Fig. 5

a Marked CD4+ lymphocytic infiltrates (red) within myofibers of horse 1, an E321G MYH1 homozygote. IHC × 20. b Serial section to c demonstrating inflammatory cell infiltrates (arrows) in horse 1. HE × 20. c Serial section to b demonstrating that fibers infiltrated by lymphocytes (vertical arrows) are 2X fibers (red) and that some fibers with cellular infiltrates (horizontal arrows) do not have any remaining myosin staining. IF × 20. d Serial section to e from horse 2 showing inflammatory cells (arrows). HE × 10. e Serial section to D demonstrating a complete absence of 2X fibers. Dark regions with no staining (arrows) correspond to regions of inflammation in D. IF × 10. f Normal fiber type distribution and fiber sizes in another homozygous wild-type horse for comparison. IF × 20. g Section of muscle from horse 3 that had a 4-month history of IMM showing a small amount of inflammatory cell infiltrates. HE × 10. h Another section of horse 3 demonstrating atrophic type 2X fibers (brown). IF × 10. i Preponderance of type 2A (yellow) or 2AX fibers (intermediate) over type 2X fibers (brown) in another region of the sample from horse 3. IF × 10. j Normal fiber type distribution of muscle from a wild-type horse (type 1 blue, type 2A yellow, type 2X brown) showing type 2X fibers that are larger than type 2A fibers. IF × 10. k Normal fiber type distribution and fiber sizes in the semimembranosus muscle that lacks inflammation from horse 4 that was homozygous for the E321G variant. IF × 20. Bars in all figures represents 100 μm