Autoimmune diseases are thought to be the result of mistaken identity. Immune cells on patrol, armed and ready to defend the body against invading pathogens, mistake normal human cells for infected cells and turn their weapons on their own healthy tissues. In most cases, though, finding the source of the confusion--the tiny fragment of normal human protein that looks dangerously similar to a protein from a pathogen--has been challenging for scientists. That missing piece of the puzzle has hampered efforts to develop effective diagnostics and specific therapies for many autoimmune conditions. That finally may be changing. A team involving researchers from Washington University School of Medicine in St. Louis, Stanford University School of Medicine, and Oxford University has developed a way to find crucial protein fragments that drive autoimmunity, as well as the immune cells that respond to them. The findings, published December 7, 2022 in Nature, open a promising pathway to diagnose and treat autoimmune diseases. The article is titled “Autoimmune-Associated T Cell Receptors Recognize HLA-B*27-Bound Peptides.”