Lymphatic and blood vessels of the popliteal node in sheep

Our aim was to describe the lymphatic and blood vascular pathways to and from the popliteal lymph node in sheep. The blood vessels and lymphatics were filled with Microfil, and were cleared in methyl salicylate. Afferent lymphatics divide and anastomose as they pass dorsally along the lateral saphenous vein, and 6–12 lymphatics reach the node. Each branches extensively on the surface of the node giving rise to 20–50 terminal afferents which enter the node over a roughly circular area. Most enter the subcapsular sinus, but some penetrate deeply into the node. Lymph leaves the node through numerous initial efferent lymphatics, many of which contain valves. These join forming progressively larger vessels, and 2–4 efferent trunks emerge from the hilus. The hilus varies considerably in shape, depth and location, and it is filled with fat. Either a single artery, or up to 10–12 arteries derived from an anastomotic network or circle, enter the node from the hilar fat pad. Arteries may also enter at other sites. The arteries originate from the caudal femoral, or the medial circumflex femoral artery; a single node may receive blood from both arteries. This arrangement may help to maintain blood flow especially during an immune response, and despite external pressures applied to the arteries and node during movements of the animal.     

The low concentration of macroglobulin antibodies in peripheral lymph

Peripheral lymph (afferent to the popliteal node) was collected from four sheep under physiological conditions. The concentration of protein in the lymph was never more than 20 per cent of that of the protein in the blood plasma. However, ultracentrifugal analysis showed that 19S macroglobulins accounted for 12 per cent of the globulins present in blood plasma but for only 4 per cent of the globulins in peripheral lymph. Thus, the concentration of macroglobulin in the lymph can be only about one-sixteenth of that in the blood. This was confirmed by titrating the amounts of both naturally occurring and induced 19S antibodies in blood and lymph.

When inflammation was induced in the area of skin drained by the lymphatic fistula the titre of 19S antibodies in the lymph doubled.

     

右旋糖酐-二乙烯三胺五乙酸-钆离子螯合物与马根维显在间质磁共振淋巴造影中的对比

目的 比较右旋糖酐-二乙烯三胺五乙酸 钆离子螯合物(dextran-DTPA-Gd)和马根维显两种对比剂在间质MRI淋巴造影中淋巴显影的价值。方法 选择健康成年新西兰兔12只,体重为2.7～3.7kg。仰卧位固定兔,经3D TOF CE-MRA序列扫描,平扫后右侧后肢第1、2、3趾蹼间隙注
射dextran-DTPA-Gd 各0.4ml(3.96×10^-3mol/L),共1.2ml;30min后左侧后肢第1、2、3趾蹼间隙注射马根维显各0.4ml(0.4998mol/L),共1.2ml,行MR增强扫描,扫描间隔分别为10、15、20、25、30、35、40、45、50、55、60min、2h、4h、24h。平扫和增强扫描的相关参数相同。分析不同
时间段淋巴显影强化程度,测量并计算腘窝淋巴结增强前后的信号强度(E%),绘制其信号强度-时间曲线,比较两种显影剂对淋巴显影的区别。结果 平扫时双侧腘窝淋巴结均呈等信号。右侧dextran-DTPA-Gd注射后10min,引流区后肢淋巴管及腘窝淋巴结信号强化明显、显示清晰,腘窝
淋巴结E%为212.7%,35min左右达到峰值,E%值为314.1%,4h后为208.2%,24h后扩清。左侧马根维显注射10min时,引流区域后肢血管强化明显,造影剂大部分吸收入血管进入膀胱,后肢淋巴管及腘窝淋巴结信号弱,腘窝淋巴结E%为78.8%,20min左右达到峰值,E%值为98.3%,4h后减至
29.0%,24h后扩清。淋巴结E%经统计学分析差异有统计学意义(P<0.05)。实验前后动物的生化检查等数据未见异常变化,其差异无统计学意义(P>0.05),送检的内脏器官组织学检查未见明显的病理学改变。结论 相比马根维显小分子造影剂,dextran-DTPA-Gd是一种有效的淋巴造影剂,
能够特异性靶向强化淋巴结及淋巴管。     

