IFN-b treatment reduces the relapse rate in MS but its mechanism of action remains incompletely understood. Our aim was to clarify the beneficial effect of IFN-b in the treatment of MS. We assessed the influence of IFN-b treatment on (i) CD73 expression on the surface of primary cultures of human blood-brain barrier endothelial cells (BBB-EC) and human astrocytes using immunofluorescence staining and flow cytometry, (ii) transmigration of CD4 1 T lymphocytes using an in vitro model of BBB and (iii) CD73 enzyme activity, i.e. ecto-5 0 -nucleotidase activity in the serum of MS patients using a radiochemical assay. IFN-b increases the expression of ecto-5 0 -nucleotidase both on BBB-EC and astrocytes. As a consequence, lymphocyte transmigration through BBB-EC is reduced. Importantly, this reduction can be reversed using a,b-methyleneadenosine-5 0 -diphosphate, a specific inhibitor of ecto-5 0 -nucleotidase. CD73 is strongly expressed in microvasculature in samples of postmortem MS brain and, moreover, in the majority of MS patients there was a clear upregulation both in the soluble serum ecto-5 0 -nucleotidase activity and skin microvascular CD73 expression after IFN-b treatment. Upregulation of ecto-5 0 -nucleotidase and a subsequent increase in adenosine production might contribute to the beneficial effects of IFN-b on MS via enhancing the endothelial barrier function.Key words: Adenosine . Blood-brain barrier . CD73 . IFN-b . MS Introduction MS is a demyelinating disease characterized by perivascular inflammatory cell infiltrates in the white matter of the CNS. MS is generally thought to be an autoimmune disease in which the immune system attack against self-antigens results in inflammation and neurological symptoms [1]. First line treatment of MS is subcutaneous or intramuscular administration of IFN-b, which leads to a reduced number of relapses and a slower disease progression [2][3][4]. The proposed beneficial effects of IFN-b include a decrease in antigen presentation, MHC class II expression, T-cell proliferation, IFN-b production, ECM degradation, and the expression of adhesion molecules [5]. Moreover, recent reports describe IFN-b as a suppressor of both myeloid [6] and Th17-cells [7]. IFN-b also reduces the number of gadolinium enhancing lesions in brain magnetic resonance imaging of MS patients [2,3,8], which is thought to reflect its ability to regulate the blood-brain barrier (BBB) function [9]. Ecto-5 0 -nucleotidase (CD73; EC 3.1.3.5) is a 70 kDa GPI-anchored glycoprotein. It is abundantly expressed on vascular endothelium and subpopulations of lymphocytes, but not on granulocytes or monocytes [10] and it also circulates in blood in a soluble
2718form [11]. Ecto-5 0 -nucleotidase activity is found on many CNS cell types such as astrocytes, oligodendrocytes, microglial cells and brain EC in many species including human, rat, mouse and bovine [12][13][14][15]. CD73 modulates the extent of immune and inflammatory responses in vitro and in vivo. These effects are mediated via its enzymatic capability ...