Migration of naive, effector and memory T cells: implications for the regulation of immune responses

Mapping the spatial distribution of T cells in repertoire dimension

T cells mediate adaptive immunity in diverse anatomic compartments through recognition of specific antigens via unique T cell receptor (TCR) structures. However, little is known about the spatial distribution of an organism's TCR repertoire. Here, using high-throughput TCR sequencing (TCRseq), we investigated the TCR repertoires of sixteen tissues in healthy C57B/L6 mice. We found that TCR repertoires generally classified into three categories (lymph nodes, non-lymph node tissues and small intestine) based on sequence similarity. Clonal distribution and diversity analyses showed that small intestine compartment had a more skewed repertoire as compared to lymph nodes and non-lymph node tissues. However, analysis of TRBV and TRBJ gene usage across tissue compartments, as well as comparison of CDR3 length distributions, showed no significant tissue-dependent differences. Interestingly, analysis of clonotype sharing between mice showed that although non-redundant public clonotypes were found more easily in lymph nodes, small intestinal CD4 + T cells harbored more abundant public clonotypes. These findings under healthy physiological conditions offer an important reference dataset, which may contribute to our ability to better manipulate T cell responses against infection and vaccination.

CD4- and CD8-expressing cells in the chambers of normal, cataract and uveitic eyes: A comparative study in dogs

The main aims of this study were to determine whether CD4⁺ and CD8⁺ cells are present in the normal chambers of the eye in dogs and to verify the hypothesis that uncomplicated cataract may be associated with the local recruitment of CD4⁺ and CD8⁺ cells. The presence of CD4⁺ and CD8⁺ cells was detected in aqueous humor (AH) of normal and cataract eyes. The study did not reveal differences in the percentage and absolute number of CD4⁺ cells between normal and cataract eyes. However, the values of these parameters in AH from cataract eyes were approximately 2- and 3-fold higher than in normal eyes, respectively. The mean percentage and absolute count of CD8⁺ cells increased approximately by 2.7- and 6-fold, respectively, in AH samples from cataract eyes compared to normal ones. The absolute count of CD4⁺ and CD8⁺ cells in AH of uveitic eyes was approximately 5- and 3-fold higher than in cataract eyes. The results indicate that CD4⁺ and CD8⁺ cells occur constitutively in the normal chambers of the eye in dogs. However, it should be pointed out that both of these cell populations appeared in trace amounts. The development of uncomplicated cataract in dogs may not be immunologically neutral in terms of the local immune response, but it may be associated with the recruitment of CD8⁺ cells into the eye chambers. This event does not seem to be of an inflammatory nature because it appears on a scale a few times smaller than in the course of uveitis.

Early drop of circulating T cells negatively correlates with the protective immune response to Yellow Fever vaccination

Lymphocyte recirculation within the human body is essential for efficient pathogen detection and immune responses. So far, immune cell migration has been investigated largely using ovine and murine models, with little evidence in humans. Here, we analyzed peripheral blood of healthy individuals following primary vaccination with the Yellow Fever vaccine YF-17D. We found that the number of leukocytes was transiently and sharply reduced in blood as detected on day 7 after vaccine administration. The T cell drop was restricted to cells expressing the lymph node-homing chemokine receptor CCR7. Interestingly, the vaccine-induced drop positively correlated with the expression of CD69 by the T cells before vaccination. This suggests that CCR7⁺ T cells are being trapped within the lymph nodes through CD69-induced suppression of egress. Strikingly, we further found that the T cell drop negatively correlated with CD8 T cell activation and with production of neutralizing antibodies. In conclusion, early and transient T cell depletion in blood negatively correlated with protective immune response events induced by YF-17D vaccination. Our data highlight baseline CD69 expression and early drop in T cells as potential biomarkers of the Yellow Fever vaccine response.

Estimating Residence Times of Lymphocytes in Ovine Lymph Nodes

The ability of lymphocytes to recirculate between blood and secondary lymphoid tissues such as lymph nodes (LNs) and spleen is well established. Sheep have been used as an experimental system to study lymphocyte recirculation for decades and multiple studies document accumulation and loss of intravenously (i.v.) transferred lymphocytes in efferent lymph of various ovine LNs. Yet, surprisingly little work has been done to accurately quantify the dynamics of lymphocyte exit from the LNs and to estimate the average residence times of lymphocytes in ovine LNs. In this work we developed a series of mathematical models based on fundamental principles of lymphocyte recirculation in the body under non-inflammatory (resting) conditions. Our analysis suggested that in sheep, recirculating lymphocytes spend on average 3 h in the spleen and 20 h in skin or gut-draining LNs with a distribution of residence times in LNs following a skewed gamma (lognormal-like) distribution. Our mathematical models also suggested an explanation for a puzzling observation of the long-term persistence of i.v. transferred lymphocytes in the efferent lymph of the prescapular LN (pLN); the model predicted that this is a natural consequence of long-term persistence of the transferred lymphocytes in circulation. We also found that lymphocytes isolated from the skin-draining pLN have a 2-fold increased entry rate into the pLN as opposed to the mesenteric (gut-draining) LN (mLN). Likewise, lymphocytes from mLN had a 3-fold increased entry rate into the mLN as opposed to entry rate into pLN. In contrast, these cannulation data could not be explained by preferential retention of cells in LNs of their origin. Taken together, our work illustrates the power of mathematical modeling in describing the kinetics of lymphocyte migration in sheep and provides quantitative estimates of lymphocyte residence times in ovine LNs.

Sleep Matters: CD4+ T Cell Memory Formation and the Central Nervous System

The mechanisms of CD4⁺ T-cell memory formation in the immune system are debated. With the well-established concept of memory formation in the central nervous system (CNS), we propose that formation of CD4⁺ T-cell memory depends on the interaction of two different cell systems handling two types of stored information. First, information about antigen (event) and challenge (context) is taken up by antigen-presenting cells, as initial storage. Second, event and context information is transferred to CD4⁺ T cells. During activation, two categories of CD4⁺ T cell develop: effector CD4⁺ T cells, carrying event and context information, enabling them to efficiently focus their response to tissues under attack; and persisting CD4⁺ T cells, providing context-independent antigen-specific memories and long-term storage. This novel hypothesis is supported by the observation that mammalian sleep can improve both CNS and CD4⁺ T-cell memory.

Virus dynamics and phyloanatomy: Merging population dynamic and phylogenetic approaches

In evolutionary biology and epidemiology, phylodynamic methods are widely used to infer population biological characteristics, such as the rates of replication, death, migration, or, in the epidemiological context, pathogen spread. More recently, these methods have been used to elucidate the dynamics of viruses within their hosts. Especially the application of phylogeographic approaches has the potential to shed light on anatomical colonization pathways and the exchange of viruses between distinct anatomical compartments. We and others have termed this phyloanatomy. Here, we review the promise and challenges of phyloanatomy, and compare them to more classical virus dynamics and population genetic approaches. We argue that the extremely strong selection pressures that exist within the host may represent the main obstacle to reliable phyloanatomic analysis.

