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Opsonic activity of the alternative complement pathway in infected human intra-abdominal fluid
Abstract:
The complement-mediated opsonic activity (CMOA) in intra-abdominal exudates collected during laparotomy from peritonitis patients was examined by an in vitro phagocytic bactericidal assay. It was found that infected intra-abdominal exudates barely promoted detectable killing of Escherichia coli 01 by polymorphonuclear leukocytes. Only the minority of bacteria recovered by differential centrifugation from the infected exudates had C3 on their surfaces. Such bacteria were not optimally opsonized in vivo, whereas they became fully coated with C3 during a brief incubation in vitro in normal human serum. The low level of CMOA in the peritoneal fluid paralleled a depletion of complement in the peripheral blood. Thus, in cases complicated by sepsis with gram-negative bacteria, the CMOA in the blood was extremely low. These data suggest that the high susceptibility of the peritoneum to infection by gut flora, despite the normal phagocytic response, may be partly explained by the low local level of functional complement which is inadequate for optimal opsonization of the bacteria.
Insights
Peritonitis patients show low complement-mediated opsonic activity (CMOA) in abdominal fluid, hindering bacterial killing. This impaired immune response, due to depleted complement, increases susceptibility to gut flora infections.
Area of Science:
- Immunology
- Infectious Diseases
- Microbiology
Background:
- Peritonitis involves infection within the abdominal cavity.
- The complement system is crucial for innate immunity and bacterial clearance.
- Polymorphonuclear leukocytes (PMNs) are key phagocytes in combating bacterial infections.
Purpose of the Study:
- To investigate the complement-mediated opsonic activity (CMOA) in intra-abdominal exudates from peritonitis patients.
- To determine the role of complement opsonization in bacterial killing by PMNs in the peritoneal cavity.
- To explore the relationship between local complement levels and susceptibility to gram-negative bacterial infections.
Main Methods:
- Collected intra-abdominal exudates from peritonitis patients during laparotomy.
- Utilized an in vitro phagocytic bactericidal assay to assess bacterial killing by PMNs.
- Employed differential centrifugation to recover bacteria and analyze C3 deposition on their surfaces.
- Measured complement levels in peripheral blood.
Main Results:
- Infected intra-abdominal exudates showed minimal promotion of Escherichia coli killing by PMNs.
- Only a small fraction of recovered bacteria exhibited C3 deposition in vivo.
- Bacteria incubated in normal human serum were efficiently coated with C3, unlike those in exudates.
- Low CMOA in peritoneal fluid correlated with depleted complement in peripheral blood, especially in sepsis cases.
Conclusions:
- The impaired complement-mediated opsonic activity in peritoneal fluid is a significant factor in the susceptibility to gut flora infections in peritonitis.
- Low local levels of functional complement lead to inadequate bacterial opsonization, despite a normal phagocytic response.
- Depletion of complement in sepsis complicates bacterial clearance and exacerbates peritonitis outcomes.