Monocyte adhesion to subendothelial components

Human monocytes have been shown to penetrate the endothelial layer of large blood vessels and to adhere to the subendothelial basement membrane. To determine the active components of this process, we have studied the ability of monocytes to adhere to isolated components of the subendothelial matrix. Using a quantitative dot-blot adhesion assay, we find that monocytes adhere preferentially to immobilized laminin and elastin. The monocytes adhere less well to fibronectin and bind poorly or not at all to collagen types I and IV, or to heparan sulfate. Monocyte binding to elastin requires an intact, crosslinked molecule as no binding was observed to soluble, acid-alcohol elastin extracts, to pepsin or elastase digests of elastin, to tropoelastin monomer, or to desmosine/isodesmosine crosslinks. Similar binding profiles to elastin, laminin, and fibronectin were seen with the established human leukocyte cell line U937. The promyelocytic cell line HL60 adhered equally well to laminin but showed slightly reduced adhesion to elastin when compared with the fresh monocytes or U937 cells. Freshly isolated human erythrocytes did not demonstrate significant adhesion to fibronectin, laminin, or elastin.