The traffic of resting lymphocytes through delayed hypersensitivity and chronic inflammatory lesions: a dynamic equilibrium

Approaches to overcome flow cytometry limitations in the analysis of cells from veterinary relevant species

Background

Flow cytometry is a powerful tool for the multiparameter analysis of leukocyte subsets on the single cell level. Recent advances have greatly increased the number of fluorochrome-labeled antibodies in flow cytometry. In particular, an increase in available fluorochromes with distinct excitation and emission spectra combined with novel multicolor flow cytometers with several lasers have enhanced the generation of multidimensional expression data for leukocytes and other cell types. However, these advances have mainly benefited the analysis of human or mouse cell samples given the lack of reagents for most animal species. The flow cytometric analysis of important veterinary, agricultural, wildlife, and other animal species is still hampered by several technical limitations, even though animal species other than the mouse can serve as more accurate models of specific human physiology and diseases.

Results

Here we present time-tested approaches that our laboratory regularly uses in the multiparameter flow cytometric analysis of ovine leukocytes. The discussed approaches will be applicable to the analysis of cells from most animal species and include direct modification of antibodies by covalent conjugation or Fc-directed labeling (Zenon™ technology), labeled secondary antibodies and other second step reagents, labeled receptor ligands, and antibodies with species cross-reactivity.

Conclusions

Using refined technical approaches, the number of parameters analyzed by flow cytometry per cell sample can be greatly increased, enabling multidimensional analysis of rare samples and giving critical insight into veterinary and other less commonly analyzed species. By maximizing information from each cell sample, multicolor flow cytometry can reduce the required number of animals used in a study.

Non-hematopoietic Control of Peripheral Tissue T Cell Responses: Implications for Solid Tumors

In response to pathological challenge, the host generates rapid, protective adaptive immune responses while simultaneously maintaining tolerance to self and limiting immune pathology. Peripheral tissues (e.g., skin, gut, lung) are simultaneously the first site of pathogen-encounter and also the location of effector function, and mounting evidence indicates that tissues act as scaffolds to facilitate initiation, maintenance, and resolution of local responses. Just as both effector and memory T cells must adapt to their new interstitial environment upon infiltration, tissues are also remodeled in the context of acute inflammation and disease. In this review, we present the biochemical and biophysical mechanisms by which non-hematopoietic stromal cells and extracellular matrix molecules collaborate to regulate T cell behavior in peripheral tissue. Finally, we discuss how tissue remodeling in the context of tumor microenvironments impairs T cell accumulation and function contributing to immune escape and tumor progression.

Odorants specifically modulate chemotaxis and tissue retention of CD4+ T cells via cyclic adenosine monophosphate induction

Retention of T cells within affected tissue is a critical component of adaptive immune inflammation. However, the mechanisms involved in T cell retention remain largely undefined. Previous studies revealed the capacity of cAMP signaling to regulate immune cell migration, as well as dynamic regulation of receptors that could induce cAMP production in immune cells. The potential for cAMP to act as a retention signal has been mostly unexplored, partially as a result of this second messenger's well-characterized inhibition of effector function in immune cells. Here, we report that cAMP regulates the tissue retention of mouse T cells at concentrations well below those that inhibited proliferation or decreased acquisition of an effector phenotype. Stimulation of CD4⁺ T cells with odorants known to be cognate ligands for T cell-expressed olfactory receptors induced cAMP and inhibited chemokine-driven chemotaxis without decreasing T cell proliferation or effector functions. Similar effects were observed following treatment with relatively low concentrations of the cAMP analog Sp-5,6-dichloro-1-β-d-ribofuranosylbenzimidazole-3',5'-monophosphorothioate. Furthermore, pretreatment with odorants or cAMP at concentrations that did not inhibit effector function induced T cell tissue retention in mice by inhibiting chemokine-dependent T cell egress from the footpad to the draining lymph node. Together, these results suggest that odorant receptor-mediated increases in intracellular cAMP can modulate T cell tissue trafficking and may offer new therapeutic targets for controlling T cell tissue accumulation.

