Regulation of Immune Function by the Lymphatic System in Lymphedema

Lymphatic dysfunction in advanced cirrhosis: Contextual perspective and clinical implications

The lymphatic system plays a very important role in body fluid homeostasis, adaptive immunity, and the transportation of lipid and waste products. In patients with liver cirrhosis, capillary filtration markedly increases, primarily due to a rise in hydrostatic pressure, leading to enhanced production of lymph. Initially, lymphatic vasculature expansion helps to prevent fluid from accumulating by returning it back to the systemic circulation. However, the lymphatic functions become compromised with the progression of cirrhosis and, consequently, the lymphatic compensatory mechanism gets overwhelmed, contributing to the development and eventual worsening of ascites and edema. Neurohormonal changes, low-grade chronic inflammation, and compounding effects of predisposing factors such as old age, obesity, and metabolic syndrome appear to play a significant role in the lymphatic dysfunction of cirrhosis. Sustained portal hypertension can contribute to the development of intestinal lymphangiectasia, which may rupture into the intestinal lumen, resulting in the loss of protein, chylomicrons, and lymphocyte, with many clinical consequences. Rarely, due to high pressure, the rupture of the subserosal lymphatics into the abdomen results in the formation of chylous ascites. Despite being highly significant, lymphatic dysfunctions in cirrhosis have largely been ignored; its mechanistic pathogenesis and clinical implications have not been studied in depth. No recommendation exists for the diagnostic evaluation and therapeutic strategies, with respect to lymphatic dysfunction in patients with cirrhosis. This article discusses the perspectives and clinical implications, and provides insights into the management strategies for lymphatic dysfunction in patients with cirrhosis.

Emerging roles for lymphatics in acute kidney injury: Beneficial or maleficent?

Acute kidney injury, a sudden decline in renal filtration, is a surprisingly common pathology resulting from ischemic events, local or systemic infection, or drug-induced toxicity in the kidney. Unchecked, acute kidney injury can progress to renal failure and even recovered acute kidney injury patients are at an increased risk for developing future chronic kidney disease. The initial extent of inflammation, the specific immune response, and how well inflammation resolves are likely determinants in acute kidney injury-to-chronic kidney disease progression. Lymphatic vessels and their roles in fluid, solute, antigen, and immune cell transport make them likely to have a role in the acute kidney injury response. Lymphatics have proven to be an attractive target in regulating inflammation and immunomodulation in other pathologies: might these strategies be employed in acute kidney injury? Acute kidney injury studies have identified elevated levels of lymphangiogenic ligands following acute kidney injury, with an expansion of the lymphatics in several models post-injury. Manipulating the lymphatics in acute kidney injury, by augmenting or inhibiting their growth or through targeting lymphatic-immune interactions, has met with a range of positive, negative, and sometimes inconclusive results. This minireview briefly summarizes the findings of lymphatic changes and lymphatic roles in the inflammatory response in the kidney following acute kidney injury to discuss whether renal lymphatics are a beneficial, maleficent, or a passive contributor to acute kidney injury recovery.

Lymphatic Proliferation Ameliorates Pulmonary Fibrosis after Lung Injury

Despite many reports about pulmonary blood vessels in lung fibrosis, the contribution of lymphatics to fibrosis is unknown. We examined the mechanism and consequences of lymphatic remodeling in mice with lung fibrosis after bleomycin injury or telomere dysfunction. Widespread lymphangiogenesis was observed after bleomycin treatment and in fibrotic lungs of prospero homeobox 1-enhanced green fluorescent protein (Prox1-EGFP) transgenic mice with telomere dysfunction. In loss-of-function studies, blocking antibodies revealed that lymphangiogenesis 14 days after bleomycin treatment was dependent on vascular endothelial growth factor (Vegf) receptor 3 signaling, but not on Vegf receptor 2. Vegfc gene and protein expression increased specifically. Extensive extravasated plasma, platelets, and macrophages at sites of lymphatic growth were potential sources of Vegfc. Lymphangiogenesis peaked at 14 to 28 days after bleomycin challenge, was accompanied by doubling of chemokine (C-C motif) ligand 21 in lung lymphatics and tertiary lymphoid organ formation, and then decreased as lung injury resolved by 56 days. In gain-of-function studies, expansion of the lung lymphatic network by transgenic overexpression of Vegfc in club cell secretory protein (CCSP)/VEGF-C mice reduced macrophage accumulation and fibrosis and accelerated recovery after bleomycin treatment. These findings suggest that lymphatics have an overall protective effect in lung injury and fibrosis and fit with a mechanism whereby lung lymphatic network expansion reduces lymph stasis and increases clearance of fluid and cells, including profibrotic macrophages.

