Ligands for L-selectin: homing, inflammation, and beyond

Understanding the molecular basis of lymphocyte homing to lymphoid organs was originally a problem of concern only to immunologists. With the discovery of L-selectin and its ligands, interested scientists have expanded to include glycobiologists, immunopathologists, cancer biologists, and developmental biologists. Going beyond its first discovered role in homing to lymph nodes, the L-selectin system is implicated in such diverse processes as inflammatory leukocyte trafficking in both acute and chronic settings, hematogenous metastasis of carcinoma cells, effector mechanisms for inflammatory demyelination of axons, and implantation of the early mammalian embryo. This review focuses on the ligands for L-selectin that are found on vascular endothelium, leukocytes, carcinoma cells, and at various extravascular sites. The discovery of selectins and their ligands has validated the long-predicted hypothesis that carbohydrate-directed cell adhesion is relevant in eukaryotic systems. Emphasis will be given to the carbohydrate and sulfation modifications of the ligands, which enable recognition by L-selectin. The rapid "homing" of labeled cells into the lymph nodes presumably had its basis in the special affinity of small lymphocytes for the endothelium of the postcapillary venules.

The effect of antigen dose on CD4+ T helper cell phenotype development in a T cell receptor-alpha beta-transgenic model

The dose of foreign antigen can influence whether a cell-mediated or humoral class of immune response is elicited, and this may be largely accounted for by the development of CD4+ T helper cells (Th) producing distinct sets of cytokines. The ability of antigen dose to direct the development of a Th1 or Th2 phenotype from naive CD4+ T cells, however, has not been demonstrated. In this report, we show that the antigen dose used in primary cultures could directly affect Th phenotype development from naive DO11.10 TCR-alpha beta-transgenic CD4+ T cells when dendritic cells or activated B cells were used as the antigen-presenting cells. Consistent with our previous findings, midrange peptide doses (0.3-0.6 microM) directed the development of Th0/Th1-like cells, which produced moderate amounts of interferon gamma (IFN-gamma). As the peptide dose was increased, development of Th1-like cells producing increased amounts of IFN-gamma was initially observed. At very high (> 10 microM) and very low (< 0.05 microM) doses of antigenic peptide, however, a dramatic switch to development of Th2-like cells that produced increasing amounts of interleukin 4 (IL-4) and diminishing levels of IFN-gamma was observed. This was true even when highly purified naive, high buoyant density CD4+ LECAM-1hi T cells were used, ruling out a possible contribution from contaminating "memory" phenotype CD4+ T cells. Neutralizing anti-IL-4 antibodies completely inhibited the development of this Th2-like phenotype at both high and low antigen doses, demonstrating a requirement for endogenous IL-4. Our findings suggest that the antigen dose may affect the levels of endogenous cytokines such as IL-4 in primary cultures, resulting in the development of distinct Th cell phenotypes.

CD11c(+)B220(+)Gr-1(+) cells in mouse lymph nodes and spleen display characteristics of plasmacytoid dendritic cells

Human plasmacytoid dendritic cells (pDCs) are major producers of IFNalpha, are activated by CpG motifs, and are believed to enter lymph nodes (LNs) via L-selectin dependent extravasation across high endothelial venules. To identify a similar murine DC type, CD11c(+) cells in the LNs of L-selectin-deficient and control BALB/c mice were compared, revealing a population of CD11c(+)CD11b(-) cells that is reduced 85% in the LNs of L-selectin-deficient mice. These cells are Gr-1(+)B220(+)CD19(-), either CD4(+) or CD8(+), and localize within T cell zones of LNs. Freshly isolated CD11c(+)Gr-1(+) cells express major histocompatibility complex class II at low levels, display a plasmacytoid morphology, and survive poorly in culture. Their survival is increased and they develop a DC-like morphology in interleukin 3 and CpG. Like human pDCs, CD11c(+)Gr-1(+) cells stimulate T cell proliferation after activation with CpG and produce IFNalpha after stimulation with influenza virus. These cells also display a strain-specific variation in frequency, being fivefold increased in the LNs of BALB/c relative to C57BL/6 mice. These CD11c(+)CD11b(-)B220(+)Gr-1(+) cells appear to be the murine equivalent of human pDCs.

