The Search for Fc Receptors on Human Tissues and Human Endothelial Cells in Culture

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Abstract
Human endothelial cells in culture and in tissue sections were examined for Fc receptors by several different methods, including the binding of fluoroisothiocyanate- and ferritin-labeled antibodies to IgG, rosette formation with sensitized sheep erythrocytes [SRBC], and binding of opsonized latex particles. Although human polymorphonuclear leukocytes reacted positively in all tests, endothelial cells freshly isolated or cultured from umbilical cord veins were consistently negative. A small number of cells cultured from umbilical arteries formed rosettes with SRBC, but cells from pulmonary arteries did not. Fc receptors were not found in vessels of the umbilical cord or in lung tissue sections, but vessels in the placenta contained prominent Fc receptors. Cultured endothelial cells that were suspended by trypsin took up latex beads and immune complexes by endocytosis. Undisturbed monolayers of cells were much less active. Apparently, the endothelium may be stimulated by proteolytic enzymes to ingest large particles or complexes, and that even without Fc receptors, the endothelium can remove potentially harmful materials from circulation by phagocytosis.