Immunobiochemical Reconstruction of Influenza Lung Infection-Melanoma Skin Cancer Interactions

It was recently reported that acute influenza infection of the lung promoted distal melanoma growth in the dermis of mice. Melanoma-specific CD8+ T cells were shunted to the lung in the presence of the infection, where they expressed high levels of inflammation-induced cell-activation blocker PD-1, and became incapable of migrating back to the tumor site. At the same time, co-infection virus-specific CD8+ T cells remained functional while the infection was cleared. It was also unexpectedly found that PD-1 blockade immunotherapy reversed this effect. Here, we proceed to ground the experimental observations in a mechanistic immunobiochemical model that incorporates T cell pathways that control PD-1 expression. A core component of our model is a kinetic motif, which we call a PD-1 Double Incoherent Feed-Forward Loop (DIFFL), and which reflects known interactions between IRF4, Blimp-1, and Bcl-6. The different activity levels of the PD-1 DIFFL components, as a function of the cognate antigen levels and the given inflammation context, manifest themselves in phenotypically distinct outcomes. Collectively, the model allowed us to put forward a few working hypotheses as follows: (i) the melanoma-specific CD8+ T cells re-circulating with the blood flow enter the lung where they express high levels of inflammation-induced cell-activation blocker PD-1 in the presence of infection; (ii) when PD-1 receptors interact with abundant PD-L1, constitutively expressed in the lung, T cells loose motility; (iii) at the same time, virus-specific cells adapt to strong stimulation by their cognate antigen by lowering the transiently-elevated expression of PD-1, remaining functional and mobile in the inflamed lung, while the infection is cleared. The role that T cell receptor (TCR) activation and feedback loops play in the underlying processes are also highlighted and discussed. We hope that the results reported in our study could potentially contribute to the advancement of immunological approaches to cancer treatment and, as well, to a better understanding of a broader complexity of fundamental interactions between pathogens and tumors.

CD25+CD127+Foxp3- Cells Represent a Major Subpopulation of CD8+ T Cells in the Eye Chambers of Normal Mice

The aim of this study has been to determine whether eye chambers constitute part of the normal migratory pathway of naive CD4⁺ and CD8⁺ T cells in mouse and if natural CD4⁺CD25⁺Foxp3⁺ and CD8⁺CD25⁺Foxp3⁺ regulatory T cells are present within these eye compartments. To this aim, the cells obtained from aqueous humor (AH) of normal mice were phenotyped in terms of the expression CD4, CD8, CD25, CD127 and transcription factor Foxp3. The mean percentage of CD8⁺ T cells in the total AH lymphocyte population was as high as 28.69%; the mean percentage of CD8^high and CD8^low cells in this population was 34.09% and 65.91%, respectively. The presence of cells with the regulatory phenotype, i.e. CD25⁺Foxp3⁺ cells, constituted only 0.32% of CD8⁺ T cell subset. Regarding the expression of CD25, AH CD8⁺ T cells were an exceptional population in that nearly 85% of these cells expressed this molecule without concomitant Foxp3 expression. Despite having this phenotype, they should not be viewed as activated cells because most of them co-expressed CD127, which indicates that they are naive lymphocytes. With regard to the markers applied in the present research, CD8⁺CD25⁺CD127⁺Foxp3^- T cells represent the most numerous subset of AH CD8⁺ cells. The results suggest that eye chambers in mice are an element in the normal migratory pathway of naive CD8⁺ T cells. The study presented herein demonstrated only trace presence of CD4⁺ cells in the eye chambers, as the mean percentage of these cells was just 0.56. Such selective and specific homing of CD8⁺ and CD4⁺ cells to the eye chambers is most clearly engaged in the induction and maintenance of ocular immune privilege.

Large Variations in HIV-1 Viral Load Explained by Shifting-Mosaic Metapopulation Dynamics

The viral population of HIV-1, like many pathogens that cause systemic infection, is structured and differentiated within the body. The dynamics of cellular immune trafficking through the blood and within compartments of the body has also received wide attention. Despite these advances, mathematical models, which are widely used to interpret and predict viral and immune dynamics in infection, typically treat the infected host as a well-mixed homogeneous environment. Here, we present mathematical, analytical, and computational results that demonstrate that consideration of the spatial structure of the viral population within the host radically alters predictions of previous models. We study the dynamics of virus replication and cytotoxic T lymphocytes (CTLs) within a metapopulation of spatially segregated patches, representing T cell areas connected by circulating blood and lymph. The dynamics of the system depend critically on the interaction between CTLs and infected cells at the within-patch level. We show that for a wide range of parameters, the system admits an unexpected outcome called the shifting-mosaic steady state. In this state, the whole body’s viral population is stable over time, but the equilibrium results from an underlying, highly dynamic process of local infection and clearance within T-cell centers. Notably, and in contrast to previous models, this new model can explain the large differences in set-point viral load (SPVL) observed between patients and their distribution, as well as the relatively low proportion of cells infected at any one time, and alters the predicted determinants of viral load variation.

A novel metapopulation model of HIV suggests that within-host infections are characterized by a highly dynamic process of localized infection followed by clearance within T cell centers.

When a person is infected with HIV, the initial peak level of virus in the blood is usually very high before a lower, relatively stable level is reached and maintained for the duration of the chronic infection. This stable level is known as the set-point viral load (SPVL) and is associated with severity of infection. SPVL is also highly variable among patients, ranging from 100 to a million copies of the virus per mL of blood. The replicative capacity of the infecting virus and the strength of the immune response both influence SPVL. However, standard mathematical models show that variation in these two factors cannot easily reproduce the observed distribution of SPVL among patients. Standard models typically treat infected individuals as well-mixed systems, but in reality viral replication is localised in T-cell centres, or patches, found in secondary lymphoid tissue. To account for this population structure, we developed a carefully parameterised metapopulation model. We find the system can reach a steady state at which the viral load in the blood is relatively stable, representing SPVL, but surprisingly, the patches are highly dynamic, characterised by bursts of infection followed by elimination of virus due to localised host immune responses. Significantly, this model can reproduce the wide distribution of SPVLs found among infected individuals for realistic distributions of viral replicative capacity and strength of immune response. Our model can also be used in the future to understand other aspects of chronic HIV infection.