Microbial stimulation fully differentiates monocytes to DC-SIGN/CD209(+) dendritic cells for immune T cell areas

Dendritic cells (DCs), critical antigen-presenting cells for immune control, normally derive from bone marrow precursors distinct from monocytes. It is not yet established if the large reservoir of monocytes can develop into cells with critical features of DCs in vivo. We now show that fully differentiated monocyte-derived DCs (Mo-DCs) develop in mice and DC-SIGN/CD209a marks the cells. Mo-DCs are recruited from blood monocytes into lymph nodes by lipopolysaccharide and live or dead gram-negative bacteria. Mobilization requires TLR4 and its CD14 coreceptor and Trif. When tested for antigen-presenting function, Mo-DCs are as active as classical DCs, including cross-presentation of proteins and live gram-negative bacteria on MHC I in vivo. Fully differentiated Mo-DCs acquire DC morphology and localize to T cell areas via L-selectin and CCR7. Thus the blood monocyte reservoir becomes the dominant presenting cell in response to select microbes, yielding DC-SIGN(+) cells with critical functions of DCs.

Diabetes induced by Coxsackie virus: initiation by bystander damage and not molecular mimicry

Viral induction of autoimmunity is thought to occur by either bystander T-cell activation or molecular mimicry. Coxsackie B4 virus is strongly associated with the development of insulin-dependent diabetes mellitus in humans and shares sequence similarity with the islet autoantigen glutamic acid decarboxylase. We infected different strains of mice with Coxsackie B4 virus to discriminate between the two possible induction mechanisms, and found that mice with susceptible MHC alleles had no viral acceleration of diabetes, but mice with a T cell receptor transgene specific for a different islet autoantigen rapidly developed diabetes. These results show that diabetes induced by Coxsackie virus infection is a direct result of local infection leading to inflammation, tissue damage, and the release of sequestered islet antigen resulting in the re-stimulation of resting autoreactive T cells, further indicating that the islet antigen sensitization is an indirect consequence of the viral infection.

Foxo1 links homing and survival of naive T cells by regulating L-selectin, CCR7 and interleukin 7 receptor

Foxo transcription factors have a conserved role in the adaptation of cells and organisms to nutrient and growth factor availability. Here we show that Foxo1 has a crucial, nonredundant role in T cells. In naive T cells, Foxo1 controlled the expression of the adhesion molecule L-selectin, the chemokine receptor CCR7 and the transcription factor Klf2, and its deletion was sufficient to alter lymphocyte trafficking. Furthermore, Foxo1 deficiency resulted in a severe defect in interleukin 7 receptor alpha-chain (IL-7Ralpha) expression associated with its ability to bind an Il7r enhancer. Finally, growth factor withdrawal induced a Foxo1-dependent increase in Sell, Klf2 and Il7r expression. These data suggest that Foxo1 regulates the homeostasis and life span of naive T cells by sensing growth factor availability and regulating homing and survival signals.

The function of follicular helper T cells is regulated by the strength of T cell antigen receptor binding

How follicular helper T cells (T(FH) cells) differentiate to regulate B cell immunity is critical for effective protein vaccination. Here we define three transcription factor T-bet-expressing antigen-specific effector helper T cell subsets with distinguishable function, migratory properties and developmental programming in vivo. Expression of the transcriptional repressor Blimp-1 distinguished T zone 'lymphoid' effector helper T cells (CD62L(hi)CCR7(hi)) from CXCR5(lo) 'emigrant' effector helper T cells and CXCR5(hi) 'resident' T(FH) cells expressing the transcriptional repressor Bcl-6 (CD62L(lo)CCR7(lo)). We then show by adoptive transfer and intact polyclonal responses that helper T cells with the highest specific binding of peptide-major histocompatibility complex class II and the most restricted T cell antigen receptor junctional diversity 'preferentially' developed into the antigen-specific effector T(FH) compartment. Our studies demonstrate a central function for differences in the binding strength of the T cell antigen receptor in the antigen-specific mechanisms that 'program' specialized effector T(FH) function in vivo.

