Ragged-red fibres detected in paraffin sections by a monoclonal antibody to inner mitochondrial membrane

An immunohistochemical method is reported using the M-II68 monoclonal antibody, which detects mitochondrial accumulations (“ragged-red fibres”) in routinely processed (formalin-fixed, paraffin-embedded) muscle tissue. Ten cases with electron-microscopically and histochemically proven mitochondrial myopathy featured 4% to 24% ragged-red fibres. In a series of 50 muscle biopsies without mitochondrial myopathy, scattered ragged-red fibres (<0.1%) were present in a few normal and pathological muscles. The immunohistochemical method is specific for mitochondria, does not require frozen tissue and permits rapid examination of large areas.