Lymphocyte Emigration Research Articles

Diabetes Induces a Transcriptional Signature in Bone Marrow-Derived CD34+ Hematopoietic Stem Cells Predictive of Their Progeny Dysfunction.

Hematopoietic stem/progenitor cells (HSPCs) participate in cardiovascular (CV) homeostasis and generate different types of blood cells including lymphoid and myeloid cells. Diabetes mellitus (DM) is characterized by chronic increase of pro-inflammatory mediators, which play an important role in the development of CV disease, and increased susceptibility to infections. Here, we aimed to evaluate the impact of DM on the transcriptional profile of HSPCs derived from bone marrow (BM). Total RNA of BM-derived CD34+ stem cells purified from sternal biopsies of patients undergoing coronary bypass surgery with or without DM (CAD and CAD-DM patients) was sequenced. The results evidenced 10566 expressed genes whose 79% were protein-coding genes, and 21% non-coding RNA. We identified 139 differentially expressed genes (p-value < 0.05 and |log2 FC| > 0.5) between the two comparing groups of CAD and CAD-DM patients. Gene Set Enrichment Analysis (GSEA), based on Gene Ontology biological processes (GO-BP) terms, led to the identification of fourteen overrepresented biological categories in CAD-DM samples. Most of the biological processes were related to lymphocyte activation, chemotaxis, peptidase activity, and innate immune response. Specifically, HSPCs from CAD-DM patients displayed reduced expression of genes coding for proteins regulating antibacterial and antivirus host defense as well as macrophage differentiation and lymphocyte emigration, proliferation, and differentiation. However, within the same biological processes, a consistent number of inflammatory genes coding for chemokines and cytokines were up-regulated. Our findings suggest that DM induces transcriptional alterations in HSPCs, which are potentially responsible of progeny dysfunction.

Halted Lymphocyte Egress via Efferent Lymph Contributes to Lymph Node Hypertrophy During Hypercholesterolemia.

Dyslipidemia is a central component of atherosclerosis and metabolic syndrome linked to chronic inflammation and immune dysfunction. Previously, we showed that hypercholesterolemic apolipoprotein E knock out (apoE−/−) mice exhibit systemic effects including skin inflammation and hypertrophic lymph nodes (LNs). However, the mechanisms accounting for LN hypertrophy in these mice remain unknown. Here, we show that hypercholesterolemia led to the accumulation of lymphocytes in LNs. We excluded that the increased number of lymphocytes in expanded LNs resulted from increased lymphocyte proliferation or entry into those LNs. Instead, we demonstrated that the egress of lymphocytes from the enlarged LN of apoE−/− mice was markedly decreased. Impairment in efferent lymphatic emigration of lymphocytes from LNs resulted from an aberrant expansion of cortical and medullary sinuses that became hyperplastic. Moreover, CCL21 was more abundant on these enlarged sinuses whereas lymph levels of sphingosine 1 phosphate (S1P) were decreased in apoE−/− mice. Normal LN size, lymphatic density and S1P levels were restored by reversing hypercholesterolemia. Thus, systemic changes in cholesterol can sequester lymphocytes in tissue draining LNs through the extensive remodeling of lymphatic sinuses and alteration of the balance between retention/egress signals leading to LN hypertrophy which subsequently may contribute to poor immunity. This study further illustrates the role of lymphatic vessels in immunity through the regulation of immune cell trafficking.

