Complement membrane attack complex is related with immune-mediated necrotizing myopathy

Abstract

This study is to investigate the expression of complement membrane attack complex (C5b-9) in the skeletal muscle of patients with necrotizing myopathy (NM), and to investigate the relationship between C5b-9 and NM. Thirteen patients with NM and control patients with polymyositis and muscular dystrophy were enrolled in this study. Examinations including creatine kinase (CK) and L-lactate dehydrogenase (LDH) in the serum, electromyogram and muscle pathological examination were performed. C5b-9 expression in the skeletal muscle was determined by immunohistochemistry and analyzed by Image Plus Pro 6.0. C5b-9 expression was particularly prominent in necrotic muscle fibers, and also positive in blood vessels. C5b-9 diffusely expressed in vascular endothelial cells and smooth muscle layer. But the intensity was not related with the elevated level of serum CK. So, C5b-9 is strongly expressed in the necrotic muscle fiber and blood vessels, and may contribute to the pathogenesis of NM.

Keywords: C5b-9; Necrotizing myopathy; complement membrane attack complex; endothelial cell; muscle fiber.

Figure 1

Immunohistochemical staining of C5b-9, C5b-9 was strongly expressed in the membrane and endochylema of necrotic muscle fibers and some non-necrotic muscle fibers (A and B, ×200). A large quantity of C5b-9 stongly expressed capillaries (C, ×200). C5b-9 strongly expressed in the small artery wall’s vascular endothelial cell layer and smooth muscle layer (D, ×400). Remarkable deposition of C5b-9 in the vessel wall of small vein (E, ×400).

Figure 2

Immunohistochemical staining of C5b-9, the number of positive muscle cells (yellow granulation in cell membrane or endochylema) in the inflammatory myopathies group except necrotizing myopathy (B, ×200) and muscular dystrophy group (C, ×200) were less observed than that in necrotizing myopathy patients (A, ×200). In necrotizing myopathy patients, the numbers of C5b-9 positive cells were significantly higher.

Figure 3

Immunohistochemical staining of C5b-9 of muscle tissues. NM: necrotizing myopathy group (n = 13), IM: inflammatory myopathies group, excluding necrotizing myopathy (n = 6), MD: muscular dystrophy group (n = 5). Muscular cells containing yellow granulation (arrow showing) in the cell membrane and endochylema, or yellow color of vascular intima were considered as C5b-9 positive reactions. The C5b-9 positive areas increased in the NM group in comparison to IM group and MD group. Data are expressed as means ± SD. P = 0.038 < 0.05 in comparison to IM group, P = 0.013 < 0.05 in comparison to MD group.