FETAL NEUTROPHILS AND EOSINOPHILS EXPRESS NORMAL LEVELS OF L-SELECTIN

L-selectin is a leukocyte adhesion molecule important in the initial s tages of the interaction of neutrophils with endothelium during neutro phil emigration from the bloodstream. Neutrophils and eosinophils from newborn infants express significantly less L-selectin than do neutrop hils and eosinophils from adults. It is not known whether L-selectin e xpression on fetal granulocytes is similarly decreased. We studied fet al blood specimens obtained for a variety of clinical indications by p ercutaneous umbilical cord sampling at 23 to 34 wk of gestation and me asured L-selectin expression by flow cytometry. Eosinophils constitute d a large proportion of the granulocytes in these fetal specimens (42 +/- 26%, n = 8), with eosinophil counts ranging from 180 to 690/mm3 (m ean +/- SD: 350 +/-220). There was no difference in L-selectin express ion of unstimulated fetal and adult neutrophils (mean +/- SD specific fluorescence: 53.0 +/- 6.8 versus 56.6 +/- 4.3, n = 6), and no differe nce between unstimulated fetal and adult eosinophils (16.0 +/- 6.5 ver sus 18.7 +/- 3.2, n = 6). Thus, neutrophils and eosinophils from fetus es as early as 23 wk expreSS L-selectin at adult levels. Furthermore, fetal neutrophils and eosinophils shed the receptor normally in respon se to stimulation in vitro. We conclude that the reduction of L-select in expression on neonatal neutrophils and eosinophils is not due to an inherent developmental limitation, but instead must be caused by chan ges occurring in the neonatal period. Elucidation of the etiology of t hese changes may aid in the development of therapeutic measures to cor rect the L-selectin-related defects of neonatal neutrophil adherence.