3D Immunocompetent Organ-on-a-Chip Models

In recent years, engineering of various human tissues in microphysiologically relevant platforms, known as organs-on-chips (OOCs), has been explored to establish in vitro tissue models that recapitulate the microenvironments found in native organs and tissues. However, most of these models have overlooked the important roles of immune cells in maintaining tissue homeostasis under physiological conditions and in modulating the tissue microenvironments during pathophysiology. Significantly, gradual progress is being made in the development of more sophisticated microphysiologically relevant human-based OOC models that allow the studies of the key biophysiological aspects of specific tissues or organs, interactions between cells (parenchymal, vascular, and immune cells) and their extracellular matrix molecules, effects of native tissue architectures (geometry, dynamic flow or mechanical forces) on tissue functions, as well as unravelling the mechanism underlying tissue-specific diseases and drug testing. In this Progress Report, we discuss the different components of the immune system, as well as immune OOC platforms and immunocompetent OOC approaches that have simulated one or more components of the immune system. We also outline the challenges to recreate a fully functional tissue system in vitro with a focus on the incorporation of the immune system.

A dual compression system: preliminary clinical insights from the US

There is growing evidence on an interconnection between the venous and lymphatic systems in venous leg ulceration, and the possible effects of prolonged oedema and lymphatic impairment in delayed wound healing. Compression therapy is a widely accepted treatment for venous and lymphatic disorders, as it decreases recurrence rates and prolongs the interval between recurrences. Compression bandages improve venous return, increase the volume and rate of venous flow, reduce oedema and stimulate anti-inflammatory processes. The pressure at the interface (IP) of the bandage and the skin is related to the elastic recoil of the product used and its resistance to expansion. The pressure difference between the IP in the supine and standing positions is called the static stiffness index (SSI). Elastic materials provide little resistance to muscle expansion during physical activity, resulting in small pressure differences between resting and activity, with an SSI <10mmHg. Stiff, inelastic materials with a stretch of <100% resist the increase of muscle volume during physical activity, producing higher peak pressures, an SSI of >10mmHg and a greater haemodynamic benefit than elastic systems. UrgoK2 is a novel dual-layer high-compression system consisting of an inelastic (short stretch) and elastic (long stretch) bandage, resulting in sustained tolerable resting pressure and elevated working pressures over extended wear times. It is indicated for the treatment of active venous leg ulcers and the reduction of chronic venous oedema. Each bandage layer has a visual aid to enable application at the correct pressure level. Published European studies have assessed this compression system, exploring its consistency of application, tolerability and efficacy. This article presents the first reports of health professionals' clinical experience of using the compression system in the US, where it has been recently launched. Initial feedback is promising.

Emerging Roles of Mast Cells in the Regulation of Lymphatic Immuno-Physiology

Mast cells (MCs) are abundant in almost all vascularized tissues. Furthermore, their anatomical proximity to lymphatic vessels and their ability to synthesize, store and release a large array of inflammatory and vasoactive mediators emphasize their significance in the regulation of the lymphatic vascular functions. As a major secretory cell of the innate immune system, MCs maintain their steady-state granule release under normal physiological conditions; however, the inflammatory response potentiates their ability to synthesize and secrete these mediators. Activation of MCs in response to inflammatory signals can trigger adaptive immune responses by dendritic cell-directed T cell activation. In addition, through the secretion of various mediators, cytokines and growth factors, MCs not only facilitate interaction and migration of immune cells, but also influence lymphatic permeability, contractility, and vascular remodeling as well as immune cell trafficking through the lymphatic vessels. In summary, the consequences of these events directly affect the lymphatic niche, influencing inflammation at multiple levels. In this review, we have summarized the recent advancements in our understanding of the MC biology in the context of the lymphatic vascular system. We have further highlighted the MC-lymphatic interaction axis from the standpoint of the tumor microenvironment.

