Fig. 4

Immune infiltrate in muscle tissue. HES staining and immunohistochemistry analysis on muscle biopsy frozen in isopentan. a HES staining at low (×100) and b moderate magnification (×200) showing an important inflammatory endomysial infiltrate. Images of myophagia are seen. c HLA class I (×100) and d HLA class II (×100) stainings show a diffuse pattern with strong sarcoplasmic membrane positivity. Lymphocytic infiltration was also assessed. e Some CD68 + histiocytes are seen (×200), while a predominant CD3 + lymphocyte infiltration (×100) was observed (f), consisting mostly of CD4 + (×100) (g) but few CD8 + lymphocytes (h ×100). i) to k) PD-L1 expression is shown at low (i ×100), moderate (j ×200) and high magnification (k ×400). PD-L1 was found to be expressed in the inflamed area, both on immune cells and myocytes