Role of resident macrophages, peripheral neutrophils, and translymphatic absorption in bacterial clearance from the peritoneal cavity

Abstract

Microbial pathogens within the peritoneal cavity are thought to encounter three categories of host defense mechanisms: (i) removal mechanisms, which occur via diaphragmatic lymphatic absorption; (ii) killing mechanisms, in which host phagocytes act as effector cells; and (iii) sequestration mechanisms due to fibrin trapping and the formation of adhesions between visceral surfaces. We sought to define and quantitate the relative role of the first two components in an experimental rat model of Escherichia coli peritonitis in which fibrinous adhesions do not form. Intraperitoneal challenge with -2 x 108 CFU of viable E. coli led to an initial decline in bacterial numbers followed by ongoing proliferation and >50% mortality. With inocula of c5 x 107 CFU, elimination of bacteria occurred after moderate initial proliferation, and no mortality ensued. Nonviable, radiolabeled E. coli organisms were utilized to examine bacterial clearance via translymphatic absorption and phagocytosis. Both processes were extremely rapid, serving to eliminate free bacteria rapidly within the peritoneal cavity. Although macrophages and polymorphonuclear leukocytes within the peritoneal cavity demonstrated similar phagocytic capacities, the predominance of macrophages at the time of the initial bacterial insult led to the conclusion that these cells, in addition to translymphatic absorption, represent the first line of host defenses, acting to eliminate bacteria in the incipient stages of infection.

Impaired neutrophil extracellular traps and inflammatory responses in the peritoneal fluid of patients with liver cirrhosis

“…4 Regarding the SBP diagnostic test by PMN count in AF, the mechanism that mediates PMN recruitment plays an important role because neutrophil migration and accumulation in the peritoneal cavity are regulated by several factors, including chemotactic agents released by resident macrophages in the peritoneum, these cells are the first to respond to peritoneal infection. 5 There is a relative neutropenic state in cirrhosis due to portal hypertension-induced splenic and splanchnic sequestration. 6 SomestudieshavealsoshownthatneutrophilsofLCpatientshave defectsintheproductionofoxygenradicals,primarilysuperoxide anionsandhydrogenperoxide,whichareessentialforeliminating bacteria through the activation of various microbicidal mechanisms,suchasneutrophilextracellulartraps(NETs).…”

Biofilm and planktonicEnterococcus faecaliselicit different responses from host phagocytesin vitro

“…Macrophages play a major role in host defense against infection and contribute to the initial inflammatory response (Dunn et al, 1985;Topley et al, 1996;Broche & Tellado, 2001;Knudsen et al, 2002). They orchestrate several functions such as phagocytosis, antigen processing, and secretion of pro-and anti-inflammatory cytokines.…”

“…They orchestrate several functions such as phagocytosis, antigen processing, and secretion of pro-and anti-inflammatory cytokines. They have also been shown to be important for the early containment of infection within the peritoneal cavity with neutrophils becoming involved in later stages of infection (Dunn et al, 1985). Following bacterial translocation across the intestinal epithelium, survival within macrophages and dendritic cells may serve as a vehicle for the bacteria to travel to the mesenteric lymph nodes and cause systemic infection.…”

Management of adult patients with ascites caused by cirrhosis†

“…12 An elevated ascitic fluid polymorphonuclear leukocyte count probably represents evidence of failure of the first line of defense, the peritoneal macrophages, to kill invading bacteria. 60 A prospective study in which two paracenteses were performed in rapid sequence (Ϸ4 hours apart), before the initiation of antibiotic therapy, shows that only 8% of patients with culture-positive ascitic fluid with an elevated PMN count become culturenegative spontaneously. 61 The majority of patients with culture-positive neutrocytic ascites show rising bacterial and PMN counts when serial samples are obtained in rapid sequence before initiation of antibiotic therapy.…”