Lymphocyte recruitment into the aortic wall before and during development of atherosclerosis is partially L-selectin dependent

Atherosclerosis is an inflammatory disease of large arteries. Flow cytometry of aortic cell suspensions showed that B and T lymphocytes and some macrophages and dendritic cells are already present in the adventitia of normal/noninflamed mouse aortas. Adoptively transferred lymphocytes constitutively homed to the aorta and resided within the adventitia up to 7 d after transfer. Lymphocyte trafficking into normal/noninflamed or atherosclerosis-prone aortas was partially L-selectin dependent. Antigen-activated dendritic cells induced increased T lymphocyte proliferation within the aorta 72 h after adoptive transfer. During progression of atherosclerosis in apolipoprotein-E-deficient mice, the total number of macrophages, T cells, and dendritic cells, but not B cells, increased significantly. This alteration in immune cell composition was accompanied by the formation of tertiary lymphoid tissue in the adventitia of atherosclerotic aortas. These results demonstrate that lymphocytes already reside within the normal/noninflamed aorta before the onset atherosclerosis as a consequence of constitutive trafficking. Atherosclerosis induces the recruitment of macrophages and dendritic cells that support antigen presentation.

Endogenous naive CD8+ T cell precursor frequency regulates primary and memory responses to infection

Through genetic recombination, the adaptive immune system generates a diverse T cell repertoire allowing recognition of a vast spectrum of foreign antigens. Any given CD8+ T cell specificity is thought to be rare, but none have been directly quantified. Here, major histocompatibility complex tetramer and magnetic-bead technology were coupled to quantitate naive antigen-specific CD8+ T cells and the early response to infection. Among six specificities measured, the number of naive antigen-specific precursors ranged from approximately 80 to 1200 cells/mouse. After vesicular stomatitis virus infection, the antigen-specific CD8+ T cell response occurred in discrete phases: prolonged activation of a subset of cells over the first 72 hr followed by a rapid proliferative burst. Naive precursor frequency altered response kinetics and regulated immunodominance, as well as the time required for the responding population to shift toward CD62L(hi) memory cells. Thus, initial endogenous precursor frequencies were surprisingly diverse and not only regulated initial immune response characteristics but also controlled memory CD8+ T cell lineage decisions.

Only the CD45RA+ subpopulation of CD4+CD25high T cells gives rise to homogeneous regulatory T-cell lines upon in vitro expansion

Thymus-derived CD4+ CD25+ regulatory T cells suppress autoreactive CD4+ and CD8+ T cells and thereby protect from autoimmunity. In animal models, adoptive transfer of CD4+ CD25+ regulatory T cells has been shown to prevent and even cure autoimmune diseases as well as pathogenic alloresponses after solid organ and stem-cell transplantations. We recently described methods for the efficient in vitro expansion of human regulatory T cells for clinical applications. We now demonstrate that only CCR7- and L-selectin (CD62L)-coexpressing cells within expanded CD4+ CD25high T cells maintain phenotypic and functional characteristics of regulatory T cells. Further analysis revealed that these cells originate from CD45RA+ naive cells within the CD4+ CD25high T-cell compartment, as only this subpopulation homogeneously expressed CD62L, CCR7, cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), and forkhead box P3 (FOXP3), produced no inflammatory cytokines and maintained robust suppressive activity after expansion. In contrast, cell lines derived from CD45RA- memory-type CD4+ CD25high T cells lost expression of lymph node homing receptors CCR7 and CD62L, contained interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) as well as IL-10-secreting cells, showed only moderate suppression and, most importantly, did not maintain FOXP3 expression. Based on these unexpected findings, we suggest that isolation and expansion of CD45RA+ naive CD4+ CD25high T cells is the best strategy for adoptive regulatory T (Treg)-cell therapies.