IκB kinase β inhibitor, IMD-0354, prevents allergic asthma in a mouse model through inhibition of CD4(+) effector T cell responses in the lung-draining mediastinal lymph nodes

IκB kinase (IKK) is important for nuclear factor (NF)-κB activation under inflammatory conditions. It has been demonstrated that IMD-0354, i.e. a selective inhibitor of IKKβ, inhibited allergic inflammation in a mouse model of ovalbumin (OVA)-induced asthma. The present study attempts to shed light on the involvement of CD4(+) effector (Teff) and regulatory (Treg) T cells in the anti-asthmatic action of IMD-0354. The animals were divided into three groups: vehicle treated, PBS-sensitized/challenged mice (PBS group); vehicle treated, OVA-sensitized/challenged mice (OVA group); and IMD-0354-treated, OVA-sensitized/challenged mice. The analyzed parameters included the absolute counts of Treg cells (Foxp3(+)CD25(+)CD4(+)), activated Teff cells (Foxp3(-)CD25(+)CD4(+)) and resting T cells (CD25(-)CD4(+)) in the mediastinal lymph nodes (MLNs), lungs and peripheral blood. Moreover, lung histopathology was performed to evaluate lung inflammation. It was found that the absolute number of cells in all studied subsets was considerably increased in the MLNs and lungs of mice from OVA group as compared to PBS group. All of these effects were fully prevented by treatment with IMD-0354. Histopathological examination showed that treatment with IMD-0354 protected the lungs from OVA-induced allergic airway inflammation. Our results indicate that IMD-0354 exerts anti-asthmatic action, at least partially, by blocking the activation and clonal expansion of CD4(+) Teff cells in the MLNs, which, consequently, prevents infiltration of the lungs with activated CD4(+) Teff cells. The beneficial effects of IMD-0354 in a mouse model of asthma are not mediated through increased recruitment of Treg cells into the MLNs and lungs and/or local generation of inducible Treg cells.

Mathematical modeling reveals kinetics of lymphocyte recirculation in the whole organism

The kinetics of recirculation of naive lymphocytes in the body has important implications for the speed at which local infections are detected and controlled by immune responses. With a help of a novel mathematical model, we analyze experimental data on migration of 51Cr-labeled thoracic duct lymphocytes (TDLs) via major lymphoid and nonlymphoid tissues of rats in the absence of systemic antigenic stimulation. We show that at any point of time, 95% of lymphocytes in the blood travel via capillaries in the lung or sinusoids of the liver and only 5% migrate to secondary lymphoid tissues such as lymph nodes, Peyer's patches, or the spleen. Interestingly, our analysis suggests that lymphocytes travel via lung capillaries and liver sinusoids at an extremely rapid rate with the average residence time in these tissues being less than 1 minute. The model also predicts a relatively short average residence time of TDLs in the spleen (2.5 hours) and a longer average residence time of TDLs in major lymph nodes and Peyer's patches (10 hours). Surprisingly, we find that the average residence time of lymphocytes is similar in lymph nodes draining the skin (subcutaneous LNs) or the gut (mesenteric LNs) or in Peyer's patches. Applying our model to an additional dataset on lymphocyte migration via resting and antigen-stimulated lymph nodes we find that enlargement of antigen-stimulated lymph nodes occurs mainly due to increased entrance rate of TDLs into the nodes and not due to decreased exit rate as has been suggested in some studies. Taken together, our analysis for the first time provides a comprehensive, systems view of recirculation kinetics of thoracic duct lymphocytes in the whole organism.

Progression of carcinogen-induced fibrosarcomas is associated with the accumulation of naïve CD4+ T cells via blood vessels and lymphatics

The tumor microenvironment comprises newly formed blood and lymphatic vessels which shape the influx, retention and departure of lymphocytes within the tumor mass. Thus, by influencing the intratumoral composition of lymphocytes, these vessels affect the manner in which the adaptive immune system responds to the tumor, either promoting or impairing effective antitumor immunity. In our study, we utilized a mouse model of carcinogen-induced fibrosarcoma to examine the composition of tumor-infiltrating lymphocytes during tumor progression. In particular, we sought to determine whether CD4(+) Foxp3(+) regulatory T cells (Tregs) became enriched during tumor progression thereby contributing to tumor-driven immunosuppression. This was not the case as the proportion of Tregs and effector CD4(+) T cells actually declined within the tumor owing to the unexpected accumulation of naïve T cells. However, we found no evidence for antigen-driven migration of these T cells or for their participation in an antitumor immune response. Our data support the notion that lymphocytes can enter tumors via aberrantly formed blood and lymphatic vessels. Such findings suggest that targeting both the tumor vasculature and lymphatics will alter the balance of lymphocyte subpopulations that enter the tumor mass. A consideration of this aspect of tumor immunology may be critical to the success of solid cancer immunotherapies.

Distant lymph nodes serve as pools of Th1 cells induced by neonatal BCG vaccination for the prevention of asthma in mice

BACKGROUND

Neonatal Bacillus Calmette-Guérin (BCG) vaccination induces vigorous T-helper type 1 (Th1) responses and inhibits allergy-related airway dysfunction, but the exact mechanisms remain unclear. The objective of this study was to address where the Th1 cells induced by neonatal BCG vaccination are generated and stored, and how they are recruited into the inflamed airway for the prevention of allergen-induced airway inflammation.

METHODS

We vaccinated neonatal C57BL/6 mice with BCG in a mouse model of asthma and analyzed the expression and function of Th1 cells in vivo and in vitro.

RESULTS

BCG vaccination-induced Th1 cells in the local inguinal lymph nodes (ILN) migrated into the lungs upon inhaled ovalbumin (OVA) challenge in OVA-sensitized mice. These CD4(+) T cells in the ILN exhibited potentials of activation, proliferation and cytokine secretion and expressed high levels of CXCR3. Adoptive transfer of CD4(+) T cells from BCG-treated ILN significantly decreased allergic airway responses. In addition, the protective effect of BCG vaccination against allergic airway inflammation was lost upon the excision of the ILN.

CONCLUSIONS

These data demonstrate that ILN serves as a 'weapon' pool of Th1 cells following BCG vaccination, and these cells are ready for the migration into the inflamed lungs upon the allergen challenge, thereby inhibiting allergen-induced airway disorder.

Analysis of naïve lung CD4 T cells provides evidence of functional lung to lymph node migration

The proportion of CD4 T cells with phenotypic and functional properties of naïve cells out of total CD4 T cells is similar in the lung parenchyma and lymph nodes. On treatment with a sphingosine-1-phosphate agonist, the frequency of these cells falls precipitously, but with a delay of ∼14 h compared with blood CD4 T cells; neither anti-CD62L nor pertussis toxin prevents entry of naïve CD4 T cells into the lung. Based on treatment with anti-CD62L and the use of CCR7(-/-) cells, lung naïve CD4 T cells appear to migrate to the mediastinal lymph nodes along a CD62L-independent, CCR7-dependent pathway. Cells that have entered the node in this manner are competent to respond to antigen. Thus, a portion (approximately one-half) of naïve CD4 T cells appears to enter the mediastinal lymph nodes through a blood-to-lung-to-lymph node route.

