Cord Blood Neutrophils Have Delayed Apoptosis Compared with Adult Neutrophils. • 1272

Apoptosis plays an important role in the ingestion of neutrophils (PMN) by macrophages, a step in the resolution of infection or inflammation. In cultured adult PMN, spontaneous apopotosis is delayed in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), while in contrast, the Fas (Apo-1/CD95)/FasL system induces apoptosis. As cord blood PMN appear to be functionally immature, we tested the hypothesis that their rate of apoptosis would also differ from that of adult PMN. Venous samples were obtained from healthy term placentas and adult donors, and PMN were isolated by density centrifugation. In up to 8 paired experiments, PMN were incubated for 6 or 24 h, either in medium alone (RPMI 1640/5% FCS; 37° C., 5% CO₂), or in the presence of GM-CSF (10 ng/mL) or anti-Fas IgM (300 ng/mL). Apoptosis was detected by morphologic analysis (pyknotic nuclear changes, Haslett, 1993), quantitative flow cytometric analysis (TdT transferase-mediated fluorescence-labeled dUTP nick end labeling [TUNEL] assay), or by DNA fragmentation gel electrophoresis. Results are shown in the table below (expressed as percent apoptosis, X ± SD; *P ≤.001 vs. adult PMN). In conclusion, cord blood PMN had decreased spontaneous apoptosis and a greater delay of its onset by GM-CSF at 24h compared with adult PMN. In addition, we confirmed the importance of the Fas/FasL system in the induction of apoptosis in cord blood PMN. We speculate that the decreased rate of apoptosis in cord blood PMN has implications for the resolution of infectious and inflammatory processes in neonates.

Table 1