Inhibition of the transendothelial migration of human lymphocytes but not monocytes by phosphodiesterase inhibitors

This study describes an in vitro model of peripheral blood mononuclear cell (PBMC) migration through human endothelial cells, held on polycarbonate inserts, which allows automatic differential counting of migrated cells as lymphocytes and monocytes. Using this system it was found that treatment of PBMC with the phosphodiesterase (PDE) inhibitors theophylline (at 1 and 10 μg/ml) and RO-20-1724 (at 1 μm) inhibited the migration of the lymphocyte component to 64.2 ± 16.4%, 48.9 ± 3.0% and 47.5 ± 5.8% of the control values, respectively, while the migration of the monocytes component was largely unaffected. The PDE inhibitors needed to be present during the assay to inhibit migration, whereas pre-treatment of either the endothelium or the PBMC did not consistently effect lymphocyte migration. The drugs also inhibited the migration of lymphocytes through control inserts, either uncoated or coated with fibronectin, suggesting that some of the inhibition is an effect on lymphocyte motility rather than lymphocyte–endothelial interactions. Lymphocyte migration through fibronectin-coated filters was significantly enhanced compared with uncoated filters. Activation of the PBMC by anti-CD3 MoAb increased motility and migration by up to 300%. This migration appeared to be greatly inhibited by the PDE inhibitors, although the effect was complicated by problems of lymphocyte aggregation. This study provides a novel method of measuring mononuclear cell transendothelial migration, and suggests a possible role of PDE inhibitors in reducing this process.     

Wnt signaling regulates transendothelial migration of monocytes

The Wnt-signaling pathway plays a critical role in directing cell fate during embryogenesis. Several lines of evidence also suggest a role in inflammatory processes. Here, we analyzed whether Wnt signaling plays a role in leukocyte inflammatory responses. Monocytes from healthy donors expressed different Frizzled receptors, which are ligands for the Wnt molecules. Activation of the Wnt/beta-catenin pathway by LiCl or Wnt3a increased beta-catenin protein levels in monocytes but not in granulocytes. It is interesting that the activation of Wnt/beta-catenin signaling via Wnt3a in monocytes resulted in a decrease in migration through an endothelial layer (human dermal microvascular endothelial cell-1). Further experiments revealed that the decrease in transendothelial migration was associated with specific monocyte adherence to endothelial cells after Wnt exposure. The specificity was verified by a lack of Wnt3a-induced adhesion to fibronectin, laminin, or collagen compared with endothelial interaction. Analysis of the distribution of beta-catenin revealed a Wnt3a-induced increase of beta-catenin in the cytoplasm. Wnt3a exposure did not result in any activation of the classical Wnt-target gene c-myc or a Wnt-target gene involved in cell adhesion (Connexin43). Our study implicates for the first time a role of canonical Wnt signaling in inflammatory processes in monocytes.     

Regulation of chemokine-induced transendothelial migration of T lymphocytes by endothelial activation: differential effects on naive and memory T cells

Human T lymphocyte transendothelial migration (TEM) was examined in response to chemokines across cytokine-activated endothelium. Monocyte chemotactic protein-1 (MCP-1), RANTES, and macrophage inflammatory protein-1alpha (MIP-1alpha) induced TEM by memory T cells, while stromal cell-derived factor-1 (SDF-1) induced TEM by both naive and memory T cells. Tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1) increased endothelial adhesion molecule (CAM) expression, whereas interferon-gamma (IFN-gamma) induced little up-regulation of CAM. However, both TNF-alpha and IFN-gamma strongly facilitated T cell migration, which was completely inhibited by pertussis toxin and both greatly increased TEM to RANTES, MIP-1alpha, and SDF-1 selectively of memory but not naive T cells. Thus, the dual selective effect on memory T cells of endothelial activation and these chemokines promotes the preferential recruitment of memory T cells to inflammatory sites. However, the enhanced chemokine-induced migration by memory T cells across activated endothelium appears to be independent of the increase in endothelial CAM expression. G-protein-linked stimuli may play an important part in T cell TEM across cytokine-activated endothelium.     

