A rapid fluorescence-based assay for classification of iNKT cell activating glycolipids

Structural variants of α-galactosylceramide (αGC) that activate invariant natural killer T cells (iNKT cells) are being developed as potential immunomodulatory agents for a variety of applications. Identification of specific forms of these glycolipids that bias responses to favor production of proinflammatory vs anti-inflammatory cytokines is central to current efforts, but this goal has been hampered by the lack of in vitro screening assays that reliably predict the in vivo biological activity of these compounds. Here we describe a fluorescence-based assay to identify functionally distinct αGC analogues. Our assay is based on recent findings showing that presentation of glycolipid antigens by CD1d molecules localized to plasma membrane detergent-resistant microdomains (lipid rafts) is correlated with induction of interferon-γ secretion and Th1-biased cytokine responses. Using an assay that measures lipid raft residency of CD1d molecules loaded with αGC, we screened a library of ～200 synthetic αGC analogues and identified 19 agonists with potential Th1-biasing activity. Analysis of a subset of these novel candidate Th1 type agonists in vivo in mice confirmed their ability to induce systemic cytokine responses consistent with a Th1 type bias. These results demonstrate the predictive value of this novel in vitro assay for assessing the in vivo functionality of glycolipid agonists and provide the basis for a relatively simple high-throughput assay for identification and functional classification of iNKT cell activating glycolipids.     

Quantitative microarray analysis of intact glycolipid-CD1d interaction and correlation with cell-based cytokine production

The protein CD1d binds self and foreign glycolipids for presentation to CD1-restricted T cells by means of TCR recognition and activates T(H)1 and T(H)2 chemokine release. In this study, a variety of glycolipid ligands were attached to a microarray surface and their binding with dimeric CD1d was investigated. An alpha-galactosyl ceramide (alpha-GalCer) bearing a carbamate group at the 6'-OH position was tethered to the surface, and the dissociation constant on surface with CD1d was determined to reflect the multivalent interaction. Competition assays were then used to determine the dissociation constants (Ki) of new and intact glycolipids in solution. The 4-fluorophenyloctanoyl-modified alpha-GalCer (18) was found to bind most strongly with CD1d (Ki 0.21 microM), 2 orders of magnitude stronger than alpha-GalCer and more than three times more selective than alpha-GalCer for IFN-gamma release from NKT cells. Various alpha-GalCer analogues were analyzed, and the results showed that the binding affinity of glycolipids to CD1d correlates well with IFN-gamma production but poorly with IL-4 secretion by NKT cells, suggesting that tighter binding ligands could bias cytokine release through the T(H)1 pathway.     

Effects of lipid chain lengths in alpha-galactosylceramides on cytokine release by natural killer T cells

Glycolipid presentation by CD1 proteins has emerged as an important aspect of antigen recognition, and presentation of alpha-glycosylceramides by CD1d to natural killer T cells has become a central focus in understanding how glycolipid presentation can influence immune responses. An alpha-galactosylceramide containing relatively long lipid chains has been the subject of intense study because, when presented by CD1d to natural killer T cells, it stimulates the release of both proinflammatory and immunomodulatory cytokines. Using an efficient synthesis of alpha-galactosylceramides, we have prepared a series of glycolipids in which the lipid chain lengths have been incrementally varied. The responses of natural killer T cells to these glycolipids have been determined, and we have found that truncation of the phytosphingosine lipid chain increases the relative amounts of immunomodulatory cytokines released. In similar fashion, the length of the acyl chain in alpha-galactosylceramides influences cytokine release profiles.     

Glycolipids for natural killer T cells

Natural killer T cells (NKT cells) play a central role in regulating immune responses influencing conditions ranging from autoimmune to infectious diseases. NKT cell responses are induced by recognition of glycolipid antigens presented by CD1d, an antigen presentation protein. In the last 10 years great strides have been made in understanding the types of glycolipids recognized by NKT cells. These advances have included determination of the lipid and carbohydrate recognition requirements for stimulation and identification of "natural" antigens for these cells.     

