PECAM-1 EXPRESSION IN HUMAN MESOTHELIAL CELLS - AN IN-VITRO STUDY

Mesothelial cells are actively involved in inflammatory processes by e xpressing a set of cell adhesion molecules (CAMs). Transmigration of l eukocytes into inflamed tissues requires a chemotactic stimulus and en gagement of platelet-endothelial cell adhesion molecule-1 (PECAM-1). T o investigate the kinetics involved in peritonitis, pure cultures of m esothelial cells are necessary. In previous studies, we have found tha t human mesothelial cells (HOMES) show a weak constitutive expression of PECAM-1, which cannot be further stimulated by cytokines. It is kno wn that all serous cavities and body fluids contain numerous macrophag es which strongly express this adhesion molecule. To identify the cell s responsible for the expression of PECAM-1, mesothelial cells freshly obtained from omental tissue were isolated using PECAM-1-conjugated m agnetic beads by cell sorting. For these studies, the negative as well as the positive fraction of isolated cells were used. As a control, f reshly isolated monocytes were studied. Cell cultures were characteriz ed by light and electron microscopy, as well as immunocytochemistry. T he negative cell fraction was cultivated and stimulated for different times with tumor necrosis factor-alpha (30 and 300 U/ml), interleukin- 1 beta (10 and 100 U/ml) and interferon-gamma (500 U/ml) and PECAM-1 e xpression was analyzed by a comparative quantitative cell enzyme immun oassay (EIA). The positive cell fraction was treated in the same manne r. Both fractions of isolated cells showed strong positivity for cytok eratins 8, 18, 7 and 19, as well as vimentin. CD68, a monocyte marker, was not detected on mesothelial cells. In addition, EIA analysis conf irmed the constitutive expression of PECAM-1 obtained from previous st udies. This expression on HOMES was not inducible, irrespective of the type and concentration of cytokine studied. These data confirm PECAM- 1 expression on mesothelial cells obtained from human omental tissue a nd suggest a critical role in transmigration of leukocytes during peri toneal inflammation.