Neonatal Neutrophils with Prolonged Survival Exhibit Enhanced Inflammatory and Cytotoxic Responsiveness

Abstract

Apoptosis is critical to the resolution of inflammation, as it promotes the removal of neutrophils (PMN) by the reticuloendothelial system. In contrast, PMN persistence characterizes the early stages of chronic inflammation. Adult PMN with delayed senescence retain some functionality, although this has not been described for neonatal PMN. We hypothesized that neonatal PMN with prolonged survival retain cytotoxic and inflammatory function. To test one aspect of inflammatory function, we determined surface CD11b expression on 0-h and 24-h PMN after chemotactic formyl-methionine-leucine-phenylalanine (fMLP) stimulation. Although fMLP induced a greater percentage upregulation of CD11b on 0-h adult PMN, this was similar between nonapoptotic cord blood and adult PMN at 24 h. Furthermore, percentage up-regulation of CD11b was more robust for 24-h than for 0-h cord blood PMN. In contrast, there was no difference in responsiveness between 0-h and 24-h adult PMN. In studies of cytotoxic potential, we determined the expression of reactive oxygen intermediates (ROI) in phorbol 12-myristate 13-acetatestimulated cord blood and adult PMN at 0 h and in 24-h nonapoptotic PMN, using the dihydrorhodamine 123 assay.Stimulated cord blood PMN generated more ROI than did adult PMN at both 0 h and 24 h; in addition, ROI levels in 24-h cord blood PMN were similar to those of 0-h adult PMN. We conclude that PMN with prolonged survival retain specific cytotoxic and inflammatory functions, and these are enhanced in cord blood PMN. We speculate that neonatal PMN with prolonged survival have the functional capacity to contribute to the pathogenesis of inflammatory disorders. Abbreviations CLD, chronic lung disease DHR, dihydrorhodamine 123 fMLP, formyl-methionine-leucine-phenylalanine PE, phycoerythrin PMA, phorbol 12-myristate 13-acetate PMN, neutrophil(s) ROI, reactive oxygen intermediates 7-AAD, 7-aminoactinomycin PMN serve as the primary line of host defense during the early stages of sepsis and inflammation (1). After activation by systemic or local factors, primed endothelial cells interact with PMN through adhesion molecules that include selectins and integrins (2). These adhesive interactions initiate a process that allows the extravasation of PMN into inflamed tissue with the goal of neutralizing the inciting stimulus. In the case of inflammation mediated by bacterial or fungal microorganisms, phagocytosis and subsequent killing of these invaders occurs through mechanisms that partly involve ROI and proteases (3,4).The concept that apoptosis of inflammatory PMN and their timely removal by resident macrophages are critical to the resolution of inflammation has been well established (5,6). During the resolution phase, PMN typically undergo the phenotypic changes associated with apoptosis, which promotes their removal by resident macrophages (7). PMN can also undergo necrosis and lysis, a process that induces cytotoxicity in surrounding tissues (8), although apoptosis is the more common and physiologically preferable route. All cells a...

Diminished Phagocytosis-Induced Cell Death (PICD) in Neonatal Monocytes upon Infection with Escherichia coli

“…5), were found to be reduced in CBMO compared with PBMO. Our data suggest, however, that in contrast with neonatal neutrophils (13,14,28), neonatal monocytes are not generally more resistant toward apoptotic signals because staurosporine-and mitomycin-induced cell death was equivalent to cells from adults (Fig. 3).…”

“…Diminished spontaneous apoptosis of neonatal neutrophils has already been described (13,14,28), which may contribute to persisting inflammation in preterm infants (13). In contrast, neonatal have not yet been compared with adult monocytes with regard to PICD.…”

“…Recent work has demonstrated diminished apoptosis in neonatal neutrophils compared with cells from adults (13,14); neonatal monocytes have not yet been investigated. We have previously shown that monocytes from cord blood (CBMO) and peripheral blood of healthy adults (PBMO) are equivalent in phagocytosis and degradation of green fluorescent protein (GFP)-labeled Escherichia coli (15).…”

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

“…To induce apoptosis, neutrophils were serumstarved overnight (19,20). We used only a minimum of macrophage-SFM medium (1 ϫ 10 8 cells/mL) at 37°C with 5% CO 2 .…”

Pulmonary inflammation and bronchopulmonary dysplasia

“…[11][12][13] Most recently, a prolonged survival of neonatal neutrophils owing to an inappropriate suppression of neutrophil apoptosis has been described. [14][15][16] Before neutrophil migration, cellular attachment to endothelial cells is mediated through a complex interaction of adhesion molecules. Increased concentrations of various cellular and endothelial adhesion molecules such as intercellular adhesion molecule (ICAM-1) and selectins have been detected in airway secretions and the circulation of preterm infants with BPD.…”