CD27 and myeloid sarcoma: The role of other peripheral blood (PB) immune cells in MS pathogenesis, such as naive B cells (CD19+IgD+CD27-), double negative B cells (CD19+IgD-CD27-) and follicular helper T cells (TFH; CD4+CD25-CD127+CXCR5+PD-1+), is still unclear.