ISG15 and myeloid sarcoma: We also found evidence of basal expression of ISG15 in Purkinje neurons in cerebellum that was unchanged in MS (MS = 4.776 ± 0.113; Control = 4.607 ± 0.393; Additional file 7: Fig. S6a, b); however, rare ISG15 + axon fibers within cerebellar white matter tracts were exclusively found in MS patients (arrows Additional file 7: Fig. S6b).