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Neutrophil Adhesion Molecule Expression in the Developing Neonatal Rat Exposed to Hyperoxia

Departments of Pediatrics and Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, Texas

Address correspondence to: Susan E. Keeney, M.D., Department of Pediatrics, Route 0526, University of Texas Medical Branch, Galveston, TX 77555-0526. E-mail: skeeney{at}utmb.edu

Neonatal rats have an increased tolerance to hyperoxia, which is associated with a diminished pulmonary inflammatory response compared with adults. To investigate this differing response, expression of the neutrophil adhesion molecules, L-selectin and CD18, and levels of soluble L-selectin, were examined using flow cytometry and sandwich enzyme-linked immunosorbent assay on air-exposed neonatal rat neutrophils at 0–24 and 72 h and 7, 10, 14, and 21 d of age compared with the adult and after exposure to hyperoxia ( 98% O₂) for 56 h in adults and for 72 h and 7 d in neonates. Expression of L-selectin in 0–24-h neonates was similar to adults, but was significantly lower than adults at 72 h and 7 d (P = 0.011). Soluble L-selectin levels were significantly higher than those in adults in the 0–24- and 72-h neonates (P < 0.001). CD18 expression in unstimulated and activated neutrophils of neonatal rats was higher at 0–24 h than in the adult (P < 0.001), but thereafter did not differ from adults. After hyperoxic exposure, L-selectin did not differ between the exposure groups but soluble L-selectin tended to increase in neonates after 7 d of O₂ exposure Finally, CD18 was significantly higher after hyperoxic exposure of the adult (P = 0.008), but did not change with oxygen exposure in the neonate. Based on these findings, we speculate that differences between neonatal and adult rats in expression of L-selectin may contribute to delayed oxygen toxicity in neonatal rats.

Abbreviations: calf serum, CS • enzyme-linked immunosorbent assay, ELISA • formylmethionylleucylphenylalanine, FMLP • lipopolysaccharide, LPS • o-phenylenediamine, OPD • phosphate-buffered saline, PBS