AQP4 and neuromyelitis optica: In addition, a peptide derived from the TAX1BP1 protein of human T cell leukemia virus type 1 virus (HTLV-1), was used to immunize mice and induced the production of antibodies against the peptide and homologous AQP4 epitope without any brain lesions, suggesting that HTLV might also be implicated in the pathogenesis of NMO (97), although a previous clinical study argued against this view (98).