**2. Antibodies-mediated demyelination in the pathogenesis of MS**

Antibodies can cause demyelination by several effector mechanisms. One of these is the opsonization of myelin for subsequent phagocytosis by macrophages, which has been observed in MS and EAE. Serum anti-myelin antibodies raise macrophage phagocytosis, and the uptake by macrophages of CNS myelin increases after opsonization with complement. Another mechanism of demyelination that involves autoantibodies is through activation of the entire complement cascade leading to membrane attack complex (MAC) deposition and complement-mediated cytolysis.

Antibodies with specificity against minor myelin components have also been detected in MS patients. MOG is the most interesting candidate B-cell autoantigen in MS. Because of its location it is an ideal target for antibody-mediated demyelination. Anti-MOG antibodies are indeed able to cause myelin destruction in EAE models, while other antibodies against major myelin proteins such as MBP or PLP, which are both not located on the myelin surface, do not cause myelin destruction on their own. Anti-MOG Abs mediate a characteristic vesicular transformation of compact myelin in acutely demyelinated lesions that also has been documented in human MS lesions strongly suggesting a role of anti-MOG Abs in MS. The B-cell response to MOG is enhanced in MS also supporting the pathogenic importance of anti-MOG Abs. Interestingly, the presence of serum anti-MOG antibodies,

Antibody-Proteases in the Pathogenesis of Autoimmune

Tellier, 2002; Nathan, 2002; Kozyr et al., 1998)

**3. Major antigenic targets of the anti-myelin autoAbs** 

targets.

MS. (Fritz et al., 1983)

**3.1 Myelin basic protein** 

Demyelination and Monitoring Patients with Multiple Sclerosis 481

designing artificial abzymes initiated the study of biological activities of natural catalytic autoantibodies and their involvement in pathogenesis of major clinical disorders, i.e., evoked the onset of the era of medical abzymology. (Suchkov et al., 2001; Zhou et al., 2002;

Medical abzymology has made a great contribution to the development of general autoimmunity theory: it has put the antibody as a *functional entity* and as the key brick of the theory to the level of *physiological functionality* by providing such antibody with the ability to catalyze and mediate direct and independent cytotoxic effect on cellular and molecular

There are extensive information on a significant portion of MS cases, characterized by the presence of autoantibodies against myelin protein components in serum of patients with MS. (Chamczuk et al., 2002; Reindl et al., 1999) Although the mechanism of the autoantibody role in MS pathogenesis is unknown , autoantibodies to MBP and MOG were proposed as biomarkers for clinical prognosis of MS. (Berger et al., 2003) Similar immunoglobulins were also found in mice with induced EAE, which is an animal model of

Myelin basic protein is by far the best studied myelin component in MS. It is the second most abundant myelin protein (approximately 30-40%) after PLP. There are five MBP isoforms with 14-21.5 kDa molecular weights in mammals that result from differential splicing of 11 axons within the Golli-MBP locus. The highly basic MBP is positioned at the intracellular surface of myelin membranes and via interactions with acidic lipid moieties is involved in maintaining the structure of compact myelin. The most abundant 18.5 kDa

Different from MOG, and PLP (proteolipid protein), MBP is found in both central and peripheral myelin, and MBP transcripts have also been demonstrated in peripheral

Fig. 1. MBP sites of proteolysis by different enzymes-proteases and Abs-proteases and as a result of spontaneous autocatalytic hydrolysis. The sequence of the encephalitogenic peptide

mettaloproteinase-3), CatD (Cathepsin D), ACat (Autocatalytic cleavage), Abz (Abzyme), LP

81–103 is shown in red. Abbrevations: GelB (Gelatinase B), MMP-3 (matrix

isoform (170 amino acid length) has been used in most immunological studies.

lymphoid organs such as lymph nodes and thymus.

(Lysosomal Proteases), Tryp4 (Trypsin 4).

with or without anti-MBP antibodies, in patients presenting with an initial clinical event suggestive of central nervous system demyelination and evidence of multifocal lesions on MRI studies, is predictive of subsequent clinical events that establish the diagnosis of clinically definitive MS. However, the presence of anti-MOG antibodies in patients with nondemyelinating diseases of the CNS, as well as in a substantial number of healthy individuals, has raised important questions about the role of these antibodies in MS, and these need to be addressed in future studies.

#### **2.1 Catalysis**

The neurodegenerative model of MS is based on the proposition of a primary lesion in myelin followed by myelin breakdown and the release of myelin-compartmentalized proteins, particularly MBP. This is followed by the generation of MBP-derived peptides that become the main sensitizers of T cells. (Hafler, 2004) The hypothesis that interactions between MBP and T cells must occur at sites other than the myelin membrane has been challenged by recent physicochemical studies demonstrating that myelin can become structurally unstable secondary to specific posttranslational modifications of MBP structure. This was shown to result in the increased surface exposure and susceptibility to proteolysis of MBP 83–92. (Husted, 2006) The close association between the proteolytic sensitivity of MBP and the pattern of posttranslational modifications of the molecule may represent one of the key regulatory mechanisms in epitope generation (Lolli et al., 2005). Proteolysis may proceed by any of four distinct pathways that may exert a concerted attack on the MBP molecule, although the mechanisms responsible for the activation and regulation of these potential activities are not known. Thus, epitope generation may occur via:

1. autocatalytic cleavage of the MBP molecule (D'Souza et al., 2005);


The last mechanism, which has been demonstrated in a number of autoimmune pathologies, remains unproven for MS (Wentworth et al., 2001). These pathways are characterized by dramatic differences in reaction velocities and in cleavage site specificity. Obviously the rates of enzymatic reactions are several times higher than those for autocatalysis and Abenzymes (abzymes), perhaps making this pathway the major player in epitope generation. In the case of abzymes, the large excess of the biocatalyst, its high specificity, and its close compartmentalization with the MBP substrate shown in demyelinating lesions are suggestive of its likely effectiveness in vivo. (Ponomarenko et al., 2006; Genain et al., 1999)

Today, the advent of antibody catalysis has demonstrated that antibodies can be programmed to perform complex cell biochemistry, and thus a logical question arises: does the original (nature-gifted) potential for catalysis relate to antibody function? In the sense of the question, it is very interesting to consider the evolution of antibodies, while generally accepting that natural enzymes are primitive molecules compared with antibodies, and that antibodies arose just after the birth of enzymes.

A great deal of evidence has been also adduced to support the medical concept of the *living soul* of abzymes and their significance for utilizing broader autoantibodies properties in the formation of pathogenic patterns and clinical settings at different autoimmune and other conditions. Moreover, the medical concept of abzymes was tested in two ways, clinically and experimentally, i.e., on human and animal models. The progress achieved earlier in designing artificial abzymes initiated the study of biological activities of natural catalytic autoantibodies and their involvement in pathogenesis of major clinical disorders, i.e., evoked the onset of the era of medical abzymology. (Suchkov et al., 2001; Zhou et al., 2002; Tellier, 2002; Nathan, 2002; Kozyr et al., 1998)

Medical abzymology has made a great contribution to the development of general autoimmunity theory: it has put the antibody as a *functional entity* and as the key brick of the theory to the level of *physiological functionality* by providing such antibody with the ability to catalyze and mediate direct and independent cytotoxic effect on cellular and molecular targets.
