Bcl-2, Bcl-x, and Bax Expression by Immunohistochemistry in Inclusion Body Myositis

Context.—Bcl-2, Bcl-x, and Bax are among the variety of proteins that have been described as being involved in the regulation of apoptotic cell death. Bcl-2 and Bcl-xL inhibit apoptosis, and Bax is proapoptotic. Objective.—To evaluate the expression of Bcl-2, Bcl-x, and Bax in inclusion body myositis (IBM). Design.—We examined muscle specimens from 27 patients (17 men, 10 women) with IBM to evaluate Bcl-2, Bcl-x, and Bax expression by immunohistochemistry. Results.—Patient ages ranged from 29 to 80 years (mean 62.2 years). All biopsies were marked by endomysial chronic inflammation, muscle fiber necrosis, and regeneration. Rimmed (autophagic) vacuoles were present in all cases. Ragged red fibers were noted in 4 biopsies (15%), and cytochrome oxidase–deficient fibers were found in 10 biopsies (37%). Ultrastructural evidence of intranuclear or cytoplasmic tubulofilamentous inclusions, confirming the diagnosis of IBM, were noted in all cases. Paracrystalline mitochondrial inclusions were seen in 5 biopsies (18.5%). Inflammatory cells stained positively with Bcl-2 in all biopsies, Bax in 26 biopsies (96%), and Bcl-x in 8 biopsies (30%). Degenerating muscle fibers were highlighted with Bax in 24 biopsies (89%), Bcl-2 in 2 biopsies (7%), and Bcl-x in 3 biopsies (11%). Regenerative muscle fibers were noted to stain with Bax in 24 muscles (89%), Bcl-2 in 21 muscles (78%), and Bcl-x in 4 muscles (15%). Rimmed vacuoles were highlighted by Bax in 24 biopsies (89%) and only rarely by Bcl-2 (n = 2, 7%) and Bcl-x (n = 3, 11%). A subsarcolemmal staining pattern was observed in 21 biopsies (78%) with Bax, 6 biopsies (22%) with Bcl-2, and only 1 biopsy (4%) with Bcl-x. Conclusions.—(1) Bax (proapoptotic) immunostaining highlighted most autophagic vacuoles; (2) subsarcolemmal Bax and Bcl-2 immunoreactivity may be associated with mitochondrial defects that are commonly noted in IBM; (3) Bcl-2 and Bax immunoreactivity were not confined to degenerating muscle fibers and in fact appeared to be expressed more commonly in regenerating fibers, suggesting that their expression may be independent of apoptosis in the setting of IBM.