Multiple sclerosis (MS) is the most common autoimmune inflammatory demyelinating disorder of the human nervous system affecting nearly 1 million people worldwide every year. Current treatments for first-line nontoxic therapy of the relapsing-remitting form of the disease are two forms of recombinant IFN(3, Ia and 1(3 andglatiramèr acetate. The pathogenesis of MS is highlighted by an inflammatory response and myelin destruction. Several recent studies have reported alterations in immune variables such as cytokine concentrations, immune-related molecules such as MHC and adhesion molecules and chemokines; which may contribute to an imbalance between Thi and Th2 T cellmediated immune response. The aims of the present study were to characterize the cytokinetic profile of MS patients through investigating the secretion of the main pro and anti-inflammatory cytokines from peripheral blood mononuclear cells of MS patients compared to controls, and to investigate cytokine receptor expression levels in T and NK cells. In addition, the induction of apoptosis and the involvement of adhesion molecules and metalloproteinases in oligodendrocyte destruction are examined. Finally, the effect of IFN(3 treatment on cytokine secretion levels as well as on the aforementioned immunoregulatory molecules was evaluated. The study population consisted of 60 MS patients (20 untreated, 20 treated with IFNf3-lcz and 20 treated with IFN(3-1(3) in parallel with 25 controls. Serumlplasma samples and peripheral blood mononuclear cells (PBMCs) were isolated from each participant. Using the enzyme linked immunospot (ELISPOT) assay the numbers of cytokine-secreting PBMCs were measured for the following cytokines: IFN-y, TNF-a, IL- 12, IL- 10 and IL-4. The expression levels of the cytokine receptors IL- 1 2R(3 1, IFN-y, IL- 1 OR, TNFaR were estimated in the surface of lymphocytes using flow cytometry and serum levels of soluble CD95, ICAM- 1, VCAM-1, metalloproteinase-9 (MMP-9) and the tissue inhibitor, metalloproteinase-1 (TIMP-1) were evaluated in all samples. The ELISPOT assay proved a very sensitive and valuable tool for characterisation of the cytokine profile of MS patients. Decreased numbers of PBMCs secreting IL-b 0 and IL-4, and increased numbers of PBMCs secreting TNF-a, IL-12 and IFN-y were observed in MS patients compared to healthy controls. Treatment with IFN(3 elevated IL-IO and IL-4 levels, and decreased TNF-a, IL-12 and IFN-y levels in these patients. IFN(3/lci was more efficient in decreasing IL-12 secreting cells and IFN(3/1(3 in decreasing IFN-y, and TNF-a secreting cells and elevating IL-4 and IL- 10 secreting cells Increased expression of IL-12Rj31 and TNF-aR was observed in NK cells and decreased expression of WN-7R and IL-I OR was shown in T cells of MS patients compared to controls. IFNf3 therapy reduced IL-12R(3l levels in I and NK cells (IFNf3-la was more effective), and TNF-uR levels in I cells (IFNj3- 1(3 was more effective), but it increased IFN-1R and IL-1OR in T and NK cells of MS patients. Increased levels of the soluble CD95 apoptosis marker were observed in serum of MS patients compared to controls, which further increased after IFN(3 treatment (IFN(3-10 was more efficient). Increased levels of soluble ICAM-1 and VCAM-1 were observed in serum of MS patients compared to controls, which were further increased after treatment with IFN(3 (IFN-1a was more efficient in increasing sICAM-1 and IFNI3-113 in increasing sVCAM- 1 levels) Increased levels of MMP-9, decreased levels of TIMP- 1, and increased MMP-9ITIMP- I ratio was found in serum of MS patients compared to controls, and treatment with IFN decreased MMP-9 levels, increased TIMP-1 levels and decreased MMP-9/TIMP-1 levels ITCXTII 1.. 4'P + tss i,p s a ,lvaS it"j*.. These results indicate an over expression of Thi type cytokines in MS accompanied by a concomitant suppression of Th2 type immune response as well as by alterations in the expression of cytokine receptors. A consequent activation of other immunoregulatory elements (sCD95, adhesion molecules, metalloproteinases) was also observed which was partly modified by IFNI3 treatment. This study provides important evidence on the role of cytokines and of other inflammatory molecules in MS pathogenesis and highlights possible mechanisms of action of IFNI3 treatment, offering new perspectives for novel, more efficient, diagnostic, and therapeutical approaches for the disease.