Most B cells in non-lymphoid tissues are naïve

The current view of lymphocyte migration states that naïve lymphocytes re-circulate between the blood and the lymph via the lymph nodes, but are not able to access non-lymphoid tissues. We examined B lymphocytes in peripheral tissues and found that the majority were phenotypically similar to naïve B cells in lymphoid tissues and were located within the parenchyma, not associated with blood vessels. The mutation rate within the Vh region of these cells was substantially less than the rate attributed to somatic hypermutation and was identical to that observed in naïve B cells isolated from the lymph nodes, showing the presence of naïve B cells in the non-lymphoid organs. Further, using FTY720-treated mice, we showed that naïve B cells migrate through the peripheral tissues and, using pertussis toxin, that the entry of B cells was not controlled by chemokine-mediated signalling events. Overall, these results show that naïve B lymphocytes constitute the majority of the total B-cell population in non-lymphoid tissues and suggest that these cells may re-circulate through the periphery as part of their normal migration pathway. This has implications for the current view of the role of naïve B cells in priming and tolerance.

Exposure to IL-15 and IL-21 enables autoreactive CD8 T cells to respond to weak antigens and cause disease in a mouse model of autoimmune diabetes

Autoreactive CD8(+) T lymphocytes play a key role in the pathogenesis of several autoimmune diseases. It is not yet well understood how autoreactive CD8(+) T cells, which express TCRs with low reactivity toward self-Ags, gain the ability to respond to autoantigens to cause disease. Previously, we have shown that prior stimulation of CD8(+) T cells with synergistic combinations of cytokines produced by the innate immune response, such as IL-21 and IL-15, induces Ag-independent proliferation. Such "cytokine-primed" CD8 T cells displayed increased responsiveness to limiting quantities of the cognate Ag. In this paper, we report that prior stimulation with IL-15 and IL-21 also enables CD8(+) T cells to respond to weakly agonistic TCR ligands, resulting in proliferation, cytokine secretion, and cytolytic activity. Using a transgenic mouse model of autoimmune diabetes, we show that cytokine-primed autoreactive CD8(+) T cells induce disease following stimulation by weak TCR ligands, but their diabetogenic potential is dependent on continuous availability of IL-15 in vivo. These findings suggest that inflammatory cytokines could facilitate the triggering of autoreactive CD8(+) T cells by weak autoantigens, and this mechanism may have important implications for autoimmune diseases associated with microbial infections and chronic inflammation.

Memory T cells are enriched in lymph nodes of selectin-ligand-deficient mice

Fucosyltransferase-IV and -VII double knockout (FtDKO) mice reveal profound impairment in T cell trafficking to lymph nodes (LNs) due to an inability to synthesize selectin ligands. We observed an increase in the proportion of memory/effector (CD44(high)) T cells in LNs of FtDKO mice. We infected FtDKO mice with lymphocytic choriomeningitis virus to generate and track Ag-specific CD44(high)CD8 T cells in secondary lymphoid organs. Although frequencies were similar, total Ag-specific effector CD44(high)CD8 T cells were significantly reduced in LNs, but not blood, of FtDKO mice at day 8. In contrast, frequencies of Ag-specific memory CD44(high)CD8 T cells were up to 8-fold higher in LNs of FtDKO mice at day 60. Because wild-type mice treated with anti-CD62L treatment also showed increased frequencies of CD44(high) T cells in LNs, we hypothesized that memory T cells were preferentially retained in, or preferentially migrated to, FtDKO LNs. We analyzed T cell entry and egress in LNs using adoptive transfer of bone fide naive or memory T cells. Memory T cells were not retained longer in LNs compared with naive T cells; however, T cell exit slowed significantly as T cell numbers declined. Memory T cells were profoundly impaired in entering LNs of FtDKO mice; however, memory T cells exhibited greater homeostatic proliferation in FtDKO mice. These results suggest that memory T cells are enriched in LNs with T cell deficits by several mechanisms, including longer T cell retention and increased homeostatic proliferation.

Naïve T cells re-distribute to the lungs of selectin ligand deficient mice

Background

Selectin mediated tethering represents one of the earliest steps in T cell extravasation into lymph nodes via high endothelial venules and is dependent on the biosynthesis of sialyl Lewis X (sLe^x) ligands by several glycosyltransferases, including two fucosyltransferases, fucosyltransferase-IV and –VII. Selectin mediated binding also plays a key role in T cell entry to inflamed organs.

Methodology/Principal Findings

To understand how loss of selectin ligands (sLe^x) influences T cell migration to the lung, we examined fucosyltransferase-IV and –VII double knockout (FtDKO) mice. We discovered that FtDKO mice showed significant increases (∼5-fold) in numbers of naïve T cells in non-inflamed lung parenchyma with no evidence of induced bronchus-associated lymphoid tissue. In contrast, activated T cells were reduced in inflamed lungs of FtDKO mice following viral infection, consistent with the established role of selectin mediated T cell extravasation into inflamed lung. Adoptive transfer of T cells into FtDKO mice revealed impaired T cell entry to lymph nodes, but selective accumulation in non-lymphoid organs. Moreover, inhibition of T cell entry to the lymph nodes by blockade of L-selectin, or treatment of T cells with pertussis toxin to inhibit chemokine dependent G-coupled receptor signaling, also resulted in increased T cells in non-lymphoid organs. Conversely, inhibition of T cell egress from lymph nodes using FTY720 agonism of S1P1 impaired T cell migration into non-lymphoid organs.

Conclusions/Significance

Taken together, our results suggest that impaired T cell entry into lymph nodes via high endothelial venules due to genetic deficiency of selectin ligands results in the selective re-distribution and accumulation of T cells in non-lymphoid organs, and correlates with their increased frequency in the blood. Re-distribution of T cells into organs could potentially play a role in the initiation of T cell mediated organ diseases.

Blood Lymphocytes, Monocytes and NK Cells Modulate Their Expression of CD44, ICAM‐1, LFA‐1 and MHC Class II After Arrival Into Lymphoid Organs

Adhesion molecules expressed on surface membranes of lymphocytes and other leukocytes enable their entry into the lymphoid and other tissues. However, little is known about molecules that govern the transit of leukocytes through the parenchyma of lymphoid organs proper. We show that in comparison to blood leukocytes, the corresponding cells isolated from lymphoid organs, i.e., lymph nodes and spleen, have a significantly augmented expression of certain surface molecules. The helper and cytotoxic subsets of T cells, as well as B cells, display the increased expression of CD44, ICAM-1 and LFA-1, whereas B cells additionally show the augmented expression of MHC class II. In comparison with blood monocytes, splenic monocytes show the increased expression of ICAM-1 and MHC class II molecules. When compared with blood NK cells, splenic NK cells only show the increased expression of ICAM-1. The molecules, which we show to be up regulated upon the entry of leukocytes into lymphoid organs, could be involved in their retention within the tissue via cell-cell or cell-extracellular matrix interactions and in control of their transit through lymphoid tissues.

