Aspiration-induced lung injury: role of complement

To examine the role of complement in the development of acid aspiration-induced lung injury in the rat. It was postulated that inhibition or depletion of complement attenuates aspiration-induced lung injury.

Controlled animal trial.

Animal Laboratory, Jefferson Medical College, Philadelphia, PA.

Anesthetized rats.

Aspiration was induced by the intratracheal administration of 0.2 mL of 0.1 N hydrochloric acid (n = 7) and lung injury was evaluated by determining water content, myeloperoxidase activity, protein concentration, and leukocyte count in bronchoalveolar lavage fluid. Muscle PO2 was directly measured using a thin-film chamber oxygen sensor and serum tumor necrosis factor-alpha was assayed by enzyme-linked immunosorbent assay. The effect of complement inhibition by recombinant human soluble complement receptor type 1 (n = 8) or complement depletion by cobra venom factor (n = 7) on lung injury was evaluated.

Acid aspiration induced pulmonary leukosequestration, edema, and a microvascular permeability defect, along with tissue hypoxia. Pretreatment with soluble complement receptor type 1 (complement inhibition) or cobra venom factor (complement depletion) significantly reduced lung edema (-61 +/- 7%; p < .05), eliminated protein accumulation in bronchoalveolar lavage fluid (p < .01), and improved (p < .05) tissue oxygenation. In contrast, there was no effect of soluble complement receptor type 1 or of cobra venom factor on leukosequestration.

Acid aspiration induces lung injury through a complement-dependent mechanism that leads to microvascular permeability defects. Therefore, the possibility that complement inhibitors may have a salutary effect in humans with aspiration-induced lung injury should be investigated.