Relevance of Catalytic Autoantibodies to Myelin Basic Protein (MBP) in Autoimmune Disorders

Abstract

Catalytic autoantibodies with proteinase enzymatic activity against myelin basic protein (MBP) are a distinctive feature of several autoimmune disorders. These autoantibodies, named abzymes (Abz), have both antibody and proteinase activity in a single molecule. Abz targeting MBP (MBP Abz) are commonly found in sera from multiple sclerosis (MS) and systemic lupus erythematosus (SLE) patients, and only recently have been identified in sera from autism spectrum disorder (ASD) patients. Their activities and specificity are similar in MS and SLE; however, although they recognize the same substrate, MBP, the catalytic activity of the Abz from autism spectrum disorder patients is controlled by different proteinase inhibitors. MBP Abz are generated as part of a process started by loss of compaction of myelin due to changes in charge after deamination of arginyl residues in MBP by the enzyme peptidylarginine deiminase. This exposes a normally hidden surface of MBP to T-cells initiating the autoimmune response. A large body of evidence suggests that MBP Abz play an important role in the pathogenesis not only of MS and SLE, but also of ASD. Many autoantibodies found in MS and SLE are also observed in healthy individuals at ranges usually considered pathological; however, clinical signs of the disease are not manifested, suggesting that expression of single autoantibodies may be inconsequential to develop the disease. However, it is the expression of hundreds of different autoantibodies, in addition to MBP Abz, that collectively lead to the clinical development of MS and SLE.