The Lymphatic Fluid

Same yet different - how lymph node heterogeneity affects immune responses

Lymph nodes are secondary lymphoid organs in which immune responses of the adaptive immune system are initiated and regulated. Distributed throughout the body and embedded in the lymphatic system, local lymph nodes are continuously informed about the state of the organs owing to a constant drainage of lymph. The tissue-derived lymph carries products of cell metabolism, proteins, carbohydrates, lipids, pathogens and circulating immune cells. Notably, there is a growing body of evidence that individual lymph nodes differ from each other in their capacity to generate immune responses. Here, we review the structure and function of the lymphatic system and then focus on the factors that lead to functional heterogeneity among different lymph nodes. We will discuss how lymph node heterogeneity impacts on cellular and humoral immune responses and the implications for vaccination, tumour development and tumour control by immunotherapy.

Nutrition in chronic inflammatory conditions: Bypassing the mucosal block for micronutrients

Nutritional Immunity is one of the most ancient innate immune responses, during which the body can restrict nutrients availability to pathogens and restricts their uptake by the gut mucosa (mucosal block). Though this can be a beneficial strategy during infection, it also is associated with non-communicable diseases-where the pathogen is missing; leading to increased morbidity and mortality as micronutritional uptake and distribution in the body is hindered. Here, we discuss the acute immune response in respect to nutrients, the opposing nutritional demands of regulatory and inflammatory cells and particularly focus on some nutrients linked with inflammation such as iron, vitamins A, Bs, C, and other antioxidants. We propose that while the absorption of certain micronutrients is hindered during inflammation, the dietary lymph path remains available. As such, several clinical trials investigated the role of the lymphatic system during protein absorption, following a ketogenic diet and an increased intake of antioxidants, vitamins, and minerals, in reducing inflammation and ameliorating disease.

Role of the Renal Lymphatic System in Heart Failure

PURPOSE OF REVIEW

The lymphatic system plays a major but overlooked role in maintaining fluid homeostasis. Given the unique fluid homeostasis functions of the kidneys, dysregulation of the renal lymphatic system underlies the development of self-propagating congestive pathomechanisms. In this review, we outline the roles of the renal lymphatic system in heart failure (HF).

RECENT FINDINGS

Studies have uncovered several pathomechanisms involving the renal lymphatic system in congestive states, such as impaired interstitial draining by the renal lymphatic system, impaired structure and valves of renal lymphatics, lymphatic-induced increase in renal reabsorption of water and sodium, and development of albuminuria with proteinuria-induced renal lymphangiogenesis. These self-propagating mechanisms result in "renal tamponade" with manifestations of cardiorenal syndrome and inappropriate renal response to diuretics. Dysregulation of the renal lymphatic system is integral to the development and progression of congestion in HF. Targeting renal lymphatics may provide a novel pathway to treat intractable congestion.

Treatment experience in a patient of complex regional pain syndrome combined with secondary lymphedema of lower extremity

BACKGROUND

Lymphedema is characterized by localized tissue swelling due to excessive interstitial space retention of lymphatic fluid. Lymphedema is easy to be misdiagnosed since itresembles other conditions of extremity swelling. We present a case of complex regionalpain syndrome (CRPS) type I with secondary lymphedema that was successfully managedwith spinal cord stimulation (SCS).

CASE

A 39-year-old female patient came to our pain clinic with complaints of lower extremity pain and edema. To find out reason of leg edema, computed tomography of extremity angiography and blood test were performed. However, all of evaluations were normal. Lastlyperformed lymphoscintigraphy showed secondary lymphedema. SCS was performed and itshowed dramatic reduction subsequent to implantation of SCS.

CONCLUSIONS

We could successfully manage the intractable pain and edema in CRPS combined with lymphedema. If a patient presents different nature of edema, coexistence of other disease needs to be considered.

Physiology of Glymphatic Solute Transport and Waste Clearance from the Brain

This review focuses on the physiology of glymphatic solute transport and waste clearance, using evidence from experimental animal models as well as from human studies. Specific topics addressed include the biophysical characteristics of fluid and solute transport in the central nervous system, glymphatic-lymphatic coupling, as well as the role of cerebrospinal fluid movement for brain waste clearance. We also discuss the current understanding of mechanisms underlying increased waste clearance during sleep.

Evaluation of Sirolimus Dosing in Neonates and Infants With Lymphatic Disorders: A Case Series

OBJECTIVE

Literature in pediatric patients suggests dosing sirolimus 1.6 mg/m2/day divided twice daily for lymphatic disorders with limited evidence available for dosing in neonates and infants. The objective of this research was to determine the sirolimus dose required to achieve therapeutic trough concentrations in infants with lymphatic disorders at Children's Hospital of Philadelphia.