Peculiarities of lymphocytes emigration from newborn thymus

Introduction. Mechanisms of mass lymphocytes’ emigration from thymus are still unclear. The process of lymphocytes migration and mechanisms, which provide it, form one of the important problems of immunomorphology.Aim of the work: to establish the peculiarities of newborn thymus structure and to reveal pathways and mechanisms which provide lymphocytes’ emigration from thymus.Materials and methods. Morphological, histological and histochemical analyses of 160 rats’ thymuses from birth up to the 7th day after birth were conducted and discussed. The animals were handled according to the European Commission Directive (86/609/EEC). The profound microscopic analysis of cell contents, lymphatic vessels morphology in morpho-functional areas of rats’ thymuses during the first week after birth in 4 hours interval was carried out. All quantitative results were estimated by the statistic methods.Results. It is settled that thymus specific density tightly depends on the quantity of degranulated mast cells, absolute quantity of microcirculatory vessels, especially of lymphatic ones. The index of specific density, lymphocyte-epithelial index change wavy during the first week after birth every 12 hours. These changes are followed by the changes of extracellular matrix structure, absolute quantity of small lymphocytes in thymic cortex and lymphocytes’ adhesive properties. The key periods are: from 0 till 2, from 12 till 16, and from 108 till 120 hours after birth. At that time discrete migration of lymphocytes from the thymus occurs through paravasal lymphatic vessels. After temporal edema reduction, lymphatic vessels turn to be empty, their quantity decreases.Conclusion. Therefore, emigration of lymphocytes from thymus takes place through lymphatic vessels on the top of periodical short-term local edema.

The role of lymphoid tissue in the attenuation of the postoperative ileus

Standardized intestinal manipulation (IM) leads to local bowel wall inflammation subsequently spreading over the entire gastrointestinal tract. Previously, we demonstrated that this so-called gastrointestinal field effect (FE) is immune-mediated. The aim of this study was to investigate the role of secondary lymphoid organs [mesenteric lymph nodes (MLN), gut-associated lymphoid tissue (GALT)] in IM-mediated FE by employing mice with deficient secondary lymphoid organs (aly/aly, MLN ex) or by administration of 2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol (FTY720), an immunomodulating agent that inhibits emigration of lymphocytes out of lymphoid organs. Small bowel muscularis, and colonic muscularis from wild-type mice as control, from aly/aly mice, FTY720-treated mice (daily dose of 1.0 mg/kg mouse ip starting 3 days before surgical procedure), and wild-type mice that had undergone removal of mesenteric lymph nodes before IM (MLN ex mice) were obtained after selective IM of the jejunum or sham operation. FE was analyzed by measuring transit time of orally administered fluorescent dextran in the gastrointestinal tract [geometric center (GC) of fluorescent dextran], colonic transit time, infiltration of myeloperoxidase-positive cells, and circular smooth muscle contractility. Furthermore, mRNA levels of inflammatory cytokines [interleukin (IL)-6, tumor necrosis factor (TNF)-α, macrophage inflammatory protein (MIP)-1α] were determined by Taqman-PCR. We observed a significantly reduced upregulation of proinflammatory cytokines (IL-6, TNF-α, MIP-1α) in colonic muscularis of MLN ex mice, aly/aly mice, and FTY720-treated mice compared with wild-type mice. Contractility of circular muscularis strips of the colon but not the jejunum was significantly improved in aly/aly mice and FTY720-treated wild-type mice. Additionally, inflammation of the colon determined by the number of myeloperoxidase-positive cells and colonic transit time were significantly improved in aly/aly mice, FTY720-treated wild-type mice, and in MLN ex mice. In summary, lack of secondary lymphoid organs (MLN + GALT) in aly/aly mice or administration of FTY720 abrogated FE after IM as opposed to wild-type mice. These data demonstrate that secondary lymphoid organs are involved in the propagation of FE and postoperative ileus. FTY720 indirectly affects FE by inhibiting migration of activated T cells from the jejunum and adjacent secondary lymphoid organs to the colon. These findings support the crucial role of the adaptive immune system in FE, most likely by a sphyngosine 1-phosphate-dependent mechanism.

