Immune Response in Deep Cervical Lymph Nodes and Spleen in the Mouse after Antigen Deposition in Different Intracerebral Sites

Brain interstitial and cerebrospinal fluid drainage into the lymphatics was studied by injections of 5 microliters of packed sheep red blood cells (SRBC) injected into the caudate nucleus, the occipital lobe, and the lateral ventricle of the brain in mice. The number of plaque-forming cells (PFC) was determined in the deep cervical lymph nodes, the axillary lymph nodes, and the spleen, and the number of PFC was compared with the response in the same tissues after intravenous immunization with 0.1 ml 10% SRBC. The weight of the deep cervical lymph nodes increased 3.0 times on day 3 after injection in the brain parenchyma compared with the weight of these nodes after intravenous immunization. The antigen-specific response peaked on day 5, 392 +/- 37 PFC/10(6) for IgG in the deep cervical lymph nodes after antigen deposition in the caudate nucleus, whereas only a minor peak in the antigen-specific response was obtained after intraventricular antigen deposition, 127 +/- 79 PFC x 10(6) for IgG on day 6. There were no increased PFC in any of the lymph nodes after intravenous immunization. The experiments show an antigen-specific response in the deep cervical lymph nodes after intracerebral antigen deposition, whereas antigens deposited in the lateral ventricles drain preferentially to the blood, with a high response in the spleen.     

Drainage of Brain Extracellular Fluid into Blood and Deep Cervical Lymph and its Immunological Significance

Cerebral extracellular fluids drain from brain to blood across the arachnoid villi and to lymph along certain cranial nerves (primarily olfactory) and spinal nerve root ganglia. Quantification of the connection to lymph in rabbit, cat and sheep, using radiolabelled albumin as a marker of flow, indicates that a minimum of 14 to 47% of protein injected into different regions of brain or cerebrospinal fluid passes through lymph. The magnitude of the outflow to lymph is at variance with the general assumption that the absence of conventional lymphatics from the brain interrupts the afferent arm of the immune response to brain antigens. The immune response to antigens (albumin or myelin basic protein) introduced into the central nervous system (CNS) has been analysed using a rat model with normal brain barrier permeability. The micro-injection of antigen into brain or cerebrospinal fluid elicits a humoral immune response, with antibody production in cervical lymph nodes and spleen, and also affects cell-mediated immunity. Furthermore, antigen may be more immunogenic when administered into the CNS than into conventional extracerebral sites. Clearly, the afferent arm of the immune response to antigens, within the CNS, is intact. Modern studies suggest that the efferent arm is also intact with passage of activated lymphocytes into the brain. Results support a new view of CNS immunology which incorporates continuous and highly regulated communication between the brain and the immune system in both health and disease.     

大鼠脑内大分子物质的引流通路及方法学研究

为探讨脑内大分子物质的引流通路,本研究微量注射示踪剂墨汁到大鼠右侧尾壳核,Ⅰ组动物使用传统的脑内注射方法,Ⅱ组动物采取改良方法防止示踪剂从进针处进入蛛网膜下腔,术后1、3、7、14、21 d处死动物,分别用肉眼、光镜及电镜观察墨汁在脑内、蛛网膜下腔、颈总动脉及颈部淋巴结的分布。结果显示:墨汁在两组动物脑实质内的分布趋势相同,即在白质内沿神经纤维弥漫性分布,7 d后在灰质内选择性地沿血管周围间隙分布,部分碳颗粒被管周细胞和巨噬细胞吞噬;Ⅱ组动物中观察到墨汁从大脑顶部进入蛛网膜下腔后沿其中的血管周围间隙分布并引流到脑的底部和嗅球及筛板区域,在耳蜗、前庭蜗神经和视神经等的脑神经鞘以及颈总动脉壁和颈部淋巴结有碳颗粒沉积;Ⅰ组动物没有这种分布。以上结果表明,大鼠脑实质内的大分子物质在白质和灰质中的引流方式不同;进入脑脊液的大分子物质可由颈部淋巴系统引流;墨汁不是很好的研究脑实质内大分子物质引流的示踪剂。     