A human mutant CD4 molecule resistant to HIV-1 binding restores helper T-lymphocyte functions in murine CD4-deficient mice

CD4 is a cell surface glycoprotein that acts as a co-receptor for the T cell antigen receptor by binding to a non-polymorphic portion of MHC molecules. CD4 also functions as a receptor for human immunodeficiency virus type-I (HIV-1) because the viral envelope glycoprotein gp120 binds to CD4 with a high affinity. We have previously demonstrated that introduction of mutations into CD4 abolished the binding of gp120 and prevented HIV-1 from entering cells and spreading. However, whether introduction of such mutations into CD4 causes decreased binding to MHC and loss of function is yet to be determined. We generated transgenic mouse lines by injecting a mutant human CD4 (muthCD4) gene under a murine CD4 enhancer/promoter to ensure tissue and stage specific expression. To exclude the influence of endogenous murine CD4, transgenic mice were crossed with murine CD4-targeted mice to produce muthCD4 transgenic mice lacking endogenous CD4 (muthCD4TG/KO mice). In these mice, T lymphocytes expressing muthCD4 expanded and matured in the thymus and were present in the spleen and lymph nodes. They also activated B cells to mount an antibody response to a T-dependent antigen. The results from this study suggest that a human variant of CD4 modified to be resistant to HIV-1 binding can rescue the signaling for T cell development in the thymus in vivo, having helper T cell functions. Thus, further characterization of muthCD4 molecules should open the way to new HIV treatment modalities.     

Glycolipids that elicit IFN-γ-biased responses from natural killer T cells

Natural killer T (NKT) cells recognize glycolipids presented by CD1d. The first antigen described, α-galactosyl ceramide (αGalCer), is a potential anticancer agent whose activity depends upon IFN-γ secretion. We report two analogs of αGalCer based on a naturally occurring glycosphingolipid, plakoside A. These compounds induce enhanced IFN-γ that correlates with detergent-resistant binding to CD1d and an increased stability of the lipid-CD1d complexes on antigen-presenting cells. Structural analysis on one of the analogs indicates that it is more deeply bound inside the CD1d groove, suggesting tighter lipid-CD1d interactions. To our knowledge, this is the first example in which structural information provides an explanation for the increased lipid-CD1d stability, likely responsible for the Th1 bias. We provide insights into the mechanism of IFN-γ-inducing compounds, and because our compounds activate human NKT cells, they could have therapeutic utility.     

Constitutive expression of 4-1BB on T cells enhances CD4+ T cell responses

4-1BB, a transmembrane molecule, member of the tumor necrosis factor receptor superfamily, is an important costimulatory molecule in the immune response, plays a key role in the clonal expansion and survival of CD8(+) T cells. In this study, we investigated 4-1BB regulation of CD4(+) T cell responses using 4-1BB transgenic (TG) mice that constitutively expressed 4-1BB on mature T cells. We first showed that CD4(+) T cells of 4-1BB TG mice had more sustained proliferative capacity in response to TCR/4-1BB stimulation in vitro compared to WT mice. Secondly, 4-1BB TG mice exhibited a more elevated contact hypersensitivity (CHS) response mediated by CD4+ Th1 cells due to more vigorous expansion of and apoptotic inhibition of CD4(+) T cells. Finally, CD4(+) T cells of 4-1BB TG mice had a heightened capacity for T cell priming. Overall, our results demonstrate the involvement of 4-1BB in CD4(+) Th1 cell responses by regulating the clonal expansion and survival of CD4(+) T cells as seen in CD8(+) T cells.     

Combinatorial peptide library for the analysis of antigen recognition by T cells

Peptides that consist of 19 residues with random sequences (X19) were considered to deliver antigenic stimuli to CD4T cells. When IL-4, IL-7, IL-9, IL-15 and agonistic Ab to CD29 were co-cultured with single peripheral CD4T cells in the presence of X19 and feeder cells, T cells exhibited clonal expansion. These T cell clones showed heterogeneous proliferation patterns against KGXXXXXXXXXGK-based and KGXXXXXXXXXGKGKK-based combinatorial peptide libraries. Pattern-match search on one of the T cell clones resulted in peptide ligand candidates, one of which induced proliferation, as did protein molecules carrying the corresponding sequence. Combinatorial chemistry was useful in determining not only peptide ligands but also peptide superagonists. For this purpose, use of reverse-phase hydrophobic interaction chromatography and mass spectrometry analysis was efficient. Detailed methods are described in the paper.     

