Differences in adhesion receptor expression between immature and older platelets and red blood cells of neonates and adults.

To examine the hypothesis that reticulated platelets and reticulocytes show elevated adhesion receptor expression compared with mature cells in both adult and neonatal cells. Flow cytometry was used to examine laminin, fibronectin (VLA-6), and thrombospondin (glycoprotein IV [GPIV]) expression in reticulated red cells, reticulated platelets, and older peripherally circulating mature red cells and mature platelets in seven newborn cord blood samples and blood samples from eight adult volunteers. The difference in the neonatal reticulated platelet percentage of 9.2+/-14.8% was not statistically significant from the adult reticulated platelet percentage of 5.0+/-1.5% in this small population. There was a statistically significant difference between the reticulated cord blood red cell mean of 7.7+/-1.8% and the adult mean of 3.1+/-0.43%. Mean expression of VLA-6 was 96% in adult reticulated platelets, 79% in adult mature platelets, 81% in cord reticulated platelets and 65% in cord mature platelets. Mean expression of GPIV was similar, with corresponding values of 90%, 71%, 78%, and 57%. Reticulated red cells in adults averaged 44% VLA-4 and 46% GPIV; cord reticulocytes were 9% and 15%, respectively. Reticulated cells newly released from the bone marrow express more adhesive receptors than mature cells in both groups. Cord blood samples showed hypoexpression of both receptor types in red blood cells and platelets.