RhoA activation promotes transendothelial migration of monocytes via ROCK

Monocyte infiltration into inflamed tissue requires the initial arrest of the cells on the endothelium followed by firm adhesion and their subsequent migration. Migration of monocytes and other leukocytes is believed to involve a coordinated remodeling of the actin cytoskeleton. The small GTPases RhoA, Rac1, and Cdc42 are critical regulators of actin reorganization. In this study, we have investigated the role of Rho-like GTPases RhoA, Rac1, and Cdc42 in the adhesion and migration of monocytes across brain endothelial cells by expressing their constitutively active or dominant-negative constructs in NR8383 rat monocytic cells. Monocytes expressing the active form of Cdc42 show a reduced migration, whereas Rac1 expression did not affect adhesion or migration. In contrast, expression of the active form of RhoA in monocytes leads to a dramatic increase in their adhesion and migration across endothelial cells. The effect of RhoA was found to be mediated by its down-stream effector Rho kinase (ROCK), as pretreatment with the selective ROCK inhibitor Y-27632 prevented this enhanced adhesion and migration. These results demonstrate that RhoA activation in monocytes is sufficient to enhance adhesion and migration across monolayers of endothelial cells.     

Reduced transendothelial migration of monocytes infected by Coxiella burnetii

The migratory properties of THP1 monocytes infected by Coxiella burnetii were determined in a transmigration assay across a human microvascular endothelial cell monolayer. Transendothelial migration of monocytes infected by virulent, but not avirulent, C. burnetii was inhibited. This inhibition was observed in spite of conserved adherence properties of infected monocytes.     

Primary human alveolar epithelial cells can elicit the transendothelial migration of CD14+ monocytes and CD3+ lymphocytes

The ability of freshly isolated primary human alveolar epithelial cells (type II pneumocytes) to induce leucocyte migration across an endothelial monolayer was investigated. Three-way factorial analysis of variance (ANOVA) demonstrated that resting alveolar endothelial cells (AEC) could produce detectable quantities of monocyte chemoattractant protein 1 (MCP-1), which was upregulated in response to tumour necrosis factor-alpha (TNF-alpha) in a dose- and time-dependent fashion. Interferon-gamma (IFN-gamma) had no significant effect on this process. TNF-alpha and IFN-gamma both induced AEC to provoke migration of CD14+ monocytes and CD3+ lymphocytes across endothelium. IFN-gamma and TNF-alpha synergized in their ability to induce production of T lymphocyte, but not monocyte, chemoattractants from AEC. Leucocyte transendothelial migration was inhibited by anti-MCP-1 neutralizing antibody and by heparin, a polyanionic glycosaminoglycan (GAG). These data suggest that human AEC play a role in the multiple mechanisms that facilitate monocyte and T lymphocyte migration into the alveolar compartment of the lung under homeostasis and inflammatory conditions. One of these mechanisms is mediated via constitutive MCP-1 production by alveolar epithelial cells, which is upregulated by TNF-alpha.     

