NEUTROPHIL ADHESION MOLECULES IN TERM AND PREMATURE-INFANTS - NORMAL OR ENHANCED LEUKOCYTE INTEGRINS BUT DEFECTIVE L-SELECTIN EXPRESSION AND SHEDDING

The functional deficits of neonatal neutrophils are well documented an d are thought to contribute to the increased susceptibility of newborn infants to infection. We measured the adhesion molecules L-selectin, CD11a/CD18 and CD11b/CD18 on neutrophils from the cord blood of term(n = 22) and premature (n = 32) infants using a whole blood method with flow cytometry and quantitative bead standards to enumerate cell surfa ce receptors. We also assayed plasma for the shed form of L-selectin ( sL-selectin). Our results suggested that L-selectin expression on term infant neutrophils is lower than that on adult neutrophils (unstimula ted and stimulated, both P < 0.001), but that stimulated premature inf ant cells express higher L-selectin than term infants (P < 0.05); it i s possible that this deficiency is caused by physiological changes occ urring around the normal time of parturition. We observed reduced sl-s electin in term infants (P < 0.001) compared with adults, and even low er concentrations in premature infants (P < 0.001). The sL-selectin co ncentrations in plasma may be a reflection of granulopoiesis, which ma y be reduced in premature infants. Our results showed increased restin g neonatal neutrophil expression of CD11b/CD18 compared with adults, a nd the absence of any neonatal deficit of the ability to up-regulate C D11b/CD18 expression on stimulation. These findings are contrary to pr evious reports. Further studies suggested that the isolation procedure s used in previous reports reduces the capability of the cells to resp ond to a formyl methionine leucine phenylalanine (fMLP) stimulus. This effect is more marked in neonatal neutrophils, suggesting that the pr eviously reported deficiency is in fact due to the isolation technique s used rather than the cells' innate ability to up-regulate CD11b/CD18 expression. The results of our study lead us to propose that the adhe sive function of neonatal neutrophils may be less defective than previ ously thought.