Rapid decrease in lymphocyte adherence to high endothelial venules in lymph nodes deprived of afferent lymphatic vessels

Occlusion of the afferent lymph flow to the lymph node (LN) results in both flattening of the endothelium of high endothelial venules (HEV) and a severe decrease in numbers of lymphocytes in transit across the walls of the flattened HEV. In the present study we have used the in vitro lymphocyte-binding assay to investigate the ability of HEV in rat LN to bind lymphocytes at various time points after occlusion of the afferent lymph flow. In addition the specificity of T and B lymphocyte adherence to HEV of such operated LN was studied. In normal LN, lymphocytes adhered to virtually all HEV using the in vitro binding assay. However, 1 and 2 weeks after operation lymphocytes bound to only 50-60% of the HEV and by 3-6 weeks 20-30%. The total numbers of lymphocytes bound to these HEV had also diminished to 10% of the control value 3-6 weeks after operation. Morphometric analysis showed that this was not only due to a reduction in the area of HEV endothelium available for lymphocyte adherence by flattening of the high endothelial cells, but also to a strong decrease in the numbers of bound lymphocytes per unit area high endothelium. In spite of the reduction in numbers of adhering lymphocytes the T/B cell ratio did not change. The results show that the reduction in lymphocyte binding of HEV in operated LN is a rapid event, probably due to loss of high endothelial cell determinants involved in binding of lymphocytes. The decrease in lymphocyte binding clearly precedes flattening of HEV endothelium suggesting that the height of high endothelial cells is of secondary importance to lymphocyte adherence.     

Demonstration of isolated follicular dendritic cells in lymphatic vessels around human immunodeficiency virus-infected lymph nodes

Follicle lysis (FL) is a peculiar disruptive change of follicular dendritic cells (FDCs) commonly observed in the germinal centres of individuals with HIV infection. To clarify the fate of FDCs during FL, 30 HIV-infected lymph nodes were studied, mostly in the persistent generalized lymphadenopathy phase. FDCs were immunostained on paraffin sections with 1F8, a FDC-specific monoclonal antibody. In advanced FL, the FDC network was shown to be divided into cell clusters of various sizes. In the final phase of FL, these were fragmented into much smaller cell clusters and dispersed in the parafollicular area. Some of these small clusters were found in the lymphatic sinuses (6/30), and unexpectedly, even in extranodal lymphatic vessels (2/30, one being apparently located in efferent vessels). No efflux of these small FDC clusters into extranodal lymphatics was observed in 15 HIV-negative control lymph nodes. These FDC clusters located in the lymphatics may work as transporters of HIV to other lymph nodes downstream, as FDCs carry the greatest HIV load.     

Tridimensional study of the deep cortex of the rat lymph node. II: Relation of deep cortex units to afferent lymphatic vessels

Recently, we reported that the deep cortex of the rat lymph node is formed of semi-rounded structures, the “deep cortex units,” contiguous to the peripheral cortex and bulging into the medulla. It was suggested that a unit represents an accumulation of lymphocytes centered on the opening of an afferent lymphatic vessel. To verify the proposal, we carried out a tridimensional analysis of serially sectioned rat nodes, fixed by perfusion and trimmed in such a way as to preserve their lymphatics. The tridimensional analysis revealed that a constant topographical relationship exists between the units and the openings of the afferent lymphatics. The results demonstrated that the topographical organization of the deep cortex of a rat node correlates with the distribution pattern of the opening(s) of its afferent lymphatic(s). The overall observations suggested the following explanation for the shape and topography of the units: factor(s) present in the lymph would spread in a radial manner from the opening(s) of an afferent lymphatic through the underlying cortex. The factor(s) would induce morphological modifications in the stimulated semi-rounded area which, in turn, would provoke a local accumulation of circulating lymphocytes.     

Disappearance and reappearance of high endothelial venules and immigrating lymphocytes in lymph nodes deprived of afferent lymphatic vessels: a possible regulatory role of macrophages in lymphocyte migration

Interruption of the afferent lymphatic vessels of the popliteal lymph node resulted in the disappearance of high endothelial venules (HEV) and immigrating lymphocytes within 3 weeks. HEV showed several characteristic morphological changes: the endothelial cells became flattened and less pyroninophilic, the chromatine became condensed and protein synthetizing and secretory cell organelles became scarce. At the same time the number of macrophages in the lymph node was severely reduced. Injection of sheep red blood cells into such lymph nodes, 6 weeks after operation, resulted in reappearance of HEV and immigrating lymphocytes, and development of many plasma cells and some germinal centres. Injection of lipopolysaccharide into the operated lymph nodes resulted in the appearance of many plasma cells and a few poorly developed germinal centres; HEV and immigrating lymphocytes, however, remained almost absent. The results show a relationship between the immigration of lymphocytes and the activity of the endothelial cells in the HEV. The activation of the latter may occur by mediators released by antigen-stimulated macrophages and T cells. Moreover, the morphological features of the HEV are independent of the presence of recirculating lymphocytes.     