The effect of transendothelial migration on eosinophil function

In bronchial asthma, eosinophils found in the airways have an enhanced inflammatory capacity. We hypothesized that, at least in part, changes in functional phenotype are due to the effect of transendothelial migration. To model in vivo eosinophil trafficking to the lung, we cultured human pulmonary microvascular endothelial cell (HPMEC) monolayers on Transwell filters. The HPMECs were activated with interleukin (IL)-1beta to increase cell expression of intercellular adhesion molecule (ICAM)-1 and, hence, eosinophil transmigration. Peripheral blood eosinophils from allergic patients were added to HPMEC-covered Transwell filters and incubated for 3 h at 37 degrees C. The eosinophils were collected from below (migrated cells) and above (nonmigrated cells) the HPMEC monolayer to determine surface receptor expression, in vitro survival, and oxidative burst. Eosinophils never exposed to HPMECs were used as controls. Eosinophil cell surface expression of CD69, human leukocyte-associated antigen-DR (HLA-DR), and CD54 (ICAM-1) was significantly increased after transendothelial migration through IL-1beta-treated HPMECs compared with control cells (CD69: P<0.0005; HLA-DR and CD54: P<0.05) and nonmigrated eosinophils (CD69 and HLA-DR: P<0.05). Moreover, the percent in vitro survival (48 h) of migrated eosinophils was also significantly greater (P<0.0001 by trypan blue exclusion, P< 0.05 by flow cytometry) than that of control or nonmigrated eosinophils. Prolonged survival of migrated eosinophils was inhibited by addition of anti-granulocyte macrophage colony-stimulating factor (GM-CSF) antibodies (P<0.05) to the 48-h survival culture, suggesting that autocrine production of GM-CSF was, at least partially, responsible for increased eosinophil survival. Although GM-CSF protein was not measurable in survival culture supernates, GM-CSF messenger RNA (mRNA) was expressed in both nonmigrated and migrated eosinophils but not in control cells. Similarly, the eosinophils' oxidative burst induced by platelet-activating factor, formylmethionyl leucylphenylalanine, or phorbol myristate acetate was equally, and significantly, increased in both nonmigrated and migrated eosinophils (P<0.05 versus control). Therefore, whereas exposure of eosinophils to cytokine-activated HPMECs can increase surface receptor expression, in vitro survival, GM-CSF mRNA, and the respiratory burst, transendothelial migration can further potentiate receptor expression and survival in migrated cells. These results suggest that the process of transendothelial migration selectively participates in determining the eventual phenotype of airway eosinophils.     

Helicobacter pylori induces transendothelial migration of activated memory T cells

Helicobacter pylori infection is associated with pronounced infiltration of granulocytes and lymphocytes into the gastric mucosa, resulting in active chronic gastritis that may develop into duodenal ulcer disease or gastric adenocarcinoma. Infiltrating T cells play a major role in the pathology of these diseases, but the signals involved in recruitment of T cells from blood to H. pylori-infected tissues are not well understood. We therefore examined H. pylori-induced T-cell transendothelial migration (TEM). The Transwell system, employing a monolayer of human umbilical vein endothelial cells, was used as a model to study TEM. H. pylori induced a significant T-cell migration, compared to spontaneous migration. CD4+ and CD8+ T cells migrated to the same extent in response to H. pylori, whereas there was significantly larger transmigration of memory T cells compared to naive T cells. Both H. pylori culture filtrate and urease induced migration, and the presence of the H. pylori cag pathogenicity island increased TEM. T-cell TEM was mediated by LFA-1-ICAM-1 interactions in accordance with an increased ICAM-1 expression on the endothelial cells after contact with H. pylori. Migrating T cells had increased expression of activation marker CD69 and chemokine receptors CXCR3, CCR4, and CCR9. Furthermore, T cells migrating in response to H. pylori secreted Th1 but not Th2 cytokines upon stimulation. In conclusion, our data indicate that live H. pylori and its secreted products contribute to T-cell recruitment to the gastric mucosa and that the responding T cells have an activated memory Th1 phenotype.     

Interleukin-8 induces neutrophil transendothelial migration.

Interleukin-8 (IL-8) is a potent neutrophil chemotactic stimulant. We have used chemically synthesized IL-8 to investigate its role in human neutrophil adhesion and transendothelial migration. IL-8 enhanced the adhesiveness of human neutrophils to plastic, and to both unstimulated and tumour necrosis factor (TNF)-stimulated endothelial monolayers in vitro. Using a two-compartment model separated by a confluent endothelial monolayer, we have shown that IL-8 chemotactic stimulation induced transmigration across the monolayer of up to 87.4 +/- 2.1% of added neutrophils (compared to random unstimulated transmigration of 2.2 +/- 0.7%), while chemokinetic stimulation led to transmigration of 21 +/- 3.8% of neutrophils. Preincubation of endothelium with TNF also induced transmigration in this model, and was additive when combined with an IL-8 chemotactic stimulus. Endothelial permeability was increased at maximal rates of chemotactic transmigration, which may correlate with increased permeability of vessels at inflammatory sites in vivo. The property of IL-8 to stimulate movement of neutrophils across endothelial monolayers in vitro supports the concept of a central role for this molecule in the accumulation of neutrophils at inflammatory lesions in vivo.     