Estimating in vivo death rates of targets due to CD8 T-cell-mediated killing

Despite recent advances in immunology, several key parameters determining virus dynamics in infected hosts remain largely unknown. For example, the rate at which specific effector and memory CD8 T cells clear virus-infected cells in vivo is hardly known for any viral infection. We propose a framework to quantify T-cell-mediated killing of infected or peptide-pulsed target cells using the widely used in vivo cytotoxicity assay. We have reanalyzed recently published data on killing of peptide-pulsed splenocytes by cytotoxic T lymphocytes and memory CD8 T cells specific to NP396 and GP276 epitopes of lymphocytic choriomeningitis virus (LCMV) in the mouse spleen. Because there are so many effector CD8 T cells in spleens of mice at the peak of the immune response, NP396- and GP276-pulsed targets are estimated to have very short half-lives of 2 and 14 min, respectively. After the effector numbers have diminished, i.e., in LCMV-immune mice, the half-lives become 48 min and 2.8 h for NP396- and GP276-expressing targets, respectively. Analysis of several alternative models demonstrates that the estimates of half-life times of peptide-pulsed targets are not affected when changes are made in the model assumptions. Our report provides a unifying framework to compare killing efficacies of CD8 T-cell responses specific to different viral and bacterial infections in vivo, which may be used to compare efficacies of various cytotoxic-T-lymphocyte-based vaccines.

Redirecting therapeutic T cells against myelin-specific T lymphocytes using a humanized myelin basic protein-HLA-DR2-zeta chimeric receptor

Therapies that Ag-specifically target pathologic T lymphocytes responsible for multiple sclerosis (MS) and other autoimmune diseases would be expected to have improved therapeutic indices compared with Ag-nonspecific therapies. We have developed a cellular immunotherapy that uses chimeric receptors to selectively redirect therapeutic T cells against myelin basic protein (MBP)-specific T lymphocytes implicated in MS. We generated two heterodimeric receptors that genetically link the human MBP84-102 epitope to HLA-DR2 and either incorporate or lack a TCRzeta signaling domain. The Ag-MHC domain serves as a bait, binding the TCR of MBP-specific target cells. The zeta signaling region stimulates the therapeutic cell after cognate T cell engagement. Both receptors were well expressed on primary T cells or T hybridomas using a tricistronic (alpha, beta, green fluorescent protein) retroviral expression system. MBP-DR2-zeta-, but not MBP-DR2, modified CTL were specifically stimulated by cognate MBP-specific T cells, proliferating, producing cytokine, and killing the MBP-specific target cells. The receptor-modified therapeutic cells were active in vivo as well, eliminating Ag-specific T cells in a humanized mouse model system. Finally, the chimeric receptor-modified CTL ameliorated or blocked experimental allergic encephalomyelitis (EAE) disease mediated by MBP84-102/DR2-specific T lymphocytes. These results provide support for the further development of redirected therapeutic T cells able to counteract pathologic, self-specific T lymphocytes, and specifically validate humanized MBP-DR2-zeta chimeric receptors as a potential therapeutic in MS.

Initiation of the adaptive immune response to Mycobacterium tuberculosis depends on antigen production in the local lymph node, not the lungs

The onset of the adaptive immune response to Mycobacterium tuberculosis is delayed compared with that of other infections or immunization, and allows the bacterial population in the lungs to expand markedly during the preimmune phase of infection. We used adoptive transfer of M. tuberculosis Ag85B-specific CD4(+) T cells to determine that the delayed adaptive response is caused by a delay in initial activation of CD4(+) T cells, which occurs earliest in the local lung-draining mediastinal lymph node. We also found that initial activation of Ag85B-specific T cells depends on production of antigen by bacteria in the lymph node, despite the presence of 100-fold more bacteria in the lungs. Although dendritic cells have been found to transport M. tuberculosis from the lungs to the local lymph node, airway administration of LPS did not accelerate transport of bacteria to the lymph node and did not accelerate activation of Ag85B-specific T cells. These results indicate that delayed initial activation of CD4(+) T cells in tuberculosis is caused by the presence of the bacteria in a compartment that cannot be mobilized from the lungs to the lymph node, where initial T cell activation occurs.

A novel mimovirus vaccine containing survivin epitope with adjuvant IL-15 induces long-lasting cellular immunity and high antitumor efficiency

Numerous evidences have indicated that CD8+ cytotoxic T lymphocytes (CTLs) played a significant role in protecting host against tumors, thus CTLs have been involved as potentially relevant candidate targets of cancer immunotherapy. Moreover it is crucial to fully elucidate antigen-specific CTL response, especially high-avidity and long-lasting CTL response in vivo. In the present study, we reported a novel tumor vaccine (mimovirus), a viron-size particulate which consisted of a cell-penetrating peptide of Tat(49-57), a CTL epitope peptide survivin(85-93) and a plasmid encoding murine interleukin-15 (IL-15). We demonstrated that this tumor vaccine could effectively mediate the expression of the gene and presentation of the tumor antigen derived peptide ex vivo. Furthermore, the tumor vaccine supported a robust memory CTL-mediated long-term immunity in vivo, which could effectively protect BALB/c mice against fatal CT26 tumor challenge and improve their survival. These findings suggest that the tumor vaccine may provide an alternative therapeutic strategy for cancer patients.

Induction of tolerance and immunity by redirected B cell-specific cytolytic T lymphocytes

Chimeric receptors bearing ligand recognition domains linked to signaling regions from the T-cell receptor can redirect T lymphocytes against non-MHC-restricted targets. Cytolytic T lymphocytes (CTL) expressing these chimeric receptors are being tested in preclinical and clinical trials for activity in cancer, infectious diseases and autoimmunity. The chimeric receptors may incorporate antigenic epitopes previously unrecognized by the immune system. Whether a receptor-specific antibody response develops to these neoantigens and whether such a response inhibits therapeutic cell activity is unknown. We hypothesized that upon engagement of a chimeric receptor-specific B cell, receptor-modified CTL will be activated, lysing the B cell and inducing tolerance to the chimeric receptor rather than immunity. We demonstrate that receptor-modified CTL are indeed stimulated by cognate receptor-specific B cells, proliferate and produce cytokines in response and kill the B cells in vitro and in vivo. However, this is insufficient to induce full B-cell tolerance. Modified CTL induce a chimeric receptor-specific antibody response independent of any other source of antigen. Nevertheless, the CTL retain substantial activity even in the presence of saturating doses of receptor-specific antibody. Thus antichimeric receptor antibody responses need to be considered in the clinical use of chimeric receptor-modified T cells. However, the inhibitory activity of these antibodies may in cases be limited.

