WHAT IT IS Phage display immunoprecipitation sequencing helps identify antibodies that bind to human proteins in cerebrospinal fluid or serum. HOW IT WORKS Scientists lay out chunks of every human protein (about 700,000 autoantibodies across all human proteins) and then clone and express them in phage. Then, they incubate the patient’s CSF with the phage, allowing the antibodies to bind to phage expressing their peptide target or antigen. The scientists capture only the phage that stick to the patient antibodies by using magnetic beads, and they wash the rest away. They then observe which proteins were bound by the patient’s antibodies by sequencing the DNA in the phage. HOW IT IS APPLIED The technique enables researchers to display the complete human peptidome and discover autoantigen biomarkers common to different disorders, including breast cancer, neuroinfectious and autoimmune diseases.