Neonatal neutrophils with prolonged survival exhibit enhanced inflammatory and cytotoxic responsiveness

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 up-regulation 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-acetate-stimulated 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.