Repopulation of macrophages in popliteal lymph nodes of mice after liposome-mediated depletion

Macrophages lining the subcapsular sinus (SCS) and those located in the medulla of popliteal lymph nodes (PLN) of mice were eliminated after subcutaneous (s.c.) injection of dichloromethylene diphosphonate (Cl2MDP)-containing liposomes. No effect of liposome-entrapped Cl2MDP could be seen on nonphagocytic cells, e.g., interdigitating cells (IDC) and B- and T-lymphocytes. One month after injection the eliminated subsets of macrophages were still absent. After 2 mo a small number of macrophages had reappeared along the SCS and in the medulla of the PLN of a few animals. Complete repopulation of the PLN with macrophages was observed only after 5 mo. This extremely long repopulation time could be shortened drastically by local administration of Freund's complete adjuvant (FCA). A small number of macrophages reappeared along the SCS and in the medulla 1 wk after FCA and after 3 wk the repopulation of the PLN with macrophages was complete. Such rapid repopulation of macrophages was not achieved after s.c. injection of paraffin oil or paratyphoid vaccine. These results indicate that the normal rate of influx of mononuclear phagocytes into the PLN is low, but that it can be sped up after administration of FCA.     

Immune response pattern of the popliteal lymph nodes of dogs with visceral leishmaniasis

The present study aimed to estimate the cell response and parasite load in the popliteal lymph nodes of dogs with visceral leishmaniasis (VL), comparing these findings with the clinical staging of the disease. From the necropsy, 33 dogs were classified as symptomatic (S), asymptomatic (A), or oligosymptomatic (O). Cytology and histopathology were used to determine any presence of microscopic lesions and immunohistochemistry, for parasite load. Dog hyperimmune serum was used as the primary antibody. The inflammatory infiltrate in lymph nodes consisted of macrophages and plasmocytes. The granulomas invaded the trabecular and sinusoid regions and sometimes compressed the lymphocytes of the cortical region (atrophy) and medullary cord cells. Parasite load intensity was unrelated to the density of the macrophages infiltrating the lymph node. Significant differences in parasite load (P < 0.05) were observed between the three groups of infected dogs. Follicular hyperplasia of the cortical region occurred among A and O, while follicular atrophy predominated among S. The parasite load was the greatest among S, followed by O. It can be concluded that, regardless of clinical condition, the most evident cell response consisted of macrophages and plasmocytes. Lymphoid atrophy was observed among animals with intense granulomatous reaction and high parasite load, such as among the symptomatic dogs (P < 0.05). Likewise, the oligosymptomatic dogs also presented high density of parasites in the lymph nodes. Thus, we can confirm that dogs with clinical manifestations of VL have an immune system that is less effective for controlling infection by Leishmania chagasi, thereby favoring parasite multiplication.     

The migration of blood-borne lymphocytes into rat popliteal lymph nodes stimulated with xenogeneic red blood cells.

The recruitment of radiolabelled blood-borne lymphocytes into rat popliteal lymph nodes (PLN) was investigated following the injection of varying doses of chicken (CRBC) or sheep red blood cells (SRBC) into the hind foot pad. Within the dose range tested (10(5)-10(8) RBC) an increase in the dose of injected antigen resulted in elevated levels of lymphocyte recruitment into the draining popliteal lymph node. The kinetics of lymphocyte recruitment with the same dose of CRBC or SRBC was similar even though these red cells differ in size and are antigenically non-cross-reactive. While little is known of the mechanisms which control the rate of entry of blood-borne lymphocytes into antigen-stimulated lymph nodes, the extent of lymphocyte recruitment was shown to be directly related to the quantity of antigen injected.     

Fluid and cellular pathways of rat lymph nodes in relation to lymphatic labyrinths and Aquaporin-1 expression

The aim of the present study was to examine the organization of lymph fluid and cellular pathways and distribution of the membrane water channel Aquaporin-1 (AQP-1) in rat lymph nodes. Lymph fluid and cellular pathways within lymph nodes were examined by fluorescent protein tracer/confocal microscopy and by scanning electron microscopy (SEM), While the distribution of AQP-1 was studied immunohistochemically. Tracer studies showed the subcapsular sinuses continued directly at the hilum or via the intermediate sinuses to the medullary sinuses, and lymphatic labyrinths originating with blind-ends in the deep cortex drained into medullary sinuses. Afferent lymph tracers were also observed in node cortex interstitium. By SEM, lymphatic labyrinths appeared densely filled with lymphocytes and had few intraluminal sinus reticular cells, while medullary sinuses possessed well-developed networks of sinus reticular cells. The presence of many lymphocytes wedged in the walls of the lymphatic labyrinth suggested that lymphocytes migrate between the node parenchyma and lymphatic labyrinths. AQP-1 was distributed on the membrane of lymphatic endothelium and reticular cells as well as on both luminal and abluminal cell membranes of high endothelial venules (HEVs). Our SEM findings support the concept that lymphocytes migrate from the node parenchyma into lymphatic labyrinths in the deep cortex. The nodal distribution of AQP-1 plus the presence of a polarized distribution of ion pumps and/or ion channels in the HEV endothelium hypothesized in our discussion could explain the mechanism of the reported lymph-to-plasma fluid flux in lymph nodes and also facilitate the entry of afferent lymph antigens into the node cortex interstitium.     

