Differences between rat alveolar and interstitial macrophages 5 wk after quartz exposure.

Macrophages play an essential role in pulmonary host defense. We investigated differences between rat alveolar (AM) and interstitial (IM) macrophages after exposure in vivo to quartz, an inducer of intensive alveolitis. Rats were exposed to 0.5 ml of saline without ( n = 8) or with ( n = 8) 10 mg of quartz by intratracheal instillation. In a third group ( n = 8), 10 mg of surfactant were added to the quartz mixture. Five weeks later, AM were recovered by bronchoalveolar lavage and IM by mechanical fragmentation of the lung, followed by enzymatic treatment. Contamination of AM to the IM fraction was calculated to be 12-15%. After quartz exposure, the expression of major histocompatibility complex class Ia was increased in both AM and IM fractions. The receptor corresponding to human complement receptor 3 increased in AM after quartz exposure, and AM from quartz-exposed animals had a lower metabolic activation. Our findings indicate that IM are immunocompetent cells and that differences between AM and IM fractions occur upon quartz-induced inflammation. This response is not affected by addition of surfactant.