METHODS

This retrospective review included patients <1 year of age at Children's Hospital of Philadelphia who were initiated on sirolimus for lymphatic disorder. Patients were included if they received at least 5 days of consecutive sirolimus therapy prior to trough concentration monitoring. Measures of central tendency and variability were used for statistical analysis.

RESULTS

A total of 16 patients met criteria for inclusion. The median initial sirolimus dose was 1 mg/m2/day (IQR, 0.5-1.6 mg/m2/day). Fourteen patients (87.5%) achieved therapeutic trough concentrations on a median sirolimus dose of 0.5 mg/m2/day. Dosing frequency to achieve therapeutic trough concentrations included 1 patient (6.25%) on twice daily dosing, 12 patients (75%) on once daily dosing, and 1 patient (6.25%) requiring every 48-hour dosing. The median time to first therapeutic trough was 15.5 days (IQR, 5.5-18.5 days), and patients required a median of 1 dose adjustment.

CONCLUSIONS

A median sirolimus dose to achieve therapeutic sirolimus trough concentrations in infants with lymphatic disorders was 0.5 mg/m2/day with a median of 1 dose adjustment. Sirolimus was well tolerated in the study population.

Fluid transport in the brain

The brain harbors a unique ability to, figuratively speaking, shift its gears. During wakefulness, the brain is geared fully toward processing information and behaving, while homeostatic functions predominate during sleep. The blood-brain barrier establishes a stable environment that is optimal for neuronal function, yet the barrier imposes a physiological problem; transcapillary filtration that forms extracellular fluid in other organs is reduced to a minimum in brain. Consequently, the brain depends on a special fluid [the cerebrospinal fluid (CSF)] that is flushed into brain along the unique perivascular spaces created by astrocytic vascular endfeet. We describe this pathway, coined the term glymphatic system, based on its dependency on astrocytic vascular endfeet and their adluminal expression of aquaporin-4 water channels facing toward CSF-filled perivascular spaces. Glymphatic clearance of potentially harmful metabolic or protein waste products, such as amyloid-β, is primarily active during sleep, when its physiological drivers, the cardiac cycle, respiration, and slow vasomotion, together efficiently propel CSF inflow along periarterial spaces. The brain's extracellular space contains an abundance of proteoglycans and hyaluronan, which provide a low-resistance hydraulic conduit that rapidly can expand and shrink during the sleep-wake cycle. We describe this unique fluid system of the brain, which meets the brain's requisites to maintain homeostasis similar to peripheral organs, considering the blood-brain-barrier and the paths for formation and egress of the CSF.

The Lymphatic System in Breast Cancer: Anatomical and Molecular Approaches

Breast cancer is one of the most important causes of premature mortality among women and it is one of the most frequently diagnosed tumours worldwide. For this reason, routine screening for prevention and early diagnosis is important for the quality of life of patients. Breast cancer cells can enter blood and lymphatic capillaries, then metastasizing to the regional lymph nodes in the axilla and to both visceral and non-visceral sites. Rather than at the primary site, they seem to enter the systemic circulation mainly through the sentinel lymph node and the biopsy of this indicator can influence the axillary dissection during the surgical approach to the pathology. Furthermore, secondary lymphoedema is another important issue for women following breast cancer surgical treatment or radiotherapy. Considering these fundamental aspects, the present article aims to describe new methodological approaches to assess the anatomy of the lymphatic network in the axillary region, as well as the molecular and physiological control of lymphatic vessel function, in order to understand how the lymphatic system contributes to breast cancer disease. Due to their clinical implications, the understanding of the molecular mechanisms governing lymph node metastasis in breast cancer are also examined. Beyond the investigation of breast lymphatic networks and lymphatic molecular mechanisms, the discovery of new effective anti-lymphangiogenic drugs for future clinical settings appears essential to support any future development in the treatment of breast cancer.

Important Role of Concomitant Lymphangiogenesis for Reparative Angiogenesis in Hindlimb Ischemia

[Figure: see text].

Endogenous Mobilization of Mesenchymal Stromal Cells: A Pathway for Interorgan Communication?

