OC 19.4 - Induction of myeloid cell hypercoagulability is a maladaptive consequence of trained immunity

Background: Individuals with chronic inflammatory disease or haematological malignancies have an increased risk of venous thrombosis, although the molecular basis for this phenomenon remains poorly understood. We hypothesised that disease-associated ‘trained immunity’ in myeloid cells, which describes long-term epigenetic and metabolic modifications that occur in response to specific inflammatory stimuli that increases responsiveness to subsequent non-specific inflammatory events, may contribute to hypercoagulability associated with chronic inflammatory disease.

Aims: To assess whether trained immunity enhanced myeloid cell procoagulant and antifibrinolytic activity.

Methods: Murine bone marrow-derived macrophages were trained with 𝜷-glucan or heme, washed, then left for 7 days before lipopolysaccharide (LPS) re-stimulation. Macrophage gene expression and function were analysed by ELISA, RNA-seq and cell-based calibrated automated thrombinography. In vivo cell training was achieved by i.p. 𝜷-glucan administration.

Results: Surprisingly, re-stimulated 𝜷-glucan- or heme-trained macrophages exhibited enhanced procoagulant and antifibrinolytic gene expression compared to macrophages stimulated with LPS alone. Moreover, trained macrophage-dependent thrombin generation was associated with significantly shortened lag-time compared to LPS-stimulated macrophages, which was dependent upon increased tissue factor activity and classical training-associated metabolic and epigenetic modifications in trained macrophages. To assess whether haematopoietic progenitor cell training contributed to enhanced myeloid cell hypercoagulability in vivo, we performed transcriptomic analysis of splenic monocytes isolated from mice trained with 𝜷-glucan 3 weeks prior to sacrifice, which identified up-regulation of genes associated with both trained immunity and hypercoagulability. Furthermore, splenic monocytes isolated from 𝜷-glucan-trained mice exhibited enhanced procoagulant activity compared to control mice monocytes. Remarkably, monocyte procoagulant activity increased in parallel with the time period since 𝜷-glucan training, consistent with the induction of a training-dependent hypercoagulable state.

Conclusion(s): This study demonstrates that a lowered threshold for myeloid cell-dependent hypercoagulability is a maladaptive consequence of innate immune cell memory. Furthermore, these data suggest that epigenetic and metabolic perturbations associated with trained immunity represent novel therapeutic vulnerabilities in immunothrombotic disease.