Fetal neutrophils and eosinophils express normal levels of L-selectin

L-selectin is a leukocyte adhesion molecule important in the initial stages of the interaction of neutrophils with endothelium during neutrophil emigration from the bloodstream. Neutrophils and eosinophils from newborn infants express significantly less L-selectin than do neutrophils and eosinophils from adults. It is not known whether L-selectin expression on fetal granulocytes is similarly decreased. We studied fetal blood specimens obtained for a variety of clinical indications by percutaneous umbilical cord sampling at 23 to 34 wk of gestation and measured L-selectin expression by flow cytometry. Eosinophils constituted a large proportion of the granulocytes in these fetal specimens (42 +/- 26%, n = 8), with eosinophil counts ranging from 180 to 690/mm3 (mean +/- SD: 350 +/- 220). There was no difference in L-selectin expression of unstimulated fetal and adult neutrophils (mean +/- SD specific fluorescence: 53.0 +/- 6.8 versus 56.6 +/- 4.3, n = 6), and no difference between unstimulated fetal and adult eosinophils (16.0 +/- 6.5 versus 18.7 +/- 3.2, n = 6). Thus, neutrophils and eosinophils from fetuses as early as 23 wk express L-selectin at adult levels. Furthermore, fetal neutrophils and eosinophils shed the receptor normally in response to stimulation in vitro. We conclude that the reduction of L-selectin expression on neonatal neutrophils and eosinophils is not due to an inherent developmental limitation, but instead must be caused by changes occurring in the neonatal period. Elucidation of the etiology of these changes may aid in the development of therapeutic measures to correct the L-selectin-related defects of neonatal neutrophil adherence.