Our current understanding of the lymphatics of the brain and spinal cord

The lymphatic system, segregated from the blood vascular system, is an essential anatomical route along which interstitial fluid, solutes, lipids, immune cells, and cellular debris, are conveyed. However, the way these mechanisms operate within the cranial compartment is mostly unknown. Herein, we review current understanding of the meningeal lymphatics, described anatomically over a century ago yet still poorly understood from a functional standpoint. We will delineate the cellular mechanisms by which the meningeal lymphatics are formed and discuss their unique anatomy. Furthermore, this review will discuss the recently‐coined “glymphatic system” and the manner by which cerebrospinal fluid (CSF) and interstitial fluid (ISF) are exchanged and thus drained by the meningeal lymphatic vasculature as a key route for conveying cellular waste, solutes, and immune traffic to the deep cervical lymph nodes. The clinical relevance of the meningeal lymphatics will also be described, as they are relevant to various common defects of the lymphatic system. Clin. Anat. 32:117–121, 2019. © 2018 Wiley Periodicals, Inc.     

Pathophysiology of the lymphatic drainage of the central nervous system: Implications for pathogenesis and therapy of multiple sclerosis

In most organs of the body, immunological reactions involve the drainage of antigens and antigen presenting cells (APCs) along defined lymphatic channels to regional lymph nodes. The CNS is considered to be an immunologically privileged organ with no conventional lymphatics. However, immunological reactions do occur in the CNS in response to infections and in immune-mediated disorders such as multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). Here, we review evidence that cervical lymph nodes play a role in B and T cell mediated immune reactions in the CNS. Then we define the separate pathways by which interstitial fluid (ISF) and CSF drain to cervical lymph nodes. ISF and solutes drain from the brain along the 100–150 nm-wide basement membranes in the walls of capillaries and arteries. In humans, this perivascular pathway is outlined by the deposition of insoluble amyloid (Aβ) in capillary and artery walls in cerebral amyloid angiopathy in Alzheimer's disease. The failure of APCs to migrate to lymph nodes along perivascular lymphatic drainage pathways may be a major factor in immunological privilege of the brain. Lymphatic drainage of CSF is predominantly through the cribriform plate into nasal lymphatics. Lymphatic drainage of ISF and CSF and the specialised cervical lymph nodes to which they drain play significant roles in the induction of immunological tolerance and of adaptive immunological responses in the CNS. Understanding the afferent and efferent arms of the CNS lymphatic system will be valuable for the development of therapeutic strategies for diseases such as MS.     

After injection into the striatum, in vitro-differentiated microglia- and bone marrow-derived dendritic cells can leave the central nervous system via the blood stream

The prototypic migratory trail of tissue-resident dendritic cells (DCs) is via lymphatic drainage. Since the central nervous system (CNS) lacks classical lymphatic vessels, and antigens and cells injected into both the CNS and cerebrospinal fluid have been found in deep cervical lymph nodes, it was thought that CNS-derived DCs exclusively used the cerebrospinal fluid pathway to exit from tissues. It has become evident, however, that DCs found in peripheral organs can also leave tissues via the blood stream. To study whether DCs derived from microglia and bone marrow can also use this route of emigration from the CNS, we performed a series of experiments in which we injected genetically labeled DCs into the striata of rats. We show here that these cells migrated from the injection site to the perivascular space, integrated into the endothelial lining of the CNS vasculature, and were then present in the lumen of CNS blood vessels days after the injection. Moreover, we also found these cells in both mesenteric lymph nodes and spleens. Hence, microglia- and bone marrow-derived DCs can leave the CNS via the blood stream.     

Th2-biased immune response in cervical lymph nodes: animal models of Graves' disease might administer autoantigen to body regions where lymphatics drain to cervical lymph nodes

It is believed that cervical lymph nodes have an important impact on Th2-biased immune response to central nervous system (CNS)-derived antigens. Obstruction of these nodes prior to a CNS-infusion of antigen markedly lowers the level of serum antibody response to the antigen. Graves' disease is a Th2-biased autoimmunity in which autoantibodies against thyrotropin receptor stimulate thyroid hormone production. The reasons for the distinct Th2-biased immune response in this hyperthyroidism are not fully understood, whereas most of the other human organ-specific autoimmune diseases are believed to be Th1 mediated. It is suggested that the drainage of the thyroid lymphatics to cervical lymph nodes may play a role in the Th2-polarized immune response of Graves' disease. Thus, the generation of Graves' disease models by immunization may become more feasible if animals are administered the autoantigen to body regions whose lymph is drained to cervical lymph nodes.     

