Tissue entry of GCA CD4 T cells is facilitated by two mechanisms: Excessive production of MMP-9 in GCA macrophages that digest the basal membrane and prepare a path for invading T cells (Watanabe et al., 2018b) and a NOTCH-NOTCH ligand interaction between circulating CD4 T cells and microvascular endothelial cells (Wen et al., 2017). The gene discussed is CD4; the disease is temporal arteritis.