Glycolipid targets of CD1-mediated T-cell responses

Chimeric Antigen Receptors Expand the Repertoire of Antigenic Macromolecules for Cellular Immunity

T-cell therapies have made significant improvements in cancer treatment over the last decade. One cellular therapy utilizing T-cells involves the use of a chimeric MHC-independent antigen-recognition receptor, typically referred to as a chimeric antigen receptor (CAR). CAR molecules, while mostly limited to the recognition of antigens on the surface of tumor cells, can also be utilized to exploit the diverse repertoire of macromolecules targetable by antibodies, which are incorporated into the CAR design. Leaning into this expansion of target macromolecules will enhance the diversity of antigens T-cells can target and may improve the tumor-specificity of CAR T-cell therapy. This review explores the types of macromolecules targetable by T-cells through endogenous and synthetic antigen-specific receptors.

Adjuvant effect in aquaculture fish of cell-wall glycolipids isolated from acid-fast bacteria

Mycobacteriosis and nocardiosis in cultured fish caused by infections with acid-fast bacteria, are responsible for large economic losses globally. In this study, we suggest a novel adjuvant using glycolipids that activates host immune systems. The immune response to glycolipids stimulation was investigated using ginbuna crucian carp. Ginbuna vaccinated with FKC (formalin-killed cells) + glycolipids isolated from Mycobacterium sp., upregulated inflammatory- and Th1-related cytokines, and a DTH (delayed-type hypersensitivity) response was confirmed only in ginbuna vaccinated with FKC + glycolipids. These observations suggest that glycolipids activated host innate and cell-mediated immunity. Subsequently, we evaluated the adjuvant effect of glycolipids against amberjack nocardiosis. In a challenge test, a higher survival rate was observed in amberjack vaccinated with FKC + glycolipids emulsified with conventional oil adjuvant than in fish vaccinated with FKC + oil adjuvant without glycolipids. Therefore, glycolipids potentially could be used as a practical, economical and safe adjuvant for aquaculture fish.

Characterization of the receptors for mycobacterial cord factor in Guinea pig

Guinea pig is a widely used animal for research and development of tuberculosis vaccines, since its pathological disease process is similar to that present in humans. We have previously reported that two C-type lectin receptors, Mincle (macrophage inducible C-type lectin, also called Clec4e) and MCL (macrophage C-type lectin, also called Clec4d), recognize the mycobacterial cord factor, trehalose-6,6′-dimycolate (TDM). Here, we characterized the function of the guinea pig homologue of Mincle (gpMincle) and MCL (gpMCL). gpMincle directly bound to TDM and transduced an activating signal through ITAM-bearing adaptor molecule, FcRγ. Whereas, gpMCL lacked C-terminus and failed to bind to TDM. mRNA expression of gpMincle was detected in the spleen, lymph nodes and peritoneal macrophages and it was strongly up-regulated upon stimulation of zymosan and TDM. The surface expression of gpMincle was detected on activated macrophages by a newly established monoclonal antibody that also possesses a blocking activity. This antibody potently suppressed TNF production in BCG-infected macrophages. Collectively, gpMincle is the TDM receptor in the guinea pig and TDM-Mincle axis is involved in host immune responses against mycobacteria.

Structural analysis for glycolipid recognition by the C-type lectins Mincle and MCL

Mincle [macrophage inducible Ca(2+)-dependent (C-type) lectin; CLEC4E] and MCL (macrophage C-type lectin; CLEC4D) are receptors for the cord factor TDM (trehalose-6,6'-dimycolate), a unique glycolipid of mycobacterial cell-surface components, and activate immune cells to confer adjuvant activity. Although it is known that receptor-TDM interactions require both sugar and lipid moieties of TDM, the mechanisms of glycolipid recognition by Mincle and MCL remain unclear. We here report the crystal structures of Mincle, MCL, and the Mincle-citric acid complex. The structures revealed that these receptors are capable of interacting with sugar in a Ca(2+)-dependent manner, as observed in other C-type lectins. However, Mincle and MCL uniquely possess shallow hydrophobic regions found adjacent to their putative sugar binding sites, which reasonably locate for recognition of fatty acid moieties of glycolipids. Functional studies using mutant receptors as well as glycolipid ligands support this deduced binding mode. These results give insight into the molecular mechanism of glycolipid recognition through C-type lectin receptors, which may provide clues to rational design for effective adjuvants.

Synthetic arabinomannan glycolipids and their effects on growth and motility of the Mycobacterium smegmatis

Arabinomannan-containing glycolipids, relevant to the mycobacterial cell-wall component lipoarabinomannan, were synthesized by chemical methods. The glycolipids were presented with tri- and tetrasaccharide arabinomannans as the sugar portion and a double alkyl chain as the lyophilic portion. Following synthesis, systematic biological and biophysical studies were undertaken in order to identify the effects of the glycolipids during mycobacterium growth. The studies included mycobacterial growth, biofilm formation and motility assays. From the studies, it was observed that the synthetic glycolipid with higher arabinan residues inhibited the mycobacterial growth, lessened the biofilm formation and impaired the motility of mycobacteria. A surface plasmon resonance study involving the immobilized glycan surface and the mycobacterial crude lysates as analytes showed specificities of the interactions. Further, it was found that cell lysates from motile bacteria bound oligosaccharide with higher affinity than non-motile bacteria.

