Neutrophil depletion abrogates lung injury in a 2-event model. Rats were pretreated with 200 μL NS or rabbit anti–rat PMN antiserum transfused over a 30-minute period (4 mL/hour), and the rats treated with the anti-PMN antibodies became neutropenic over a 24-hour period, as evidenced by a leukocyte differential obtained from the femoral vein prior to initiating the ALI protocol. The rats then received either NS or LPS intraperitoneally, and 2 hours later were infused with NS, 10% D42 PRBCs, or 0.15 mg/kg OX27. The figure depicts ALI (% BAL EBD/% plasma EBD) as a function of treatment group. Rats injected with NS and infused with NS (■) or injected with LPS and infused with NS () did not evidence ALI. Rats that were infused with isotypic antibody controls, treated with LPS, and infused with either 10% D42 PRBCs or 0.15 mg/kg OX27 had a significant amount of ALI (). However, rats given the PMN antisera 24 hours prior to induce neutropenia, as confirmed by leukocyte differentials, did not evidence ALI (▧), similar to the controls. (*P < .05 from LPS/NS; n = 3.)