Effect of traumatic stress on the lymph properdin level

Changes in the properdin level in different types of lymph and in the blood were studied in dogs after burns of the hind limbs (group 1) and after head injury (group 2). The properdin level in the lymph of the cervical duct and the efferent lymph flow of the popliteal lymph node were increased in dogs of both groups. The properdin level in the afferent lymph of the popliteal lymph node, thoracic duct, and blood fell after burns and rose after head injury. The total protein concentration in the afferent and efferent lymph of the popliteal lymph node and the cervical and thoracic ducts increased whereas in the blood it decreased.Course of Pathophysiology, Mordovian University, Saransk. (Presented by Academician of the Academy of Medical Sciences of the USSR P. D. Gorizontov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 4, pp. 403–405, April, 1978.     

The specific influence of carbon dioxide and carbamate compounds on the buffer power and Bohr effects in human haemoglobin solutions

1. Lymph from the lungs of lambs and sheep was found to enter both the right lymph duct and the thoracic duct. Right lymph duct flow was collected by constructing a venous sac, the venous tributaries of which were ligated but which the right lymph duct entered; thoracic duct flow was collected by cannulating the duct. Lymph from sites other than the lungs was excluded from the collections.

2. Measurements were made of the surface tension characteristics of lung extracts and of the liquid present in foetal lungs. These values were used together with gestational age and crown-rump length to designate the foetal lambs into mature and immature groups.

3. Lymph flow from the lungs averaged 0·99 ml./kg body wt./hr in immature foetal lambs, and 1·81 ml./kg/hr in mature foetal lambs before the start of ventilation. Lymph flow from the lungs of spontaneously delivered new-born lambs (mean age 51 hr) averaged 0·86 ml./kg/hr. In adult ewes right lymph duct flow averaged 0·11 ml./kg/hr and total lung lymph flow was estimated indirectly to be 0·33 ml./kg/hr. Calculated rates of protein flow in lung lymph (flow × protein concentration) were greater in foetal lambs than in adult sheep.

4. Total thoracic duct flow averaged 2·48 ml./kg/hr in immature foetal lambs, 5·30 ml./kg/hr in mature foetal lambs, 3·65 ml./kg/hr in new-born lambs, and 2·92 ml./kg/hr in adult ewes.

5. At the start of ventilation there was an increase in lymph flow from the lungs, which at 15-30 min reached a mean of 6·4 ml./kg/hr in mature lambs and 2·6 ml./kg/hr in immature lambs. At the same time the protein concentration of lymph decreased but the calculated protein flow increased.

6. The lungs of foetal lambs weighed more than the lungs of spontaneously delivered new-born lambs, and the difference could be accounted for by liquid which could be aspirated through the trachea of the foetal lamb. On ventilation of the lungs for 2 hr, without first allowing the escape of any lung liquid, lung weight measurements indicated that about 66% of the lung liquid had been taken up in mature lambs and about 50% in immature lambs.

7. It was concluded that the rate at which lymph is formed in the lungs is greater per kilogram body weight in foetal than in new-born lambs and greater in them than in ewes. The increase in lymph flow at the start of ventilation could account for the removal of about 40% of the liquid present in the lungs of the mature foetus and about 25% of the liquid in the lungs of the immature foetus.

     

Reactive murine lymph nodes uniquely permit parenchymal access for T cells that enter via the afferent lymphatics

Whereas naïve T cells access the lymph nodes predominantly via the high endothelial venules, their effector counterparts can also enter via the afferent lymphatics. It is unclear if such cells are confined to the lymphatic spaces during their transit through the lymph node or whether they can access the lymphocyte‐ and dendritic cell‐rich parenchyma with its potentially stimulatory environment. We used a flank HSV inoculation model that featured neuronal‐mediated movement of virus to distinct areas of skin to study the lymphatic‐mediated transit of activated T cells between different skin‐draining lymph nodes. These experiments showed that activated T cells released from the brachial lymph node, draining the primary site of inoculation, entered the downstream axillary lymph node. These activated T cells accessed the subcapsular areas of the axillary lymph node via lymphatic vessels exiting the upstream brachial node regardless of whether the former drained skin that was associated with active infection. However, T cells remained within the sinusoidal network of the axillary lymph node unless it was directly associated with peripheral infection. Thus, activated T cells that enter a given lymph node using the afferent lymphatics do not have automatic access to the parenchyma unless it is a reactive node involved with peripheral inflammation or infection. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

