HLA-DR expression and C5b-9 deposition in ASM and DM. A-F: Regular myofiber HLA-DR expression in perifascicular areas in ASM (A, C-F) contrasting with the lack or very few number of positive myofibers in DM (B); positive staining of endomysial vessels (arrows) is physiological (C). G, H: C5b-9 deposition observed at the surface of perifascicular myofibers in ASM (G) and in endomysial vessel walls (arrows) in DM (H). I, J: Percentage of HLA-DR-positive myofibers (I) and of contiguous HLA-DR-positive perifascicular myofibers (J) in ASM and DM. K: Percentages of cases with presence of C5b-9 deposition at the surface of non-necrotic myofibers in ASM and DM. (*) indicates p < 0.05.Frozen sections (A-H); immunoperoxidase technique for HLA-DR (A-F) and C5b-9 (G, H).