The Role of Lymphatic Vascular Function in Metabolic Disorders

In addition to its roles in the maintenance of interstitial fluid homeostasis and immunosurveillance, the lymphatic system has a critical role in regulating transport of dietary lipids to the blood circulation. Recent work within the past two decades has identified an important relationship between lymphatic dysfunction and patients with metabolic disorders, such as obesity and type 2 diabetes, in part characterized by abnormal lipid metabolism and transport. Utilization of several genetic mouse models, as well as non-genetic models of diet-induced obesity and metabolic syndrome, has demonstrated that abnormal lymphangiogenesis and poor collecting vessel function, characterized by impaired contractile ability and perturbed barrier integrity, underlie lymphatic dysfunction relating to obesity, diabetes, and metabolic syndrome. Despite the progress made by these models, the contribution of the lymphatic system to metabolic disorders remains understudied and new insights into molecular signaling mechanisms involved are continuously developing. Here, we review the current knowledge related to molecular mechanisms resulting in impaired lymphatic function within the context of obesity and diabetes. We discuss the role of inflammation, transcription factor signaling, vascular endothelial growth factor-mediated signaling, and nitric oxide signaling contributing to impaired lymphangiogenesis and perturbed lymphatic endothelial cell barrier integrity, valve function, and contractile ability in collecting vessels as well as their viability as therapeutic targets to correct lymphatic dysfunction and improve metabolic syndromes.

Characteristics and outcomes of lymphaticovenular anastomosis in older patients with bilateral involvement versus younger patients with unilateral involvement in lower extremity lymphedema

OBJECTIVE

We have previously reported that patients with idiopathic primary lymphedema of adult onset can be classified into an older group with bilateral involvement and a younger group with unilateral involvement and that there are significant differences in the characteristics of these groups. The aims of this study were to investigate the features of these two groups further by evaluating the lymphatics while performing lymphaticovenular anastomosis (LVA) and to compare the effectiveness of LVA between the two groups.

METHODS

This study enrolled 74 patients (136 edematous legs) in whom indocyanine green (ICG) lymphography and LVA were performed. The rate of detection and the diameter of the lymphatic vessels were recorded. The lower extremity lymphedema index (the total sum of the squares of the circumference for five areas in each leg divided by the body mass index) was obtained before and 6 months after LVA. The rate of improvement in the affected lower limbs after LVA was also calculated.

RESULTS

The clinical lymphedema pattern was determined to be bilateral in 62 patients and unilateral in 12. Patients with bilateral lymphedema were significantly older than those with unilateral lymphedema (77.1 ± 7.8 years vs 55.5 ± 12.77 years; P < .01). A linear pattern was seen in 23 patients (46 legs), a low enhancement (LE) pattern in 12 patients (24 legs), a distal dermal backflow (dDB) pattern in 20 patients (40 legs), and an extended dermal backflow (eDB) pattern in 7 patients (14 legs). The lymphedema was unilateral in 12 patients (12 legs). There were significant between-group differences in lymphatic diameter in relation to lower leg area: linear (0.9 ± 0.1 mm) vs dDB (0.7 ± 0.2 mm), linear vs eDB (0.7 ± 0.2 mm), linear vs unilateral (0.5 ± 0.1 mm), LE (0.9 ± 0.2 mm) vs dDB, LE vs eDB, LE vs unilateral, and dDB vs unilateral, P < .01; and eDB vs unilateral, P < .05. There were also significant between-group differences in the rate of improvement in the lower extremity lymphedema index according to the ICG lymphography pattern and laterality: linear (10.5% ± 2.4%) vs unilateral (6.7% ± 0.6%), LE (10.4% ± 1.5%) vs unilateral, dDB (11.0% ± 1.3%) vs eDB (8.9% ± 1.5%), and dDB vs unilateral, P < .01; linear vs eDB, P < .05; and eDB vs unilateral, P < .05.

CONCLUSIONS

The lymphatic vessel diameter tended to be greater in older patients with bilateral lymphedema than in younger patients with unilateral lymphedema. The rate of detection and improvement tended to decrease with worsening of the ICG lymphography pattern. LVA is thought to be more effective in older patients with early-stage bilateral lower leg lymphedema than in their younger counterparts with late-stage unilateral lymphedema.

Molecular pathways involved in lymphedema: Hydroxytyrosol as a candidate natural compound for treating the effects of lymph accumulation

Lymphedema is a chronic accumulation of interstitial fluid due to inefficient lymph drainage. Major causes of lymphedema are malformations of lymphatic vessels, trauma, toxic damage and surgery. The swelling typically affects the limbs. Lymphedema may be primary, caused by genetic mutations and relatively rare, or secondary (acquired), due to external causes such as infections or surgery. Fluid accumulation induces pathological changes: activation of the inflammatory cascade, immune cell infiltration, tissue fibrosis, adipose accumulation. We focused on the inflammatory phenotype mediated by leukotriene B4, a lipid mediator of the inflammatory pathway, and the potential therapeutic effect of hydroxytyrosol. We conducted an electronic search in PubMed using "lymphedema", "lymphedema pathway", "hydroxytyrosol" as keywords. We found that lymphedema deregulates at least six molecular pathways and that hydroxytyrosol, a compound with antioxidant activity, can improve endothelial dysfunction, hemostatic and lipid profiles, and decrease oxidative stress and inflammation through inhibition of leukotriene B4 activity. This review is the first to highlight the possibility of using hydroxytyrosol to treat the secondary effects of lymphedema, especially inflammation. The possible effects of hydroxytyrosol on lymphedema should be tested in vitro and in vivo to find the best way to treat patients with lymphedema in order to improve their health status.

