LEVELS OF ADHESION PROTEINS ON NEUTROPHILS OF THE NEONATAL RAT DURING THE FIRST THREE WEEKS OF LIFE. † 1241

Neutrophils of the neonatal rat show decreased migration into the lung after hyperoxia compared to adults. To investigate the mechanism of this impairment, expression of the neutrophil adherence molecules, L-selectin and CD18, were examined on neonatal rat neutrophils at 0-24 hrs, 72 hrs, and 7, 10, 14, and 21 days of age. Staining of whole blood was analyzed by flow cytometry (results expressed as mean channel fluorescence). Soluble L-selectin in the serum was measured using a sandwich ELISA (results expressed as absorbance). Results are as follows (mean ± S.D., * p<0.05 for adult vs. neonate): Table

Table 1

Exposure of neonatal rats to ≥98% O₂ for 3, 7, and 10 days did not affect levels of the adhesion molecules. We conclude that 1) expression of L-selectin in 24 hr neonates is similar to adults, but declines significantly at 72 hrs and 7 days; 2) levels of soluble L-selectin do not differ between adults and neonates; and 3) CD18 is higher in neonatal rats through 14 days. The pattern of decreased L-selectin and increased CD18 in the neonatal rat suggests an activation event occurring shortly after birth. These differences in expression of neutrophil adhesion molecules may decrease the inflammatory potential of the neonatal neutrophil.