Inhibitory and stimulatory effects of Pseudomonas aeruginosa pyocyanine on human T and B lymphocytes and human monocytes.

Pyocyanine, a pigment produced by Pseudomonas aeruginosa, has dual dose-dependent stimulatory as well as inhibitory effects on immune responses in vitro as measured by DNA synthesis of human T and B lymphocytes, interleukin-2 (IL-2) production by human T lymphocytes, immunoglobulin production by human B lymphocytes, and monokine production by human monocytes. In general, stimulatory activity was found at low concentrations of pyocyanine, whereas high concentrations of the pigment resulted in an inhibition of responses. At a pyocyanine concentration of 0.1 micrograms/ml or less the proliferation of T and B lymphocytes was enhanced, but at 0.5 micrograms/ml it was suppressed. IL-2 production by T lymphocytes was enhanced at concentrations up to 0.5 micrograms/ml but totally inhibited at 1.0 micrograms/ml. The differentiation of B lymphocytes to become immunoglobulin-producing cells was also enhanced in the presence of low doses of pyocyanine, whereas secretion of immunoglobulin by B lymphocytes was suppressed at all concentrations of pyocyanine. In contrast to the dual effects of pyocyanine on lymphocyte response, lipopolysaccharide-induced IL-1 and tumor necrosis factor release by monocytes was markedly enhanced by low as well as high concentrations of pyocyanine. From these results we conclude that this property of pyocyanine may lead to suppression of specific defense mechanisms and enhance harmful inflammatory reactions of the host during infection with Pseudomonas aeruginosa.     

Infection of human endothelial cells with Chlamydia pneumoniae stimulates transendothelial migration of neutrophils and monocytes

We have previously shown that different isolates of Chlamydia pneumoniae display heterogeneity in the in vitro stimulation of chemokines and adhesion molecules from infected human endothelial cells. In the present study, we examined the ability of different isolates of C. pneumoniae to promote transendothelial migration of neutrophils and monocytes. Human umbilical vein endothelial cells (HUVEC) were infected with low (<15)-passage C. pneumoniae isolates A-03, PS-32, and BR-393 and high (>40)-passage isolates BAL-16, TW-183, and T-2634, and levels of neutrophil and monocyte transendothelial migration were determined following 24 h of infection. Compared to mock-infected controls, significant increases in neutrophil migration were observed in response to most C. pneumoniae isolates examined (P < 0.001). Levels of monocyte migration were significantly increased in response to TW-183 and T-2634 (P < 0.001). Serial passage (>40 times) of the three low-passage isolates in HEp-2 cell cultures prior to infection of HUVEC generally resulted in the promotion of higher levels of neutrophil and monocyte transendothelial migration. These findings were compatible with differences observed in the extent of interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) stimulation between low- and high-passage A-03, PS-32, and BR-393. As opposed to C. pneumoniae, infection with C. trachomatis L2 caused only a slight increase in neutrophil transendothelial migration, which correlated with the lack of measurable IL-8 levels by this species. However, significant levels of monocyte migration were induced in response to C. trachomatis L2 despite a lack of measurable MCP-1 stimulation. C. trachomatis serovars A and E also failed to induce IL-8 and MCP-1 production in HUVEC. Results from this study indicate that the passage history of C. pneumoniae may play a role in the divergence of stimulatory activities observed among isolates in human endothelial cells. In addition, the differences observed between this organism and C. trachomatis suggest that the upregulation of IL-8 and MCP-1 in endothelial cells may be unique to C. pneumoniae.     

