High availability of intravascular tissue factor in neonates.

In the present study, we compared the levels of intravascular tissue factor (TF) present in cord versus adult whole blood (WB) prior and after lipopolysaccharide (LPS) stimulation. High levels of intravascular TF might help to explain the clinically observed efficient clotting of cord blood despite low levels of procoagulatory factors. Quantitative reverse transcription-polymerase chain reaction revealed same (basal) TF mRNA expression levels in both native cord and adult WB, and approximately same increase in TF mRNA expression owing to LPS incubation in both cord and adult WB (normalized to the housekeeping gene beta-actin). Flow-cytometric (fluorescence activated cell sorting) analysis revealed significantly higher surface TF antigen exposure on the neonatal monocyte membrane in native WB samples, and approximately same ability of neonatal and adult monocytes to express TF upon LPS-stimulation. Thrombelastography revealed significantly shorter clotting times of native cord versus adult WB (527+/-41 vs. 592+/-23 s, P<0.05). Moreover, shortening of clotting times owing to LPS-stimulation was significantly more pronounced in cord versus adult WB (29.65+/-3.35% vs. 12.03+/-6.23%, P<0.05). Because both quantitative reverse transcription-polymerase chain reaction and fluorescence activated cell sorting analysis revealed same capability of both neonatal and adult monocytes to express TF upon LPS-stimulation, this efficient shortening effect in cord WB might be explained by the constitutively high number of monocytes present in neonates. We suggest that the high levels of intravascular TF present in neonates (prior and after LPS-stimulation) might help to explain the clinically observed efficient clotting of cord blood despite low levels of procoagulatory factors.