Identification of intimal subendothelial cells from human aorta in primary culture.

Subendothelial cells (SEC) were obtained from the inner intimal layer of adult human aorta by collagenase treatment. SEC were identified in primary culture either as smooth muscle cells by staining with FITC-labeled antisera against human smooth muscle myosin or as macrophages, foam cells and contaminating endothelial cells by their uptake of malondialdehyde treated low density lipoproteins labeled with fluorescent dye 3,3'-dioctadecylindocarbocyanine. Between 1 and 5 days in culture, along with smooth muscle cells (SMC, 38-82%), endothelial cells (0-9%), macrophages and foam cells (2-32%), one more type of cell was found. This cell type resembled SMC in size and shape, but was not stained by antisera to SMC myosin. By ultrastructural criteria these cells were characterized as modulated SMC for they contained prominent rough endoplastic reticulum and Golgi complex together with basement membrane and a large number of plasmalemmal vesicles. Like SMC they reacted with phalloidin and were stained by anti-vimentin but not by anti-desmin monoclonal antibodies. The proportion of such cells varied from 5 to 33% of total cell number and increased in parallel to macrophages and foam cells in vessels with well developed atherosclerotic lesions. We conclude that the applied technique may be used for identification of cultured vascular cells including modulated SMC.

Contact inhibition of phagocytosis in epithelial sheets: alterations of cell surface properties induced by cell-cell contacts.

Contact inhibition of phagocytosis was found to be characteristic for epithelial sheets formed in cultures by several cell types: normal and transformed mouse kidney cells, and differentiated mouse hepatoma cells. In these sheets most central cells surrounded by other cells had very low phagocytic activity. In contrast, marginal cells having a free edge were able to perform an active phagocytosis. Contact inhibition of phagocytosis was absent in dense cultures of mouse embryo fibroblasts and in cultures of anaplastic mouse hepatoma 22a. The upper surface of epithelial sheets was nonadhesive for prelabeled epithelial cells and fibroblasts. In contrast, the upper surface of dense cultures of mouse fibroblasts was adhesive for these cells. These and other data strengthen the suggestion that contact inhibition of phagocytosis is a result of different adhesiveness of the upper cell surface and of the surfaces near the free edge. Agents inhibiting cell surface movements at the free edges of marginal epithelial cells (cytochalasin, azide, sorbitol, low temperature) prevented adhesion of particles to these edges. Possibly, the surface of actively moving cytoplasmic processes is the only cell part that has adhesive properties necessary for the formation of attachments with other cellular and noncellular surfaces. In epithelial sheets, in contrast to fibroblast cultures, Colcemid did not activate movements of immobile contacting cell edges. These results indicate that mechanisms of contact immobilization of cell surface may be different in epithelium and fibroblasts. Firm contacts formed between epithelial cells are sufficient for stable immobilization of the surface; additional stabilization of the surface by microtubules is not essential. Fibroblasts do not form firm contacts and the Colcemid-sensitive stabilization process is essential for maintenance of the immobile state of their surfaces. Differences in the stability of cell surface immobilization produced by cell-cell contacts may also explain different adhesiveness of the upper surfaces of dense fibroblastic and epithelial cultures.