There is an endomysial inflammatory infiltrate with infiltration of non-necrotic fibres by lymphocytes (a, b, arrows). There is variation in fibre size and fibre necrosis (b, *). The lymphocytic infiltrate is composed predominantly of T-cells (c) and these can be confirmed to have invaded viable fibres (d, arrow). MHC class I is expressed on the sarcolemma and often in the sarcoplasm of fibres (e). (a, b): Haematoxylin and eosin; (c, d): CD3 immunohistochemistry; (e): MHC class I immunohistochemistry. Bar in (a) represents 50 μm in (a, c, e) and 25 μm in (b, d) (Image courtesy of Zane Jaunmuktane and Sebastian Brandner)