Live-Cell Microscopy Reveals That Human T Cells Primarily Respond Chemokinetically Within a CCL19 Gradient That Induces Chemotaxis in Dendritic Cells.

Evert J Loef,P Rod Dunbar,Nigel P Birch,Hilary M Sheppard

doi:10.3389/fimmu.2021.628090

Abstract

The ability to study migratory behavior of immune cells is crucial to understanding the dynamic control of the immune system. Migration induced by chemokines is often assumed to be directional (chemotaxis), yet commonly used end-point migration assays are confounded by detecting increased cell migration that lacks directionality (chemokinesis). To distinguish between chemotaxis and chemokinesis we used the classic “under-agarose assay” in combination with video-microscopy to monitor migration of CCR7+ human monocyte-derived dendritic cells and T cells in response to a concentration gradient of CCL19. Formation of the gradients was visualized with a fluorescent marker and lasted several hours. Monocyte-derived dendritic cells migrated chemotactically towards the CCL19 gradient. In contrast, T cells exhibited a biased random walk that was largely driven by increased exploratory chemokinesis towards CCL19. This dominance of chemokinesis over chemotaxis in T cells is consistent with CCR7 ligation optimizing T cell scanning of antigen-presenting cells in lymphoid tissues.

Highlights

Cell migration is a key process in a myriad of physiological functions [1]
At one-hour post addition of CCL19 and dextrans, a “wave” of monocyte-derived dendritic cells (mDCs) migrating out of the well and going under the agar can be observed. This matches the visualized diffusion of the fluorescent dextrans, which reached the mDCs in the middle well in the agar at that time
The increased directional migration of the mDCs compared to the control condition lacking CCL19 (Supplementary Video 2) lasted for up to six hours, gradually getting less directional as the steepness of the gradient decreases over time, again matching the gradient as visualized by the dextrans

Summary

Introduction

Cell migration is a key process in a myriad of physiological functions [1]. Homing of both T cells and dendritic cells to lymph nodes is largely dependent on activation of the chemokine receptor CCR7 [1]. The CCR7 ligand CCL19 is considered to be strongly chemotactic for both T cells and dendritic cells (DCs), potentially driving their co-localization. Intra-vital microscopy in mice has revealed that migration of T cells within lymph nodes does not have strong features of directional chemotaxis [3]. Understanding how CCL19 might act through the same receptor to generate different types of migratory behavior in T cells and DCs is central to understanding the dynamic control of T cell responses

Methods

Results

Conclusion