The lymphatic system and sentinel lymph nodes: conduit for cancer metastasis

The lymphatic system is a complicated system consisting of the lymphatic vessels and lymph nodes draining the extracellular fluid containing cellular debris, excess water and toxins to the circulatory system. The lymph nodes serve as a filter, thus, when the lymph fluid returns to the heart, it is completely sterile. In addition, the lymphatic system includes the mucosa-associated lymphoid tissue, such as tonsils, adenoids, Peyers patches in the small bowel and even the appendix. Taking advantage of the drainage system of the lymphatics, cancer cells enter the lymphatic vessels and then the lymph nodes. In general, the lymph nodes may serve as a gateway in the majority of cases in early cancer. Occasionally, the cancer cells may enter the blood vessels. This review article emphasizes the structural integrity of the lymphatic system through which cancer cells may spread. Using melanoma and breast cancer sentinel lymph node model systems, the spread of early cancer through the lymphatic system is progressive in a majority of cases. The lymphatic systems of the internal organs are much more complicated and difficult to study. Knowledge from melanoma and breast cancer spread to the sentinel lymph node may establish the basic principles of cancer metastasis. The goal of this review article is to emphasize the complexity of the lymphatic system. To date, the molecular mechanisms of cancer spread from the cancer microenvironment to the sentinel lymph node and distant sites are still poorly understood and their elucidation should take major priority in cancer metastasis research.

     

Tumor-induced sentinel lymph node lymphangiogenesis and increased lymph flow precede melanoma metastasis

Lymphangiogenesis is associated with human and murine cancer metastasis, suggesting that lymphatic vessels are important for tumor dissemination. Lymphatic vessel alterations were examined using B16-F10 melanoma cells implanted in syngeneic C57Bl/6 mice, which form tumors metastasizing to draining lymph nodes and subsequently to the lungs. Footpad tumors showed no lymphatic or blood vessel growth; however, the tumor-draining popliteal lymph node featured greatly increased lymphatic sinuses. Lymph node lymphangiogenesis began before melanoma cells reached draining lymph nodes, indicating that primary tumors induce these alterations at a distance. Lymph flow imaging revealed that nanoparticle transit was greatly increased through tumor-draining relative to nondraining lymph nodes. Lymph node lymphatic sinuses and lymph flow were increased in mice implanted with unmarked or with foreign antigen-expressing melanomas, indicating that these effects are not due to foreign antigen expression. However, tumor-derived immune signaling could promote lymph node alterations, as macrophages infiltrated footpad tumors, whereas lymphocytes accumulated in tumor-draining lymph nodes. B lymphocytes are required for lymphangiogenesis and increased lymph flow through tumor-draining lymph nodes, as these alterations were not observed in mice deficient for B cells. Lymph node lymphangiogenesis and increased lymph flow through tumor-draining lymph nodes may actively promote metastasis via the lymphatics.     

Contribution of lymph formation in the popliteal node to efferent lymph flow following stimulation of the sympathetic chain in the sheep

Lymph flow and contraction frequency were measured in popliteal efferent lymphatics. Stimulation of the ipsilateral sympathetic chain resulted in an approximate threefold increase in lymph flow, while contraction frequency increased 28% (n = 6). Occlusion of the metatarsal afferent lymphatics with a pneumatic cuff reduced efferent flow from 18 to 4 microliters/min after 25 min (n = 5), indicating that approximately 80% of popliteal efferent lymph is derived from the foot. After occlusion of the afferent lymphatics, sympathetic stimulation failed to increase efferent lymph flow significantly, while efferent contraction frequency still showed a significant rise. It is concluded that lymph formation in the popliteal node does not contribute to the rise in efferent lymph flow following sympathetic stimulation.     

