Prolonged exposure to M. faeni in strain II guinea-pigs: pulmonary interstitial inflammation.

Models of hypersensitivity pneumonitis (HP) should exhibit progression of pulmonary histological abnormalities during continuing challenges. Strain II guinea-pigs were sensitized with Micropolyspora faeni and received 2, 4, or 8 weekly intratracheal (i.t.) particulate M. faeni challenges. Control animals received normal saline (NS). Four days after the last exposure, randomly selected microscopic fields of lung (200/animal) were judged to be normal or abnormal. If abnormal, the location and nature of the abnormalities were determined. Compared with NS treated guinea-pigs, those exposed to 2, 4 and 8 weekly M. faeni challenges exhibited more extensive (P less than 0.001) pulmonary histological abnormalities which involved both the intraalveolar and interstitial compartments. More extensive abnormalities in the 8 week group compared with the 4 week group were caused by increased extent of interstitial mononuclear cell infiltration. The extent of pulmonary interstitial histological abnormalities transiently (four challenges) decreases, but then increases, so that progressive pulmonary inflammation occurs during continuing challenges.