Autoimmune diseases molecular mimicry

The mechanism most commonly invoked to explain the association of infection with autoimmune disease is molecular mimicry that is, the concept that antigens (or more properly, epitopes) of the microorganism closely resemble self-antigens.50 The induction of an immune response to the microbial antigen thus results in cross-reactivity with selfantigens and the induction of autoimmunity. Although epitope specific cross-reactivity has been shown in some animal models,48,51 53 molecular mimicry is clearly demonstrated to be the causative mechanism in few, if any, human diseases.3 54,55... 

There is considerable interest in the role of infectious agents in the development of autoimmune diseases. Some of this interest is based on the concept of molecular mimicry as a causal mechanism. Molecular mimicry refers to the possible pathologic role of cross-reactive antibodies or T cells to a self-antigen that is structurally similar to, and thus shares epitopes with, a viral or other infectious agent. For most autoimmune diseases, however, evidence of molecular mimicry leading to disease is not conclusive.1819 Viruses and other infections also have a less-specific immune effect, stimulating toll-like receptors and proinflammatory cytokine secretion, which is another mechanism that has been postulated to influence autoimmune disease risk.20... 

Bystander activation activation of autoreactive cells through nonspecific inflammation and induction of inflammatory cytokines and chemokines is also of pathological consequence in MS. It has been suggested that bystander activation, induced by persistent virus infection or primed by molecular mimicry may activate autoreactive T-cells specific for the CNS (McCoy et al., 2006). Einally, cryptic antigens may also play a role in immune activation. In other immune-mediated diseases such as Chronic Lymphocytic Thyroiditis and Chagas Heart Disease, exposure of cryptic epitopes leads to the activation of autoimmune cells and further contributes to... 

Le vin MC, Lee SM, Kalume L, Morcos Y, Dohan PC, Jr., Hasty KA, Callaway JC, Zunt J, Desiderio D, Stuai t JM (2002b) Autoimmunity due to molecular mimicry as a cause of neui ological disease. Nat Med 8 509-513. 

Nevertheless, the potential for autoimmune disease would clearly exist if one considers the polyspecificity of immune recognition molecules such as B cell receptors, antibodies, T cell receptors and MHC molecules. Further, the polyspecificity of immune receptors is also able to transcend the biochemically defined classes of biomolecules. For instance, the monoclonal antibody SYA/J6 has been demonstrated to have a dual specificity, binding a specific carbohydrate or a specific peptide with comparable affinity.68 Detailed analysis of the interatomic interactions between the antibody combining site and either the carbohydrate or the peptide antigens demonstrated that functional mimicry is possible without exact structural mimicry. This example underlines the case that it is not possible to predict with certainty whether the molecular surfaces of all potentially cross-reactive epitopes, whether of foreign or self molecules, will, or will not, be able to bind to a specific antibody. 

Autoimmune disease can also arise from a foreign substance possessing an epitope very similar to an epitope that is found on a host molecule. This situation, termed molecular mimicry, is the cause of post-streptococcal rheumatic fever because an epitope on the streptococcal M protein elicits formation antibody that reacts with an epitope on myosin. 

Oldstone MB (1987) Molecular mimicry and autoimmune disease. Cell, 50 819-820. 

Oldstone, M. B. (1989) Molecular mimicry as a mechanism for the cause and a probe uncovering etiologic agent(s) of autoimmune disease. Curr. Top. Microbiol. Immunol. 145,127-35. 

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