Surgical excision of CNS‐draining lymph nodes reduces relapse severity in chronic‐relapsing experimental autoimmune encephalomyelitis

Despite lack of classical lymphatic vessels in the central nervous system (CNS), cells and antigens do reach the CNS‐draining lymph nodes. These lymph nodes are specialized to mediate mucosal immune tolerance, but can also generate T‐ and B‐cell immunity. Their role in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) therefore remains elusive. We hypothesized that drainage of CNS antigens to the CNS‐draining lymph nodes is vital for the recurrent episodes of CNS inflammation. To test this, we surgically removed the superficial cervical lymph nodes, deep cervical lymph nodes, and the lumbar lymph nodes prior to disease induction in three mouse EAE models, representing acute, chronic, and chronic‐relapsing EAE. Excision of the CNS‐draining lymph nodes in chronic‐relapsing EAE reduced and delayed the relapse burden and EAE pathology within the spinal cord, which suggests initiation of CNS antigen‐specific immune responses within the CNS‐draining lymph nodes. Indeed, superficial cervical lymph nodes from EAE‐affected mice demonstrated proliferation against the immunizing peptide, and the deep cervical lymph nodes, lumbar lymph nodes, and spleen demonstrated additional proliferation against other myelin antigen epitopes. This indicates that intermolecular epitope spreading occurs and that CNS antigen‐specific immune responses are differentially generated within the different CNS‐draining lymphoid organs. Proliferation of splenocytes from lymphadenectomized and sham‐operated mice against the immunizing peptide was similar. These data suggest a role for CNS‐draining lymph nodes in the induction of detrimental immune responses in EAE relapses, and conclusively demonstrate that the tolerance‐inducing capability of cervical lymph nodes is not involved in EAE. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Pathways of Fluid Drainage from the Brain - Morphological Aspects and Immunological Significance in Rat and Man

There is firm physiological evidence for the lymphatic drainage of interstitial fluid and cerebrospinal fluid from the brains of rats, rabbits and cats. The object of this review, is to describe firstly the morphological aspects of lymphatic drainage pathways from the rat brain and secondly, to explore through scanning and transmission electron microscope techniques, the possibility of similar lymphatic drainage pathways in man. Interstitial and oedema fluid spreads diffusely through the white matter in the rat and appears to drain into the ventricular cerebrospinal fluid. In grey matter, however, tracers pass along perivascular spaces to the surface of the brain and into the cerebrospinal fluid. Paravascular compartments in the subarachnoid space follow the course of major arterial branches to the circle of Willis and thence along the ethmoidal arteries to the cribriform plate of the ethmoid bone. Particulate tracers, such as Indian ink, enter channels in the arachnoid beneath the olfactory bulbs and connect directly with nasal lymphatics through channels which pass through holes in the cribriform plate. Proteins and other solutes may also drain along other cranial nerves. Thus, there is a bulk flow pathway for interstitial and cerebrospinal fluid from the rat brain into cervical lymphatics. In man, it is probable that diffuse interstitial drainage of fluid from the white matter occurs in a similar way to that in the rat. Furthermore, the anatomical pathways exist by which bulk drainage of fluid could occur along perivascular spaces from the grey matter into perivascular spaces of the leptomeningeal arteries and thence into the cerebrospinal fluid (CSF).(ABSTRACT TRUNCATED AT 250 WORDS)     

下颌下腺的淋巴流向

本文用5个月至足月胎儿的新鲜尸体50具:以淋巴管间接注射法,观察了下颌下腺的淋巴流向。6侧(6％)下颌下腺浅部和深部的淋巴先注入下颌下淋巴结。经下颌下淋巴结的输出管再注入颈深上淋巴结(颈二腹肌淋巴结,甲状淋巴结、颈肩胛舌骨肌淋巴结)。94侧(94％)下颌下腺浅部和深部的淋巴在直接注入下颌下淋巴结的同时,亦直接注入颈深上淋巴结,脊副淋巴结、锁骨上淋巴结,颈外侧浅淋巴结和颏下淋巴结;其中下颌下腺的淋巴直接回流至颈外侧浅淋巴结和颌下淋巴结尚未见报道。     

Update on the current knowledge of lymphatic drainage system and its emerging roles in glioma management