Nanosystems for simultaneous imaging and drug delivery to T cells

The T-cell response defines the pathogenesis of many common chronic disease states, including diabetes, rheumatoid arthritis, and transplant rejection. Therefore, a diagnostic strategy that visualizes this response can potentially lead to early therapeutic intervention, avoiding catastrophic organ failure or prolonged sickness. In addition, the means to deliver a drug dose to those cells in situ with the same specificity used to image those cells would provide for a powerful therapeutic alternative for many disease states involving T cells. In this report, we review emerging nanosystems that can be used for simultaneous tracking and drug delivery to those cells. Because of their versatility, these systems--which combine specific receptor targeting with an imaging agent and drug delivery--are suited to both basic science and applications, from developing therapeutic strategies for autoimmune and alloimmune diseases, to noninvasive tracking of pathogenic T-cell migration.

Cell wall-associated alpha-glucan is instrumental for Mycobacterium tuberculosis to block CD1 molecule expression and disable the function of dendritic cell derived from infected monocyte

We previously described an escape mechanism exploited by Mycobacterium tuberculosis (Mtb) to prevent the generation of fully competent dendritic cells (DC). We have now tested the effect of isolated mycobacterial components on human monocyte differentiation into DC and demonstrated that cell wall (CW)-associated alpha-glucan induces monocytes to differentiate into DC (Glu-MoDC) with the same altered phenotype and functional behaviour of DC derived from Mtb-infected monocytes (Mt-MoDC). In fact, Glu-MoDC lack CD1 molecule expression, fail to upregulate CD80 and produce IL-10 but not IL-12. We also showed that Glu-MoDC are not able to prime effector T cells or present lipid antigens to CD1-restricted T-cell clones. Thus, we propose a mechanism of Mtb-monocyte interaction mediated by CW-associated alpha-glucan, which allows the bacterium to evade both innate and acquired immune responses.

Key factors in the organized chaos of early T cell development

A fundamental issue in T cell development is what controls whether a thymocyte differentiates into a gammadelta T cell or an alphabeta T cell, each defined by their distinct T cell receptor. Most likely, lessons learned in studying that issue will also provide insight into how the thymus produces T cell subsets with distinct functional and regulatory potentials. Here we review recent experiments, focusing on three factors that regulate thymocyte differentiation up to and including the expression of the first products of antigen receptor gene rearrangements. Those factors are the archetypal developmental regulator Notch, intrinsic signals emanating from antigen-receptor complexes, and trans conditioning, which reflects communication between different subsets of thymocytes. We also review new findings on the positive selection of gammadelta T cells and on extrathymic T cell development.

T-cell migration: a naive paradigm?

Naive T cells have long been thought to recirculate exclusively between secondary lymphoid organs via the lymph and blood. Evidence is now emerging that this view may be too simplistic and that naive T cells routinely traffic through non-lymphoid organs in a manner similar to that of memory T cells, albeit in lower numbers. This represents a fundamental shift in the current paradigm of T-cell migration through different types of tissue. This review summarizes these recent findings, along with the similarities and differences in migratory properties of naive and memory T cells, and discusses how and why naive T cells might access non-lymphoid tissues.

Imatinib mesylate selectively impairs expansion of memory cytotoxic T cells without affecting the control of primary viral infections

Imatinib mesylate (imatinib) is a potent inhibitor of defined tyrosine kinases (TKs) and is effective in the treatment of malignancies characterized by constitutive activation of these TKs such as chronic myeloid leukemia and gastrointestinal stromal tumors. TKs also play an important role in T-cell receptor (TCR) signal transduction. Inhibitory as well as stimulating effects of imatinib on T cells and dendritic cells have been described. Here, we analyzed the effects of imatinib treatment on antiviral immune responses in vivo. Primary cytotoxic T-cell (CTL) responses were not impaired in imatinib-treated mice after infection with lymphocytic choriomeningitis virus (LCMV) or after immunization with a tumor cell line expressing LCMV glycoprotein (LCMV-GP). Similarly, neutralizing antibody responses to vesicular stomatitis virus (VSV) were not affected. In contrast, secondary expansion of LCMV-specific memory CTLs was reduced in vitro and in vivo, resulting in impaired protection against reinfection. In addition, imatinib treatment delayed the onset of diabetes in a CTL-induced diabetes model. In summary, imatinib treatment in vivo selectively inhibits the expansion of antigen-experienced memory CTLs without affecting primary T- or B-cell responses. Therefore, imatinib may be efficacious in the suppression of CTL-mediated immunopathology in autoimmune diseases without the risk of acquiring viral infections.

Evidence that a significant number of naive T cells enter non-lymphoid organs as part of a normal migratory pathway

Only activated and effector memory T cells are thought to access non-lymphoid tissues. In contrast, naive T cells are thought to circulate only between the blood, lymph and secondary lymphoid organs. We examined the phenotype of endogenous T cells in various non-lymphoid organs and showed that a subset of cells exhibited an apparently naive phenotype and were functionally inactive. FTY720 treatment selectively depleted this population from the non-lymphoid tissues. In addition, RAG-deficient TCR transgenic CD4 and CD8 T cells were present in non-lymphoid tissues in bone marrow chimeric mice and in situ imaging analysis revealed their location in the parenchymal tissues. Moreover, migration of TCR transgenic T cells to non-lymphoid tissues after adoptive transfer was pertussis-toxin resistant. Overall, the results suggest that naive T cells may circulate through non-lymphoid tissues as part of their normal migratory pathway.

Induction of T 'regulatory' cells by standardized house dust mite immunotherapy: an increase in CD4+ CD25+ interleukin-10+ T cells expressing peripheral tissue trafficking markers

BACKGROUND

Clinically effective subcutaneous allergen-specific immunotherapy (SIT) is associated with altered circulating T cell cytokine production and altered local cytokine responses with increased IL-10 following allergen challenge in target organs.

OBJECTIVE

This study aimed to elucidate mechanisms for these T cell changes, by examining surface expression of markers for peripheral tissue trafficking on circulating cytokine-positive T cells following standardized house dust mite- (HDM-) SIT.

METHODS

A randomized conventional HDM immunotherapy study was performed on a panel of 12 HDM-allergic subjects. Nine subjects received treatment with conventional HDM immunotherapy using a standardized extract and three subjects were treated by standard pharmacotherapy alone. Symptom and medication scores and allergen-induced cutaneous late-phase responses were assessed before and 9 months after institution of therapy. Before and at 3 and 9 months of SIT, peripheral blood mononuclear cells were cultured for 14 days with HDM extract and CD4+ and CD8+ T cell expression of CD62L, CD49d and CCR5 and production of IL-10, IFN-gamma and IL-4 were analysed by flow cytometry. Allergen-specific T cell proliferation was assessed by 3H-thymidine incorporation.