Talin1 is required for integrin-dependent B lymphocyte homing to lymph nodes and the bone marrow but not for follicular B-cell maturation in the spleen

AbstractTalin1 is a key integrin coactivator. We investigated the roles of this cytoskeletal adaptor and its target integrins in B-cell lymphogenesis, differentiation, migration, and function. Using CD19 Cre-mediated depletion of talin1 selectively in B cells, we found that talin1 was not required for B-cell generation in the bone marrow or for the entry of immature B cells to the white pulp of the spleen. Loss of talin1 also did not affect B-cell maturation into follicular B cells but compromised differentiation of marginal zone B cells. Nevertheless, serum IgM and IgG levels remained normal. Ex vivo analysis of talin1-deficient spleen B cells indicated a necessary role for talin1 in LFA-1 and VLA-4 activation stimulated by canonical agonists, but not in B-cell chemotaxis. Consequently, talin1 null B splenocytes could not enter lymph nodes nor return to the bone marrow. Talin1 deficiency in B cells was also impaired in the humoral response to a T cell-dependent antigen. Collectively, these results indicate that talin1 is not required for follicular B-cell maturation in the spleen or homeostatic humoral immunity but is critical for integrin-dependent B lymphocyte emigration to lymph nodes and optimal immunity against T-dependent antigens.

Reining in FoxP3+ regulatory T cells by the sphingosine 1‐phosphate‐S1P1 axis

Reining in FoxP3⁺ regulatory T cells by the sphingosine 1‐phosphate‐S1P1 axis

Impaired Initiation of Contact Hypersensitivity by FTY720

FTY720 inhibits lymphocyte emigration from lymphoid organs to peripheral blood by binding one of the sphingosine-1-phosphate (S1P) receptors, S1P(1). We investigated the effects of FTY720 in relation to murine contact hypersensitivity (CHS). CHS was impaired by FTY720 when administered during the sensitization but not the elicitation phase. Consistently, adoptive transfer of immunized lymph node cells from mice treated with FTY720 during the sensitization phase was virtually incapable of inducing CHS response in recipients. FTY720 decreased the number of blood CD44(-)-naive T cells markedly and that of CD44(+) memory T cells modestly. Among memory T cells, the CD62L(-) effector memory subset was more resistant to FTY720 than the CD62L(+) central memory subset. Accordingly, the level of S1P chemotactic response was high in naive T cells, marginal in effector memory T cells, and very low in central memory T cells. Consistently, the S1P(1) mRNA expression level was much lower in memory T cells than in naive T cells. These findings demonstrate that S1P-S1P(1) signaling is essential for recirculation of naive T cells. FTY720 seems to decrease the incidence of interactions between antigen-loaded dendritic cells and circulating naive T-cell clones in the lymph nodes, thereby depressing the sensitization of naive T cells in CHS.

Silencing S1P1 Receptors Regulates Collagen-V Reactive Lymphocyte-Mediated Immunobiology in the Transplanted Lung

Type V collagen (col[V])-reactive lymphocytes contribute to lung transplant rejection, but the mechanisms for emigration into the graft are unknown. Sphingosine-1-phosphate-1 receptors (S1P(1R)) are believed to be required for lymphocyte emigration in other studies, but their role in col(V)-reactive lymphocyte rejection responses is not known. Utilizing small interfering RNA (siRNA) to reduce S1P(1R) expression on col(V)-reactive lymphocytes, we examined the role of S1P(1R) in the rejection response. Quantitative polymerase chain reaction (PCR) revealed strong expression of S1P(1R) messenger RNA (mRNA)on col(V)-reactive lymphocytes isolated from immunized rats. S1P(1R)-specific siRNA (S1P(1R) siRNA) reduced expression of S1P(1R) mRNA and protein, whereas scramble siRNA (SC siRNA) had no effect. Adoptive transfer of lymphocytes treated with S1P(1R) siRNA to rat Wistar Kyoto (WKY) lung isograft recipients resulted in retention of cells within the liver with fewer cells in mediastinal lymph nodes when compared to cells exposed to SC siRNA. S1P(1R)-deficient cells proliferated in response to alloantigens, but not in response to col(V), and produced less interferon (IFN)-gamma in response to col(V) compared to controls. Downregulating S1P(1R) did not affect production of interleukin (IL)-10and tumor necrosis factor (TNF)-alpha, or expression of adhesion molecules critical for migration, but prevented rejection pathology and lowered local levels of IFN-gamma post adoptive transfer. These data demonstrate novel roles of S1P(1R,) which include regulating emigration and modulating lymphocyte activation.

