Cytokines, growth factors and proteases in medium and large vessel vasculitis.

Giant cell arteritis and Takayasu arteritis are autoimmune vasculitides that cause aneurysm formation and tissue infarction. Extravascular inflammation consists of an intense acute phase response. Deeper understanding of pathogenic events in the vessel wall has highlighted the loss of tissue protective mechanisms, the intrusion of immune cells into "forbidden territory", and the autonomy of self-renewing vasculitic infiltrates. Adventitial vasa vasora critically control vessel wall access and drive differentiation of tissue-invasive T cells. Selected T cells establish tissue residency and build autonomous, self-sufficient inflammatory lesions. Pathogenic effector T cells intrude and survive due to failed immune checkpoint inhibition. Vasculitis-sustaining T cells and macrophages provide a broad portfolio of effector functions, involving heterogeneous populations of pro-inflammatory T cells and diverse macrophage subsets that ultimately induce wall capillarization and intimal hyperplasia. Redirecting diagnostic and therapeutic strategies from control of extravascular inflammatory markers to suppression of vascular inflammation will improve disease management.