In the present study we found that: 1) CD4+ T-cell activity to myelin basic protein (MBP) in untreated MS patients was associated with decreased expression of IFN-β-inducible genes in PBMCs; 2) IFN-β-treated MS patients had decreased CD4+ T-cell activity to MBP; 3) IFN-β-treated MS patients had increased expression of IL10 and IL27 in monocytes in vivo; and 4) monocytes had immunoregulatory effects, and exogenous and endogenous IL-10 inhibited antigen-specific CD4+ T-cells activation in vitro. The gene discussed is IL10; the disease is myeloid sarcoma.