Vascular endothelial growth factor c/vascular endothelial growth factor receptor 3 signaling regulates chemokine gradients and lymphocyte migration from tissues to lymphatics

BACKGROUND

Circulation of leukocytes via blood, tissue and lymph is integral to adaptive immunity. Afferent lymphatics form CCL21 gradients to guide dendritic cells and T cells to lymphatics and then to draining lymph nodes (dLN). Vascular endothelial growth factor C and vascular endothelial growth factor receptor 3 (VEGFR-3) are the major lymphatic growth factor and receptor. We hypothesized these molecules also regulate chemokine gradients and lymphatic migration.

METHODS

CD4 T cells were injected into the foot pad or ear pinnae, and migration to afferent lymphatics and dLN quantified by flow cytometry or whole mount immunohistochemistry. Vascular endothelial growth factor receptor 3 or its signaling or downstream actions were modified with blocking monoclonal antibodies (mAbs) or other reagents.

RESULTS

Anti-VEGFR-3 prevented migration of CD4 T cells into lymphatic lumen and significantly decreased the number that migrated to dLN. Anti-VEGFR-3 abolished CCL21 gradients around lymphatics, although CCL21 production was not inhibited. Heparan sulfate (HS), critical to establish CCL21 gradients, was down-regulated around lymphatics by anti-VEGFR-3 and this was dependent on heparanase-mediated degradation. Moreover, a Phosphoinositide 3-kinase (PI3K)α inhibitor disrupted HS and CCL21 gradients, whereas a PI3K activator prevented the effects of anti-VEGFR-3. During contact hypersensitivity, VEGFR-3, CCL21, and HS expression were all attenuated, and anti-heparanase or PI3K activator reversed these effects.

CONCLUSIONS

Vascular endothelial growth factor C/VEGFR-3 signaling through PI3Kα regulates the activity of heparanase, which modifies HS and CCL21 gradients around lymphatics. The functional and physical linkages of these molecules regulate lymphatic migration from tissues to dLN. These represent new therapeutic targets to influence immunity and inflammation.

Chemoattractant receptors and lymphocyte egress from extralymphoid tissue: changing requirements during the course of inflammation

Memory/effector T cells traffic efficiently through extralymphoid tissues, entering from the blood and leaving via the afferent lymph. During inflammation, T cell traffic into the affected tissue dramatically increases; however, the dynamics and mechanisms of T cell exit from inflamed tissues are poorly characterized. In this study, we show, using both a mouse and a sheep model, that large numbers of lymphocytes leave the chronically inflamed skin. Many T cells capable of producing IFN-γ and IL-17 also entered the draining afferent lymph, demonstrating that memory/effector T cells egress from sites of inflammation. Whereas efficient egress from acutely inflamed skin required lymphocyte-expressed CCR7, chronic inflammation promoted significant CCR7-independent exit as well. Lymphocyte exit at late time points of inflammation was sensitive to pertussis toxin but was only partially affected by the drug FTY720, implying the contribution of alternative chemoattractant receptors other than spingosine 1-phosphate receptor 1. Our data show that CCR7 is an important receptor for lymphocyte egress from both resting and inflamed extralymphoid tissues, but that alternative exit receptors come into play during chronic inflammation.

Memory T-cell trafficking: new directions for busy commuters

The immune system is unique in representing a network of interacting cells of enormous complexity and yet being based on single cells travelling around the body. The development of effective and regulated immunity relies upon co-ordinated migration of each cellular component, which is regulated by diverse signals provided by the tissue. Co-ordinated migration is particularly relevant to the recirculation of primed T cells, which, while performing continuous immune surveillance, need to promptly localize to antigenic sites, reside for a time sufficient to carry out their effector function and then efficiently leave the tissue to avoid bystander damage. Recent advances that have helped to clarify a number of key molecular mechanisms underlying the complexity and efficiency of memory T-cell trafficking, including antigen-dependent T-cell trafficking, the regulation of T-cell motility by costimulatory molecules, T-cell migration out of target tissue and fugetaxis, are reviewed in this article.

