Expression of leukocyte integrins and tissue factor in mononuclear phagocytes

Coagulation is intimately involved in the pathology of inflammation. The leukocyte beta2-integrins have several functions, including serving as receptors for coagulation factor X and fibrinogen. Tissue factor (TF) is a receptor for factor VII and a very potent trigger of coagulation. The intention of this study was to examine a possible coexpression of beta2-integrins (CD11b/CD18 and CD11c/CD18) and the procoagulant TF in alveolar macrophages (AM) and blood monocytes, i.e. cells of the same differentiation lineage. The expression of beta2-integrins in human AM isolated by bronchoalveolar lavage and in blood monocytes was analysed by flow cytometry, whereas TF activity was analysed in a one-stage clotting assay. In monocytes, TF activity, CD11b and CD11c expression were highly inducible by lipopolysaccharide (LPS), with a 13-, 19- and four-fold increase, respectively. In AM, TF and beta2-integrins were all constitutively expressed, but the expression could not be further enhanced by LPS stimulation. CD11b and CD11c expression varied inversely with the cell size of AM, in contrast to TF activity which is known to be proportional to AM cell size. In vitro expression of beta2-integrins and tissue factor in lipopolysaccharide-stimulated blood monocytes seems to be intimately coregulated, whereas the expression of these receptors in alveolar macrophages seems to be unresponsive to lipopolysaccharide. These results indicate that blood monocytes and alveolar macrophages have different roles and use different mechanisms in cell-induced fibrin formation.