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Are linear AChR epitopes the real culprit in ocular myasthenia gravis?
Wu, Xiaorong; Tüzün, Erdem.
Afiliação
  • Wu X; Department of Ophthalmology, First Affiliated Hospital, Nanchang University, Nanchang 330006, PR China.
  • Tüzün E; Department of Neuroscience, Institute for Experimental Medical Research, Istanbul University, Istanbul 34390, Turkey. Electronic address: drerdem@yahoo.com.
Med Hypotheses ; 99: 26-28, 2017 Feb.
Article em En | MEDLINE | ID: mdl-28110692
Extraocular muscle weakness occurs in most of the myasthenia gravis (MG) patients and it is often the initial complaint. Approximately 10-20% of MG patients with extraocular muscle weakness display only ocular symptoms and rest of the patients subsequently develop generalized muscle weakness. It is not entirely clear why some MG patients develop only ocular symptoms and why extraocular muscle weakness almost always precedes generalized muscle weakness. These facts are often explained by increased susceptibility of extraocular muscles due to their reduced endplate safety factor and lower complement inhibitor expression. Findings of a recently developed animal model of ocular MG suggest that additional factors might be in play. While immunization of HLA transgenic and wild-type (WT) mice with the native acetylcholine receptor (AChR) pentamer carrying conformational epitopes generates severe generalized muscle weakness, immunization of the same mouse strains with recombinant unfolded AChR subunits containing linear epitopes induces ptosis with or without mild generalized muscle weakness. Notably, immunization of mice with deficient T helper cell-mediated antigen presentation with recombinant AChR subunits or whole native AChR pentamer also induces ocular symptoms, AChR-reactive B cells and AChR antibodies. Based on these findings, we hypothesize that ocular symptoms observed in the earlier stages of MG might be triggered by linear and non-conformational AChR epitopes expressed by thymic cells or invading microorganisms. This initial AChR autoimmunity might be managed by T cell-independent and B cell mediated mechanisms yielding low affinity AChR antibodies. These antibodies are putatively capable of inducing muscle weakness only in extraocular muscles which have increased vulnerability due to their inherent biological properties. After this initial attack, as AChR bearing immune complexes form and the immune system gains access to the native AChR expressed by muscle and thymic myoid cells, a more robust anti-AChR autoimmunity develops giving way to high affinity AChR antibodies, thymic germinal center formation and severe generalized muscle weakness. Accurate characterization of chain if events leading to ocular and generalized symptoms in MG might enable development of novel therapeutics that might prevent the transition from mild ocular symptoms to severe generalized weakness in earlier stages of the disease.
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Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Receptores Colinérgicos / Debilidade Muscular / Miastenia Gravis / Epitopos Tipo de estudo: Etiology_studies / Prognostic_studies Limite: Animals / Humans Idioma: En Revista: Med Hypotheses Ano de publicação: 2017 Tipo de documento: Article País de publicação: Estados Unidos

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Receptores Colinérgicos / Debilidade Muscular / Miastenia Gravis / Epitopos Tipo de estudo: Etiology_studies / Prognostic_studies Limite: Animals / Humans Idioma: En Revista: Med Hypotheses Ano de publicação: 2017 Tipo de documento: Article País de publicação: Estados Unidos