The draining of brain interstitial fluid (ISF) to cerebrospinal fluid (CSF) and the subsequent draining of CSF to meningeal lymphatics is well-known. Nonetheless, its role in the development of glioma is a remarkable finding that has to be extensively understood. The glymphatic system (GS) collects CSF from the subarachnoid space and brain ISF through aquaporin-4 (AQP4) water channels. The glial limiting membrane and the perivascular astrocyte-end-feet membrane both have elevated levels of AQP4. CSF is thought to drain through the nerve sheaths of the olfactory and other cranial nerves as well as spinal meningeal lymphatics via dorsal or basal lymphatic vessels. Meningeal lymphatic vessels (MLVs) exist below the skull in the dorsal and basal regions. In this view, MLVs offer a pathway to drain macromolecules and traffic immunological cells from the CNS into cervical lymph nodes (CLNs), and thus can be used as a candidate curing strategy against glioma and other associated complications, such as neuro-inflammation. Taken together, the lymphatic drainage system could provide a route or approach for drug targeting of glioma and other neurological conditions. Nevertheless, its pathophysiological role in glioma remains elusive, which needs extensive research. The current review aims to explore the lymphatic drainage system, its role in glioma progression, and possible therapeutic techniques that target MLVs in the CNS.     

Cervical lymph nodes are found in direct relationship with the internal carotid artery: Significance for the lymphatic drainage of the brain

The brain has no conventional lymphatics, but solutes injected into it drain along artery walls and reach lymph nodes in the neck. This study seeks to identify cervical lymph nodes related to the human internal carotid artery (ICA) that could act as the first regional lymph nodes for the brain. Bilateral dissections were carried out on four embalmed human heads, from the level of the carotid bifurcation in the neck, to the base of the skull. Lymph nodes from every specimen were processed for histological examination. A total of 51 deep cervical lymph nodes were identified: 12 lymph nodes (confirmed by histological examination) were observed to be in direct relationship with the ICA. These lymph nodes were found within the carotid sheath and had average diameters of 13.5 × 4.8 mm. Solutes and interstitial fluid from the brain may drain along the walls of cerebral arteries and reach these lymph nodes. They may be sites of stimulation of immune responses against antigens from the brain. Clin. Anat. 23:43–47, 2010. © 2009 Wiley‐Liss, Inc.     

吞噬细胞在脑淋巴引流中的作用

目的:研究吞噬细胞在脑淋巴引流中的作用。方法:将荧光蛋白作为脑淋巴引流的示踪剂微量注射到大鼠大脑皮层内,用荧光显微镜观察其在大脑皮层和颈部淋巴结的分布。结果:荧光显微镜下,大脑皮层内可见红色荧光沿血管周围间隙分布,还可见室管膜周围和脑室内有强荧光信号。高倍光镜下,可见大脑皮层内点状散在分布的红色荧光,为吞噬了荧光蛋白的细胞。颈部淋巴结内见红色点状荧光信号沿淋巴窦分布。结论:脑淋巴内的大分子物质可引流到颈部淋巴结。大分子物质在大脑皮层内沿血管周围间隙分布,脑内的吞噬细胞参与脑淋巴内大分子物质的引流。脑淋巴内的大分子物质可沿神经纤维间隙经室管膜进入脑室,加入脑脊液循环。     

Elimination of neurospecific proteins from CNS: pathogenetic and methodical aspects

Appearance of neurospecific proteins (NSP) outside the brain plays a certain pathogenetic role in the development of autosensitization occurring in many kinds of CNS injuries and diseases. Analysis of modern views of cerebrospinal fluid (CSF) exchange allows us to suppose that NSP are eliminated from the brain tissue within CSF, moving from the subarachnoid space into cranial veins, and by lymphatic way, into deep cervical lymph nodes. Elevation of NSP level in CSF indicates an actual neudegenerative process. Serum levels of NSP are determined by the balance between the elimination of NSP from the brain, on the one hand, and their metabolism and the response of the immune system to the appearance of these autoantigenes in the blood stream, on the other. Basing on their own data on the dynamics of NSP (NSE, GFAR, and MBP) concentrations and the proportions of these proteins in CSF and serum (coefficient of elimination) in rats after ischemic, hypoxic, and autoimmune cerebral lesions, the authors offer an algorithm of pathogenetic evaluation, including, on the one part, a conclusion on the presence or absence of a neurodegenerative process, and, on the other, a conclusion on a normal or lowered rate of NSP elimination (metabolism). The results of such an analysis may have a clinical significance in terms of the development of a pathogenetic therapy, including, in every individual case, not only neuroprotectors, but also pharmaceuticals directed towards correction of the functional condition of the immune system.     