RESULTS

At 9 months, all SIT-treated patients showed reduced symptom scores and late-phase cutaneous responses to HDM compared with baseline levels. The proportions of CD4+ T cells which were IL-10+ were increased (P < 0.01), and the proportions of CD4+ and CD8+ T cells which were IL-4+ decreased (P < 0.05) compared with baseline. CD4+ and CD8+ T cell IFN-gamma production, expression of surface markers for peripheral tissue trafficking and allergen-specific proliferation remained unchanged during SIT treatment. However, increased proportions of CD4+CD62L(-), CD4+CD49d(hi), CD4+CCR5+ T cells expressing IL-10 were detected at 9 months of SIT compared with baseline (P < 0.05). IL-10 staining co-localized with CD4+CD25+ T cells.

CONCLUSION

Clinically effective subcutaneous immunotherapy with a standardized HDM Dermatophagoides pteronyssinus preparation results in decreased numbers of IL-4+ T cells and expansion of CD4+IL-10+ T cells expressing a peripheral tissue trafficking phenotype. The co-localization of IL-10+ staining to CD4+CD25+ T cells is consistent with the induction of a T regulatory cell population by SIT.

Rebuilding an immune-mediated central nervous system disease: weighing the pathogenicity of antigen-specific versus bystander T cells

Although both self- and pathogen-specific T cells can participate in tissue destruction, recent studies have proposed that after viral infection, bystander T cells of an irrelevant specificity can bypass peptide-MHC restriction and contribute to undesired immunopathological consequences. To evaluate the importance of this mechanism of immunopathogenesis, we determined the relative contributions of Ag-specific and bystander CD8+ T cells to the development of CNS disease. Using lymphocytic choriomeningitis virus (LCMV) as a stimulus for T cell recruitment into the CNS, we demonstrate that bystander CD8+ T cells with an activated surface phenotype can indeed be recruited into the CNS over a chronic time window. These cells become anatomically positioned in the CNS parenchyma, and a fraction aberrantly acquires the capacity to produce the effector cytokine, IFN-gamma. However, when directly compared with their virus-specific counterparts, the contribution of bystander T cells to CNS damage was insignificant in nature (even when specifically activated). Although bystander T cells alone failed to cause tissue injury, transferring as few as 1000 naive LCMV-specific CD8+ T cells into a restricted repertoire containing only bystander T cells was sufficient to induce immune-mediated pathology and reconstitute a fatal CNS disease. These studies underscore the importance of specific T cells in the development of immunopathology and subsequent disease. Because of highly restrictive constraints imposed by the host, it is more likely that specific, rather than nonspecific, bystander T cells are the active participants in T cell-mediated diseases that afflict humans.

Exogenous IL-7 increases recent thymic emigrants in peripheral lymphoid tissue without enhanced thymic function

Interleukin 7 (IL-7) is critical in maintaining thymic-dependent and thymic-independent pathways of T-cell homeostasis. T-cell receptor (TCR) rearrangement excision circles (TRECs) have been used as markers for recent thymic emigrants (RTEs) in assessing human thymic function. To study the thymic and peripheral effects of IL-7 on RTEs, we measured TREC content and peripheral naive T-cell subsets and turnover in IL-7-treated mice. Short-term administration of IL-7 into thymus-intact mice resulted in increased total TREC numbers, consistent with RTE accumulation. Decreases in TREC frequency were attributable to dilution secondary to increased cell turnover. Significantly, IL-7 administration into thymectomized mice resulted in patterns of decreased TREC frequency and increased total TREC number similar to those in IL-7-treated thymus-intact mice. Distinct patterns of naive cell and RTE distribution among peripheral immune organs and altered expression of CD11a were observed following IL-7 treatment in thymus-intact and thymectomized mice. These results demonstrate (1) that total TREC number and not TREC frequency accurately reflects quantitative changes in RTEs; (2) that short-term IL-7 administration results in preferential accumulations of RTEs among peripheral immune organs, accounting for the increase in TRECs in the total peripheral lymphoid pool; and (3) no evidence for regulation of thymic function by short-term IL-7 administration. (Blood. 2004;104:1110-1119)

Specifically activated memory T cell subsets from cancer patients recognize and reject xenotransplanted autologous tumors

Bone marrow of breast cancer patients was found to contain CD8(+) T cells specific for peptides derived from breast cancer-associated proteins MUC1 and Her-2/neu. Most of these cells had a central or effector memory phenotype (CD45RA(-)CD62L(+) or CD45RA(-)CD62L(-), respectively). To test their in vivo function, we separated bone marrow-derived CD45RA(+) naive or CD45RA(-)CD45RO(+) memory T cells, stimulated them with autologous dendritic cells pulsed with tumor lysate, and transferred them into NOD/SCID mice bearing autologous breast tumors and normal skin transplants. CD45RA(-) memory but not CD45RA(+) naive T cells infiltrated autologous tumor but not skin tissues after the transfer. These tumor-infiltrating cells had a central or effector memory phenotype and produced perforin. Many of them expressed the P-selectin glycoprotein ligand 1 and were found around P-selectin(+) tumor endothelium. Tumor infiltration included cluster formation in tumor tissue by memory T cells with cotransferred dendritic cells. It was associated with the induction of tumor cell apoptosis and significant tumor reduction. We thus demonstrate selective homing of memory T cells to human tumors and suggest that tumor rejection is based on the recognition of tumor-associated antigens on tumor cells and dendritic cells by autologous specifically activated central and effector memory T cells.

The level of virus-specific T-cell and macrophage recruitment in porcine reproductive and respiratory syndrome virus infection in pigs is independent of virus load

Porcine reproductive and respiratory syndrome virus (PRRSV) is the most important infectious disease agent of pigs worldwide, causing reproductive failure in pregnant sows and respiratory problems in nursing and growing pigs. PRRSV infection is characterized by a prolonged viremia of 30 or more days and an extended persistent infection of lymphoid tissues. To better understand the immunological basis for prolonged acute and persistent PRRSV infection, we have examined the cell-mediated immune (CMI) response throughout the course of infection and compared the results to the local distribution and abundance of PRRSV in infected tissues. PRRSV-specific T cells, enumerated by gamma interferon enzyme-linked immunospot assay, did not appear until 2 weeks after PRRSV inoculation, and their abundance exhibited substantial variation over time and among animals. In all cases the T-cell response was transient. High levels of viral RNA were present in lymphoid tissues of all animals in the acute phase of infection. Viral loads were decreased 1,000-fold or more in persistent infections, with the primary sites of persistence being tonsil, sternal lymph node, and inguinal lymph node. The abundance of virus-specific T cells in either acutely or persistently infected animals was highly variable and showed no correlation to the level of virus in lymphoid tissues. No significant difference in antigen-specific T-cell abundance was observed in secondary lymphoid tissues in either acute or persistent infection except for tonsil, in which the number of responding cells was extremely low. CD4(+)- and CD8(+)-T-cell frequencies did not change after PRRSV infection, though a decrease in gammadelta T cells was observed. Macrophages, the permissive cell type for PRRSV, were present in various levels in all tissue preparations and were not in proportion to local virus load. These findings indicate that a weak CMI response contributes to prolonged PRRSV infection and suggests that PRRSV suppresses T-cell recognition of infected macrophages. Thus, the slow but eventual resolution of PRRSV infection may be dependent on limiting permissive macrophages and on innate immune factors.

