Peritonitis is accompanied by a massive influx of polymorphonuclear leukocytes (PMN) into the peritoneal cavity, little is known, however, about the process of neutrophil transmigration across the peritoneal membrane. The study presented here, therefore, investigates the adherence of human PMN to human peritoneal mesothelial cell monolayers and examines the importance of intercellular adhesion molecule-1 (ICAM-1) in the process. Human peritoneal mesothelial cells (HPMC) constitutively expressed ICAM-1 protein and mRNA. Stimulation with IL-1 beta or TNF alpha resulted in time- and dose-dependent upregulation of ICAM-1 mRNA transcript and increased cell-surface immunoreactive protein expression. Peak surface expression of ICAM-1 occurred between 12 and 24 h after cytokine stimulation when the level of expression was increased by on average threefold above control. The adherence of PMN to HPMC after stimulation with either IL-1 beta or TNF alpha was both dose- and time-dependent. Peaks of PMN binding to HPMC occurred at 2 and 12 h after stimulation. After 12 h, the number of PMN binding to HPMC increased from 71.3 +/- 12.5 in control cells to 180 +/- 36.5 and 125 +/- 23.6 (x 10(3) PMN), after IL-1 beta (100 pg/mL) and TNF alpha (1000 pg/mL), respectively (z = 2.52 and 2.38, N = 6, P < 0.02 versus control for both). The roles of HPMC ICAM-1 and the PMN counter receptor LFA-1 (CD11a/CD18) in the adherence of PMN to HPMC were confirmed by using anti-CAM Fab2' fragments, and anti-integrin antibodies, all of which significantly reduced the adherence of PMN to both control and cytokine-treated HPMC. These data suggest that ICAM-1 expression by HPMC may be one mechanism by which neutrophils adhere to the mesothelium during their transmigration into the inflamed peritoneal cavity.