Sphingosine 1‐phosphate regulates innate and acquired intestinal IgA production

Intestinal IgA plays an important role in the innate and acquired phases of immunosurveillance by recognizing T‐independent (TI) and T‐dependent (TD) antigens, respectively. Sphingosine 1‐phosphate (S1P) is known to regulate lymphocyte emigration from organized lymphoid tissues, but its immunological role in the induction of intestinal IgA production remains to be elucidated. Here we show that intestinal IgA productions against TI and TD antigens are controlled by S1P. We found that disruption of S1P‐mediated signaling by the treatment of mice with FTY720, a modulator of S1P receptors, resulted in the marked reduction of intestinal IgA production against TI phosphorylcholine induced by oral immunization with heat‐killed Streptococcal pneumoniae (R36A). Similarly, FTY720 reduced production of intestinal IgA against ovalbumin (OVA), a typical TD antigen, in mice orally immunized with OVA plus mucosal adjuvant, cholera toxin. The decreased TI and TD antigen‐specific intestinal IgA productions were associated with the impaired trafficking of peritoneal B1 and Peyer s patch B2 cells into the intestinal lamina propria, respectively. These findings point to a pivotal role for S1P in innate and acquired phases of intestinal B cell immunity.

Phosphorylation of vascular endothelial cadherin controls lymphocyte emigration

Lymphocytes emigrate from the circulation to target tissues through the microvascular endothelial cell (EC) barrier. During paracellular transmigration cell-cell junctions have been proposed to disengage and provide homophilic and heterophilic interaction surfaces in a zip-like process. However, it is not known whether ECs modulate junction proteins during this process. Here we show that tyrosine phosphorylation of adherens junction vascular endothelial cadherin (VEC) is required for successful transendothelial lymphocyte migration. We found that adhesion of lymphocytes or activation of the endothelial intercellular adhesion molecule 1 (ICAM1) led to tyrosine phosphorylation of VEC. Substitution of tyrosine for phenylalanine in VEC at positions 645, 731 or 733 produced ECs that were significantly less permissive to lymphocyte migration. We also found that these same tyrosine residues are involved in ICAM1-dependent changes of VEC phosphorylation. ICAM1 activation enhanced transendothelial permeability, suggesting the occurrence of junction disassembly. In agreement, the expression of VEC mutated at Y645F, Y731F or Y733F predominantly affected lymphocyte transmigration in paracellular areas. Taken together, these results demonstrate that phosphorylation of adherens junctions constitutes a molecular endpoint of lymphocyte-induced vascular EC signaling and may be exploited as a new target of anti-inflammatory therapies.

Blockade of Hyaluronan Inhibits IL-2-Induced Vascular Leak Syndrome and Maintains Effectiveness of IL-2 Treatment for Metastatic Melanoma

Vascular leak syndrome (VLS) is a life-threatening toxicity induced during IL-2 treatment of cancer patients. The mechanism of IL-2-induced VLS is still poorly understood. At present, there is no specific therapy for VLS. Previous studies from our laboratory demonstrated that hyaluronan (HA), a large glycosaminoglycan, abundant in the extracellular matrix and on the cell surface, caused a marked increase of IL-2-induced VLS in the lungs and liver of C57BL/6 mice. Conversely, blockade or knockout of its major receptor, CD44, resulted in a marked decrease of VLS, thereby suggesting a role for HA in VLS. In this study, we report a novel means to prevent IL-2-induced VLS by blocking endogenous HA with HA-specific binding peptide, Pep-1, a newly isolated peptide which specifically binds to soluble, cell-associated, and immobilized forms of HA. Our results demonstrated that blocking HA with Pep-1 dramatically inhibited IL-2-induced VLS in both normal mice as well as in mice bearing melanoma. Moreover, Pep-1 treatment maintained the effectiveness of IL-2 and prevented the metastasis of melanoma. IL-2-induced emigration of lymphocytes across the endothelium and cytotoxicity against tumor by lymphokine-activated killer cells were not affected by Pep-1. Instead, use of Pep-1 maintained endothelial integrity and reduced their apoptosis during IL-2-induced VLS. These data suggested that HA plays a critical role in regulating endothelial cell damage and induction of IL-2-mediated VLS. Also, blockade of HA using Pep-1 could constitute a novel therapeutic modality to prevent IL-2-mediated toxicity, thereby facilitating the effectiveness of high-dose IL-2 in the treatment of metastatic melanomas.

