality control and improving its 44 suitability as a diagnostic adjunct. 45