Macrophage-mediated bystander T cell activation in varicose veins
Background: Up to one-third of all adults are affected by chronic venous insufficiency, with varicose veins being a common manifestation of the condition. It is believed that inflammation plays a central role in the progression of the disease; however, the immune cell populations and mechanisms involved remain unclear. Methods: Varicose veins were subjected to a stepwise mechanical and enzymatic dissociation, and the mononuclear cells resulting from these steps were characterized by flow cytometry. CD206-negative connective tissue macrophages and CD206-positive venous wall macrophages were sorted from five donors and subjected to transcriptomic profiling. Cytokine production by T cells in varicose veins was characterized following inhibition of intracellular protein transport. The ability of cytokines identified in macrophage transcriptomes to induce cytokine production in CD8+ and CD4+ effector and memory T cells was investigated using combinations of recombinant cytokines. Results: Varicose veins harbor CD206neg IL-1+ S100A8/9+ macrophages in the connective tissue and pro-resolving and tissue regenerating CD206+ TIMD4+ LYVE1+ macrophages in the vein wall. T cells predominantly localize within the connective tissue, express an effector-memory T cell phenotype and produce IFN-{gamma} in situ. Cytokines identified in the macrophage transcriptome collectively induced IFN-{gamma}, as well as TNF-, IL-22, and GM-CSF in effector memory T cells; in addition to IL-15 and IL-18, TNF- and IL-10 proved to be key drivers. Conclusions: The identified macrophage-T cell cytokine axis contributes to chronic venous insufficiency pathogenesis and represents a potential therapeutic target.