Acid-aspiration-induced injury is one of the leading causes of adult respiratory distress syndrome. Intercellular adhesion molecule-1 (ICAM-1) is a ligand for lymphocyte-function-associated antigen-1 alpha (LFA-1 alpha), and it has been shown to be required for leukocyte migration into inflamed areas. The purpose of this report was to investigate the role of the ICAM-1/LFA-1 alpha pathway in a rat model of acid-aspiration-induced injury. Animals received 3.0 ml/kg HCI (0.1N; pH, 1.0) intratracheally pretreated with control monoclonal antibodies (mAbs) (HCI group) or anti-ICAM-1 and LFA-1 alpha mAbs (Test group). In the HCI group, increases in lung resistance (RL) (229 +/- 23% baseline), lung wet-to-dry weight ratio (W/D) (11.9 +/- 0.4), protein concentration (TP) (0.447 +/- 0.054 mg/ml), and the number of neutrophils (PMN) (159.0 +/- 19.4 x 10(4)) of bronchoalveolar lavage fluid were observed. In the Test group, HCI-induced injury was significantly reduced (RL, 122 +/- 7% baseline; W/D, 7.2 +/- 0.1; TP, 0.277 +/- 0.016 mg/ml; PMN, 8.8 +/- 0.8 x 10(4)). The administration of mAbs to ICAM-1 and LFA-1 alpha after HCI instillation partially attenuated HCI-induced responses. These observations suggest that the ICAM-1/LFA-1 alpha pathway might be involved in the pathogenesis of adult respiratory distress syndrome caused by acid aspiration.