Inherent biomechanical traits enable infective filariae to disseminate through collecting lymphatic vessels.

Filariases are diseases caused by arthropod-borne filaria nematodes. The related pathologies depend on the location of the infective larvae when their migration, the asymptomatic and least studied phase of the disease, comes to an end. To determine factors assisting in filariae dissemination, we image Litomosoides sigmodontis infective larvae during their escape from the skin. Burrowing through the dermis filariae exclusively enter pre-collecting lymphatics by mechanical disruption of their wall. Once inside collectors, their rapid and unidirectional movement towards the lymph node is supported by the morphology of lymphatic valves. In a microfluidic maze mimicking lymphatic vessels, filariae follow the direction of the flow, the first biomechanical factor capable of helminth guidance within the host. Finally, non-infective nematodes that rely on universal morpho-physiological cues alone also migrate through the dermis, and break in lymphatics, indicating that the ability to spread by the lymphatic route is an ancestral trait rather than acquired parasitic adaptation.

Experimental Drainage Device to Reduce Lymphoedema in a Rat Model.

OBJECTIVE: Despite recent advances in pharmacological research and microsurgery, lymphoedema remains an incurable disease that deeply affects quality of life. There is an urgent need for innovative approaches to restore continuous lymph flow in affected tissues. To this end, the efficacy of a subcutaneously implanted draining device in reducing lymphoedema volume in a rat hindlimb lymphoedema model was tested. METHODS: A rat model of chronic lymphoedema was developed by surgical removal of popliteal and inguinal lymph nodes, followed by irradiation. The model was characterised by monitoring limb volume via tape measure, skin water content via dielectric constant measurement, and lymphatic drainage via lymphofluoroscopy. After lymphoedema establishment in 16 Wistar rats, a device made of fenestrated tubing equipped with a miniaturised pumping system, was implanted subcutaneously in the affected limb to restore continuous recirculation of interstitial fluid. RESULTS: Lymphofluoroscopy imaging showed impaired lymphatic drainage following lymphadenectomy and irradiation. Affected limb volume and skin water content increased significantly compared with the untreated limb, with a median (interquartile range) of 3.85 (0.38) cm3 versus 3.03 (0.43) cm3 for volume (n = 16, p = .001) and 26.6 (9.1) versus 16.6 (3.7) cm3 for skin dielectric constant (n = 16, p = .001). Treatment of lymphoedema with the implanted drainage device showed that 5 weeks post-implant excess volume was significantly reduced by 51 ± 18% compared with the pre-implant situation (n = 9 sham group, n = 7 pump group). CONCLUSION: Lymphoedema volume in the rat model was significantly reduced by restoring continuous drainage of excess fluid using a novel subcutaneously implanted device, opening the way to the development of an artificial lymphatic vessel.

Transcellular Pathways in Lymphatic Endothelial Cells Regulate Changes in Solute Transport by Fluid Stress.

RATIONALE: The transport of interstitial fluid and solutes into lymphatic vessels is important for maintaining interstitial homeostasis and delivering antigens and soluble factors to the lymph node for immune surveillance. Transendothelial transport across lymphatic endothelial cells (LECs) is commonly considered to occur paracellularly, or between cell-cell junctions, and driven by local pressure and concentration gradients. However, emerging evidence suggests that LECs also play active roles in regulating interstitial solute balance and can scavenge and store antigens, raising the possibility that vesicular or transcellular pathways may be important in lymphatic solute transport. OBJECTIVE: The aim of this study was to determine the relative importance of transcellular (vesicular) versus paracellular transport pathways by LECs and how mechanical stress (ie, fluid flow conditioning) alters either pathway. METHODS AND RESULTS: We demonstrate that transcellular transport mechanisms substantially contribute to lymphatic solute transport and that solute uptake occurs in both caveolae- and clathrin-coated vesicles. In vivo, intracelluar uptake of fluorescently labeled albumin after intradermal injection by LECs was similar to that of dermal dendritic cells. In vitro, we developed a method to differentially quantify intracellular solute uptake versus transendothelial transport by LECs. LECs preconditioned to 1 µm/s transmural flow demonstrated increased uptake and basal-to-apical solute transport, which could be substantially reversed by blocking dynamin-dependent vesicle formation. CONCLUSIONS: These findings reveal the importance of intracellular transport in steady-state lymph formation and suggest that LECs use transcellular mechanisms in parallel to the well-described paracellular route to modulate solute transport from the interstitium according to biomechanical cues.

Fibronectin binding modulates CXCL11 activity and facilitates wound healing.

Engineered biomatrices offer the potential to recapitulate the regenerative microenvironment, with important implications in tissue repair. In this context, investigation of the molecular interactions occurring between growth factors, cytokines and extracellular matrix (ECM) has gained increasing interest. Here, we sought to investigate the possible interactions between the ECM proteins fibronectin (FN) and fibrinogen (Fg) with the CXCR3 ligands CXCL9, CXCL10 and CXCL11, which are expressed during wound healing. New binding interactions were observed and characterized. Heparin-binding domains within Fg (residues 15-66 of the ß chain, Fg ß15-66) and FN (FNI1-5, but not FNIII12-14) were involved in binding to CXCL10 and CXCL11 but not CXCL9. To investigate a possible influence of FN and Fg interactions with CXCL11 in mediating its role during re-epithelialization, we investigated human keratinocyte migration in vitro and wound healing in vivo in diabetic db/db mice. A synergistic effect on CXCL11-induced keratinocyte migration was observed when cells were treated with CXCL11 in combination with FN in a transmigration assay. Moreover, wound healing was enhanced in full thickness excisional wounds treated with fibrin matrices functionalized with FN and containing CXCL11. These findings highlight the importance of the interactions occurring between cytokines and ECM and point to design concepts to develop functional matrices for regenerative medicine.

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

Dendritic cell (DC) homing to the lymphatics and positioning within the lymph node is important for adaptive immunity, and is regulated by gradients of CCL19 and CCL21, ligands for CCR7. Despite the importance of DC chemotaxis, it is not well understood how DCs interpret gradients of these chemokines in a complex 3D microenvironment. Here, we use a microfluidic device that allows rapid establishment of stable gradients in 3D matrices to show that DC chemotaxis in 3D can respond to CCR7 ligand gradients as small as 0.4%, which helps explain how DCs sense lymphatic vessels in an environment where broadcast distance for chemokine diffusion is hindered by convective flows into the vessel. Interestingly, DCs displayed similar sensitivities to both chemokines at small gradients (≤ 60 nM/mm), but migrated more efficiently towards higher gradients of CCL21, which unlike CCL19 binds strongly to matrix proteoglycans and signals without the need for internalization. Furthermore, cells preferentially migrated towards CCL21 when exposed to equal and opposite gradients of CCL21 and CCL19 simultaneously, even when matrix-binding of CCL21 was prevented. Although these ligands have similar binding affinity to CCR7, our results demonstrate that, in a 3D environment, CCL21 is a more potent directional cue for DC migration than CCL19. These findings provide new quantitative insight into DC chemotaxis in a physiological 3D environment and suggest how CCL19 and CCL21 may signal differently to fine-tune DC homing and positioning within the lymphatic system. These results also have broad relevance to other systems of cell chemotaxis, which remain poorly understood in the 3D context.