Trophoblast L-selectin-mediated adhesion at the maternal-fetal interface

Trophoblast adhesion to the uterine wall is the requisite first step of implantation and, subsequently, placentation. At the maternal-fetal interface, we investigated the expression of selectin adhesion systems that enable leukocyte capture from the bloodstream. On the maternal side, human uterine epithelial cells up-regulated selectin oligosaccharide-based ligands during the window of receptivity. On the fetal side, human trophoblasts expressed L-selectin. This ligand-receptor system was functional, because beads coated with the selectin ligand 6-sulfo sLe(x) bound to trophoblasts, and trophoblasts bound to ligand-expressing uterine luminal epithelium in tissue sections. These results suggest that trophoblast L-selectin mediates interactions with the uterus and that this adhesion mechanism may be critical to establishing human pregnancy.

Distinct roles of CTLA-4 and TGF-beta in CD4+CD25+ regulatory T cell function

Both CTLA-4 and TGF-beta have been implicated in suppression by CD4+CD25+ regulatory T cells (Treg). In this study, the relationship between CTLA-4 and TGF-beta in Treg function was examined. Blocking CTLA-4 on wild-type Treg abrogated their suppressive activity in vitro, whereas neutralizing TGF-beta had no effect, supporting a TGF-beta-independent role for CTLA-4 in Treg-mediated suppression in vitro. In CTLA-4-deficient mice, Treg development and homeostasis was normal. Moreover, Treg from CTLA-4-deficient mice exhibited uncompromised suppressive activity in vitro. These CTLA-4-deficient Treg expressed increased levels of the suppressive cytokines IL-10 and TGF-beta, and in vitro suppression mediated by CTLA-4(-/-) Treg was markedly reduced by neutralizing TGF-beta, suggesting that CTLA-4-deficient Treg develop a compensatory suppressive mechanism through CTLA-4-independent production of TGF-beta. Together, these data suggest that CTLA-4 regulates Treg function by two distinct mechanisms, one during functional development of Treg and the other during the effector phase, when the CTLA-4 signaling pathway is required for suppression. These results help explain contradictions in the literature and support the existence of functionally distinct Treg.

A central role for microvillous receptor presentation in leukocyte adhesion under flow

Leukocyte adhesion to endothelium requires specialized mechanisms for contact initiation under flow. L-selectin (CD62L), an efficient initiator of adhesion, is clustered on the tips of leukocyte microvilli. To test whether microvillous presentation is critical for contact formation ("tethering"), we transfected lymphoid cells with chimeras of L-selectin and CD44, an adhesion molecule that is excluded from microvilli. CD44 transmembrane and intracellular (TM-IC) domains targeted the L-selectin ectodomain to the planar body, whereas L-selectin TM-IC segments conferred CD44 ectodomain clustering on microvilli. Wild-type and chimeric transfectants bound similarly to anti-ectodomain MAbs in static assays, but MAb binding under flow was much more efficient in the context of microvillous presentation. Similarly, wild-type and chimeric L-selectin possessed equivalent lectin activity, but microvillous presentation dramatically enhanced contact initiation on a native ligand. These findings demonstrate a critical role for receptor topography in leukocyte adhesion and suggest a novel regulatory mechanism of leukocyte trafficking.

