Micropolyspora faeni causes airway inflammation but not hyperresponsiveness in sensitized ponies.

We assessed the effect of aerosol Micropolyspora faeni challenge in two groups of ponies by measuring lung function, airway reactivity to aerosol histamine, and bronchoalveolar lavage fluid cytology. One group of ponies was sensitized by subcutaneous injection of M. faeni in complete Freund's adjuvant, and the other group served as control. In both groups of ponies, measurements were made at base line and 5 h after aerosol administration of 30 ml of saline or 30 ml of 1% wt/vol particulate M. faeni antigen in saline. Saline challenge had no effect on any of the measured variables. M. faeni challenge had no effect on pulmonary mechanics or gas exchange in the control group but significantly increased respiratory frequency and minute ventilation and decreased arterial CO2 tension in the sensitized ponies. In both groups of ponies, aerosol M. faeni challenge significantly increased total white blood cell count and neutrophil numbers in bronchoalveolar lavage fluid while large mononuclear cell numbers decreased. Airway responsiveness was unaltered by saline or M. faeni challenge in both pony groups. We conclude that aerosol M. faeni challenge induces pulmonary neutrophilia and abnormalities of ventilation but is not accompanied by airway hyperresponsiveness in sensitized ponies.