We report here that interleukins have a dramatic effect on extracellular matrix production by cultured endothelial cells. Human umbilical vein endothelial cells incubated with growth media conditioned by lectin-activated human peripheral blood mononuclear leukocytes undergo marked changes in cell shape and elaborate a highly organized extracellular material that is not detectable in untreated cultures. This material has the following characteristics: (a) it is not recognizable by electron microscopy unless the cationic dye, Alcian blue, is added to the fixative; (b) it is visualized as a network of branching and anastomosing fibrils of various thickness that can be resolved into bundles of fine filaments; (c) it is associated with the cell surface, extends between contiguous cells, and coats the culture substrate; (d) it is removed by digestion with glycosaminoglycan-degrading enzymes, such as crude heparinase and chondroitinase ABC. These results demonstrate that soluble factors released by activated peripheral blood mononuclear leukocytes (interleukins) stimulate cultured human umbilical vein endothelial cells to produce a highly structured pericellular matrix containing glycosaminoglycans (probably chondroitin sulfate and/or hyaluronic acid) as a major constituent. We speculate that this phenomenon corresponds to an early step of angiogenesis as observed in vivo as a consequence of interleukin release.Because of its unique and strategic position, vascular endothelium participates in a wide range of normal and pathological processes, including inflammation and lymphocyte traffic through specialized postcapillary venules in lymphoid tissue (14, 34). The role played by endothelial cells in these events would be better defined if the factors that modulate their physiological properties were identified.There is increasing evidence that lymphoid cell products may profoundly affect vascular endothelium. Antigen-or mitogen-activated mononuclear leukocytes synthesize and release an array of soluble factors (collectively called lymphokines or interleukins) that have a wide spectrum of regulatory activities on both lymphoid (38, 44) and nonlymphoid cells (33,44,54), and several observations suggest that endothelial cells can also be a target of interleukin activity (2,9,12,13,39,41,49). This prompted us to investigate the effect of interleukins on endothelial ceils in an in vitro system. For this purpose, monolayer cultures of human umbilical vein endothelial (HUVE) ~ cells were incubated with cell-free supernatants from cultures of lectin-activated mononuclear leukocytes and examined by electron microscopy. The results of this study show that interleukins induce cultured HUVE cells to elaborate a highly organized pericellular matrix containing cytochemically recognized glycosaminoglycans (GAG) as a major constituent. MATERIALS AND METHODSCell Culture: Primary cultures of HUVE cells were prepared by an adaptation of previously described methods (17,28). Briefly, the umbilical vein was perfused with 50 ml of Han...

We incubated mouse peritoneal macrophages for 3-8 min at 37°C with antibodycoated sheep erythrocytes and examined regions of close interaction between the two cell types by electron microscopy. At sites of focal macrophage-erythrocyte contact we observed a distinctive specialization of the macrophage plasma membrane consisting of a prominent subplasmalemmal band of electron-dense material, ~25-35 nm in thickness. In many instances, this band showed a periodic substructure similar to that seen in clathrin coats. Moreover, many slender erythrocyte processes penetrated into invaginations of the macrophage surface which were bristle-coated at their blind extremity. As previously shown for clathrin-coated pits, the segments of the macrophage plasma membrane beneath which the dense material was found were selectively resistant to the membrane-perturbing effect of the antibiotic, filipin. This structural speciaPization of the macrophage plasma membrane at sites of ligand-receptor interaction during immune phagocytosis of antibody-coated erythrocytes may represent the morphological counterpart of the zipper mechanism of phagocytosis previously demonstrated by functional studies.Phagocytosis is the uptake of foreign particles within intracellular plasma membrane-derived vacuoles (1-3). In mammals, this function is primarily assumed by macrophages and polymorphonuclear leukocytes, which are considered as "professional" phagocytes (4) playing a crucial role in host defense against invading microorganisms (1, 2, 5, 6).Although a wide variety of foreign bodies are ingested by phagocytosis, the uptake of antibody-coated (opsonized) particles has received particular attention, since it involves a specific interaction between the Fc-portion of particle-bound antibodies and Fc receptors on the surface of the phagocytic cell (2, 7-10). Griffin and co-workers (11-13) have demonstrated that the initial interaction of particle-bound hgands with their corresponding macrophage receptors generate a signal leading to the extension of pseudopods in the area of contact between the macrophage and the particle to be ingested. This brings additional receptors into apposition with hgands on the particle's surface, resulting in the generation of additional signals and further pseudopod extension. The process continues in stepwise fashion until the plasma membranes of the advancing pseudopods meet and fuse with one another around the particle, enclosing the latter within a phagocytic vacuole. Thus, according to the above outlined "zipper model'" (11-13), phagocytosis requires the repeated, circumferential apposition of receptor-carrying macrophage plasma membrane segments with particle-bound hgands.Whether the membrane segments involved in phagocyteparticle interaction have a specific organization at the ultrastructural level is still unknown. To investigate this point, we studied by electron microscopy the early steps of phagocytosis of antibody-coated erythrocytes by peritoneal macrophages. Our results indicate that regions of the ma...