This asparagine endopeptidase was shown to initiate processing of the tetanus toxin antigen in human B cells (12, 13), to be capable of destroying an immunodominant peptide of myelin basic protein (MBP, 85–99) an auto antigen implicated in the autoimmune disease multiple sclerosis (14) and to perform the early step of Ii chain degradation in human B-EBV cells (15). Here, MBP is linked to autoimmune disease.