GM-CSF acts primarily on myeloid cells, promoting activation of dendritic cells and macrophages and differentiation of monocytes into dendritic cells, but other cell types may also respond.28–30 GM-CSF mRNA has been detected in arterial lesions of GCA, and GM-CSF protein production by circulating peripheral blood mononuclear cells from GCA patients is increased compared with healthy controls.22 24 According to its known biological functions, GM-CSF may have a role in promoting and amplifying vascular inflammation and injury in GCA. This evidence concerns the gene CSF2 and temporal arteritis.