Interaction of the peritoneal cavity to intraperitoneal stimulation: A peritoneal model system to monitor cellular and extracellular events in the formation of granulation tissue

The intraperitoneal injection of bacterial toxin and complete Freund's adjuvant in mice produced the classical inflammatory response. However, when allowed to continue, this process led to the formation of granulation tissue of the mesothelial surface. The initial lesion of the reaction was characterized by the deposition of a copious amount of fibrin filaments which were involved in the adhesion and aggregation of peritoneal cells into discrete cellular mounds on the peritoneal mesothelial surface. By 1 week postinjection, fibrin was markedly diminished and appeared as electron-dense precipitates upon which collagen fibrils were deposited. By 2 weeks, the amount of collagen was greatly increased; and the granular components of fibrin were markedly diminished. Coincident with the deposition of collagen fibrils, there was also a neovascularization of the cellular aggregates. This process occurred when the blood and lymphatic vessels within the submesothelial connective tissue branched and invaded the newly aggregated cellular mounds. By 1 month, the cellular aggregates had taken on the appearance of granulation tissue with foci of closely packed macrophages, fibroblasts, and a network of newly formed blood and lymphatic capillaries. This intraperitoneal stimulation provides an in vivo system in which the various cellular and extracellular events of inflammation leading to the formation of granulation tissue can be monitored.