Autoantibodies to myelin basic protein catalyze site-specific degradation of their antigen

Abstract

Autoantibody-mediated tissue destruction is among the main features of organ-specific autoimmunity. This report describes ''an antibody enzyme'' (abzyme) contribution to the site-specific degradation of a neural antigen. We detected proteolytic activity toward myelin basic protein (MBP) in the fraction of antibodies purified from the sera of humans with multiple sclerosis (MS) and mice with induced experimental allergic encephalomyelitis. Chromatography and zymography data demonstrated that the proteolytic activity of this preparation was exclusively associated with the antibodies. No activity was found in the IgG fraction of healthy donors. The human and murine abzymes efficiently cleaved MBP but not other protein substrates tested. The sites of MBP cleavage determined by mass spectrometry were localized within immunodominant regions of MBP. The abzymes could also cleave recombinant substrates containing encephalytogenic MBP 85-101 peptide. An established MS therapeutic Copaxone appeared to be a specific abzyme inhibitor. Thus, the discovered epitope-specific antibodymediated degradation of MBP suggests a mechanistic explanation of the slow development of neurodegeneration associated with MS.

Multiple sites of the cleavage of 17- and 19-mer encephalytogenic oligopeptides corresponding to human myelin basic protein (MBP) by specific anti-MBP antibodies from patients with systemic lupus erythematosus

“…It was recently shown that incubation of many individual IgGs with iodoacetamide (a specific inhibitor of thiol proteases) or pepstatin A (a specific inhibitor of acidic proteases) has moderate effect (5-15%) on SLE Ab-dependent hydrolysis of MBP [9]; the same was demonstrated for MS IgGs, IgAs and IgMs [27][28][29][30][31]. However, PMSF, AEBSF (specific inhibitors of serine proteases), and EDTA (an inhibitor of metalloproteases) significantly suppressed the proteolytic activity of SLE and MS pIgGs in the case of MBP and OPs as substrates [9].…”

“…It was recently shown that, anti-MBP IgGs from the sera of patients with MS [27][28][29][30][31] and SLE [9] efficiently hydrolyze globular MBP but not many other tested proteins. No activity was found for IgG fraction of healthy donors in the hydrolysis of MBP or different OPs (Fig.…”

“…1) [27][28][29][30][31]. The sites of MBP cleavage by MS IgGs determined by mass spectrometry were localized within four known immunodominant regions of MBP [31]. SLE IgGs hydrolyzed MBP within the same immunodominant regions of MBP [9].…”

“…Then, for the revealing of the SLE Ab-dependent cleavage sites we have used X-OPs, while the cleavage sites in the case of MS IgGs were identified using digestion of intact globular MBP [31]. In this connection it should be mentioned, that catalytic centers of proteolytic abzymes (including MS and SLE anti-MBP IgGs [9,27]) are usually located on the light chain, while the heavy chain is more often responsible for specific antigen recognition and increased antigen affinity for Abs [1][2][3][4][5][6][7][8].…”

“…It has been recently shown that MBP-hydrolyzing activity is an intrinsic property of IgGs, IgMs, and IgAs from the sera of MS patients [27][28][29][30] and the specific sites of the neural antigen cleaved by abzymes have been established [31]. Recognition and degradation of MBP peptides by serum auto-Abs was confirmed as a novel biomarker for MS [31].…”