Background: The propensity for sustained inflammation after bacterial infection in neonates, resulting in inflammatory sequelae such as bronchopulmonary dysplasia and periventricular leucomalacia, is well known, but its molecular mechanisms remain elusive. Termination of inflammatory reactions physiologically occurs early after removal of bacteria by phagocytosis-induced cell death (PICD) of immune effector cells such as monocytes. PICD from cord blood monocytes (CBMOs) was shown to be reduced as compared with that of peripheral blood monocytes (PBMOs) from adult donors in vitro.
Methods: PBMOs, CBMOs, and Fas (CD95)-deficient (lpr) mouse monocytes were analyzed in an in vitro infection model using green fluorescence protein-labeled Escherichia coli (E. coli-GFP). Phagocytosis and apoptosis were quantified by flow cytometry and CD95L secretion was quantified by enzyme-linked immunosorbent assay.
Results: We demonstrate the involvement of the CD95/CD95 ligand pathway (CD95/CD95L) in PICD and provide evidence that diminished CD95L secretion by CBMOs may result in prolonged activation of neonatal immune effector cells.
Conclusion: These in vitro results offer for the first time a molecular mechanism accounting for sustained inflammation seen in neonates.