Naive T lymphocytes chemotax long distance to CCL21 but not to a source of bioactive S1P

Naive T lymphocytes traffic through the organism in search for antigen, alternating between blood and secondary lymphoid organs. Lymphocyte homing to lymph nodes relies on CCL21 chemokine sensing by CCR7 receptors, while exit into efferent lymphatics relies on sphingolipid S1P sensing by S1PR1 receptors. While both molecules are claimed chemotactic, a quantitative analysis of naive T lymphocyte migration along defined gradients is missing. Here, we used a reductionist approach to study the real-time single-cell response of naive T lymphocytes to CCL21 and serum rich in bioactive S1P. Using microfluidic and micropatterning ad hoc tools, we show that CCL21 triggers stable polarization and long-range chemotaxis of cells, whereas S1P-rich serum triggers a transient polarization only and no significant displacement, potentially representing a brief transmigration step through exit portals. Our in vitro data thus suggest that naive T lymphocyte chemotax long distances to CCL21 but not toward a source of bioactive S1P.