DIFFERENCES BETWEEN RAT ALVEOLAR AND INTERSTITIAL MACROPHAGES 5 WK AFTER QUARTZ EXPOSURE

Macrophages play an essential role in pulmonary host defense. We inves tigated differences between rat alveolar (AM) and interstitial (IM) ma crophages after exposure in vivo to quartz, an inducer of intensive al veolitis. Rats were exposed to 0.5 ml of saline without (n = 8) or wit h (n = 8) 10 mg of quartz by intratracheal instillation. In a third gr oup (n = 8), 10 mg of surfactant were added to the quartz mixture. Fiv e weeks later, AM were recovered by bronchoalveolar lavage and IM by m echanical fragmentation of the lung, follow ed by enzymatic treatment, Contamination of AM to the IM fraction was calculated to be 12-15%. A fter quartz exposure, the expression of major histocompatibility compl ex class Ia was increased in both AM and IM fractions. The receptor co rresponding to human complement-receptor 3 increased in AM after quart z exposure, and AM from quartz-exposed animals had a lower metabolic a ctivation. Our findings indicate that IM are immunocompetent cells and that differences between AM and IM fractions occur upon quartz-induce d inflammation. This response is not affected by addition of surfactan t.