B.3: Leukocyte Penetration of the Blood-Brain Barrier

Participants: Lydia Sorokin, Rupert Hallmann, Friedemann Kiefer, Michael Schäfers, Jan Vahrenhold, Dietmar Vestweber, Heinz Wiendl

The mammalian BBB is a highly specialized structure comprising endothelial cells interconnected by complex tight junctions plus a second barrier constituted by an ensheathing layer of astrocyte endfeet and an associated parenchymal BM. Hence, leukocyte penetration of the BBB not only requires transmigration of the endothelial barrier as in other inflamed tissues but also of the parenchymal BM and astrocyte endfeet. Studies in EAE have shown that migration across these two barriers involves distinct mechanisms that are independent of each other. We will examine the role of junctional molecules and the endothelial cell BM in endothelial transmigration and of MMP-2 and MMP-9 in the control of leukocyte infiltration into the CNS parenchyma. Different systemic and ex vivo models to study BBB transmigration and perivascular reactions (active and adoptive transfer EAE in transgenic mice, spontaneous CNS autoimmunity in opticospinal EAE) will be used and will be complemented by proof-of-concept studies in humans (MS patients, CNS/CSF specimens). 2-photon intravital microscopy and associated mathematical image analysis of leukocyte extravasation into the CNS in mice expressing fluorescently tagged endothelial contacts or endothelial BM proteins will permit temporo-spatial characterization of leukocyte migration into the CNS parenchyma. Injectable, labelled MMP-specific or leukocyte-specific probes will be employed in state-of-the-art whole-body animal imaging (SPECT, PET) to assess defined steps in the inflammatory cascade in murine EAE in vivo over time. These studies provide a direct translational link to development of diagnostic strategies for MS patients.