T cells as pioneers: antigen-specific T cells condition inflamed sites for high-rate antigen-non-specific effector cell recruitment

Cellular infiltration is a classic hallmark of inflammation. Whereas the role of T cells in many types of inflammation is well established, the specific impact of antigen recognition on their migration into the site and on the accumulation of other effector cells are still matters of debate. Using a model of an inflammatory effector phase driven by T-cell receptor (TCR) transgenic T cells, we found (i) that antigen-specific T cells play a crucial role as 'pioneer cells' that condition the tissue for enhanced recruitment of further T effector cells and other leucocytes, and (ii) that the infiltration of T cells is not dependent on antigen specificity. We demonstrate that a small number of antigen-specific T cells suffice to initiate a cascade of cellular immigration into the antigen-loaded site. Although antigen drives this process, accumulation of T cells in the first few days of inflammation was not dependent on T-cell reactivity to the antigen. Both transgenic and wild-type T effector cells showed enhanced immigration into the site of antigen challenge after the initial arrival and activation of antigen-specific pioneer cells. This suggests that bystander accumulation of non-specific effector/memory T cells is a general feature in inflammation. Furthermore, tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma were identified as mediators that contribute to conditioning of the inflammatory site for high-rate accumulation of T effector cells in this T-cell-driven model.

In situ activation of antigen-specific CD8+ T cells in the presence of antigen in organotypic brain slices

The activation of Ag-specific T cells locally in the CNS could potentially contribute to the development of immune-mediated brain diseases. We addressed whether Ag-specific T cells could be stimulated in the CNS in the absence of peripheral lymphoid tissues by analyzing Ag-specific T cell responses in organotypic brain slice cultures. Organotypic brain slice cultures were established 1 h after intracerebral OVA Ag microinjection. We showed that when OVA-specific CD8(+) T cells were added to Ag-containing brain slices, these cells became activated and migrated into the brain to the sites of their specific Ags. This activation of OVA-specific T cells was abrogated by the deletion of CD11c(+) cells from the brain slices of the donor mice. These data suggest that brain-resident CD11c(+) cells stimulate Ag-specific naive CD8(+) T cells locally in the CNS and may contribute to immune responses in the brain.

Monitoring cellular movement in vivo with photoconvertible fluorescence protein "Kaede" transgenic mice

Kaede is a photoconvertible fluorescence protein that changes from green to red upon exposure to violet light. The photoconversion of intracellular Kaede has no effect on cellular function. Using transgenic mice expressing the Kaede protein, we demonstrated that movement of cells with the photoconverted Kaede protein could be monitored from lymphoid organs to other tissues as well as from skin to the draining lymph node. Analysis of the kinetics of cellular movement revealed that each subset of cells in the lymph node, such as CD4(+) T, CD8(+) T, B, and dendritic cells, has a distinct migration pattern in vivo. Thus, the Kaede transgenic mouse system would be an ideal tool to monitor precise cellular movement in vivo at different stages of immune response to pathogens as well as in autoimmune diseases.

Glial grafting for demyelinating disease

Remyelination of demyelinated central nervous system (CNS) axons is considered as a potential treatment for multiple sclerosis, and it has been achieved in experimental models of demyelination by transplantation of pro-myelinating cells. However, the experiments undertaken have not addressed the need for tissue-type matching in order to achieve graft-mediated remyelination since they were performed in conditions in which the chance for graft rejection was minimized. This article focuses on the factors determining survival of allogeneic oligodendrocyte lineage cells and their contribution to the remyelination of demyelinating CNS lesions. The immune status of the CNS as well as the suitability of different models of demyelination for graft rejection studies are discussed, and ways of enhancing allogeneic oligodendrocyte-mediated remyelination are presented. Finally, the effects of glial graft rejection on host remyelination are described, highlighting the potential benefits of the acute CNS inflammatory response for myelin repair.

A novel mechanism of immune regulation: interferon-gamma regulates retention of CD4 T cells during delayed type hypersensitivity

The local immune response is characterized by an increase in the rate of entry of lymphocytes from the blood into regional lymph nodes and changes in the output of cells in lymph. While significant data are available regarding the role of inflammation-induced vascular adhesion processes in regulating lymphocyte entry into inflamed tissues and lymph nodes, relatively little is known about the molecular processes governing lymphocyte exit into efferent lymph. We have defined a novel role for lymphatic endothelial cells in the regulation of lymphocyte exit during a delayed type hypersensitivity (DTH) response to mycobacterial purified protein derivative (PPD). Soluble, pro-adhesive factors were identified in efferent lymph concomitant with reduced lymphocyte output in lymph, which significantly increased lymphocyte binding to lymphatic endothelial cells. While all lymphocyte subsets were retained, CD4+ T cells appeared less susceptible than others. Among a panel of cytokines in inflammatory lymph plasma, interferon (IFN)-gamma alone appeared responsible for this retention. In vitro adhesion assays using physiological levels of IFN-gamma confirmed the interaction between recirculating lymphocytes and lymphatic endothelium. These data demonstrate a new level of immune regulation, whereby the exit of recirculating lymphocytes from lymph nodes is selectively and sequentially regulated by cytokines in a manner equally as complex as lymphocyte recruitment.

