Clearance of Apoptotic Neutrophils Is Diminished in Cord Blood Monocytes and Does Not Lead to Reduced IL-8 Production

Abstract

Phagocytosis of apoptotic cells, e.g., neutrophils, by monocytes is essential for resolution of inflammation. Delayed removal leads to secondary necrosis, perpetuating inflammation, and tissue destruction. Common histologic features in neonatal chronic inflammatory disorders are an accumulation of apoptotic cells in inflamed tissues. We hypothesized that apoptotic cell removal by monocytes is compromised in newborns. PKH-26 labeled autologous or allogeneic apoptotic neutrophils were fed to monocytes of adult donors (PBMO) and cord blood (CBMO), and phagocytic activity was analyzed by flow cytometry and confocal microscopy. Relative mRNA-expression levels of 21 surface receptors and bridging molecules relevant for apoptotic cell removal were measured, as was postphagocytic IL-8 production upon LPS-stimulation. Compared with PBMO, CBMO exhibited a significantly diminished phagocytotic competence for autologous and allogeneic apoptotic neutrophils. mRNA-expression levels of milk fat globule-EGF factor 8 and T cell immunoglobulin-and mucin-domain-containing molecule, two crucial members of the phagocytic synapse of apoptotic cell removal, were reduced in CBMO. In PBMO, interaction with autologous apoptotic neutrophils reduced LPS-induced IL-8 production whereas it was enhanced in CBMO. Our data suggest a specific defect in CBMO during clearance of apoptotic neutrophils resulting in impaired anti-inflammatory capacity. (Pediatr Res 66: 507-512, 2009) P hagocytosis of apoptotic cells by monocytes is a crucial step for normal tissue homeostasis by removing invaded immune cells, e.g., neutrophils, from inflamed tissue (1,2). Delayed removal may lead to secondary necrosis of the apoptotic cell, thus perpetuating inflammation and consecutive tissue destruction. Apart from a safe disposal of apoptotic debris, monocytes secrete anti-inflammatory signals, whereas inflammatory reactions are suppressed, hence enforcing the resolution of inflammation (1). Engulfment is mediated through receptors on the phagocyte, which can either bind structures on the apoptotic cell directly or by the help of bridging molecules, such as mucin-domain-containing molecule E8 (MFG-E8), which form a "phagocytic synapse" (reviewed in Ref. 1).During the neonatal period, tissue damage often results in chronic inflammatory responses such as bronchopulmonary dysplasia (BPD), periventricular leucomalacia (PVL), or necrotising enterocolitis (NEC) (3-10). One common histologic feature is the accumulation of apoptotic neutrophils, epithelial, or parenchymal cells in the inflamed tissues (11,12). This observation is unexpected as apoptotic cells are removed rapidly in healthy adults. One reason could be that neonatal monocytes do not engulf apoptotic cells as efficiently as their adult counterparts. Although neonatal monocytes show functional differences compared with those from adults (13), they are not impaired in their phagocytic competence for Grampositive (14) or Gram-negative bacteria in vitro (15,16).Therefore, we investigated whether neonat...

Differential modulation of cord blood and peripheral blood monocytes by intravenous immunoglobulin

“…In each group, IVIG was added prior to infection. As previously shown (12, 19, 20, 24, 28, 29), phagocytic activity of CBMO and PBMO were not different, neither with respect to cells actively participating in phagocytosis (phagocytic index, Fig. 1A, first and third columns) or in the amount of bacteria ingested per cell (phagocytic capacity, Fig.…”

“…Neonatal sepsis often is devastating, and effector cells, for example, monocytes, taken from cord blood (CBMO), differ from PBMO with respect to a variety of aspects: they were found to be less sensitive towards the two most common bacterial species [ Escherichia coli ( E. coli ) and streptococcus group B]‐mediated PICD than PBMO (12) and were shown to have deficiencies in both, costimulatory and cytotoxic functions: Due to diminished IFN‐γ effects on B7 molecules (CD80 and CD86), CBMO inhibit monocyte‐dependent T cell proliferation (18). CBMO have a diminished capacity to induce antibody‐dependent cellular cytotoxicity, ADCC, (19) and to remove apoptotic particles (20).…”

Flow Cytometry in the Detection of Neonatal Sepsis

“…Higher plasma death ligands (TNF- α , Fas), main mediators of apoptosis pathway, associated with lower antiapoptotic molecules (Bcl-2, NF- κ B), are associated with increased apoptosis in neonatal sepsis [58]. Furthermore, clearance of apoptotic neutrophils through monocytes is diminished, resulting in impaired anti-inflammatory capacitiy [19]. Several in vitro studies reveal inhibiting or preventing apoptosis as a therapeutic option for adult sepsis (reviewed in [57]).…”

“…A high percentage of adults' monocytes perishes after bacterial infection due to phagocytosis-induced cell death by apoptosis and loses the function for cytokine production [17, 18]. Neonatal monocytes are affected much less by this process, and an extended production of pro-inflammatory cytokines occurs [19], a phenomenon which is referred to as “sustained inflammation” [20]. …”

Diagnostic Value of Immature Myeloid Information in Early-onset Bacterial Infection in Term and Preterm Neonates

“…Neonatal bacterial infection is classified into an early-onset form (EOBI) within the first 72 h of life and a late-onset form (LOBI). Preterm infants are known for increased inflammatory response to bacterial infection compared to adults [16,17,34,35]. Clinical diagnosis is difficult because symptoms are variable and nonspecific [37,38].…”