Interaction of mesothelium to intraperitoneal stimulation. I. Aggregation of peritoneal cells.

The effect of intraperitoneal injections of bacterial toxin and adjuvant on the diaphragmatic mesothelium and their interaction with peritoneal cells was investigated in mice. At 30 minutes to 8 hours after stimulation, large numbers of neutrophils were seen on the mesothelial surface. Many of these cells exhibited features characteristic of locomotion over the mesothelial surface, whereas others appeared to be in the process of entering and passing through stomata into lymphatic vessels. By 24 hours numerous neutrophils, macrophages, and a small number of lymphocytes formed cellular aggregates that were surrounded by fibrin filaments. At 48 hours, the peritoneal cells were more closely aggregated and formed several layers on the mesothelial surface. By 72 hours fibrin filaments appeared to be broken down in many areas, with a resultant electron-dense precipitate occupying large areas of the intercellular spaces and on the surfaces of cells. It is suggested that the fibrin provides a matrix for the adhesion and subsequent aggregation of peritoneal cells to the mesothelial surface. The separation of neighboring mesothelial cells which surrounded stomata caused a widening of mesothelial pores (stomata), thereby facilitating the egress of the increased fluid and cellular infiltrations caused by the stimulation. The presence of patent stomata underlying the cellular aggregate demonstrates the importance of the diaphragmatic stomata as a major passageway for the removal of fluids and cells in the unstimulated, as well as during the inflammatory, response.