Suppression of tumor growth and angiogenesis in vivo by a truncated form of 24-kd fibroblast growth factor (FGF)-2

Efforts to treat tumors have routinely depended on disruption of cell proliferation by a variety of methods, many involving stimulation of apoptosis. We have previously shown that a truncated form of 24-kd basic fibroblast growth factor consisting of the amino terminal 86 amino acids inhibits migration of tumor and endothelial cells in vitro. In the present study, this peptide was tested for its ability to suppress angiogenesis and tumor growth using the murine dorsal skin-fold chamber model in vivo. Treatment of MCF-7 breast carcinoma tumor spheroids with this peptide resulted in cessation of the angiogenic response and a significant reduction in tumor size. Blood vessels that did form were poorly developed. In addition to inhibiting angiogenesis, the peptide also inhibited migration of Lewis lung carcinoma cells away from the tumor core before onset of angiogenesis indicating that the peptide-mediated inhibition of migration affects both angiogenesis and tumor growth independently. Despite inhibition of tumor cell migration, the peptide had no effect on neutrophil or eosinophil chemotaxis. This study demonstrates that the truncated form of 24-kd basic fibroblast growth factor is effective in suppressing tumor development in vivo through inhibition of angiogenesis as well as inhibition of tumor cell migration without compromising other homeostatic events.

Immunological Foundations to the Quest for New Vaccine Adjuvants

Developing efficient adjuvants for human vaccines that elicit broad and sustained immune responses at systemic or mucosal levels remains a formidable challenge for the vaccine industry. Conventional approaches in the past have been largely empirical and--at best--partially successful. Importantly, recent advances in our understanding of the immune system, most particularly with respect to early proinflammatory signals, are leading to the identification of new biological targets for vaccine adjuvants. This review covers both the current status of adjuvant testing in humans, the residual needs for vaccines in development, and the emerging immunological foundations for adjuvant design. A better understanding of the biology of toll-like receptors, non-conventional T cell subpopulations, T and B cell memory, regulatory T cells, and mucosal immunity has profound implications for a modern approach to adjuvant screening and development. The future lies in the high throughput screening of synthetic chemical entities targeting well-characterized biological molecules. Used alone or in combination, such synthetic adjuvants will allow stimulation or modulation in a safe and efficient manner of strong effector, regulatory and memory immune mechanisms.

The sympathetic control of blood supply is different in the spleen and lymph nodes

OBJECTIVES

The noradrenergic innervation of lymphoid organs controls several immune cell functions and local blood perfusion. Considering that cell and antigen uptake depend on the blood supply to lymphoid organs, the hypothesis was tested that feedback signals from activated immune cells control sympathetic vasomotor activity.

METHODS

We determined the blood flow in spleen and mesenteric lymph nodes (mLN) of Wistar Kyoto rats during immune stimulation with endotoxin (LPS; 10 microg/kg) and following disruption of the noradrenergic transmission.

RESULTS

Our data indicate that (a) the splenic noradrenaline content, which reflects the density of the sympathetic innervation, is 5 times higher in the spleen than in other peripheral organs and the spleen receives stronger tonic sympathetic input than mLN; (b) immune stimulation with LPS causes a 4-fold increase in the IL-1beta production in the spleen, but only 2-fold in mLN; (c) IL-1beta causes an inhibition of the sympathetic vasoconstrictor tonus in the spleen, but has no significant effect on the noradrenergic vascular tonus in mLN, and (d) in mLN, the local hyperemia induced by LPS is attenuated by the degranulation of vesicular stores of histamine and serotonin, indicating that these monoamines participate in the vasodilator effect of LPS in mLN.

CONCLUSIONS

The present experiments, taken together with our previous studies, indicate that the control of blood supply to the spleen and mLN involves different mechanisms. While blood perfusion in the spleen depends on the inhibition of the noradrenergic vasoconstriction by endogenously produced IL-1beta, other vasoactive mediators such as serotonin and histamine play a role in the control of mLN perfusion.

Analyzing the migration of labeled T cells in vivo: an essential approach with challenging features

T cells are involved in the pathogenesis of many diseases. To exert a pathological effect, T cells enter the tissues. We show that the determination of their entry site requires isolation of the respective T cell population, injection into genetically un-manipulated animals, and identification of the cells in vivo at various time points after injection. We indicate variables influencing in vivo migration experiments artificially, and outline how resulting problems can be either avoided or taken into account. Reviewing experiments performed according to the outlined criteria reveals two types of migration patterns for T cell subsets in vivo: 1). Naïve and memory T cells enter lymphoid and non-lymphoid organs in comparable numbers, but selectively accumulate in lymphoid tissues over time, 2). Effector T cells, too, enter lymphoid and non-lymphoid organs in comparable numbers. However, most of them die within 24 hours. Depending on the presence of cytokines, chemokines and extracellular matrix compounds they are able to survive, thereby preferentially accumulating in their target tissues. This information might help to understand the role of migration in the pathogenesis of T cell mediated diseases.

The fate of effector T cells in vivo is determined during activation and differs for CD4+ and CD8+ cells

Effector T cells generated in the mesenteric lymph nodes (mLN) are known to accumulate in mLN and the tissue drained by them after circulating in the blood. Their accumulation is due less to preferential entry into mLN but more to preferential proliferation within mLN. The factors regulating the proliferation of effector T cells in vivo are unclear, and it is unknown whether they are different for CD4(+) and CD8(+) effector T cells. Rat T cells from mLN or peripheral lymph nodes (pLN) were stimulated polyclonally via the TCR and CD28 and injected i.v. into congenic recipients. Using three-color flow cytometry and immunohistochemistry, they were identified in mLN, pLN, and blood over time, and proliferation was determined by measuring bromodeoxyuridine incorporation. Only effector mLN T cells showed a significantly increased proliferation rate after entry into mLN compared with that in pLN (2.4 +/- 1.8% vs 0.8 +/- 0.4%). Proliferation among the injected cells was higher when they had contact with dendritic cells within mLN (9.0 +/- 4.3%) than when they did not (4.1 +/- 2.1%). Furthermore, effector mLN T cells which were observed 56 days after injection maintained the capacity for preferential proliferation within mLN. Interestingly, CD4(+) effector mLN T cells proliferated at a higher rate (4.8 +/- 0.7%), remaining in mLN, whereas CD8(+) effector mLN T cells proliferated at a lower rate (3.3 +/- 1.0%) and were able to leave the mLN into the blood. Elucidating the factors regulating the proliferation of effector T cells in vivo will help to modify their distribution for therapeutic purposes.