Neutrophil adhesion molecules in term and premature infants: normal or enhanced leucocyte integrins but defective L-selectin expression and shedding

The functional deficits of neonatal neutrophils are well documented and 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 surface 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 (unstimulated and stimulated, both P < 0.001), but that stimulated premature infant cell express higher L-selectin than term infants (P < 0.05); it is possible that this deficiency is caused by physiological changes occurring around the normal time of parturition. We observed reduced sL-selectin in term infants (P < 0.001) compared with adults, and even lower concentrations in premature infants (P < 0.001). The sL-selectin concentrations in plasma may be a reflection of granulopoiesis, which may be reduced in premature infants. Our results showed increased resting neonatal neutrophil expression of CD11b/CD18 compared with adults, and the absence of any neonatal deficit of the ability to up-regulate CD11b/CD18 expression on stimulation. These findings are contrary to previous reports. Further studies suggested that the isolation procedures used in previous reports reduces the capability of the cells to respond to a formyl methionine leucine phenylalanine (fMLP) stimulus. This effect is more marked in neonatal neutrophils, suggesting that the previously reported deficiency is in fact due to the isolation techniques used rather than the cells' innate ability to up-regulate CD11b/CD18 expression. The results of our study lead us to propose that the adhesive function of neonatal neutrophils may be less defective than previously thought.