Effect of systemic fibrinogen depletion on intraabdominal abscess formation

Deposition of fibrin within the peritoneal cavity is an integral host response to local infection. To directly assess the role of fibrin deposition in the pathogenesis of intraabdominal abscess formation, the ability to induce abscesses in fibrinogen-depleted mice was examined. We hypothesized that systemic defibrinogenation with ancrod would limit the availability of fibrinogen for deposition within the peritoneal cavity and would therefore impair intraabdominal abscess formation. A gelatin capsule containing 50% sterile feces plus Bacteroides fragilis 1 x 10(9) CFU was inserted IP into control or defibrinogenated mice. System defibrinogenation resulted in alteration of the character of abscess formation, as manifested by reduced abscess size and degree of purulence. Abscesses were significantly smaller (0.18 +/- 0.02 gm [n = 29] vs. 0.09 +/- 0.02 gm [n = 11], p less than 0.01) and less purulent (p less than 0.001) in the ancrod-treated mice than in control animals, despite equal numbers of bacteria in the abscesses recovered from both groups. The effect of ancrod was specific for defibrinogenation, because IP repletion with fibrinogen reversed the ancrod effect on abscess size. In addition to its local effects, systemic fibrinogen depletion resulted in a significant elevation in mortality following IP infection (1 of 30 control animals vs. 10 of 23 ancrod-treated animals, p less than 0.01). However, this was not due to an increase in the magnitude of the B. fragilis bacteremia. These studies demonstrate that fibrin deposition contributes to the pathogenesis of purulent abscess formation and that systemic depletion of fibrinogen may alter host susceptibility to the consequences of infection.