Neonatal neutrophil activation is a function of labor length in preterm infants

To understand better the development of the neonatal immune system, we evaluated the role of labor length, gestational age, and mode of delivery on the expression of the neonatal neutrophil cell surface antigens CD11b, CD11c, CD15, CD33, and CD66b in premature newborns. Peripheral blood samples from 68 apparently healthy preterm infants were obtained within 12 h of birth and incubated with MAb to the CD antigens. Samples were lysed, fixed, and analyzed by flow cytometry. Multivariate analysis was used to study the simultaneous effect of the labor length and gestational age on the neonatal neutrophil cell surface antigen expression. A positive correlation was demonstrated between neutrophil antigen expression and labor length (p < 0.001-0.026) but not with the mode of delivery (p = 0.191-0.638). There was no significant correlation between expression of neutrophil antigens and gestational age at delivery (p = 0.057-0.866), except for CD15 (p = 0.010). Our results indicate labor length is a significant factor in neonatal neutrophil activation at birth. These findings are independent of gestational age in preterm newborns. Mode of delivery does not seem to influence neonatal neutrophil activation. The neutrophils of premature infants can be activated antenatally and/or during labor.