Host-reactive CD8+ memory stem cells in graft-versus-host disease

Graft-versus-host disease (GVHD) is caused by alloreactive donor T cells that trigger host tissue injury. GVHD develops over weeks or months, but how this immune response is maintained over time is unknown. In mouse models of human GVHD, we identify a new subset of postmitotic CD44(lo)CD62L(hi)CD8(+) T cells that generate and sustain all allogeneic T-cell subsets in GVHD reactions, including central memory, effector memory and effector CD8(+) T cells, while self-renewing. These cells express Sca-1, CD122 and Bcl-2, and induce GVHD upon transfer into secondary recipients. The postmitotic CD44(lo)CD62L(hi)CD8(+) T cells persist throughout the course of GVHD, are generated in the initial phase in response to alloantigens and dendritic cells and require interleukin-15. Thus, their long life, ability to self-renew and multipotentiality define these cells as candidate memory stem cells. Memory stem cells will be important targets for understanding and influencing diverse chronic immune reactions, including GVHD.

Basophils and the T helper 2 environment can promote the development of lupus nephritis

In systemic lupus erythematosus (SLE), self-reactive antibodies can target the kidney (lupus nephritis), leading to functional failure and possible mortality. We report that activation of basophils by autoreactive IgE causes their homing to lymph nodes, promoting T helper type 2 (T(H)2) cell differentiation and enhancing the production of self-reactive antibodies that cause lupus-like nephritis in mice lacking the Src family protein tyrosine kinase Lyn (Lyn(-/-) mice). Individuals with SLE also have elevated serum IgE, self-reactive IgEs and activated basophils that express CD62 ligand (CD62L) and the major histocompatibility complex (MHC) class II molecule human leukocyte antigen-DR (HLA-DR), parameters that are associated with increased disease activity and active lupus nephritis. Basophils were also present in the lymph nodes and spleen of subjects with SLE. Thus, in Lyn(-/-) mice, basophils and IgE autoantibodies amplify autoantibody production that leads to lupus nephritis, and in individuals with SLE IgE autoantibodies and activated basophils are factors associated with disease activity and nephritis.

Immunological microenvironments in the human vagina and cervix: mediators of cellular immunity are concentrated in the cervical transformation zone

Cell-mediated immunity (CMI) is key to defense against intracellular pathogens such as Chlamydia trachomatis and viruses that infect the lower female genital tract, but little is known about CMI at this site. Recent studies indicate that there are immunological microenvironments within the female genital tract, and that immune functions are affected by hormones as well as infections and inflammatory processes. To determine the distribution of mediators of CMI within the lower female genital tract, we have enumerated and characterized T-lymphocyte subsets and natural killer and antigen presenting cells (APCs; macrophages and dendritic cells) in the introitus, vagina, ectocervix, endocervix and cervical transformation zone (TZ) from healthy women, and have examined the effects of the menstrual cycle, menopause and inflammation on these parameters. In women without inflammation, T cells and APCs were most prevalent in the cervical TZ and surrounding tissue. Intraepithelial lymphocytes were predominantly CD8+ T cell+; most CD8+ cells in the TZ and endocervix, and a proportion of cells in the ectocervix, expressed T-cell internal antigen-1, a marker of cytotoxic potential. In contrast, the normal vaginal mucosa contained few T cells and APCs. Cervicitis and vaginitis cases had increased numbers of intraepithelial CD8+ and CD4+ lymphocytes and APCs. The menstrual cycle and menopause had no apparent effect on cellular localization or abundance in any of the lower genital tract tissues. These data indicate that the cervix, especially the TZ, is the major inductive and effector site for CMI in the lower female genital tract. Because CD4+ T cells and APCs are primary host cells for human immunodeficiency virus type 1 (HIV-1), these data also provide further evidence that the cervix is a primary infection site of HIV-1, and that inflammation increases the risk of HIV transmission.

