Mechanisms of lymphocyte transmigration across the blood-brain barrier using an in vitro model that mimics blood flow and simulates inflammatory conditions as observed in the most frequent autoimmune disorder of the central nervous system, multiple sclero

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Multiple sclerosis (MS) is a common neurological disease with about 2,000,000 people affected worldwide. The infiltration of autoreactive immune cells into the central nervous system is a crucial step in its pathogenesis as these cells cause injury to the brain tissue. Proof of principle comes from drugs like Natalizumab that prevent immune cells from crossing the blood-brain barrier (BBB) and provide benefit for patients. However, the mechanisms of cell trafficking across the BBB remain incompletely resolved. The aim of the proposed project is to study cellular transmigration in more detail. For that purpose, Dr. Ransohoff and his team have developed an in vitro model of the BBB which represents the in vivo situation very well. It comprises a tight monolayer of human brain microvascular endothelial cells which is exposed to cytokines that simulate inflammation. Further, shear forces are incorporated to mimic physiological blood flow. Previous studies in the lab using this model revealed that monocytes, but not lymphocytes, adhered efficiently on the inflamed endothelium upon encounter with the chemokine CXCL12 although both cell types expressed the appropriate chemokine receptor CXCR4 (Man S et al., 2012). Unexpectedly, monocyte arrest gave rise to the transmigration of T and B cells. We hypothesize that monocyte-endothelial interactions promote secretion of factors (chemokines, cytokines, proteolytic enzymes) which render the endothelial surface permissive for interaction with lymphocytes. We will test this hypothesis and address related questions using our innovative flow-based in vitro BBB model. First, we will examine molecular modulations of the endothelium after monocyte arrest. Next, we will ask whether those monocyte-mediated changes of the endothelial surface promote lymphocyte transmigration. We also take into account that lymphocytes may be capable to transmigrate without the help of monocytes but in the presence of a chemokine that selectively signals to lymphocytes. We aim to identify such an arrest chemokine specific for lymphocytes in our project. In addition, video microscopy will be used in order to visualize and characterize kinetics of interactions between endothelium, monocytes and lymphocytes under flow. Results arising from that research may reveal new perspectives on the development of selective therapeutics that prevent infiltration of autoreactive immune cells in MS.