Role of the Popliteal Lymph Node in Infection with Mycobacterium marinum of the Hind Footpad of the Mouse, and Source of the Cells that Characterize the Process

We examined the possibility that the popliteal lymph node serves as the source of the lymphocytes that, together with macrophages, characterize Ihc lesion produced by infection with Mycobacterium marinum in the hind footpad of Ihc mouse. Naive mice were partially protected against challenge with M. marinum in the hind footpad by intravenous infusion of lymphoc) its harvested from the popliteal nodes of donor mice infected with M. marinum 7 days earlier. Lymphocytes harvested from the popliteal nodes of infected donors, labelled in vitro with ³H-uridine, and infused intravenously into naive mice that were immediately challenged in the hind footpads with M. marinum, localized in the popliteal nodes of the recipient mice but nol in the footpad lesions. Lymphocytes harvested from the spleens of naive donors and labelled in vitro appeared to home to the popliteal nude draining the M. marinum-infected footpad. Thus, the primary rule of the popliteal lymph node appeared to be passive trapping of the lymphocytes brought to it by the circulairon or afferent lymphatics. We then tried lo locate the sources of bolh lymphocytes and macrophages that characterize the lesion. Temporary occlusion of the abdominal aorta prevented labelling by intravenously infused ³H-thymidine (³H-TdR) of the mononuclear cells of both footpad lesion and popliteal node. Temporary occlusion of the left common iliac artery during ³H-TdR infusion prevented immediate labelling on the ipsilateral side. After 24 and 48 h, however, small numbers of labelled lymphocyles were found in the left hind footpad lesion. Amputation of the right leg at the hip joint, but run right poplitial lymphadenectomy, performed immediately after re-estublishment of patency of the left common iliac artery, prevented the late influx of labelled lymphocytes into the lesion of the left hind footpad. Thus, the chief source of both the lymphocytes and the macrophages of the footpad lesion appeared lo be the lesion ilself.     

The lymphatics of the kidney and the formation of renal lymph

1. The anatomy of the renal lymphatics and the flow and composition of renal lymph have been investigated in sheep. Lymphatic capillaries were demonstrated in the cortex and cortico-medullary areas of the sheep's kidney but not within the medulla. The lymph formed in the sheep's kidney drains from the hilum through several small lymphatics; there is no lymphatic drainage from the renal capsule.2. Lymph flow from the sheep's kidney varied from 0.5 to 3.0 ml./hr. The concentrations of electrolytes and urea in renal lymph were found to be similar to lymph from other regions of the body, but the concentration of endogenous creatinine was lower. The average concentration of protein in renal lymph was 43% of the plasma levels; there was a significantly higher proportion of albumin in renal lymph than in plasma. When labelled albumin was injected intravenously, the specific activities of the plasma and renal lymph albumin equilibrated in about 2 hr.3. When [(14)C]inulin, [(125)I]hippuran or [(14)C]creatinine were infused intravenously radioactivity appeared rapidly in the renal lymph. When steady-state levels were reached in the circulating plasma, the renal lymph/jugular vein plasma ratios for [(14)C]inulin and [(14)C]creatinine were 0.82 while for [(125)I]hippuran the ratio was 0.34. It was considered that the concentration of these substances in renal lymph was similar to the concentration in renal vein plasma.4. The concentration of renin enzyme was on the average about 8 times higher in renal lymph than in jugular vein or renal vein plasma or in lymph from the hind limbs.5. Renal lymph appeared to be formed principally, if not entirely, in the renal cortex and appeared to be a modified filtrate derived from post-glomerular blood capillaries. If any contribution to renal lymph does come from the medulla, it must be small in relation to the volume of lymph formed in the cortex.     