LPS differentially regulates adhesion and transendothelial migration of human monocytes under static and flow conditions

One of the key components of the innate immune response is the recognition of microbial products such as LPS by Toll-like receptors on monocytes and neutrophils. We show here that short-term stimulation of primary human monocytes with LPS led to an increase in adhesion of monocytes to endothelial cells and a dramatic decrease in transendothelial migration under static conditions. In contrast, under normal physiological flow, monocyte adhesion and migration across a human umbilical vein endothelial cell monolayer appeared to be unaffected by LPS treatment. LPS stimulation of monocytes activated beta(1) and beta(2) integrins, but did not increase their surface expression levels. During septic shock, reduction in blood flow as a result of vasodilation and vascular permeability leads to adhesion and accumulation of LPS-stimulated circulating monocytes onto the blood vessel walls. The different findings of monocyte migration under static and flow conditions in our study may offer one explanation for this phenomenon. The rapid engagement of LPS-activated monocytes preventing transendothelial migration could represent a novel mechanism of bacterial exclusion from the vasculature. This occurs during the early stages of sepsis, and in turn may modulate the severity of the pathophysiology.     

The effect of cytokines and chemotactic agonists on the migration of T lymphocytes into skin.

The migration of lymphocytes and neutrophils into skin sites stimulated with chemotactic agonists or with cytokines known to induce leucocyte-endothelial adhesion molecules was examined in sheep. Lymphocytes, collected from efferent prefemoral lymph, labelled in vitro with [111In]oxine and reinjected intravenously, migrated in large numbers into delayed-type hypersensitivity (DTH) reactions elicited by purified protein derivative (PPD) and into sites stimulated with tumour necrosis factor-alpha (TNF-alpha) or interferon-gamma (IFN-gamma). In contrast, interleukin (IL)-1 alpha, a potent inducer of endothelial leucocyte adhesion molecule-1 (ELAM-1), caused moderate accumulation of [111In]lymphocytes at concentrations that induced intense accumulation of 111In-labelled neutrophils. The chemotactic agonists IL-8 and zymosan-activated plasma (ZAP) caused accumulation of very large numbers of neutrophils but only small numbers of lymphocytes, whereas platelet-activating factor (PAF) and leukotriene B4 (LTB4) failed to recruit lymphocytes into skin. IFN-gamma was the only mediator to recruit lymphocytes in preference to neutrophils into skin. The results suggest that those lymphocyte chemotactic agonists which lack the ability to induce adhesion molecules on endothelium play only a minor role in directing migration of lymphocytes into skin. Immunohistological examination of skin lesions confirmed the findings of studies with 111In-labelled lymphocytes and indicated that there was a tendency for CD4+ cells to outnumber CD8+ cells in infiltrates induced by all mediators. In contrast to the elevated numbers of T19+ subset of T-cell receptor (TcR+) gamma delta cells present in DTH reactions, none of the mediators induced migration of T19+ cells into skin.     