Chemokine receptor CCR7 required for T lymphocyte exit from peripheral tissues

Lymphocytes travel throughout the body to carry out immune surveillance and participate in inflammatory reactions. Their path takes them from blood through tissues into lymph and back to blood. Molecules that control lymphocyte recruitment into extralymphoid tissues are well characterized, but exit is assumed to be random. Here, we showed that lymphocyte emigration from the skin was regulated and was sensitive to pertussis toxin. CD4(+) lymphocytes emigrated more efficiently than CD8(+) or B lymphocytes. T lymphocytes in the afferent lymph expressed functional chemokine receptor CCR7, and CCR7 was required for T lymphocyte exit from the skin. The regulated expression of CCR7 by tissue T lymphocytes may control their exit, acting with recruitment mechanisms to regulate lymphocyte transit and accumulation during immune surveillance and inflammation.

Basic principles of immunological surveillance of the normal central nervous system

Unlike most bodily organs, the central nervous system (CNS) exists behind a blood-tissue barrier designed to minimize the passage of cells and macromolecules into the neural parenchyma. Yet, the CNS is routinely and effectively surveyed by the immune system. This review examines the mechanisms and participants in this immunological surveillance mechanism. The nature of the healthy blood-brain barrier, factors modifying it, and its central position in determining the number and nature of leukocytes permitted to enter, are considered. In addition the role in surveillance played by lymphatic drainage, migrating T and B lymphocytes, and elements of the monocyte/macrophage/microglia family are considered. While all these participants are known to be important in responding to a CNS antigen and/or establishing a site of inflammation in the nervous system, they also are major elements in maintaining the homeostasis of the CNS and permitting the necessary immunological surveillance of that organ.

Epinephrine causes a reduction in lymph node cell output in sheep

The lymphatic system has a critical role in the return of fluids, proteins, and cells to the circulatory system. However, the effects of stress, including exercise, on this system have not been adequately studied. We investigated the effect of a physiological dose (1 mg) of epinephrine (Epi) on lymph flow, cell concentration, and lymphocyte subsets in efferent subcutaneous lymph in sheep. Blood leukocyte numbers, differential, lymphocyte subsets, and blood and lymph pools of lymphocytes were determined simultaneously. A significant acute increase in lymph flow was followed by a post-injection decrease in flow and cellular output. No changes in lymphocyte subsets or pools of lymphocytes were seen in either blood or lymph. The timing of elevated plasma and lymph concentrations of Epi and norepinephrine (NE) corresponded with the increased lymph flow. In conclusion, Epi injection caused no change in lymphocyte subset distribution, leukocyte concentration, or pools of lymphocytes. A decrease in lymph flow and cellularity was documented post-injection, indicating that lymphatic tissue has no role in the leukocytosis seen after Epi injection. Lymphocyte retention by lymph nodes, however, may contribute to post-injection lymphopenia.Key words: lymphocyte recirculation, catecholamines, exercise, stress, lymph.

Stochastic regulation of cell migration from the efferent lymph to oxazolone-stimulated skin

The systemic immune response is a dynamic process involving the trafficking of lymphocytes from the Ag-stimulated lymph node to the peripheral tissue. Studies in sheep have demonstrated several phases of cell output in the efferent lymph after Ag stimulation. When skin contact sensitizers are used as Ag, the efferent lymph cell output peaks approximately 96 h after Ag stimulation and is temporally associated with the recruitment of cells into the skin. To investigate the relative contribution of this high-output phase of efferent lymphocytes to lymphocytic inflammation in the skin, we used a common contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone (oxazolone) to stimulate the skin and draining prescapular lymph node of adult sheep. The efferent lymph ducts draining the Ag-stimulated and contralateral control lymph nodes were cannulated throughout the experimental period. The lymphocytes leaving the lymph nodes during the 72-h period before maximum infiltration were differentially labeled with fluorescent tracers, reinjected into the arterial circulation, and tracked to the site of Ag stimulation. Quantitative tissue cytometry of the skin at the conclusion of the injection period (96 h after Ag stimulation) demonstrated more migratory cells derived from the Ag-stimulated lymph node than the contralateral control (median 18.5 vs 15.5 per field; p < 0.05). However, when corrected for total cell output of the lymph node, the Ag-stimulated migratory cells were 3.8-fold more prevalent in the skin than the contralateral control cells. These results suggest that the in situ immune response generally mirrors the frequency of recruitable lymphocytes in the peripheral blood.