Activation of B cells using Schneider 2 cells expressing CD40 ligand for the enhancement of antigen presentation in vitro

CD40 ligand (CD40L) expressed by activated CD4+ T cells is a family member of membrane bound TNF family ligand and its interaction with CD40 expressed in APC has been shown to contribute in enhancing immune response. Exogenous stimulation through CD40 has been performed using soluble trimeric CD40L, anti-CD40 monoclonal antibody and cells expressing CD40L. Schneider 2 (S2) cells, a cell line derived from Drosophila melanogaster, was transfected with a plasmid vector, pAc5.1/V5-HisA, for the constitutive expression of CD40L (S2-CD40L). Upon incubation of S2-CD40L with B-lymphocytes for 6 days, activated B cells were examined by counting B cell numbers and for activation markers including CD86 and HLA Class II molecules. The activated B cells were tested for its efficient APC function by mixed lymphocyte reactions (MLR) and enzyme-linked Immunospot (ELISPOT) assay. S2-CD40L was cultured for a year and maintained CD40L expression (>90%). S2-CD40L induced B cell activation as demonstrated by increment of total B cells and up-regulation of CD86 and MHC Class II molecules. Activated B cells pulsed with peptide from human cytomegalovirus pp65 antigen efficiently induced both proliferation and IFN-gamma secretion of T cells. Our result suggests that S2-CD40L can efficiently and conveniently generate B cells as a functional APC and represents a potential role for B-cell mediated cancer immunotherapy.     

Label-free characterization of cell adhesion using reflectometric interference spectroscopy (RIfS)

Reflectometric interference spectroscopy (RIfS) is a label-free, time-resolved technique for detecting interactions of molecules immobilized on a surface with ligands in solution. Here we show that RIfS also permits the detection of the adhesion of tissue culture cells to a functionalized surface in a flow system. Interactions of T cells with other leukocytes or epithelial cells of blood vessels are crucial steps in the regulating immune response and inflammatory reactions. Jurkat T cell leukemia cells rapidly attached to a transducer functionalized with a monoclonal antibody directed against the T cell receptor (TCR)/CD3 complex, followed by activation-dependent cell spreading. RIfS curves were obtained for the Jurkat derivative JCaM 1.6 (which lacks the key signaling protein Lck), cells preincubated with cytochalasin D (an inhibitor of actin polymerization), and for surfaces functionalized with an antibody directed against the coreceptor CD28. These curves differed with respect to the maximum signal and the initial slope of the increase in optical thickness. The testing of chemical inhibitors, cell surface molecules and gene products relevant to a key event in T cell immunity illustrates the potential of label-free techniques for the analysis of activation-dependent cell-surface contacts. The first two authors contributed equally to this paper     

A comparative analysis of alterations in protein expression after activation or human immunodeficiency virus, type 1 infection of human CD4+ T cells

We have previously described an in vitro model for studying human immunodeficiency virus, type 1 (HIV-1) infection in CD4+ T cells [1]. This model employs the WE17/10 cell line, which loses expression of its T cell receptor/CD3 (TCR/CD3) after several months of productive infection. We have used this model to analyze the synthesis and posttranslational modification of viral and cellular proteins after HIV-1 infection and to determine the relationship of these changes to TCR/CD3 expression. Mainly we observe positive changes in protein expression after infection. A phosphoprotein, referred to as WH:1, appears in infected cells that still express their TCR/CD3 complex, and its persistence is linked to the presence of the complex. We examined whether loss of the TCR/CD3 complex could be associated with alterations in the T cell activation pathway as a result of infection. We used T cell activators and inhibitors to determine whether there were common elements between the two events. Quantitative enhancement in one spot, Cs:1, occurred after both Cyclosporin A treatment of uninfected cells and HIV-1 infection of untreated cells. Taken altogether, these data suggest that a correlation exists between negative regulation of late events in the T cell activation pathway and down regulation of the TCR/CD3 complex after HIV-1 infection.     

Detection of homodimer formation of CD99 through extracelluar domain using bimolecular fluorescence complementation analysis

Although various functions of CD99 have been reported, such as apoptosis and homotypic aggregation of thymocyte and transendothelial migration of immune cells, biochemical/molecular natures of CD99 are still elusive. Using mouse CD99 gene, we show that CD99 forms homodimer through its extracellular domain. Expression of mouse CD99 is up-regulated on T cells after CD3-mediated activation, like the case for human CD99. The potential of CD99 to form homodimer was tested with a recently developed bimoleular fluorescence complementation analysis (BiFC). In BiFC analysis, the dimerization-induced fluorescence was strong near the perinuclear region and was faded at the cell membrane. However, surface expression of CD99 was still detected by flow cytometry, suggesting that CD99 either in monomer form or in association with other molecules exists on the cell surface. In BiFC analysis using CD99 mutants with its extracellular, transmembrane, or cytosolic domains changed to corresponding human CD4 domains, the mutant replaced with human CD4-extracellular domain did not produce fluorescence. Purified soluble CD99-Fc fusion proteins bound to CD99-Fc immobilized onto the gold sensor chip in surface plasmon resonance analysis, confirming that the extracellular domain was responsible for dimer formation. Intracytoplasmic staining for CD99 expression in the thymocytes and mature T cells showed that most of the cells, even the cells with low surface level of CD99, contained the molecule inside the cell. Our results suggest that majority of CD99 homodimers may exit in the cell and be exported to the cell surface, dissociating from each other, after a certain regulatory signal is delivered.     