Sphingosine 1-phosphate regulates peritoneal B-cell trafficking for subsequent intestinal IgA production

AbstractSphingosine 1-phosphate (S1P) is known to play a pivotal role in the regulation of lymphocyte emigration from organized lymphoid tissues such as the peripheral lymph nodes and thymus, but its immunologic role in unorganized and diffused tissues remains to be elucidated. Here we show that the trafficking of peritoneal B cells is principally regulated by S1P. All peritoneal B cells including B1a, B1b, and B2 B cells express comparable levels of the type 1 S1P receptor. Thus, treatment with FTY720, an S1P receptor modulator, caused the rapid disappearance of peritoneal B cells by inhibiting both their emigration from parathymic lymph nodes and their recirculation from the blood into the peritoneal cavity without affecting their progenitor populations. These changes did not affect natural plasma antibody production or phosphorylcholine (PC)–specific antibody production in serum after peritoneal immunization with heat-killed Streptococcal pneumoniae (R36A). However, FTY720 dramatically reduced peritoneal B cell-derived natural intestinal secretory IgA production without affecting the expression of J-chain and polyimmunoglobulin receptors. Additionally, FTY720 impaired the generation of PC-specific fecal IgA responses after oral immunization with R36A. These findings point to a pivotal role for S1P in connecting peritoneal B cells with intestinal B-cell immunity.

Blockade of hyaluronan, a CD44 ligand, inhibits IL-2–induced vascular leak syndrome while maintaining effective treatment of melanoma (48.30)

Abstract High-dose IL-2 therapy is an effective mode of treatment against melanomas; however, its use is limited by accompaniment of vascular leak syndrome (VLS), a life-threatening toxicity. The precise mechanism/s of VLS is unclear and there is no specific therapy to block VLS and enhance IL-2 based immunotherapy. Previous studies from our laboratory demonstrated that CD44 plays a critical role in VLS; administration of hyaluronan (HA), a primary ligand for CD44, caused a marked increase in IL-2 induced VLS. In this study, we report a novel means to prevent VLS by blocking endogenous HA with HA-specific binding peptide, Pep-1. Our results demonstrated that administration of Pep-1 into IL-2 treated mice dramatically inhibited IL-2-induced VLS in the lungs and liver. Interestingly, Pep-1 treatment did not affect the effectiveness of IL-2 in treatment of melanoma. Pep-1 treatment did not affect the emigration of lymphocytes across the endothelium and the activation of CTL seen during IL-2 treatment. Also, blocking HA with Pep-1 maintained endothelial integrity and prevented their apoptosis. Our results demonstrate that HA plays a role in regulating endothelial damage and blockade of HA could be a novel means for prevention and treatment of VLS thereby facilitating IL-2-induced immunotherapy of melanomas. (Supported by NIH grants RO1 AI 053703, RO1 DA 016545, RO1 AI 058300, RO1 HL 058641 and RO1 ES 09098)

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.

Rac1 mediates collapse of microvilli on chemokine-activated T lymphocytes.

