IL1B and major depressive disorder: Interestingly, it was found that an increasing number of OPCs and remyelination are usually observed in focal areas infiltrated with activated T cells in MDD patients [187–189], indicating that high expression of CCL-2, IL-33, IL-1β and MMP9 in OPCs possibly participates in the modulation of immunoactivity and is involved in CNS repair processes [190–192].