Tolerance to phosgene is associated with a neutrophilic influx into the rat lung

Exposures to 100% oxygen, ozone, nitrogen oxides, and phosgene increase both lung lavage protein concentrations and neutrophils. The inhibition of the neutrophil influx can diminish lavage protein concentrations after exposures to these oxidant gases. Similarly, this injury can be reduced by pre-exposure to either the same (tolerance) or a different (cross-tolerance) oxidant gas. We tested the hypothesis that diminished injury after the development of tolerance of phosgene (COCl2) is associated with a decreased incursion of neutrophils. Sixty-day-old rats (n=12/group) were exposed to varying concentrations of COCl2. Lung lavage (n = 6/group) 24 h after a first phosgene exposure demonstrated an increase in both protein concentrations and percentage neutrophils. The remaining animals (n = 6/group) were exposed to COCl2 2 ppm x 60 min 1 wk later. Lavage confirmed the development of tolerance with protein concentrations diminished after the second exposure in those rats that had inhaled higher doses of COCl2 during the first exposure. However, the neutrophilic influx was not diminished but rather was increased. The association of the neutrophil incursion with a protective effect was further established in studies employing colchicine and dextran. Colchicine decreased neutrophil influx occurring after the first exposure and subsequently diminished the development of tolerance after a second exposure. Intratracheal instillation of dextran produced a neutrophil incursion and subsequently decreased injury after a phosgene exposure. In investigations using both colchicine and dextran, neutrophil influx increased with the development of adaptation. Thus, lung injury after the development of tolerance to phosgene provides a unique animal model of a respiratory distress syndrome in which neutrophils are not associated with injury but rather with a protective effect.