Surfactant degradation activity in bronchoalveolar lavage fluid from guinea pigs challenged with antigen

Surfactant dysfunction is a characteristic of bronchial asthma, but mechanisms of dysfunction following antigen exposure are not understood. The aim of this study was to examine whether bronchoalveolar lavage fluid (BALF) has surfactant degradation activity after antigen challenge, using an animal model of asthma.

BALF was collected 24 h after a challenge with aerosolized antigen solution in actively sensitized guinea pigs and from non-sensitized control guinea pigs. The surface tension of BALF was measured by pulsating bubble surfactometer. Surfactant activity was expressed as the minimum surface tension of BALF after 5 min of pulsation. BALF was separated into a cellular phospholipid fraction and supernatant, and reconstituted into 'pellet + supernatant' and 'pellet + saline' fractions.

Surfactant activity of BALF from sensitized antigen-challenged animals was reduced after 4 h of incubation at 37 degrees C but a decrease was not observed in BALF from non-sensitized control animals. The decrease of surfactant activity in BALF from challenged animals was prevented by incubation at 4 degrees C. Disappearance of surfactant activity after incubation at 37 degrees C was observed in the 'pellet + supernatant', but not in the 'pellet + saline' fraction. The decrease of surfactant activity in BALF was also partially suppressed by the secretory phospholipase A2 inhibitor, indoxam, and by a cocktail of protease inhibitors.

Surfactant-degrading activity was present in the supernatant of BALF from antigen-challenged guinea pigs. This activity may be attributed to secretory phospholipase A2 and to proteases present in the antigen-challenged airway.