Human neonatal neutrophils are resistant to apoptosis with lower caspase-3 activity

The incidence of neonatal inflammatory diseases remains high despite improved strategies for dealing with infection. Neutrophils are believed to play a significant role in neonatal inflammatory diseases due to their secretion of harmful mediators. Neutrophils rapidly undergo apoptosis following activation; dysregulation of the neutrophil apoptotic pathway may be an underlying mechanism of neonatal inflammatory disorders. In this study, we determined whether neonatal neutrophils are intrinsically resistant to apoptosis relative to their adult counterparts. Twelve healthy full-term newborn infants and 12 healthy adult volunteers, aged 20 to 45 years, were enrolled in this study. Neutrophils were isolated from umbilical cord blood or fresh venous peripheral blood, and neutrophils of each subject were cultured for up to 48 hours. Flow cytometric analysis revealed that spontaneous apoptosis of adult neutrophils increased with culture time (23% ± 2% at 12 h, 49% ± 4% at 24 h and 76% ± 3% at 48 h), whereas the frequency of apoptosis was significantly lower in neutrophils from neonates (9% ± 2% at 12 h, 30% ± 4% at 24 h and 49% ± 3% at 48 h) (p < 0.01 for each time point). Importantly, the expression levels of caspase-3 mRNA and a precursor form of caspase-3 protein were lower in neonatal neutrophils than adult neutrophils, as judged by RT-PCR and Western blot analyses. Moreover, caspase-3 activity was lower in neonatal neutrophils, compared to adult neutrophils. These findings suggest that neonatal neutrophils are intrinsically apoptosis-resistant, which may be due to the low expression of caspase-3.