Impact of sugar stereochemistry on natural killer T cell stimulation by bacterial glycolipids

Natural killer T (NKT) cells recognize glycolipids produced by Sphingomonas bacteria, and these glycolipids contain C6-oxidized sugars, either glucuronic acid or galacturonic acid, linked to ceramides. Glycolipids with gluco stereochemistry are the most prevalent. Multiple studies have demonstrated that galactosylceramides are more potent stimulators of NKT cells than their glucose isomers. To determine if this stereoselectivity is retained in the context of the C6-oxidized sugars found in bacterial glycolipids, we prepared two sets of gluco and galacto-glycolipids oxidized at their C6 positions and compared their NKT stimulatory properties. In the context of carboxylic acid groups at C6, gluco stereochemistry gave the more potent responses. We also prepared bacterial glycolipids containing more complex ceramide groups to determine if these chains impact NKT cell responses.     

Treatment of cutaneous T cell lymphoma with extracorporeal photopheresis induces Fas-ligand expression on treated T cells,but does not suppress the expression of co-stimulatory molecules on monocytes

Following extracorporeal photopheresis (ECP), lymphocytes become apoptotic and upregulate class I MHC antigenic peptides. Conversely, ECP treated monocytes demonstrate activation markers and have an increased avidity for the phagocytosis of apoptotic T cells. Processing of apoptotic T cells by monocytes, following ECP, is thought to induce an immunomodulatory response, which targets untreated, but clonal T cells. Recently we detected apoptotic lymphocytes immediately post ECP. Although enhanced CD95 (Fas) expression has been observed 24 h post ECP, CD95 and Fas-ligand (Fas-L) expression have not been determined at this very early apoptotic stage. Exposure of monocytes to UV has previously suppressed expression of the co-stimulatory molecules required for the presentation of processed antigens to T cells. Our data demonstrate no increase in CD95 or Fas-L expression on T cells tested immediately following ECP. However, the number of T cells expressing Fas-L significantly increased 24 h post ECP (P<0.005). The expression of the co-stimulatory molecules, CD54, CD80 and CD86, remained unaltered on monocytes treated by ECP. Although the mechanism responsible for early induction of lymphocyte apoptosis remains unclear, the later apoptosis involves Fas-L expression. The maintenance of co-stimulatory molecules, on treated monocytes, indicates that they retain the ability to induce an immunomodulatory response.     

Synthesis of alpha-galactosyl ceramide,a potent immunostimulatory agent

Alpha-galactosyl ceramide has been identified to be a potent stimulatory agent for a novel immunological process, mediated by CD1 molecules. This paper describes a short and efficient synthesis of alpha-galactosyl ceramide. Starting from commercially available 2-deoxy galactose, a suitable sphingosine derivative was obtained in nine steps and 36% overall yield, which was subsequently glycosylated to give the target molecule. This flexible route will provide various glycolipids for further exploration of this interesting biological process.     

T lymphocyte migration to lymph nodes is maintained during homeostatic proliferation.

The immune system maintains appropriate cell numbers through regulation of cell proliferation and death. Normal tissue distribution of lymphocytes is maintained through expression of specific adhesion molecules and chemokine receptors such as L-selectin and CCR7, respectively. Lymphocyte insufficiency or lymphopenia induces homeostatic proliferation of existing lymphocytes to increase cell numbers. Interestingly, homeostatic proliferation of T lymphocytes induces a phenotypic change from na?ve- to memory-type cell. Na?ve T cells recirculate between blood and lymphoid tissues whereas memory T cells migrate to nonlymphoid sites such as skin and gut. To assess effects of homeostatic proliferation on migratory ability of T cells, a murine model of lymphopenia-induced homeostatic proliferation was used. Carboxyfluorescein diacetate, succinimidyl ester-labeled wild-type splenocytes were adoptively transferred into recombination activation gene-1-deficient mice and analyzed by flow cytometry, in vitro chemotactic and in vivo migration assays, and immunofluorescence microscopy. Homeostatically proliferated T cells acquired a mixed memory-type CD44high L-selectinhigh CCR7low phenotype. Consistent with this, chemotaxis to secondary lymphoid tissue chemokine in vitro was reduced by 22%-34%. By contrast, no differences were found for migration or entry into lymph nodes during in vivo migration assays. Therefore, T lymphocytes that have undergone homeostatic proliferation recirculate using mechanisms similar to na?ve T cells.     

