Primitive endothelial cell lines from the porcine embryonic yolk sac

Summary

Endothelial cell lines have been established from cells that were isolated from porcine yolk sacs from day 18 and day 22 embryos and propagated in vitro under various growth conditions. After expansion in vitro, the general properties of the cells proved similar for the different media used. The endothelial cells expressed cell surface receptors for acetylated low-density lipoprotein and also expressed cell surface-associated angiotensin-converting enzyme. The cells showed a characteristically high level of binding for Bandeiraea simplicifolia lectin I and Dolichos biflorus agglutinin but did not bind significant amounts of Ulex europaeus lectin I. The cells expressed low but serologically detectable levels of Class I major histocompatibility complex (MHC) antigens but failed to bind antibodies directed against Class II MHC antigens. α5β1 integrins were weakly expressed, whereas vascular cell adhesion molecule-1 (CD106) and αvβ3 integrins were not detected. Three-dimensional tube formation was readily observed in cultures grown on Matrigel and occurrel even in uncoated plastic dishes in the absence of Matrigel. In contrast to most of the adult porcine endothelial cells, yolk sacderived endothelial cells did not posses serologically detectable receptors for porcine growth hormone (GH), an observation consistent with the finding that GH did not increase the proliferative rate of these cells. Electron microscopic examination demonstrated the presence of Weibel-Palade bodies, tight endothelial cell junctions, and typical rough endoplasmic reticulum. Exposure of the cells to either concanavalin-A-stimulated porcine splenocyte culture supernatants or to human tumor necrosis factor α did not cause upregulation of VCAM-1 or Class II MHC antigens. Addition of prrcine interferon-γ led to an increase in the level of expression of Class I MHC. Yolk sac endothelial cells from day 22 embryos showed a low but detectable level of expression of Class II MHC antigens, whereas the endothelial cells from day 18 embryos showed no expression of Class II antigens after interferon-γ stimulation. The cells maintained competence to develop vascular structures in vitro and could do so after coinjection with murine tumor cells into adult, immunocompromised mice.