Antigen localization in lymphopenic states: II. Further studies on whole body X-irradiation

The gross and microscopic distribution of ¹²⁵I polymerized flagellin from Salmonella adelaide was studied in adult rats at various times following 800 r whole body X-irradiation. Injections of radioactive antigen were made in both hind footpads, and the popliteal lymph nodes were excised for autoradiographic study 1 day later. This dose of irradiation caused a progressive decline in the ability of lymphoid follicles of popliteal nodes to capture and retain antigen. Irradiation had no detectable effect upon antigen uptake by whole lymph nodes or upon the number of grains overlying the phagocytic cells of the medullary sinuses of popliteal nodes.

Various substances capable of restoring follicular antigen uptake in the irradiated rat were studied by means of injecting the test substance into one hind footpad 1 hour prior to the injection of antigen into both feet. The distribution of antigen in each popliteal node was compared, each animal thus acting as its own control. It was found that 0.01 ml of specific anti-flagellar immune serum, or 0.25 ml of normal adult rat serum significantly improved follicular antigen uptake when tested ten days after irradiation. Foetal calf serum, homologous lymphocytes, and the media from pooled concentrated lymphocyte cultures were without demonstrable effects when given by regional injection. Shielding of the popliteal nodes at the time of irradiation improved follicular antigen uptake, whereas shielding of the femoral bone marrow and appendix was ineffective. No agent found capable of improving follicular antigen capture in the irradiated rat significantly altered footpad retention of antigen, whole organ counts of the popliteal nodes, or antigen localization in the phagocytic cells of the lymph node medulla.

The results favour the interpretation that the follicular antigen trapping mechanism is extremely sensitive to changes in levels of opsonins; that substances present in normal adult rat serum act as `follicular opsonins'; that these substances decline exponentially following irradiation; and that these substances are secreted by small lymphocytes or their progeny.

     

Studies on the afferent and efferent lymph of lymph nodes draining the site of application of fluorodinitrobenzene (FDNB)

Peripheral lymph (afferent to the popliteal node) or intermediate lymph (efferent from the popliteal or prefemoral node) was collected from unanaesthetized sheep before and after painting the skin of the drainage area with a 10 per cent solution of fluorodinitrobenzene (FDNB) in acetone. In some experiments FDNB labelled with tritium ([³H]FDNB) was used.The changes in the cell population of efferent lymph from nodes thus stimulated were generally similar to those which occur following stimulation with conventional antigens, i.e., between 90–120 hours later many large basophilic lymphoid blast cells (immunoblasts) appeared in the lymph and specific antibody appeared in the lymph plasma.Studies with [³H]FDNB showed that although some of it appeared in afferent lymph almost immediately after application, substantial amounts were not present usually until 20 hours or so later. All of the FDNB in the afferent lymph was bound to soluble proteins in the plasma and none was found in association with the lymph cells. Apparently, this protein bound FDNB was inefficiently phagocytosed in the regional node because much of it passed through the node so that it could be recovered in the efferent lymph for 100 hours or more following the original application.It was concluded that skin sensitizing chemicals of the FDNB class are transported to the node after they have combined with soluble proteins that enter the lymph; in the combined form they behave like other soluble protein antigens and provoke similar cellular responses in the regional tissue.     

Structure and function of rat lymph nodes

The lymph node comprises a critical crossroad for encounters between antigen presenting cells, antigens from lymph, and lymphocytes recruited into lymph nodes from the blood. The node consists of spaces lined with lymphatic endothelial cells and parenchyma. The former spaces can be divided into the subcapsular sinuses, lymphatic labyrinths in the deep cortex, intermediate sinuses, and medullary sinuses. The sponge-like framework of the node parenchyma is composed of collagen fibers invested with reticular cells. The parenchyma can be divided into the cortex, deep cortex, and medullary cord. Lymphocytes migrate from the node parenchyma into the lymphatic labyrinths in the deep cortex. Close to the labyrinths are high endothelial venules (HEVs), through which circulating lymphocytes enter the node parenchyma. HEVs strongly express Aquaporin-1, suggesting that HEVs are involved in the net absorption of water, but not protein, from lymph coming through afferent lymphatics. Many LYVE-1 positive sinus reticular cells (i.e., lymphatic endothelial cells) with attached macrophages form a network within the lumen of the medullary sinuses. Fluids and migrating cells arriving at the node preferentially flow through the subcapsular sinuses, intermediate sinuses, and medullary sinuses in this order. Fluids and migrating cells may also enter the cortex through gaps in the floor of the subcapsular sinuses.     

