F Ogushi, S Sone, K Tani, H Takehara, T Endo, T Haku, Y Nakamura, T Ogura, M Kamada and T Aono
Third Department of Internal Medicine, University of Tokushima, School of Medicine, Japan.

Immunoglobulin binding factor (IgBF), which is abundant in human seminal plasma, is known to bind immunoglobulin, interact with anti-Fc gamma RIII antibodies, and block pokeweed mitogen (PWM)-stimulated lymphocyte blastogenesis. In this study, we investigated whether IgBF is present in the lower respiratory tract, whose secretions come into contact with the external environment. For this, IgBF was measured in brochoalveolar lavage fluid (BALF) from 42 healthy normal subjects (23 nonsmokers and 19 smokers) by enzyme-linked immunosorbent assay (ELISA). IgBF was detected in BALF from these normal subjects, and its level was significantly higher in BALF from smokers (127.2 +/- 98.7 ng/ml versus 23.3 +/- 20.7 ng/ml). On gel filtration chromatography of BALF, IgBF was eluted in a region corresponding to a molecular weight of 27 kD. Western blot testing with a monoclonal antibody to IgBF indicated that IgBF in BALF had a molecular weight of 27 kD under nonreducing conditions and of 16 kD under reducing conditions. Thus, the migration pattern of IgBF in BALF corresponded to that of IgBF in seminal plasma. IgBF immunoreactivity was detected histochemically in mucus glands and goblet cells in the lower respiratory tract. These results demonstrate that IgBF is present in the lower respiratory tract, and that smoking may cause its increased production in this region.