A study showed that penetration of the BBB by pathogenic TH17 cells in a multiple sclerosis mouse model depended on RANKL signaling; TH17 cells expressing RANKL interact with RANK-expressing astrocytes, which in turn secrete C-C motif chemokine ligand 20 (CCL20), further attracting C-C motif chemokine receptor 6 (CCR6)-expressing cells into the central nervous system (CNS) (Fig. 2e) [83]. This evidence concerns the gene CCL20 and multiple sclerosis.