Biologically stressed muscle fibers in sporadic IBM

Sporadic inclusion body myositis (sIBM) is a common form of idiopathic inflammatory myopathy in older patients.1 Its etiology remains elusive and immunomodulatory treatments in most cases do not lead to long-lasting and significant improvement of muscle strength.2 Several “alien” molecules are overexpressed in sIBM muscle fibers.3 Some of these are also found in excess in brains of Alzheimer patients.4 This prompted Banwell and Engel5 to investigate the possible overexpression of αB-crystallin (αBC) in muscle fibers of sIBM patients and in appropriate controls, as αBC is also overexpressed in astrocytes and microglial cells near senile plaques of Alzheimer brains.4 Banwell and Engel5 studied αBC expression by microscopic immunocytochemistry in transverse cryostat sections of muscle biopsies from 11 patients with sIBM, as well as from 50 disease controls and 4 normal controls. Various patterns of conspicuous overexpression of αBC were noted in various types of muscle fibers, including those that contained rimmed vacuoles, were partially invaded by CD8+ lymphocytes and macrophages, showed immunoreactivity with antibodies either to SMI-31 or ubiquitin, or showed Congo red positivity with red fluorescence. However, the most striking observation was that immunoreactive αBC was the most prevalent (2.6 to 19% of total fibers) in microscopically normal fibers (“X fibers”). Such fibers …