Lymphocytes circulate in the blood and upon chemokine activation rapidly bind, where needed, to microvasculature to mediate immune surveillance. Resorption of microvilli is an early morphological alteration induced by chemokines that facilitates lymphocyte emigration. However, the antecedent molecular mechanisms remain largely undefined. We demonstrate that Rac1 plays a fundamental role in chemokine-induced microvillar breakdown in human T lymphocytes. The supporting evidence includes: first, chemokine induces Rac1 activation within 5 s via a signaling pathway that involves Galphai. Second, constitutively active Rac1 mediates microvilli disintegration. Third, blocking Rac1 function by cell permeant C-terminal "Trojan" peptides corresponding to Rac1 (but not Rac2, Rho, or Cdc42) blocks microvillar loss induced by the chemokine stromal cell-derived factor 1alpha (SDF-1alpha). Furthermore, we demonstrate that the molecular mechanism of Rac1 action involves dephosphorylation-induced inactivation of the ezrin/radixin/moesin (ERM) family of actin regulators; such inactivation is known to detach the membrane from the underlying actin cytoskeleton, thereby facilitating disassembly of actin-based peripheral processes. Specifically, ERM dephosphorylation is induced by constitutively active Rac1 and stromal cell-derived factor 1alpha-induced ERM dephosphorylation is blocked by either the dominant negative Rac1 construct or by Rac1 C-terminal peptides. Importantly, the basic residues at the C terminus of Rac1 are critical to Rac1's participation in ERM dephosphorylation and in microvillar retraction. Together, these data elucidate new roles for Rac1 in early signal transduction and cytoskeletal rearrangement of T lymphocytes responding to chemokine.

FTY720: from bench to bedside

FTY720, a synthetic myriocin analogue derived from culture filtrates of Isaria sinclairii, is a novel immunosuppressant that in experimental animals and nonhuman primates produces lymphocytopenia and prolongs allograft survival in dose-dependent fashion. FTY720 exerts synergistic interactions not only with calcineurin antagonists, but also with proliferation signal inhibitors. These interactions proffer the possibility of reducing exposure to and mitigating toxicity of existing drugs. The mechanism of drug action is not entirely clear. FTY720 appears to undergo phosphorylation by sphingosine phosphokinase 2, rendering it capable of interacting with the specific G protein-linked receptors for its structural homologue—sphingosine-1-phosophate. However, it is not clear how this interaction leads to emigration of lymphocytes from the peripheral blood and sequestration in secondary lymphoid structures. Present theories suggest that the drug prevents emigration rather than directing the onset of sequestration. Thus, the drug is the archetype of a new class of agents that alter lymphocyte homing patterns: the adhesion-migration paradigm. These modalities reduce interstitial infiltration of grafts and attenuate their release from lymph nodes. Since FTY720 seems to spare nonspecific elements of host resistance, it may not only represent a useful addition to the immunosuppressive armamentarium but also address the not infrequent complications of infections associated with existing therapies.

Lymphocyte egress from thymus and peripheral lymphoid organs is dependent on S1P receptor 1.

Adaptive immunity depends on T-cell exit from the thymus and T and B cells travelling between secondary lymphoid organs to survey for antigens. After activation in lymphoid organs, T cells must again return to circulation to reach sites of infection; however, the mechanisms regulating lymphoid organ exit are unknown. An immunosuppressant drug, FTY720, inhibits lymphocyte emigration from lymphoid organs, and phosphorylated FTY720 binds and activates four of the five known sphingosine-1-phosphate (S1P) receptors. However, the role of S1P receptors in normal immune cell trafficking is unclear. Here we show that in mice whose haematopoietic cells lack a single S1P receptor (S1P1; also known as Edg1) there are no T cells in the periphery because mature T cells are unable to exit the thymus. Although B cells are present in peripheral lymphoid organs, they are severely deficient in blood and lymph. Adoptive cell transfer experiments establish an intrinsic requirement for S1P1 in T and B cells for lymphoid organ egress. Furthermore, S1P1-dependent chemotactic responsiveness is strongly upregulated in T-cell development before exit from the thymus, whereas S1P1 is downregulated during peripheral lymphocyte activation, and this is associated with retention in lymphoid organs. We find that FTY720 treatment downregulates S1P1, creating a temporary pharmacological S1P1-null state in lymphocytes, providing an explanation for the mechanism of FTY720-induced lymphocyte sequestration. These findings establish that S1P1 is essential for lymphocyte recirculation and that it regulates egress from both thymus and peripheral lymphoid organs.

Trafficking of Th1 cells to lung: a role for selectins and a P-selectin glycoprotein-1-independent ligand.

