CIITA and primary progressive multiple sclerosis: Consistent with recent reports that OL lineage cells acquire inflammatory and immunomodulatory function when exposed to stress/inflammatory conditions (Kirby et al., 2019; Fernandez-Castaneda et al., 2020; Harrington et al., 2020; Madsen et al., 2020; Desu et al., 2021; Kirby and Castelo-Branco, 2021), our screen showed dysregulated expression of genes associated with immune activation in PPMS OLs, including HLA-B, HLA-DRA, and CIITA, all important for antigen presentation.