OC 56.3 - Activated protein C regulates aberrant thrombo-inflammatory CD4+ T cell activity in inflammatory bowel disease.

Background: Inflammatory bowel disease (IBD) patients experience up to 6-fold increased risk of venous thromboembolism (VTE) compared to the general population, although the mechanistic basis for this increased risk is unknown. Pre-clinical studies suggest an important role for diminished protein C (PC)-pathway activity in IBD pathophysiology.

Aims: To evaluate the procoagulant activity of colitogenic T-cells and assess the impact of APC signalling in regulating T-cell immunothrombotic activity.

Methods: Dysregulation of coagulation associated genes in IBD patient biopsies were determined using meta-transcriptomic analysis. To elucidate the effect of activated protein C (APC) on T-cell responses, ex-vivo functional assays were performed using CD4+ T-cells treated with APC. The pro-thrombotic potential of T-cells was determined using thrombin generation and clot formation assays, confocal microscopy and flow cytometry.

Results: We found that pro-inflammatory CD4+ T-cells express TF and promote rapid TF-dependent plasma thrombin generation and clot formation. Confocal microscopy confirmed the presence of TF+CD4+CD3+ T-cells in the colons of both colitogenic mice and paediatric IBD patients during active disease. TF is typically expressed in an ‘encrypted’ state and requires decryption for optimal procoagulant activity. Notably, activated T-cells express significantly increased acid sphingomyelinase and protein disulfide isomerase, critical mediators for TF decryption, on their cell membrane compared to naïve T-cells. To understand how this process might be regulated, we performed meta-transcriptomic analysis of IBD patient gut biopsy tissue, identifying dysregulated expression of genes involved in the regulation of coagulation, including PC (PROC) and its receptor (EPCR; PROCR) in IBD patients, revealing an environment permissive to, but deficient in, PC-pathway anti-inflammatory activity. Subsequent functional studies revealed that APC signalling reduced colitogenic T-cell generation and activity, potently impaired TF decryption and significantly reduced T-cell-mediated thrombin generation and clot formation.

Conclusion(s): These data implicate activated T-cell thrombogenicity in IBD and demonstrate a prominent role for APC signalling in regulating colitogenic T-cell thrombo-inflammatory activity.