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Migration toward chemoattractants is a hallmark of T-cell trafficking and is essential to produce an efficient immune response. Here, we have analyzed the function of the Rac activator Tiam1 in the control of T-cell trafficking and transendothelial migration. We found that Tiam1 is required for chemokine- and S1P-induced Rac activation and subsequent cell migration. As a result, Tiam1-deficient T cells show reduced chemotaxis in vitro, and impaired homing, egress, and contact hypersensitivity in vivo. Analysis of the T-cell transendothelial migration cascade revealed that PKCzeta/Tiam1/Rac signaling is dispensable for T-cell arrest but is essential for the stabilization of polarization and efficient crawling of T cells on endothelial cells. T cells that lack Tiam1 predominantly transmigrate through individual endothelial cells (transcellular migration) rather than at endothelial junctions (paracellular migration), suggesting that T cells are able to change their route of transendothelial migration according to their polarization status and crawling capacity.

Original publication




Journal article



Publication Date





6138 - 6147


Animals, Brain, Cell Adhesion, Chemotaxis, Leukocyte, Endothelium, Vascular, Flow Cytometry, Guanine Nucleotide Exchange Factors, Immunoblotting, Lysophospholipids, Mice, Mice, Knockout, Phosphorylation, Protein Kinase C-delta, Signal Transduction, Sphingosine, T-Lymphocytes, T-Lymphoma Invasion and Metastasis-inducing Protein 1, rac GTP-Binding Proteins