Characterization of immunoglobulin binding factor in sputum from patients with chronic airway diseases

Immunoglobulin binding factor (IgBF) is known to bind immunoglobulin, to interact with anti-Fc gamma-III antibodies and to be present in the lower respiratory tract of normal healthy subjects. In this study, in order to clarify the role of IgBF in respiratory diseases, we investigated whether IgBF exists in the airway of patients with chronic airway diseases.

IgBF was measured in the sputum of 28 normal subjects and 59 patients with chronic airway diseases including 37 cases of chronic bronchitis, 18 bronchiectasis, and four diffuse panbronchiolitis by enzyme-linked immunosorbent assay.

Immunoglobulin binding factor concentration in the sputum of patients with chronic airway diseases (purulent sputum, 50.2 +/- 8.2 microg/mL; mucoid sputum, 88.6 +/- 12.8 microg/mL) was higher than that in induced sputum of normal subjects (6.3 +/- 5.5 microg/mL; P < 0.001). Immunoglobulin binding factor level in mucoid sputum was significantly higher than that in purulent sputum (P < 0.05). A significant inverse correlation was shown between the IgBF level and the elastase activity in sputum, and the concentration of IgBF purified from seminal plasma was decreased by treatment with neutrophil elastase, indicating that IgBF might be degraded by elastase. In the gel filtration chromatography of both types of sputum, IgBF was eluted in a region corresponding to a molecular weight of 27 kDa as a single peak. Western blot analysis with a monoclonal antibody to IgBF indicated that IgBF in both types of sputum had a molecular weight of 27 kDa under non-reducing conditions and of 16 kDa under reducing conditions.

These results demonstrate that a high level of IgBF is present in the respiratory tract of patients with chronic airway diseases and may be related to the pathogenesis of these diseases.