Immobilized Chemokine Fields and Soluble Chemokine Gradients Cooperatively Shape Migration Patterns of Dendritic Cells

Abstract

Chemokines orchestrate immune cell trafficking by eliciting either directed or random migration and by activating integrins in order to induce cell adhesion. Analyzing dendritic cell (DC) migration, we showed that these distinct cellular responses depended on the mode of chemokine presentation within tissues. The surface-immobilized form of the chemokine CCL21, the heparan sulfate-anchoring ligand of the CC-chemokine receptor 7 (CCR7), caused random movement of DCs that was confined to the chemokine-presenting surface because it triggered integrin-mediated adhesion. Upon direct contact with CCL21, DCs truncated the anchoring residues of CCL21, thereby releasing it from the solid phase. Soluble CCL21 functionally resembles the second CCR7 ligand, CCL19, which lacks anchoring residues and forms soluble gradients. Both soluble CCR7 ligands triggered chemotactic movement, but not surface adhesion. Adhesive random migration and directional steering cooperate to produce dynamic but spatially restricted locomotion patterns closely resembling the cellular dynamics observed in secondary lymphoid organs.

Dendritic cell chemotaxis in 3D under defined chemokine gradients reveals differential response to ligands CCL21 and CCL19

“…3B) for CCL21, but not for CCL19, suggesting that cells may be more adaptable to varying CCL19 levels than to CCL21. The higher adaptability to CCL19 vs. CCL21 levels could have implications for long-range signaling, because CCL19 concentrations strongly vary between tissues (42, 43) and its relatively non-matrix-binding characteristics imply shallower gradients over longer distances, while matrixbound CCL21 gradients are more strongly localized to lymphatic vessels and the T cell zone of the lymph node (14).…”

“…Because the cells may have experienced different signaling from bound vs. soluble chemokines (14), we next asked whether the CCL21 needed to be matrix-bound to drive preferential DC chemotaxis. MG provides many more binding sites for CCL21 compared to type I collagen, we repeated the experiment in MG-free matrix and still found a strong chemotactic preference for CCL21 (Fig.…”

“…Specifically, the positively charged C terminus of CCL21 gives it strong binding affinity to a wide range of proteoglycans [as well as type IV collagen (10)], unlike CCL19 (11)(12)(13). Additionally, matrix-bound CCL21 can activate DC and T cell adhesion to adhesion ligands like ICAM-1 (14,15). This study addresses the question of how DCs respond to gradients of CCR7 ligands in 3D environments-in particular, whether they differentiate between soluble vs. matrix-bound signals, and the relative importance of gradient steepness vs. average concentration.…”

Role of Lymphatic Vessels in Tumor Immunity: Passive Conduits or Active Participants?

“…Lymph enters the subcapsular sinus of the draining LN through afferent vessels and moves through the medullary sinus via a network of conduits, formed by follicular dendritic cells in the B cell zone and fibroblastic reticular cells (FRCs) in the T cell zone, prior to leaving the LN via efferent vessels [56,57]. FRCs express podoplanin (gp38) and the CCR7 ligands, CCL21 and CCL19; CCL21 is readily immobilized into the proteoglycan components of the extracellular matrix to form solid-phase gradients upon which DCs and T cells migrate [58,59].…”

Recent Developments in Electrotaxis Assays

“…Some examples include effective neutrophil navigation in coexisting chemical gradient arrays 16 ; dendritic cell migration guided by coexisting soluble and surface-bound chemokine gradients. 17 In wound healing, a combination of dcEF, chemical gradients, and other cues provide coexisting guiding environments to direct the migration of relevant cell types at the wound. Interestingly, dcEF was suggested to override other guiding cues to direct cell migration in wound healing.…”