Morphological indications for considerable diffuse reabsorption of cerebrospinal fluid in spinal meninges particularly in the areas of meningeal funnels

Transmission and scanning electron microscopical observations in the rat indicate a considerable capacity of the spinal meninges to reabsorb cerebrospinal fluid. The density of blood vessels and lymphatics in the duramater is extremely high, particularly in the areas of meningeal funnels and spinal nerve root sleeves. Arterioles with closely related unmyelinated nerve fibres, many fenestrated capillaries and venules predetermine these areas as sites where absorption processes could take place. At certain sites of the meningeal angle region, the arachnoid membrane, mostly multilayered, is reduced to only three or four layers. Intercellular discontinuities and cytoplasmic fenestrations occurring in the arachnoid lining cell layer result in direct communications between the subarachnoid space and cisterns of the arachnoid reticular layer. These cisterns are partly fluid-filled, partly occupied by a net of collagen fibre bundles. Some cisterns harbour macrophages that often project filiform processes through the lining cell layer into the subarachnoid space, contacting cerebrospinal fluid. Desmosomes and gap junctions are present in all layers of the arachnoid. However, tight junctions and the continuous electrondense intercellular gap, known to occur normally within the arachnoid barrier layer, were not seen in many sites of the meningeal angle region. Numerous arachnoid cells display a high degree of vesiculation. Cationized ferritin, introduced in vivo into the rat subarachnoid space, passes inter- and intracellularly from the cerebrospinal fluid compartment through the arachnoid membrane, reaching durai blood vessels and lymphatics. Tracer could be visualized both in the cytoplasm of the endothelium and on the luminal surface of the cells. Tracer also passed through pial cell layers into pial vessels, through leptomeningeal sheaths into vessels crossing the subarachnoid space, into the connective tissue compartment and into vessels of spinal dorsal root ganglia. In the angle region, a particularly large number of macrophages can be found on the surface of leptomeninges, within the arachnoid reticular layers, and in close relation to dural and epidural capillaries, venules and lymphatics. Their possible role in the process of cerebrospinal fluid reabsorption is discussed.     

The lymphatics of the liver

An overview of our current knowledge of the hepatic lymph vessels is given, and the different lymph node stations that are related to the liver are described. The lymphatics of the liver itself can be divided into a superficial and a deep system. The superficial vessels are mainly situated in the liver capsule, the deep ones follow the triads of Glisson or the efferent hepatic veins. There are no direct communications between spaces in the liver parenchyma and the first lymphatic capillaries, which end blindly in the surrounding connective tissue. Nevertheless, the perisinusoidal space of Disse, the space of Mall, directly adjacent to the outer limiting plate of the parenchyma, and the space of Comparini, surrounding the sublobular hepatic veins can be regarded as prelymphatic spaces from which the hepatic lymph could originate. The extracellular matrix in the space of Disse is apparently continuous with the extraparenchymal areas of the connective tissue. Collagens and proteoglycans offer a morphological pathway for the transport of fluid, the physiological prerequisites of which are discussed.     

The lymphatics of the liver

An overview of our current knowledge of the hepatic lymph vessels is given, and the different lymph node stations that are related to the liver are described. The lymphatics of the liver itself can be divided into a superficial and a deep system. The superficial vessels are mainly situated in the liver capsule, the deep ones follow the triads of Glisson or the efferent hepatic veins. There are no direct communications between spaces in the liver parenchyma and the first lymphatic capillaries, which end blindly in the surrounding connective tissue. Nevertheless, the perisinusoidal space of Disse, the space of Mall, directly adjacent to the outer limiting plate of the parenchyma, and the space of Comparini, surrounding the sublobular hepatic veins can be regarded as prelymphatic spaces from which the hepatic lymph could originate. The extracellular matrix in the space of Disse is apparently continuous with the extraparenchymal areas of the connective tissue. Collagens and proteoglycans offer a morphological pathway for the transport of fluid, the physiological prerequisites of which are discussed.     