Subset-specific regulation of the lymphatic exit of recirculating lymphocytes in vivo

The blood-to-lymph recirculation of lymphocytes is required for the maintenance of immune surveillance and the dissemination of memory. Although the ability of lymph-borne cells to recirculate has been well documented, relatively less is known about the migration capacity of PBLs. We have found a clear preference for PBLs to recirculate through s.c. rather than intestinal lymph nodes. This preference could be directly attributed to the migratory characteristics of gammadelta-T cells. gammadelta-T cells were found to express significantly higher levels of L-selectin than other subsets, suggesting that at least some of this preferential migration could be attributed to their interaction with ligands on vascular endothelium. More detailed experiments showed that gammadelta-T cells migrated through lymph nodes with greater efficiency than alphabeta T cells or B cells, which clearly indicated an enhanced ability of gammadelta-T cells to exit lymph nodes in the efferent lymph independent of entry from the blood. This hypothesis was supported by histological examination, where gammadelta-T cells were found almost exclusively in the interfollicular traffic areas within lymph nodes. These data indicate that gammadelta-T cells are the most active recirculating lymphocyte subset in ruminants and suggest new mechanisms to regulate the traffic of lymphocyte subsets through normal lymph nodes.

An enhanced role for the recirculating lymphocyte in the neonatal immune system

Lymphocytes continually recirculate between the blood and the tissues via the lymph independent of antigen. A great deal is known regarding both the physiology and the molecular mechanisms responsible for the process in adults. However, relatively little is known regarding the development of the recirculating lymphocyte pool in very young animals or fetuses. We have directly measured the recirculation of lymphocyte subsets in antigen-inexperienced newborn animals, and found extensive recirculation of T cells through both intestinal and subcutaneous lymph nodes. Apparent selective migration of recirculating lymphocytes could be attributed to subset-specific migration of gammadelta-T cells through subcutaneous lymph nodes. This clearly demonstrates that the preference for gammadelta-T cells to recirculate through SCLN is lineage specific, and independent of the presence of antigen. Most surprising was the observation that the recirculating lymphocyte pool was proportionately larger in neonatal animals than in adults, which correlated with the histological appearance of newborn lymph nodes. This data strongly suggests that development of the recirculating lymphocyte pool is inversely correlated with antigen exposure, and decreases in size with age and the acquisition of immunological memory.

Engineering mouse T lymphocytes specific to type II collagen by transduction with a chimeric receptor consisting of a single chain Fv and TCR zeta

The chimeric cell surface receptor scC2Fv/CD8/zeta was constructed to engineer primary mouse T lymphocytes with antibody-type specificity to type II collagen (CII). Such cells could be used as gene carriers in the anti-inflammatory gene therapy of an autoimmune arthritis. This receptor includes the single chain Fv domain (scFv) of the anti-CII monoclonal antibody (mAb) C2, hinge region of CD8alpha and the transmembrane and cytoplasmic domains of TCRzeta. The scC2Fv/CD8/zeta gene was transduced into T cell hybridomas and primary mouse lymphocytes using retrovirus-mediated gene transfer. The chimeric receptor scC2Fv/CD8/zeta forms covalently bound homodimers, as demonstrated in T cell hybridomas and packaging fibroblasts. It does not associate with endogenous signalling subunits of the TCR complex. When scC2Fv/CD8/zeta-expressing clones of T cell hybridomas MD.45 and HCQ6 were stimulated with CII they produced IL-2. The level of their IL-2 response correlated with the expression level of the chimeric receptor on the cell surface. Splenocytes isolated from DBA/1 mice were stimulated with Con A in vitro to facilitate retrovirus-mediated transfer of the scC2Fv/CD8/zeta gene. As a result of transduction, approximately 4% of the Con A-activated splenocytes expressed the chimeric receptor scC2Fv/CD8/zeta on the cell surface. These cells proliferated in response to stimulation with CII.