Pathogenesis

Giant cell arteritis (GCA) is an inflammatory disease which mainly affects the extracranial branches of the carotid artery, particularly the temporal arteries. The onset of GCA requires a breakdown of arterial immunoprivilege with the infiltration of immune cells, mainly CD4+ T lymphocytes, macrophages, and dendritic cells (DCs) across the arterial wall. Local production of cytokines, chemokines, growth factors, and enzymes can lead to the amplification of the inflammatory responses and to arterial remodeling. The hyperplasia of the intimal layer can result in luminal stenosis and ischemic events. The etiology of GCA is unknown. However, age-related immune alterations, in genetically predisposed subjects, and environmental triggers seem necessary for the development of the disease. In addition, the existence of a specific GCA-inducing leukocyte repertoire in peripheral blood and the activation of arteries to allow leukocyte entry seem required for the development of GCA. Some immune effectors have been demonstrated to have a role in GCA pathogenesis: the activation of vascular DCs and T cells, TLR4, TLR5, Janus kinases 1 and 3, CD28 co-stimulation, NOTCH-Jagged pathway, CCR6 expression by T cells, defective PD-1 checkpoint; the production of IL-6, VEGF, MMP-9, IFNγ, ET-1, PDGF, IL-12, IL-23, acute-phase serum amyloid A.