CD4 effector T cell subsets in the response to influenza: heterogeneity, migration, and function

The immune response of naive CD4 T cells to influenza virus is initiated in the draining lymph nodes and spleen, and only after effectors are generated do antigen-specific cells migrate to the lung which is the site of infection. The effector cells generated in secondary organs appear as multiple subsets which are a heterogeneous continuum of cells in terms of number of cell divisions, phenotype and function. The effector cells that migrate to the lung constitute the more differentiated of the total responding population, characterized by many cell divisions, loss of CD62L, down-regulation of CCR7, stable expression of CD44 and CD49d, and transient expression of CCR5 and CD25. These cells also secrete high levels of interferon gamma and reduced levels of interleukin 2 relative to those in the secondary lymphoid organs. The response declines rapidly in parallel with viral clearance, but a spectrum of resting cell subsets reflecting the pattern at the peak of response is retained, suggesting that heterogeneous effector populations may give rise to corresponding memory populations. These results reveal a complex response, not an all-or-none one, which results in multiple effector phenotypes and implies that effector cells and the memory cells derived from them can display a broad spectrum of functional potentials.

Neutrophil-neutrophil interactions under hydrodynamic shear stress involve L-selectin and PSGL-1. A mechanism that amplifies initial leukocyte accumulation of P-selectin in vitro

Leukocytes attach to and roll on inflamed endothelium and on leukocyte monolayers that form on the endothelial cells. Leukocyte-leukocyte interactions occurring under hydrodynamic shear stress are mediated by binding of L-selectin to unknown sialomucin-like glycoproteins. We show that purified neutrophil PSGL-1, a sialomucin glycoprotein that serves as a ligand for both P- and E-selectin, can also support the attachment and rolling of free flowing neutrophils in vitro. Neutrophil rolling on PSGL-1 was abolished by the anti-L-selectin mAb DREG200 and by the anti-PSGL-1 mAb PL1, indicating that L-selectin can interact directly with PSGL-1. Neutrophil rolling on neutrophil monolayers was also blocked by PL1 (60 +/- 9% SEM inhibition); however, DREG200 blocked more efficiently (93 +/- 7% SEM inhibition), suggesting that other L-selectin ligands may exist on the neutrophil surface. These studies demonstrate that PSGL-1 on the neutrophil surface is a major functional ligand for L-selectin. The avidity of this L-selectin-dependent adhesion event was sufficient to allow individual neutrophils rolling on P-selectin to capture free flowing neutrophils, which progressed to form linear strings and discrete foci of rolling neutrophils. Neutrophil accumulation on P-selectin accelerated with time as a result of neutrophil-assisted capture of free flowing neutrophils. When neutrophil-neutrophil interactions were blocked by DREG200, neutrophils accumulated on P-selectin in a random pattern and at a uniform rate. Thus, leukocyte-assisted capture of flowing leukocytes may play an important role in amplifying the rate of initial leukocyte recruitment at sites of inflammation.

Antibodies to CD44 and integrin alpha4, but not L-selectin, prevent central nervous system inflammation and experimental encephalomyelitis by blocking secondary leukocyte recruitment

The role of various adhesion molecules in lymphocyte homing to the brain and in inflammatory autoimmune disease of the central nervous system (CNS) was examined in mice. Activated T cell lines and clones expressed CD44 and integrin alpha4, but not L-selectin, and entered the CNS independent of their antigen specificity. mAbs directed against CD44 and integrin alpha4 prevented the transfer of experimental autoimmune encephalomyelitis (EAE) by myelin basic protein-specific T cells. T cells preincubated with anti-CD44 or antiintegrin alpha4 were blocked only partially from entering the brain parenchyma. However, both antibodies efficiently prevented CNS inflammation and clinical expression of EAE when injected in vivo. This effect lasted as long as antibodies were administered. Antibodies specific for L-selectin had no effect on homing of encephalitogenic T cells to the brain or development of EAE. Antiintegrin alpha4 and anti-CD44 did not impair the activation and function of encephalitogenic T cells in vitro and did not deplete integrin alpha4- or CD44-positive cells in vivo. These data suggest that, in the absence of leukocyte recruitment, the entry of a reduced number of activated myelin basic protein-reactive T cells in the CNS is not sufficient for the development and expression of EAE. We propose that antibodies to integrin alpha4 and CD44 prevent clinical disease by partially targeting the primary influx of encephalitogenic T cells and by preventing the secondary influx of leukocytes to lesions initiated by the transferred T cells.

