Macrophage infiltration following chronic aspiration of gastric fluid. The relative macrophage quantities in bronchoalveolar lavage (BAL) specimens following chronic aspiration of either gastric fluid or normal saline are shown. The ratio of macrophages in the left to the macrophage in the right lung is shown as a function of time. In the inset, the ratio of macrophages in the left to the macrophages in the right lung is shown for all rats, regardless of the duration of treatment. †p < 0.10, *p < 0.05, **p < 0.01 based on two-tailed Student's t test.