What is the role of humoral immunity to the pathophysiology of sporadic inclusion body myositis (s-IBM)?

Updated: Jun 08, 2018
  • Author: Michael P Collins, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Humoral immunity may also play a role in the pathogenesis of s-IBM. Microarray studies have shown that many of the highest differentially expressed genes in s-IBM are immunoglobulin (Ig) genes. Indeed, Ig gene transcripts are expressed to a much greater degree in s-IBM and polymyositis than in dermatomyositis. [18, 19] Although B cells are rarely encountered in s-IBM muscle, plasma cells occur in the endomysium of patients with s-IBM in numbers 4 times higher than B cells. [8] Moreover, an analysis of antigen receptor H chain gene transcripts of B and plasma cells isolated from s-IBM muscle showed evidence of clonal expansion and variation, isotype switching, and somatic hypermutation, indicative of a local antigen-driven humoral response. [20]

Additional evidence for a primary immune etiology includes the fact that as many as 20-33% of patients with s-IBM have a concomitant systemic or neurologic autoimmune disease. [21, 22] Monoclonal gammopathies are identified with increased frequency in patients with s-IBM compared to age-related controls. [23] In addition, s-IBM is known to occur in association with chronic viral infections known to produce immune dysregulation (eg, HIV, human T-cell lymphotrophic virus I [HTLV-I], and hepatitis C). [24, 25, 26, 27]


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