We investigated the role of human mesothelium in an in vitro model of peritonitis with emphasis on the secretion of the neutrophil chemoattractant interleukin-8 (IL-8) and the migration of polymorphonuclear leucocytes (PMN) across monolayers of peritoneal mesothelial cells. PMN showed minimal migration across non-activated mesothelial monolayers (< 2%). However, migration was induced after mesothelial cell activation by IL-1 beta (24%) and this induced migration was significantly blocked by antibodies against IL-8 (63% inhibition; P < or = 0.01). IL-1 beta-activated mesothelial monolayers were shown to secrete IL-8 in a polarized way, which was preferentially oriented towards the apical side of the monolayer. Our results indicate that the influx of PMN into the peritoneal cavity is, at least in part, controlled by the mesothelial cell layer of the peritoneal membrane.