肝深淋巴管的分布及其与肝浅淋巴管的交通

目的：探讨肝浅淋巴管和深淋巴管的交通，以及肝淋巴管的交通在肝脏病理学方面的意义。材料和方法：采用普鲁士蓝注射、厚片透明和组织切片的方法，在５２例小儿和８例胎儿的肝脏对肝淋巴管作了形态学观察。结果：肝深淋巴管包括小叶间淋奥管和小叶下淋巴管，分别位于门管区的疏松结缔组织和小叶下静脉的外膜内。星状浅淋巴管和少数区域洒巴管经肝表面的小凹或裂隙注入小叶间淋巴管。阻断肝深淋巴管时，注射剂经肝深淋巴管返流人肝浅     

Lymphocyte Targeting of the Central Nervous System: A Review of Afferent and Efferent CNS-Immune Pathways

The central nervous system (CNS) is considered to be an immunological privileged site. However, inflammatory reactions in response to virus infections, in multiple sclerosis (MS) and in experimental autoimmune encephalomyelitis (EAEl suggest that there are definite connections between the CNS and the immune system. In this review, we examine evidence for afferent and efferent pathways of communication between the CNS and the immune system, the pivotal role of regional lymph nodes in T-cell mediated autoimmune disease of the CNS, and the factors involved in lymphocyte targeting of the CNS. Afferent pathways of lymphatic drainage of the brain are well established in a variety of species, especially rodents. Fluid and antigens appear to drain along perivascular spaces populated by immunocompetent perivascular cells. Drainage pathways connect directly via the cribriform plate to nasal lymphatics and cervical lymph nodes. Soluble antigens draining from the brain induce antibody production in the cervical lymph nodes. Using a model of cryolesion-enhanced EAE, we review the role of lymphatic drainage and cervical lymph nodes in the enhancement of cerebral EAE. If a brain wound in the form of a cryolesion is produced 8 days post inoculation (dpi) of antigen in the induction of acute EAE, there is a 6-fold increase in severity of cerebral EAE by 15 dpi. Removal of the cervical lymph nodes significantly reduces such enhancement of EAE. These findings suggest that drainage of antigens from the brain to the cervical lymph nodes, in the presence of activated lymphocytes in the meninges or CNS, resuIts in an enhanced second wave of lymphocytes targeting the brain. In examining the efferent immune pathway by which lymphocytes home to the CNS, several studies have characterized the phenotype of infiltrating T lymphocytes by the use of immunocy-tochemistry or FACS analysis. T-cells infiltrating the CNS are recently activated/memory lymphocytes typified by their high expression of CD44, LFA-1 and ICAM-1 and low expression of CD45RB in the mouse. Following the induction of EAE in susceptible mice, ICAM-1 and VCAM-1 are dramatically upregulated on CNS vessels; lymphocytes bind to such vessels via the interaction of their known ligands, LFA-1/Mac-1 and 1times4-integrins, at least in vitro. It appears that 1times4-integrin plays a key role in lymphocyte recruitment across the blood-brain barrier and may be a major factor in lymphocyte targeting of the CNS. Definition of factors involved in the afferent and efferent connections between the CNS and the immune system may clarify mechanisms involved in immune privilege of the CNS and may open significant therapeutic opportunities for multiple sclerosis.     

Lymphatic drainage function and its immunological implications: from dendritic cell homing to vaccine design

The slow interstitial flow that drains fluid from the blood capillaries into the lymphatic capillaries provides transport of macromolecular nutrients to cells in the interstitium. We discuss herein how this flow also provides continuous access to immune cells residing in the lymph nodes of antigens from self or from pathogens residing in the interstitium. We also address mechanisms by which dendritic cells in the periphery sense interstitial flow to home efficiently into the lymphatics after activation, and how lymphatic endothelium can be activated by this flow, including how it can act as a lymphatic morphoregulator. Further, we present concepts on how interstitial flow can be exploited with biomaterial systems to deliver antigen and adjuvant molecules directly into the lymphatics, to target dendritic cells residing in the lymph nodes rather than in the peripheral tissues, using particles that are small enough to be carried along by flow through the network structure of the interstitium. Finally, we present recent work on lymphatic and lymphoid tissue engineering, including how interstitial flow can be used as a design principle. Thus, an understanding of the physiological processes that govern transport in the interstitium guides new understanding of both immune cell interactions with the lymphatics as well as therapeutic interventions exploiting the lymphatics as a target.