Microfluidics for understanding basic aspects of directed immune cell migration and translational research

Abstract

Immune cell migration is essential for mounting protective immune responses, yet fundamental also to the pathogenesis of autoimmune diseases such as multiple sclerosis. Trafficking of immune cells is regulated by a complex interplay of chemokine receptors and chemokines. Advances in the field of microfluidics have expanded our possibilities to study chemotaxis – the directed migration towards soluble chemokines. Upon encounter of a danger signal, dendritic cells (DCs) maturate and upregulate among other processes the chemokine receptor CCR7 which enables homing of these cells to lymph nodes along gradients of immobilized CCL21. Chemotaxis of DCs has typically been linked to spatial sensing, with cells sensing concentration differences along their diameter. However, recent data suggest that DCs can also navigate by temporal sensing characterized by the detection of temporal changes of chemokine concentrations at specific subcellular sites. So far, no experimental systems have been available to ultimately test these two hypotheses. In this work, we aimed at assessing whether dendritic cells navigate by spatial or temporal sensing in gradients of soluble CCL19, the second ligand for CCR7. To this end, we established a microfluidic migration device which allowed us to expose dendritic cells to precisely controlled chemokine gradient scenarios and monitor cells by time-lapse microscopy including quantification of cell morphology. The gradient scenarios developed in this study were characterized by a sequence of reversing stable and dynamic chemokine gradients and the response to the second gradient was assessed. We observed that the majority of DCs migrating in a stable CCL19 gradient reoriented towards the opposite direction when the chemokine gradient was reversed. This was independent of the concentration of the second chemokine gradient and whether the second chemokine gradient was kept stable or was dynamically increased. These findings strongly suggest that dendritic cells have the capacity to navigate by spatial gradient sensing. Moreover, we observed that cell size as a simple, yet intriguing parameter is linked to the capacity to navigate in chemokine gradients. This finding that a measure of cell geometry is linked to cellular navigation is well compatible with the concept of spatial gradient sensing. In a second project we have established a workflow to assess the migration capacities of cells derived from clinical samples containing only a few hundred cells. This offers opportunities for translational research as for example the analysis of cell migration of cells derived from the cerebrospinal fluid of multiple sclerosis patients