Compromised OX40 function in CD28-deficient mice is linked with failure to develop CXC chemokine receptor 5-positive CD4 cells and germinal centers

Mice rendered deficient in CD28 signaling by the soluble competitor, cytotoxic T lymphocyte-associated molecule 4-immunoglobulin G1 fusion protein (CTLA4-Ig), fail to upregulate OX40 expression in vivo or form germinal centers after immunization. This is associated with impaired interleukin 4 production and a lack of CXC chemokine receptor (CXCR)5 on CD4 T cells, a chemokine receptor linked with migration into B follicles. Germinal center formation is restored in CTLA4-Ig transgenic mice by coinjection of an agonistic monoclonal antibody to CD28, but this is substantially inhibited if OX40 interactions are interrupted by simultaneous injection of an OX40-Ig fusion protein. These data suggest that CD28-dependent OX40 ligation of CD4 T cells at the time of priming is linked with upregulation of CXCR5 expression, and migration of T cells into B cell areas to support germinal center formation.

Transfer of allogeneic CD62L- memory T cells without graft-versus-host disease

The major challenge in allogeneic hematopoietic cell transplantation is how to transfer allogeneic T-cell immunity without causing graft-versus-host disease (GVHD). Here we report a novel strategy to selectively prevent GVHD by depleting CD62L(+) T cells (naive and a subset of memory T cells). In unprimed mice, CD62L(-) T cells (a subset of memory T cells) failed to proliferate in response to alloantigens (which the mice have never previously encountered) and were unable to induce GVHD in allogeneic hosts. CD62L(-) T cells contributed to T-cell reconstitution by peripheral expansion as well as by promoting T-cell regeneration from bone marrow stem/progenitor cells. CD62L(-) T cells from the animals previously primed with a tumor cell line (BCL1) were able to inhibit the tumor growth in vivo but were unable to induce GVHD in the third-party recipients. This novel technology may allow transfer of allogeneic recall antitumor and antimicrobial immunity without causing GVHD.

Transforming growth factor beta induced FoxP3+ regulatory T cells suppress Th1 mediated experimental colitis

BACKGROUND AND AIMS

The imbalance between effector and regulatory T cells plays a central role in the pathogenesis of inflammatory bowel diseases. In addition to the thymus, CD4+CD25+ regulatory T cells can be induced in the periphery from a population of CD25- T cells by treatment with transforming growth factor beta (TGF-beta). Here, we analysed the in vivo function of TGF-beta induced regulatory T (Ti-Treg) cells in experimental colitis.

METHODS

Ti-Treg cells were generated in cell culture in the presence or absence of TGF-beta and tested for their regulatory potential in experimental colitis using the CD4+CD62L+ T cell transfer model.

RESULTS

Ti-Treg cells significantly suppressed Th1 mediated colitis on CD4+CD62L+ T cell transfer in vivo, as shown by high resolution endoscopy, histology, immunohistochemistry, and cytokine analysis. Further analysis of in vivo and in vitro expanded Ti-Treg cells showed that exogenous interleukin 2 (IL-2) was crucial for survival and expansion of these cells.

CONCLUSION

Our data suggest that regulatory Ti-Treg cells expand by TGF-beta and exogenous IL-2 derived from effector T cells at the site of inflammation. In addition to Tr1 and thymic CD4+CD25+ T cells, peripheral Ti-Treg cells emerge as a class of regulatory T cells with therapeutic potential in T cell mediated chronic intestinal inflammation.