Angiomyomatous hamartoma of a popliteal lymph node: an unusual cause of posterior knee pain

Angiomyomatous hamartoma is a primary vascular tumor primarily found in the inguinal and femoral lymph nodes characterized by the replacement of nodal tissue by smooth muscle cells and fibrous tissue in sclerotic lymphatic stroma. There has been 1 report of an angiomyomatous hamartoma of a cervical lymph node, and this is the first reported case occurring in an extremity. We present a case of angiomyomatous hamartoma occurring in a single popliteal lymph node.     

The influence of the lymph node on the protein concentration of efferent lymph leaving the node.

1. Experiments have been performed in sheep to determine the contribution of lymph formed within a lymph node to the total protein output in lymph leaving the node. 2. The lymphatic duct leaving the popliteal lymph node was cannulated and the protein and lymphocyte output in efferent lymph determined. The afferent lymph flow to the popliteal node was then diverted and lymph formed only within the lymph node collected from the efferent cannula. It appeared from the results that the popliteal lymph node forms lymph at the rate of approximately 1 ml. per hour and may contribute 30-50% of the protein output observed in efferent lymph. 3. The importance of lymph formation within the lymph node varied between nodes found in different regions of the body. This was due in part to the different protein concentrations in the afferent lymph to the different nodes. 4. A positive correlation was found between the protein and lymphocyte concentrations in efferent lymph from the popliteal lymph node in seven out of eleven sheep and in lymph formed within the popliteal lymph node in two out of three sheep. It is suggested that this relationship may be due to an increased transfer of plasma proteins through the post-capillary venules in the lymph node accompanying the continual traffic of lymphocytes across the wall of these vessels. The results indicated that the protein transfer across the post-capillary venules was not an indiscriminate transfer of plasma per se but a selective transport from the blood plasma compartment based on molecular size.     

Microlymphatics and lymph flow

A careful review of several different organs shows that with the information available today the beginnings of the microlymphatics in the tissue consist of endothelialized tubes only. Lymphatic smooth muscle within the collecting lymphatics appears further downstream, in some organs only outside the parenchyma. This particular anatomic picture has been observed in many different mammalian organs and in humans. The nonmuscular, so-called initial, lymphatics are the site of interstitial fluid absorption that requires only small and transient pressure gradients from the interstitium into the initial lymphatics. A fundamental question concerns the mechanism that causes expansion and compression of the initial lymphatics. I presented several realistic proposals based on information currently on hand relevant to the tissue surrounding the initial lymphatics. To achieve a continuous lymphatic output, periodic (time variant) tissue stresses need to be applied. They include arterial pressure pulsations; arteriolar vasomotion; intestinal smooth muscle contractions and motilities; skeletal muscle contraction; skin tension; and external compression, such as during walking, running, or massage, respiration, bronchiole constriction, periodic tension in tendon, contraction and relaxation of the diaphragm, tension in the pleural space during respiration, and contractions of the heart. The nonmuscular initial lymphatic system drains into a set of contractile collecting lymphatics, which by way of intrinsic smooth muscle propel lymph fluid. The exact transition between noncontractile and contractile lymphatics has been established only in a limited number of organs and requires further exploration. Retrograde flow of lymph fluid is prevented by valves. There are the usual macroscopic bileaflet valves in the initial and collecting lymphatics and also microscopic lymphatic endothelial valves on the wall of the initial lymphatics. The latter appear to prevent convective reflow into the interstitium during lymphatic compression. Many of the lymph pump mechanisms have been proposed in the past, and most authors agree that these mechanisms influence lymph flow. However, the decisive experiments have not been carried out to establish to what degree these mechanisms are sufficient to explain lymph flow rates in vivo. Because individual organs have different extrinsic pumps at the level of the initial lymphatics, future experiments need to be designed such that each pump mechanism is examined individually so as to make it possible to evaluate the additive effect on the resultant whole organ lymph flow.(ABSTRACT TRUNCATED AT 400 WORDS)     

