[Complement, granulocytes and pulmonary capillaries].

The activation, aggregation and adhesion of polymorphonuclear leukocytes on the endothelial wall of the pulmonary capillaries are responsible for lesions of variable severity on the alveolar-capillary membrane. The mechanism and the contribution of this leukocyte aggregation was studied to explain the respiratory abnormalities observed during the course of haemodialysis, leukapharesis and the end of extra-corporeal circulation. The activation of complement, by the formation of C5a is probably the initiator of this phenomenon. Based on these experimental models, the varied steps in the intra-capillary aggregation of leukocytes is envisaged as an explanation for the lesions in the acute respiratory distress syndrome, alveolitis caused by immune complexes and pulmonary toxicity caused by oxygen. Corticosteroids may inhibit leukocyte aggregation under certain conditions. These studies allow for a more precise pathophysiological approach for the use of steroids in their disorders.