Abstract 384: Interleukin-6 Mediates the Altered Platelet Function Associated with Experimental Colonic Inflammation

Abstract

Patients with inflammatory bowel disease (IBD) are susceptible to microvascular thrombosis and thromboembolism. The increased incidence of thrombosis is accompanied by enhanced coagulation and abnormalities in platelet function. Clinical studies have also revealed alterations in platelet activation, enhanced platelet-leukocyte interaction, and elevated plasma levels of prothrombotic cytokines, such as IL-6. This study was directed towards determining whether: 1) experimental colitis, induced by 6 days of dextran sodium sulfate (DSS) ingestion, is associated with platelet activation and the formation of platelet-leukocyte aggregates (PLAs), 2) IL-6 deficiency alters these responses to DSS colitis, and 3) the platelet abnormalities observed in DSS mice can be recapitulated by chronic infusion of murine recombinant IL-6. Flow cytometry was used to characterize platelet function in heparin-anticoagulated whole blood. Platelets were identified by characteristic light scattering and membrane expression of CD41. Platelet activation was monitored using the expression of an activation epitope of GPIIb/IIIa integrin (with JON/A antibody). The combination of CD41, CD45.2, Gr-1, F4/80 and isotype control antibodies were used to detect and quantify aggregates of leukocytes, neutrophils and monocytes with platelets in control, wild type (WT) colitic, IL-6 -/- colitic, and WT mice implanted with IL-6 loaded Alzet osmotic minipumps (for 6 days). Our results indicate that DSS colitis is associated with increased numbers of activated platelets and the formation of aggregates of leukocytes (PLA), neutrophils (PNA) and monocytes (PMA) with platelets. These platelet responses to experimental colitis were largely undetected in IL-6 -/- mice. Chronic infusion (at a rate that yielded plasma IL-6 levels similar to those detected in DSS colitic mice) of IL-6 recapitulated the increased platelet activation and formation of PLA, PNA, and PMA observed in DSS-colitic mice. Collectively, these findings show that the altered platelet function detected in human IBD can be reproduced in an animal model of colonic inflammation and that interleukin-6 plays a critical role in the genesis of these platelet abnormalities in the setting of experimental IBD.