Lymphatic vessel dysfunction contributes to severe dengue pathogenesis
Dengue virus (DENV) infection is a major global health threat, affecting more than half of the worlds population. Severe dengue is a life-threatening condition characterised by systemic bleeding, vascular leakage, and interstitial fluid accumulation that can progress to hypovolaemic shock. Circulating DENV non-structural protein 1 (NS1) has long been implicated in driving vascular hyperpermeability through its disruptive effects on endothelial cell junctions and the glycocalyx. The lymphatic system, which runs alongside the vascular network, plays a critical role in resorbing and recirculating interstitial fluid and immune cells extravasated from blood vessels. Despite its importance in maintaining tissue fluid homeostasis, the impact of dengue disease on lymphatic vessels has not previously been explored. Here, we present the first evidence that DENV-2 NS1 induces marked hyperpermeability in lymphatic endothelial cells, as measured by transendothelial electrical resistance, and impairs lymphangiogenesis in vitro. These effects were not attributable to changes in cell viability, morphology, or metabolic activity, as assessed by live/dead and metabolic assays and image analysis. Instead, we observed a defect in lymphatic endothelial cell migration, measured by scratch assay, which may underlie the reduced lymphangiogenic potential. Bulk RNA-seq, immunocytochemistry, and advanced image analysis further demonstrated pronounced reorganisation of cell-cell junctions, the cytoskeleton, and focal adhesions. Notably, junctional proteins including VE-cadherin, ZO-1, and Claudin-5 were not downregulated but instead displayed disorganised distribution along the cell junctions or aberrant cytoplasmic localisation. These structural disruptions became even more pronounced under flow conditions produced using a microfluidic system. Together, these findings demonstrate for the first time that DENV-2 NS1 directly disrupts lymphatic endothelial cell function, leading to junctional disorganisation and hyperpermeability. Such impairment of lymphatic drainage may contribute to the pathophysiology of severe dengue. Author SummaryDengue is a rapidly expanding mosquito-borne disease that now affects many tropical and subtropical regions worldwide. Severe cases can lead to extensive fluid leakage from blood vessels, which causes tissue swelling and, in the most dangerous situations, shock. Although much research has focused on how dengue damages the blood vascular system, almost nothing is known about its impact on the lymphatic system, which is responsible for removing fluid from tissues and returning it to the bloodstream. Because both systems work together to maintain fluid balance, understanding how dengue affects lymphatic vessels is important for explaining why fluid accumulation becomes so severe in critical disease. In our study, we examined whether the viral protein NS1, which circulates during infection, directly affects the cells that line lymphatic vessels. We found that NS1 increases the permeability of these cells and reduces their ability to form new vessel structures. These effects were not caused by cell death but by disruptions in how the cells organise their junctions, internal scaffolding, and interactions with neighbouring cells. By showing that NS1 can directly impair lymphatic vessel function, our work identifies a previously overlooked mechanism that may contribute to fluid build-up in severe dengue and suggests new avenues for future therapeutic research.