Opposing roles of endothelial and leukocyte-expressed IL-7Rα in the regulation of psoriasis-like skin inflammation

The interleukin 7 receptor alpha chain (IL-7Rα) is predominately expressed by lymphocytes, and activation by its ligand IL-7 supports the development and maintenance of T cells and boosts T-cell mediated immunity. We recently reported that lymphatic endothelial cells (LECs) in dermal lymphatics also express IL-7 and its receptor chains (IL-7Rα and CD132) and that IL-7 supports lymphatic drainage. This suggested that activation of IL-7Rα signaling in lymphatics could exert inflammation-resolving activity, by promoting the clearance of excess tissue fluid. Here we investigated how the potentially opposing effects of IL-7Rα signaling in immune cells and in the lymphatic vasculature would affect the development and progression of psoriasis-like skin inflammation. We found that during acute and chronic skin inflammation mice with an endothelial-specific deletion of IL-7Rα (IL-7Rα^ΔEC mice) developed more edema compared to control mice, as a consequence of impaired lymphatic drainage. However, systemic treatment of wild-type mice with IL-7 exacerbated edema and immune cell infiltration in spite of increasing lymphatic drainage, whereas treatment with IL-7Rα blocking antibody ameliorated inflammatory symptoms. These data identify IL-7Rα signaling as a new pathway in psoriasis-like skin inflammation and show that its pro-inflammatory effects on the immune compartment override its anti-inflammatory, drainage-enhancing effects on the endothelium.

[Lower limb lymphedema: A rare manifestation of spondyloarthropathy]

INTRODUCTION

Spondyloarthritis include articular (axial, peripheral or enthesitic) and extra-articular manifestations. We reported three cases of limb lymphedema associated with a spondyloarthritis.

CASE REPORTS

We report on two men and one female aged of 75, 52 and 39 years, respectively. The rheumatic disease was an ankylosing spondylitis HLA B27 positive in two patients and a psoriatic arthritis in the remaining one. Lymphedema, always unilateral, confirmed by the Stemmer's sign, involved the whole lower limb (n=2) or only the foot and calf (n=1). Lymphedema occurred 3 months, 40 and 9 years after the onset of spondyloarthritis. Lower limb lymphoscintigraphy was abnormal in all cases: decrease (n=2) or absence (n=1) of inguinal lymph node uptake, and visualization of the popliteal lymph node related to deep lymphatic pathway (n=1). Treatment of the spondyloarthritis did not improve lymphedema. Both the low-stretch bandage and elastic compression treatment allowed its reduction and stabilization.

CONCLUSION

Limb lymphedema is a rare extra-articular manifestation of spondyloarthritis. Its course appears to be independent of joint disease. Its management is specific and should be associated to that of the rheumatologic disorder.

Lymphedema microsurgery reduces the rate of implant removal for patients who have pre-existing lymphedema and total knee arthroplasty for knee osteoarthritis

INTRODUCTION

Patients with pre-existing lymphedema who undergo total knee arthroplasty (TKA) for osteoarthritis (OA) are at high risk for periprosthetic joint infection. This complication usually requires removal of the implant. This study aimed to investigate whether surgical treatment of lymphedema reduces the rate of prosthesis removal in such patients.

MATERIALS AND METHODS

We retrospectively reviewed our prospective database of patient information collected between January 2009 and December 2018. A total of 348 cases of lower extremity lymphedema were reviewed, and those who underwent total knee TKA for OA of the knee were included. Patient demographics, clinical data, lymphedema surgical history, and TKA surgical history including any episodes of removal were collected and analyzed.

RESULTS

There were nine of 15 lymphedema patients with knee OA who subsequently underwent TKA. The mean patient age was 70.4 ± 7.1 years. A total of 18 TKAs were performed in nine patients. The knee prosthesis removal rate was 66.7% (12/18). The prosthesis removal rate was 40% (2/5) in patients who underwent lymphedema microsurgery vs 76.9% (10/13) for those who did not (P = .03).

CONCLUSIONS

Pre-existing lymphedema is associated with a high rate of knee prosthesis removal. Lymphedema microsurgery reduced the removal rate of knee prostheses. We recommend that lymphedema microsurgery be considered for patients who require TKA as a treatment for of the knee.