HMGB1抑制剂对脓毒症小鼠T淋巴细胞和单核细胞的作用机制

目的 探讨高迁移率族蛋白B1（high modility groupbox 1,HMGB1）抑制剂对脓毒症T淋巴细胞和单核细胞的作用机制。 方法 将30只C57BL/6雄性小鼠随机分为3组,每组10只,依次为假手术组、模型组、抑制剂组。模型组、抑制剂组采用盲肠结扎穿孔手术构建脓毒症小鼠模型,假手术组小鼠仅暴露盲肠后即进行伤口缝合,不结扎。抑制剂组小鼠术后腹腔注射HMGB1特异性抑制剂甘草酸（10 mg/kg）,每6 h注射1次,连续4次,假手术组和模型组腹腔注射等剂量的生理盐水。处死小鼠后,无菌分离小鼠的胸腺组织,常规提取胸腺中的T淋巴细胞和单核细胞。MTT法与流式细胞术测定T淋巴细胞的增殖活性和凋亡情况,Transwell趋化实验与ELISA法测定单核细胞的趋化活性以及分泌炎性因子TNF-α、IL-6及IL-10的情况,Western blot检测胸腺组织中HMGB1和第10号染色体同源丢失性磷酸酶-张力蛋白（phosphatase and tensin homolog deleted onchromosometen,PTEN）的表达水平。 结果 与假手术组相比,模型组小鼠胸腺组织T淋巴细胞的增殖活性和凋亡率、单核细胞的趋化活性和TNF-α、IL-6、IL-10蛋白的表达、HMGB1和PTEN的表达明显升高（均P<0.05）;与模型组相比,抑制剂组小鼠胸腺组织T淋巴细胞凋亡率、TNF-α、IL-6蛋白的表达、HMGB1和PTEN的表达明显降低,T淋巴细胞的增殖活性、单核细胞的趋化活性、IL-10蛋白的表达明显升高（均P<0.05）。 结论 HMGB1抑制剂可降低脓毒症小鼠胸腺T细胞的凋亡率,增强T细胞的增殖活性和单核细胞的趋化活性,提高单核细胞抗炎因子IL-10的分泌,抑制促炎因子TNF-α、IL-6的分泌。     

The effects of complement activation by cobra venom factor on the migration of T and B lymphocytes into rat thoracic duct lymph.

Experiments were done to see whether C3 or C3-split products are involved in lymphocyte recirculation, with particular reference to B lymphocytes which have C3b receptors. Rats were injected with cobra venom factor (CVF), and the output of subclasses of lymphocytes was measured in thoracic duct lymph in hourly collections during the subsequent 24 h. During the period of acute C3 activation which lasted for 2-8 h, the output of lymphocytes decreased by 47%, but returned to normal at later times, when C3 levels were reduced to less than 20% normal. There was no effect on the output of C3b receptor lymphocytes, and this receptor was not blocked probably because initial C3 levels in lymph were only 13% of blood levels, so that only small amounts of C3b were generated in lymph. When these lymphocytes were labelled and injected i.v. they migrated with the slow rate which is characteristic of normal B lymphocytes. The main effect of CVF was to reduce the output of T lymphocytes by 58% during the phase of acute C3 activation. When normal thoracic duct lymphocytes were labelled and injected, their rate of reappearance in thoracic duct lymph was only reduced during this phase. It was concluded that recirculation of lymphocytes is not C3 dependent, and that insufficient C3b is generated in lymphoid tissues to block C3b receptors on B lymphocytes during periods of rapid C3 activation. However the migratory rate of T lymphocytes through these tissues is reduced during this period, and it is suggested that this may be due to an effect of C3 split products on macrophages which lie along T-lymphocyte traffic routes.     

Importance of HLA-D antigens for the cooperation between human monocytes and T lymphocytes.

The ability of autologous and allogeneic monocytes to restore the responsiveness of purified T lymphocytes to tuberculin (PPD) was studied in twelve different experiments involving eleven unrelated T lymphocyte donors and a large number of related and unrelated monocyte donors. T lymphocyte suspensions were prepared by passage of peripheral blood mononuclear cell suspensions through Ig-anti-Ig-coated columns. Monocyte-enriched suspensions were prepared from mononuclear suspensions by density gradient centrifugation on albumin solution and added to the T cell suspension in a final concentration of 3%. Autologous monocytes and monocytes from related donors sharing one HLA haplotype with the T cell donor partly restored the responsiveness to PPD, and so did monocytes from unrelated donors who shared HLA-D alleles with the T cells. None of eight monocyte suspensions from eight unrelated donors sharing no HLA-D antigens with the T cell donor were able to restore the responsiveness to PPD. The difference between HLA-D-sharing and nonsharing monocytes could not be explained by a simultaneous allogeneic reaction, as the addition of monocytes autologous with the T cells to mixtures of non-HLA-D-sharing T cells and monocytes partly restored the response. Moreover, experiments with the addition of PPD to ordinary mixed leukocyte cultures revealed only a moderate depression on the PPD response. It is concluded that in man – as in mice and guinea pigs – some HLA-D identity between monocytes and T lymphocytes is necessary for a cooperation to take place in the secondary immune response. This observation emphasizes the homology between HLA-D antigens in man and Ia antigens in animals.     

