AQP4 and hepatitis C virus infection: Higher BAFF levels are observed in the CSF of AQP4-antibody positive NMO patients [136,137], in the group of I-IFN treated hepatitis C patients progressing to NMO [138,139] or to other types of antibody-associated autoimmune diseases [140–143], and in the serum of patients with other antibody-driven autoimmune diseases like Sjögren ́s syndrome [144,145] or systemic lupus erythematosus [146].