The barrier function of the lymph nodes in infection

Summary Fixation ofB. coli commune by the popliteal lymph nodes was studied as follows: Lymph nodes were perfused by a suspension ofB. coli commune, and studies were made of lymph taken at operation by means of fistulae in the thoracic duct and lymphatic vessels of a dog's hind limb. The ability of the lymph node to fixate bacteria is increased by immunization, particularly when the immunizing culture is injected into the area corresponding to the given node. The barrier function of the nodes increases, particularly when inflammation is provoked in them either by infectious or noninfectious agents. The nonspecific phenomena, which include intensification of the mechanical filtration and increase of phagocytic activity of the cells of the node play a significant part in the increase of lymph node barrier function in immunization.(Presented by Active Member AMN SSSR N. N. Sirotinin) Translated from Byulleten's eksperimental'noi biologii i meditsiny Vol. 49, No. 1, pp. 49–53, January, 1960     

Effect of interferon-alpha-2a on the output of recirculating lymphocytes from single lymph nodes.

The output of recirculating lymphocytes from cannulated popliteal lymph nodes in sheep was measured after administration of human recombinant interferon (rIFN)-alpha-2a. Interferon (IFN) injection caused a dramatic decrease in lymphocyte output from lymph nodes. Following a single s.c. or i.d. injection of 2 x 10(7) U IFN into the drainage area of the popliteal lymph node, lymphocyte output fell to below 1% of the pre-treatment level and remained depressed for up to 35 hr. A substantial decrease in lymphocyte output from cannulated nodes also occurred after IFN was injected either i.v., into the skin of the opposite non-cannulated hind leg or into an afferent lymphatic vessel leading to the popliteal lymph node. After the period of depressed lymphocyte output, a seemingly compensatory surge of cell traffic occurred that lasted 2-3 days. During this phase there was a relative increase in the proportion of CD4+ T cells in lymph. Similar changes occurred after each treatment in animals given multiple doses of IFN. These effects are unlikely to be antigen-induced since there was no blast cell response in any treated animal. The analysis of blood and lymph plasma samples showed that the most severe depression of lymphocyte output was associated with high levels of IFN, while there was no apparent correlation between the reduction in lymphocyte traffic and concentrations of cortisol in plasma. These results suggest that IFN-alpha-2a is involved directly in the regulation of lymphocyte output from lymph nodes.     

Tumor location and nature of lymphatic vessels are key determinants of cancer metastasis

Tumor metastasis to lymph nodes is a key indicator of patient survival, and is enhanced by the neo-lymphatics induced by tumor-secreted VEGF-C or VEGF-D, acting via VEGFR-3 signalling. These targets constitute important avenues for anti-metastatic treatment. Despite this new understanding, clinical observations linking metastasis with tumor depth or location suggest that lymphangiogenic growth factors are not the sole determinants of metastasis. Here we explored the influence of tumor proximity to lymphatics capable of responding to growth factors on nodal metastasis in a murine VEGF-D over-expression tumor model. We found that primary tumor location profoundly influenced VEGF-D-mediated lymph node metastasis: 89 % of tumors associated with the flank skin metastasised, in contrast with only 19 % of tumors located more deeply on the body wall (p < 0.01). Lymphatics in metastatic tumors arose from small lymphatics, and displayed distinct molecular and morphological profiles compared with those found in normal lymphatics. Smaller lymphatic subtypes were more abundant in skin (2.5-fold, p < 0.01) than in body wall, providing a richer source of lymphatics for VEGF-D⁺ skin tumors, a phenomenon also confirmed in human samples. This study shows that the proximity of a VEGF-D⁺ primary tumor to small lymphatics is an important determinant of metastasis. These observations may explain why tumor location relative to the lymphatic network is prognostically important for some human cancers.