Interaction of murine peritoneal leukocytes and mesothelial cells: in vitro model system to survey cellular events on serosal membranes during inflammation.

All serosal cavities including peritoneum are lined with a simple squamous mesothelium. Primary culture of murine mesothelial cells has been established to study their cellular interactions with peritoneal leukocytes. The mesothelial character was determined by the cytokeratin and vimentin expression. The mesothelial cells expressed ICAM-1 and CD44 molecules. The expression of ICAM-1, but not CD44, was significantly enhanced by the treatment with TNF-alpha (100 U/ml). We have also investigated possible influence of transforming growth factors, TGF-alpha (20 ng/ml) and TGF-beta (2 ng/ml), and epidermal growth factor (20 ng/ml). These factors were not found to modulate ICAM-1 or CD44 expression in vitro. During coculture experiments unstimulated mesothelial cells were almost nonadherent for both resident and elicited peritoneal mononuclear leukocytes for several hours. TNF-alpha or EGF pretreatment of mesothelial cells greatly enhanced their adhesive affinity to peritoneal mononuclear leukocytes, while TGF-beta pretreatment even reduced the low basal adhesion. Prolonged coculture for 3 weeks resulted in remarkable proliferation and differentiation of both resident and elicited monocytes/macrophages on the mesothelial surface. The stimulation of mesothelial cell culture with EGF resulted in the macrophage colony-stimulating activity (M-CSA) production. M-CSA was mainly due to M-CSF as confirmed with anti M-CSF monoclonal antibody; the residual M-CSA was not formed by GM-CSF. After several passages the mesothelial cells started to produce M-CSA spontaneously.