We used the phage display library Ph.D.-12 and 3 alternating rounds of negative selection on control human IgG (SubcuviaTM) to deplete phages with peptides binding to irrelevant antibodies or serum proteins, and of positive selection on single NMO-IgGs to enrich phages displaying peptides binding to the AQP4-reactive antibodies (Fig. 1). Here, AQP4 is linked to neuromyelitis optica.