Meconium stimulates a pro-inflammatory response in peritoneal macrophages: implications for meconium peritonitis

Although meconium peritonitis is a rare condition, the mortality rate can be as high as 40%. Meconium peritonitis is a result of intestinal perforation in utero, which leads to dense inflammation in the peritoneal cavity. The fetus has relatively immature peritoneal defense mechanisms, so the cause of this dense inflammation is unclear. The peritoneal macrophage is a key cell in the peritoneal inflammatory response in adults. The purpose of this investigation was to determine if sterile meconium had a direct stimulatory effect on the peritoneal macrophage.

Peritoneal macrophages were harvested from adult C3H/HEN mice. The cells were placed in microtiter wells at 10(5) cells per well. Sterile human meconium was diluted in media and placed in the wells at varying concentrations for 8 hours. Lipopolysaccharide (LPS) (10 microg/mL) served as a positive control. Supernatants were harvested and assayed for tumor necrosis factor alpha (TNF-alpha) using a commercial ELISA kit. Separate cells were assayed for TNF-alpha message using polymerase chain reaction (PCR). In another series of experiments, procoagulant activity (PCA) was determined on freeze-thawed cells using a two-stage amidolytic assay. To test for the role of protein kinase C (PKC) in the PCA response H7, a PKC inhibitor, was used as well.

Meconium stimulation resulted in a significant increase in TNF-alpha compared with negative controls with a peak at 0.1% meconium (121 pg/mL v 11 pg/mL, P<.05). There was a significant increase in PCA, with a 10-fold increase with 1% meconium compared with controls (P<.05). This response was limited to less than 5% by PKC inhibition.

Sterile meconium results in a marked proinflammatory response in the peritoneal macrophage with elevations of both PCA and TNF-alpha. The TNF response is likely mediated at a pretranscriptional level because there is a marked increase in TNF mRNA. These data suggest that the PCA response is regulated by a PKC mechanism similar to LPS. Stimulation of the peritoneal macrophage by meconium is a possible cause of the marked inflammation seen in meconium peritonitis.