To coordinate specialized organs, inter-tissue communication appeared during evolution. Consequently, individual organs communicate their states via a vast interorgan communication network (ICN) made up of peptides, proteins, and metabolites that act between organs to coordinate cellular processes under homeostasis and stress. However, the nature of the interorgan signaling could be even more complex and involve mobilization mechanisms of unconventional cells that are still poorly described. Mesenchymal stem/stromal cells (MSCs) virtually reside in all tissues, though the biggest reservoir discovered so far is adipose tissue where they are named adipose stromal cells (ASCs). MSCs are thought to participate in tissue maintenance and repair since the administration of exogenous MSCs is well known to exert beneficial effects under several pathological conditions. However, the role of endogenous MSCs is barely understood. Though largely debated, the presence of circulating endogenous MSCs has been reported in multiple pathophysiological conditions, but the significance of such cell circulation is not known and therapeutically untapped. In this review, we discuss current knowledge on the circulation of native MSCs, and we highlight recent findings describing MSCs as putative key components of the ICN.

Pancreas Optical Clearing and 3-D Microscopy in Health and Diabetes

Although first described over a hundred years ago, tissue optical clearing is undergoing renewed interest due to numerous advances in optical clearing methods, microscopy systems, and three-dimensional (3-D) image analysis programs. These advances are advantageous for intact mouse tissues or pieces of human tissues because samples sized several millimeters can be studied. Optical clearing methods are particularly useful for studies of the neuroanatomy of the central and peripheral nervous systems and tissue vasculature or lymphatic system. Using examples from solvent- and aqueous-based optical clearing methods, the mouse and human pancreatic structures and networks will be reviewed in 3-D for neuro-insular complexes, parasympathetic ganglia, and adipocyte infiltration as well as lymphatics in diabetes. Optical clearing with multiplex immunofluorescence microscopy provides new opportunities to examine the role of the nervous and circulatory systems in pancreatic and islet functions by defining their neurovascular anatomy in health and diabetes.

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.

Age-related decline of lymphatic drainage from the eye: A noninvasive in vivo photoacoustic tomography study

We aim to determine whether lymphatic drainage from the eye changes with age. Using quantitative photoacoustic tomography, groups of young and older mice were studied in the live state. 10 CD-1 mice of 2-3 months (5M/5F) were studied in addition to 13 older mice of 12-13 months (6M/7F). In each of 23 mice, near-infrared tracer (a near-infrared dye, QC-1 conjugated with Bovine Serum Albumin) was injected into the right eye, and imaging of ipsilateral cervical lymph nodes was performed with laser pulses at 11 different wavelengths prior to and 20 min, 2, 4 and 6 h after injection. Mean pixel intensities (MPIs) of nodes were calculated at each imaging session. The areas under the curves (AUC) were calculated for both groups of mice and compared using the t-test. The slopes of MPI of each region of interest were compared using the linear mixed model before and after adjusting for sex, body weight and intraocular pressure of the right eye. The mean intraocular pressure of right eyes before injection was similar in older and younger groups (12.77 ± 2.01 mmHg and 12.90 ± 2.38 mmHg, respectively; p = 0.888). In each mouse, the photoacoustic signal was detected in the right cervical lymph nodes at the 2-h time point following tracer injection into the right eye. At the 4 and 6 h imaging times, a steady increase of tracer signal was observed. Areas under the curve in the right cervical nodes were decreased significantly in older mice compared to younger mice (p = 0.007). The slopes of MPI in the nodes were significantly decreased in old mice compared to young mice both before and after adjusting for sex, body weight and intraocular pressure of the right eye (p = 0.003). In conclusion, lymphatic drainage from the eye is significantly reduced in older eyes. This finding suggests that impaired lymphatic clearance of aqueous humor, proteins and antigens from the eye may contribute to age-related disease of the eye such as glaucoma and inflammatory eye disease.

Lymphatic system identification, pathophysiology and therapy in the cardiovascular diseases

The mammalian circulatory system comprises both the cardiovascular system and the lymphatic system. In contrast to the closed, high-pressure and circular blood vascular circulation, the lymphatic system forms an open, low-pressure and unidirectional transit network from the extracellular space to the venous system. It plays a key role in regulating tissue fluid homeostasis, absorption of gastrointestinal lipids, and immune surveillance throughout the body. Despite the critical physiological functions of the lymphatic system, a complete understanding of the lymphatic vessels lags far behind that of the blood vasculatures due to the challenge of their visualization. During the last 20 years, discoveries of underlying genes responsible for lymphatic vessel biology, combined with state-of-the-art lymphatic function imaging and quantification techniques, have established the importance of the lymphatic vasculature in the pathogenesis of cardiovascular diseases including lymphedema, obesity and metabolic diseases, dyslipidemia, hypertension, inflammation, atherosclerosis and myocardial infraction. In this review, we highlight the most recent advances in the field of lymphatic vessel biology, with an emphasis on the new identification techniques of lymphatic system, pathophysiological mechanisms of atherosclerosis and myocardial infarction, and new therapeutic perspectives of lymphangiogenesis.