A new application of Streptavidin ImmunoCAP® for measuring IgG antibodies against non-available commercial antigens

BackgroundEnzyme immunoassay has been successfully used for the diagnosis of hypersensitivity pneumonitis (HP), but there are difficulties in standardising this method because of the difficulty in obtaining stable solid phases from a huge variety of heterogeneous antigenic sources. With this in mind, the aim of this work was to demonstrate the usefulness of the standard available fluoro-enzyme-immuno-assay (FEIA) to measure specific IgG to uncommon, commercially unavailable HP-causing antigens.MethodsSerum samples from patients suffering from HP caused by canary and pigeon protein exposure with positive immunoprecipitation values, as well as cystic fibrosis patients, patients with respiratory allergies, asymptomatic subjects exposed to canary proteins (canary breeders) and healthy unexposed individuals were evaluated by FEIA using biotinylated serum proteins coupled to streptavidin-activated solid phases. Statistical analyses were performed to compare the different groups and to evaluate the performance of this technique.ResultsThe group of patients with hypersensitivity pneumonitis caused by exposure to canary proteins showed the highest value of specific IgG (35.70 mg IgG/mL).ROC analysis demonstrated an optimal cut-off value of 8.44 mg IgG/mL with a sensitivity of 100% and a specificity of 91.76%. Comparisons with other groups revealed statistically significant differences. Comparison between ELISA and FEIA results revealed a strong positive relationship between values obtained in both assays.ConclusionThe results demonstrate that Streptavidin ImmunoCAP® is a sensitive, specific and efficient laboratory method for routine diagnostic testing of HP caused by protein antigens that are not commercially available.