Dose dependent effects of platelet derived chondroitinsulfate A on the binding of CCL5 to endothelial cells

Background: Chemokines immobilized on endothelial cells play a
central role in the induced firm adhesion and transendothelial
migration of leukocytes. Activation of platelets at sites of
vascular injury is considered to support leukocyte adhesion and
extravasation. However, activated platelets also secrete soluble
glycosaminoglycans that can interfere with immobilization of
chemokines. We therefore analyzed the impact of platelet derived
glycosaminoglycans on the immobilization of the chemokine CCL5
(RANTES) on human microvascular endothelial cells and their
influence on CCL5-CCR5 interactions. Results: We confirm that
undiluted serum in contrast to plasma decreases binding of CCL5 to
endothelial cells. However, when lower concentrations of serum were
used, CCL5-presentation on endothelial cells was markedly enhanced.
This enhancement was neutralized if serum was digested with
chondroinitase ABC. Using different chondroitinsulfate-subtypes we
demonstrate that chondroitinsulfate A mediates the enhanced
presentation of CCL5 on endothelial cells, whereas
chondroitinsulfate B/C even at low concentrations block CCL5
binding. CCR5 downregulation on CCR5-transfected CHO cells or human
monocytes is increased by preincubation of CCL5 with serum or
chondroitinsulfate A. Conclusion: We show that chondroitinsulfate A
released from platelets increases the binding of chemokines to
endothelial cells and supports receptor internalization in a dose
dependent manner. These data help to understand the proinflammatory
effects of activated platelets.