Rapid analysis of long‐chain glycolipids in heterocystous cyanobacteria using high‐performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry

Under nitrogen‐depleted conditions, N₂‐fixing cyanobacteria of the order Nostocales and Stigonematales differentiate vegetative cells into heterocysts. The cell envelope of these specialized cells contains unique glycolipids, consisting of a sugar moiety glycosidically bound to long‐chain diols, triols and hydroxyketones. Only few reports have been published on these glycolipids in cultured cyanobacteria and none has reported them in natural environments. Here we show that heterocyst glycolipids can be rapidly and sensitively analyzed using high‐performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC/ESI‐MS²). Positive ion mass spectra of the glycolipids consisted of protonated molecules and diagnostic product ions, indicating losses of sugar groups as well as hydroxyl and carbonyl functionalities from an alkyl chain. Using this method, heterocyst glycolipids were for the first time identified in a natural ecosystem, i.e., a microbial mat from the North Sea barrier island Schiermonnikoog, The Netherlands. This technique will facilitate the quick screening of cyanobacterial cultures and natural environments for the presence of heterocyst glycolipids, which may aid in assessing the role of heterocystous cyanobacteria in the global nitrogen cycle. Copyright © 2009 John Wiley & Sons, Ltd.     

Inflammatory mimetic microfluidic chip by immobilization of cell adhesion molecules for T cell adhesion

Leukocyte adhesion to adhesion molecules on endothelial cells is important in immune function, cancer metastasis and inflammation. This cell-cell binding is mediated via cell adhesion molecules such as E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) found on endothelial cells. Because these adhesion molecules on endothelial cells vary significantly across several disease conditions such as autoimmune diseases, inflammation or cancer metastasis, investigations of therapeutic agents that down-regulate leukocyte-endothelial interactions have been based on in vitro models using endothelial cell lines. Here we report a new model, an inflammatory mimetic microfluidic chip, which emulates leukocyte binding to cell adhesion molecules (CAM) by controlling the types and ratio of adhesion molecules. In our model, E-selectin was essential for the synergic binding of Jurkat T cells. Immunosuppressive drugs, such as tacrolimus (FK506) and cyclosporine A (CsA), were used to inhibit T cell interactions under the physiologic model of T cell migration at a ratio of 5?:?4.3?:?3.9 (E-selectin?:?ICAM-1?:?VCAM-1). Our results support the potential usefulness of the inflammatory mimetic microfluidic chip as a T cell adhesion assay tool with modified adhesion molecules for applications such as immunosuppressive drug screening. The inflammatory mimetic microfluidic chip can also be used as a biosensor in clinical diagnostics, drug efficacy tests and high throughput drug screening due to the dynamic monitoring capability of the microfluidic chip.     

Oclacitinib,a Janus Kinase Inhibitor,Reduces the Frequency of IL-4- and IL-10-, but Not IFN-γ-, Producing Murine CD4+ and CD8+ T Cells and Counteracts the Induction of Type 1 Regulatory T Cells

The purpose of the present study was to broaden the knowledge and understanding of the effects of oclacitinib (OCL), a Janus kinase inhibitor, on T cells in the context of both the immune mechanisms underlying anti-inflammatory and anti-allergic properties of the drug and its safety. The results indicate that beneficial effects of OCL in the treatment of skin allergic diseases may be partially mediated by the inhibition of IL-4 production in CD4⁺ and CD8⁺ T cells. To a certain extent, the antiproliferative effect of OCL on CD8⁺ T cells may also contribute to its therapeutic effect. The study found that OCL does not affect the proliferation of CD4⁺ T cells or the number of IFN-γ- and IL-17-producing CD4⁺ and CD8⁺ T cells. Moreover, OCL was found to counteract the induction of type 1 regulatory T (Tr1) cells and to act as a strong inhibitor of IL-10 production in both CD4⁺ and CD8⁺ T cells. Thus, these results indicate that beneficial effects of OCL in the treatment of skin allergic diseases are not mediated through: (a) the abolishment of IFN-γ and IL-17-production in CD4⁺ and CD8⁺ T cells; (b) generation of Tr1 cells; (c) inhibition of CD4⁺ T cell proliferation; (d) induction of IL-10 production in CD4⁺ T cells. The results of this study strongly suggest that, with respect to the evaluated parameters, OCL exerts a suppressive effect on Th2- but not Th1-mediated immunity.