Pathways between lymph vessels and sinuses in lymph nodes: a study in horses

The pathways through which lymph flows from terminal afferent lymphatics to the lymph sinuses, and from the sinuses to initial efferent lymphatics, were studied in horse lymph nodes by using Microfil casts and electron microscopy. Terminal afferent lymphatics are continuous with the subcapsular sinus through oval holes, about 3 microns wide, along their length, and through larger openings near their end. Other terminal afferents penetrate into the node within trabeculae and are supported by processes across the lumen. They connect with trabecular and medullary sinuses through oval or round holes, generally 20-30 microns across. Some of these have processes, similar to the luminal strands of the adjacent sinuses, extending across them, apparently providing reinforcement. Initial efferent lymphatics receive lymph from medullary sinuses through holes which are similar to those in afferent lymphatics, though more common, especially near the origin of the vessel. Initial efferents within the medulla appear to be supported by the luminal strands of the surrounding medullary sinuses. It seems likely that these strands, like the trabeculae which surround the penetrating afferent lymphatics, may help to keep the lymphatic vessels open as the node swells while draining an area of infection.     

颈淋巴引流阻滞对清醒自由活动大鼠的血压的影响

 目的：观察颈淋巴引流阻滞（CLB）对清醒自由活动大鼠的血压的影响，并初步探讨其机制。 方法： 采用SD大鼠，随机分为假手术组（Sham组）和CLB组。应用监测清醒自由活动大鼠血流动力学变化的手段，分别连续记录两组大鼠在假手术和CLB手术术前及术后第1、3、7、11、15 d收缩压（SBP）、舒张压（DBP）、心率（HR）的变化。测定两组大鼠术前、术后第1、7及15 d压力感受性反射敏感性（BRS）。脱机分析其相应的血压波动性（BPV）、心率变异性（HRV）。 结果： CLB术后第1天SBP、DBP、MAP、HR及BRS下降，第7天降至最低，BRS在7 d后无明显恢复，而血压及心率随着CLB时间的延长呈先下降后上升。相反，HRV、BPV先上升后下降。 结论： CLB可导致清醒自由活动大鼠血压降低，心血管系统神经调节功能下降。     

The kinetics and morphology of the rosette-forming cell response in the popliteal lymph nodes of rats

A modified ICA technique was used to study the kinetics and morphology of the RFC response in rat popliteal lymph nodes after an inoculation of SRBC into the hind footpad. The primary response was followed over a 10-day period. RFC were classified as either macrophages, haemocytoblasts, plasmacytes or lymphocytes.RFC present in the popliteal lymph nodes of uninoculated rats were identified as macrophages and lymphocytes. After inoculation the number of RFC rose rapidly to reach a peak at 5–6 days. It was shown that after incubation at 37° certain RFC from inoculated rats had several layers of adherent SRBC and it was suggested that this was an indication of an active secretion of haemagglutinin. 3–4 days after innoculation large mature haemocytoblasts were actively secreting haemagglutinin whilst from the 5th to the 10th day plasmacytes were the RFC involved in the haemagglutinin production. It is suggested that the large haemagglutinin producing haemocytoblasts arise without mitosis via a process of cell transformation and that RF plasmacytes arise via lymphocyte activation into small haemocytoblasts, mitotic division and eventual maturation into immature plasmacytes. RF lymphocytes were thought not to be involved to any extent in haemagglutinin production.     

Taking the lymphatic route: dendritic cell migration to draining lymph nodes

In contrast to leukocyte migration through blood vessels, trafficking via lymphatic vessels (LVs) is much less well characterized. An important cell type migrating via this route is antigen-presenting dendritic cells (DCs), which are key for the induction of protective immunity as well as for the maintenance of immunological tolerance. In this review, we will summarize and discuss current knowledge of the cellular and molecular events that control DC migration from the skin towards, into, and within LVs, followed by DC arrival and migration in draining lymph nodes. Finally, we will discuss potential strategies to therapeutically target this migratory step to modulate immune responses.     

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.     

Primary Kaposi's sarcoma in lymph nodes concurrent with chronic lymphatic leukemia.

Both Kaposi's sarcoma and chronic lymphatic leukemia affect the lymph nodes, and not infrequently, the same patient. The authors describe the occurrence of both diseases in the same lymph node. The rarity of this finding suggests different histopathogenic origins of the two diseases.