Trafficking of lymphocytes to lung is a critical component of pulmonary immune defense and surveillance. Selectins, expressed on vascular endothelium, regulate T lymphocyte emigration into tissues, such as skin, but the role of the selectins in trafficking of T cells to lung has not been well characterized. Here, we used a model of lung inflammation induced by adoptive transfer of alloreactive Th1 cells to analyze the role of P- and E-selectin in Th1 cell trafficking to lung in vivo. We found that both P- and E-selectin play an important role in Th1 lymphocyte migration to lung. We confirmed that the Th1 cells express P-selectin glycoprotein ligand-1, which was functional in binding to P- and E-selectin in vitro. However, our studies reveal that a ligand distinct from P-selectin glycoprotein-1 also binds these selectins in vitro and appears to play a physiologic role in in vivo emigration of Th1 lymphocytes into the lung.

FTY720: A new kid on the block for transplant immunosuppression

FTY720, a synthetic analogue of myriocin (ISP-1), is derived from culture filtrates of the fungus Isaria sinclairii. As a sphingosine analogue, FTY720 appears to undergo phosphorylation and thereby interact with specific G-protein-linked receptors. In vivo, FTY720 causes emigration of lymphocytes from peripheral blood to secondary lymphoid structures. Thus, the drug is the archetype of a new class of agents that alter cellular homing patterns: the adhesion–migration paradigm. Since FTY720 seems to spare nonspecific elements of host resistance, it may address the not infrequent complications of infections associated with existing therapies. In experimental rodent, canine and non-human primate models, FTY720 produces lymphopenia and immunosuppression, prolonging the survival of allografts. Because of synergistic interactions, it promotes the immunosuppressive effects not only of calcineurin antagonists, but also of proliferation signal inhibitors. These interactions proffer the possibility of large reductions in exposure to and mitigated toxicity of existing drugs. In humans, FTY720 causes dose-dependent peripheral blood lymphopenia, a reduced incidence of acute rejection episodes and only one apparent adverse reaction – a negative chronotropic effect – particularly after the loading dose. While the clinical utility of FTY720 is difficult to predict before completion of Phase III studies that elucidate its benefits versus unanticipated side effects, the initial data suggest several potential advantages: it does not produce hyperlipidaemia, diabetes mellitus, nephrotoxicity, neurotoxicity or myelosuppression, which are characteristic of other immunosuppressants. Furthermore, it displays high oral bioavailability and a low interindividual coefficient of variation. Clearly, structural analogues, as well as other agents that alter the balance of chemokines or affect cellular adhesion to activated endothelium, will represent important components of future regimens.

Molecular and functional characterization of SLC26A11, a sodium‐independent sulfate transporter from high endothelial venules

Lymphocyte emigration from the blood into most secondary lymphoid organs and chronically inflamed tissues occurs at the level of high endothelial venules (HEV). A unique characteristic of HEV endothelial cells (HEVEC) is their capacity to incorporate large amounts of sulfate into sialomucin-type counter-receptors for the lymphocyte homing receptor L-selectin. We have previously shown that sulfate uptake into HEVEC is mediated by two distinct functional classes of sulfate transporters: Na+-coupled transporters and sulfate/anion exchangers. Here, we report the molecular characterization from human HEVEC of SLC26A11, a novel member of the SLC26 sulfate/anion exchanger family. Functional expression studies in COS-7 and Sf9 insect cells revealed that SLC26A11 is targeted to the cell membrane and exhibits Na+-independent sulfate transport activity, sensitive to the anion exchanger inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). Northern blot analysis showed the highest SLC26A11 transcript levels in placenta, kidney, and brain. The SLC26A11 gene mapped to human chromosome 17q25, very close to the hereditary hearing loss diseases loci DFNA20, DFNA26, and USH1G. RT-PCR analysis of SLC26 sulfate transporters in human HEVEC revealed coexpression of SLC26A11 with SLC26A2/DTDST and lack of SLC26A1/SAT1, SLC26A3/DRA, and SLC26A8/TAT1. Together, our results indicate that SLC26A11 is a novel Na+-independent sulfate transporter that may cooperate with SLC26A2 to mediate DIDS-sensitive sulfate uptake into HEVEC.