Mechanisms of clearance from the peritoneal cavity

Staphylococcal enterotoxin B induces fever, brain c-Fos expression, and serum corticosterone in rats

The paraventricular nucleus of the hypothalamus (PVH) occupies a pivotal point within the network of brain nuclei coordinating critical host-defense responses. In mice, T cell-dependent immune stimuli, including the bacterial superantigen staphylococcal enterotoxin B (SEB), can activate the PVH. To determine whether T cell-dependent immune stimuli activate the PVH in rats, we assessed plasma corticosterone (Cort) levels, fever responses, and c-Fos expression in the PVH in animals treated with intraperitoneal injections of SEB. In animals with previously implanted abdominal thermisters, intraperitoneal injection of 1 mg/kg SEB resulted in a significant rise in body temperature, with a latency of 3.5-4 h. In separate animals, intraperitoneal injection of 1 mg/kg SEB resulted in a significant elevation of plasma Cort and induced c-Fos expression in parvocellular neurons within the PVH. These results support the idea that T cell-dependent immune stimuli activate brain pathways mediating host-defense responses such as fever and neuroendocrine changes.

Bacterial peritonitis in continuous ambulatory peritoneal dialysis: effect on dialysis on host defense mechanisms

We have used an experimental model of continuous ambulatory peritoneal dialysis (CAPD) to investigate the effect of dialysis on host defense mechanisms in the peritoneal cavity. Laboratory rats undergoing regular dialysis were challenged with a single bolus of Staphylococcus epidermidis, Staphylococcus aureus, Candida albicans, and Pseudomonas aeruginosa. Intraperitoneal challenges with all four microbial strains underwent a rapid clearance during the first 4 hours, irrespective of whether the host was undergoing dialysis. Studies using S epidermidis showed that the rapid clearance was not mediated by the diaphragmatic stomata as might have been expected. Dialysis did, however, cause delays over the following 48 hours with all of the pathogens except C albicans. Bacterial clearance over a 10-day period was strain dependant, and microbial persistence was related to adhesion formation around the cannula. Again C albicans was an exception. Our conclusions are that dialysis does not affect the innate defense mechanisms involved in the early clearance of a bolus challenge to the peritoneal cavity but can cause delays in eradicating microorganisms that survive this phase. Because these experiments were carried out using a bolus inoculum, it may be necessary to reevaluate the effect of dialysis on host defenses in the peritoneal cavity under conditions in which the challenge more closely approximates a touch contamination event.