To investigate the functional impairment of neonatal neutrophils, we measured the expression of the neutrophil adherence molecule, L-selectin, on the neutrophils of full-term (>36 weeks gestation) and premature human neonates. In addition, soluble L-selectin was measured in the serum and compared to levels in the adult. Neonatal blood was drawn at 24 hrs, 72 hrs, 1 wk, and 2 wks of life. Staining of whole blood for L-selectin was analyzed with flow cytometry. Mean channel fluorescence for adult L-selectin was 128.25± 48.3. Results for neonates are as follows (mean ± S.D., + p<0.05 for adult vs. newborn, * p<0.05 for term vs. preterm):Table

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Stimulation with FMLP resulted in loss of L-selectin in all age groups. Soluble L-selectin (ng/ml) averaged over all time points during the first 2 weeks of life in each age group were as follows: 921 ± 265 for adult, 739 ± 200 for term neonates and 307 ± 129 for preterm neonates(p <0.05 for preterm vs adult and term). We conclude that 1) expression of L-selectin is lower on term neonatal neutrophils for at least the first week of life; 2) L-selectin expression is significantly higher in preterm than term neonates for the first 2 weeks of life; and 3) soluble L-selectin is lower in the preterm neonate than in other age groups. These studies indicate that the lower expression of L-selectin on neutrophils of term infants may occur as a developmental phenomenon as the fetus matures. These events may allow the fetus some protection in utero and benefit the term newborn by temporarily decreasing the inflammatory potential of the neutrophil.