FTY720对小肠移植物中淋巴细胞及单核细胞浸润的影响

目的：研究FTY720对同种异体小鼠小肠移植排斥反应的作用及可能机制。方法：以C3H小鼠（H-2k）为供者，C57BL/6小鼠(H-2b）为受者，行异位小肠移植。分别建立FTY720治疗组、空白对照组及同系移植组，在移植后6 d与12 d进行组织学观测评定排斥分数，流式细胞术分析移植物肠系膜淋巴结（MLN）、派氏结（PP）、粘膜上皮细胞间淋巴组织（IEL）与固有层淋巴组织（LPL）中淋巴细胞中受者淋巴细胞及单核细胞浸润情况。结果：FTY720在移植后6 d可有效抑制排斥反应，但在移植后14 d，排斥反应仍可发生在空白对照组，移植后6 d移植物内受者淋巴细胞基本取代供者细胞；而在FTY720治疗组，受者淋巴细胞进入移植物的速度及数量明显减缓，包括CD4+与CD8+ T细胞，以及CD19+ B细胞。受者来源的γδT淋巴细胞也显著减少。FTY720对Gr1+CD11b+单核细胞系也有一定的抑制作用。结论：FTY720可通过减少受者淋巴细胞及单核细胞进入移植小肠，起到缓解排斥反应的作用。     

Factors governing the intranodal migration behavior of T lymphocytes

Summary: With the advent of two-photon microscopic imaging, the last few years have witnessed remarkable progress regarding our understanding of the movement behavior and interaction dynamics of different immune cells within lymphoid organs. The basal intranodal motility of naive T lymphocytes in the absence of antigenic or inflammatory stimuli, although at first glance representing a phenomenon of apparent simplicity, is far from being completely understood. The most important open question in this context relates to the origin of intranodal T-cell motility itself: how are these highly dynamic cells ‘motivated’ to carry out their relentless scanning of dendritic cells present in the lymph node (LN)? This review summarizes recent advances in the search for factors governing the intranodal migration behavior of naive T lymphocytes, focusing in particular on the role of extracellular pro-migratory cues, intracellular signaling components, and the influence of the structural LN environment on intranodal T-cell motility.     

Recruitment of effector lymphocytes by initiator lymphocytes. In vivo migration of in vitro sensitized initiator T lymphocytes.

We previously found that mouse T lymphocytes sensitized in vitro against allo- or syngeneic fibroblasts, upon injection into syngeneic recipients, do not themselves differentiate into effector cells, but recruit effector T lymphocytes within the draining lymph nodes. As a result of sensitization, these initiator lymphocytes acquire a trypsin-sensitive membrane property which is necessary for recruitment. We now report studies on the in vivo migratory behavior of initiator lymphocytes following sensitization. We injected 51Cr-labeled initiator lymphocytes into recipient footpads and found significantly increased migration of sensitized cells to the draining popliteal lymph node (PLN) during the first day. By amputation of the foot at various times, we showed that migration during the first 12-24 hours was critical for subsequent recruitment. Trypsin treatment of initiator lymphocytes abolished this accelerated migration. Lymphocytes triggered nonspecifically by Con A migrated to the PLN like antigen-sensitized cells. We also compared the migration of injected lymphocytes from the footpad to the PLN in graft-versus-host and host-versus-graft reactions, and found these reactions to differ both from each other and from recruitment in terms of lymphocyte migration. These findings are discussed in terms of the physiology of the cell-mediated immune response and the notion of peripheral sensitization.