Fucoidan induces apoptosis of human HS-sultan cells accompanied by activation of caspase-3 and down-regulation of ERK pathways

Fucoidan, a sulfated polysaccharide in brown seaweed, was found to inhibit proliferation and induce apoptosis in human lymphoma HS-Sultan cell lines. Fucoidan-induced apoptosis was accompanied by the activation of caspase-3 and was partially prevented by pretreatment with a pan-caspase inhibitor, z-VAD-FMK. The mitochondrial potential in HS-Sultan cells was decreased 24 hr after treatment with fucoidan, indicating that fucoidan induced apoptosis through a mitochondrial pathway. When HS-Sultan was treated with 100 microg/mL fucoidan for 24 hr, phosphorylation of ERK and GSK markedly decreased. In contrast, phosphorylation of p38 and Akt was not altered by treatment with fucoidan. L-selectin and P-selectin are known to be receptors of fucoidan; however, as HS-Sultan does not express either of these selectins, it is unlikely that fucoidan induced apoptosis through them in HS-Sultan. The neutralizing antibody, Dreg56, against human L-selectin did not prevent the inhibitory effect of fucoidan on the proliferation of IM9 and MOLT4 cells, both of which express L-selectin; thus it is possible fucoidan induced apoptosis though different receptors. These results demonstrate that fucoidan has direct anti-cancer effects on human HS-Sultan cells through caspase and ERK pathways.

Both memory and CD45RA+/CD62L+ naive CD4(+) T cells are infected in human immunodeficiency virus type 1-infected individuals

Cellular activation is critical for the propagation of human immunodeficiency virus type 1 (HIV-1) infection. It has been suggested that truly naive CD4(+) T cells are resistant to productive HIV-1 infection because of their constitutive resting state. Memory and naive CD4(+) T-cell subsets from 11 HIV-1-infected individuals were isolated ex vivo by a combination of magnetic bead depletion and fluorescence-activated cell sorting techniques with stringent criteria of combined expression of CD45RA and CD62L to identify naive CD4(+) T-cell subsets. In all patients HIV-1 provirus could be detected within naive CD45RA+/CD62L+ CD4(+) T cells; in addition, replication-competent HIV-1 was isolated from these cells upon CD4(+) T-cell stimulation in tissue cultures. Memory CD4(+) T cells had a median of fourfold more replication-competent virus and a median of sixfold more provirus than naive CD4(+) T cells. Overall, there was a median of 16-fold more integrated provirus identified in memory CD4(+) T cells than in naive CD4(+) T cells within a given patient. Interestingly, there was a trend toward equalization of viral loads in memory and naive CD4(+) T-cell subsets in those patients who harbored CXCR4-using (syncytium-inducing) viruses. Within any given patient, there was no selective usage of a particular coreceptor by virus isolated from memory versus naive CD4(+) T cells. Our findings suggest that naive CD4(+) T cells may be a significant viral reservoir for HIV, particularly in those patients harboring CXCR4-using viruses.

Enhanced responses to a DNA vaccine encoding a fusion antigen that is directed to sites of immune induction

Viral infection and vaccination with DNA both induce similar immune responses to encoded antigens that are produced by the host. The availability of antigens in lymphoid organs is important in generating an immune response to viral challenge. Antigen availability may also be important in the response to DNA vaccines, because immune responses are stronger when antigen is secreted from DNA-transfected cells. We directed antigen to lymphoid organs by vaccination with DNA encoding antigen-ligand fusion proteins. The two ligands examined bind to receptors that are present on high endothelial venule cells of lymph nodes or on antigen-presenting cells. Here we show that both the humoral and the cellular immune responses to a model DNA vaccine were enhanced using either antigen-targeting strategy. Moreover, directing antigen to antigen-presenting cells speeded up, and altered the form of, the immune response. Directing antigen to sites of immune-response induction may represent a generic means of tailoring a potent and effective immune response to a DNA vaccine.