CD4 and myeloid sarcoma: In this regard, key factors in the occurrence of relapse are thought to be autoreactivity of IL-17 expressing CD4+ T cells (i.e. T helper 17 cells (TH17)), CD4+ T helper 1 cells (Th1), CD8+ T cells and the insufficient function of regulatory T cells (T regs) [15–19], indicating that T cells are clearly important in MS pathogenesis.