Platelet Activation and Platelet-leukocyte Aggregation Elicited in Experimental Colitis Are Mediated by Interleukin-6

There is growing evidence for an interdependence of inflammation, coagulation, and thrombosis in acute and chronic inflammatory diseases. Inflammatory bowel diseases (IBD) are associated with a hypercoagulable state and an increased risk of thromboembolism. Although the IBD-associated prothrombogenic state has been linked to the inflammatory response, the mediators that link these 2 conditions remain unclear. Recent evidence suggests that interleukin-6 (IL-6) may be important in this regard. The objective of this study was to more fully define the contribution of IL-6 to the altered platelet function that occurs during experimental colitis. The number of immature and mature platelets, activated platelets, and platelet-leukocyte aggregates were measured in wild-type and IL-6(-/-) mice with dextran sodium sulfate (DSS)-induced colonic inflammation. DSS treatment of WT mice was associated with significant increases in the number of both immature and mature platelets, activated platelets, and platelet-leukocyte aggregates. These platelet responses to DSS were not observed in IL-6(-/-) mice. Chronic IL-6 infusion (through an Alzet pump) in WT mice reproduced all of the platelet abnormalities observed in DSS-colitic mice. IL-6-infused mice also exhibited an acceleration of thrombus formation in arterioles, similar to DSS. These findings implicate IL-6 in the platelet activation and enhanced platelet-leukocyte aggregate formation associated with experimental colitis, and support a role for this cytokine as a mediator of the enhanced thrombogenesis in IBD.