V alpha14 i NKT cells are innate lymphocytes that participate in the immune response to diverse microbes

Natural Killer T (NKT) cells constitute a conserved T lymphocyte sublineage that has been implicated in the regulation of various immune responses, including the responses to viruses, bacteria, and parasites. NKT cells recognize self and foreign glycolipids presented by CD1d, a non-classical antigen-presenting molecule, and they rapidly produce various cytokines. Many studies have shown that NKT cells have protective roles following microbial infection through the amplification of innate and adaptive immunity, although NKT cells have detrimental roles in some cases. Recent studies have shed light on the natural antigens recognized by NKT cells and the mechanisms whereby they contribute to host defense, and they suggest that these unique T cells have evolved to jump start the immune response to microbes.

Synthesis and mycobacterial growth inhibition activities of bivalent and monovalent arabinofuranoside containing alkyl glycosides

Arabinofuranosides constitute one of the important components of cell wall structures of mycobacteria. With this importance of arabinofuranosides in mind, alkyl glycosides bearing arabinofuranoside trisaccharides were prepared, wherein the sugars were presented either in the monovalent or bivalent forms. Following the synthesis, the monovalent and bivalent alkyl glycosides were tested for their activities in a mycobacterial growth assay. The growth of the mycobacterial strain M. smegmatis was assessed in the presence of the alkyl glycosides and it was realized that the alkyl glycosides acted as inhibitors of the mycobacterial growth. The inhibition of the growth, caused by the above alkyl glycosides, was not observed for the arabinofuranose trisaccharide alone, without the alkyl groups, and for an alkyl glycoside bearing maltose as the sugar component.

CD1-restricted T cells in host defense to infectious diseases

CD1 has been clearly shown to function as a microbial recognition system for activation of T cell responses, but its importance for mammalian protective responses against infections is still uncertain. The function of the group 1 CD1 isoforms, including human CD1a, CDlb, and CDLc, seems closely linked to adaptive immunity. These CD1 molecules control the responses of T cells that are highly specific for particular lipid antigens, the best known of which are abundantly expressed by pathogenic mycobacteria such as Mycobacterium tuberculosis and Mycobacterium leprae. Studies done mainly on human circulating T cells ex vivo support a significant role for group I CD1-restricted T cells in protective immunity to mycobacteria and potentially other pathogens, although supportive data from animal models is currently limited. In contrast, group 2 CD1 molecules, which include human CD1d and its orthologs, have been predominantly associated with the activation of CD1d-restricted NKT cells, which appear to be more appropriately viewed as a facet of the innate immune system. Whereas the recognition of certain self-lipid ligands by CD d-restricted NKT cells is well accepted, the importance of these T cells in mediating adaptive immune recognition of specific microbial lipid antigens remains controversial. Despite continuing uncertainty about the role of CD 1d-restricted NKT cells in natural infections, studies in mouse models demonstrate the potential of these T cells to exert various effects on a wide spectrum of infectious diseases, most likely by serving as a bridge between innate and adaptive immune responses.

Putting the pieces of the puzzle together - a series of hypotheses on the etiology and pathogenesis of type 1 diabetes

This paper presents a series of 10 hypotheses on the etiology of type 1 diabetes. We begin with the hypothesis that wheat gluten is one of the elusive environmental triggers in type 1 diabetes. Habitual consumption of wheat gluten increases the intestinal synthesis of dipeptidyl peptidase IV. This enzyme helps to shape the repertoire of peptides released into the small intestine following the ingestion of wheat gluten by catalyzing the release of X-Pro dipeptides from the N-terminus of the proline-rich glutenins and gliadins in wheat gluten. The release of gluten-derived peptides causes the tight junctions of the small intestine to open through a zonulin-dependent mechanism, which allows these peptides to enter the lamina propria where they get presented as antigens by HLA-DQ, -DR and CD1d molecules. Binding of one or more gluten peptides by CD1d leads to abrogation of oral tolerance, and a marked increase in peripheral immune responses to wheat proteins. Furthermore, it is our contention, that in response to beta cell apoptosis during normal remodeling of the pancreas and CCL19/CCL21 expression within the pancreatic lymph nodes (PLNs), gluten-loaded dendritic cells migrate from the small intestine to the PLNs. These dendritic cells present gluten-derived antigens on the surface of the PLNs, which leads to migration of CD4(-)CD8(-) gammadelta and CD4(-)CD8(+) alphabeta T cells to the pancreas where they mediate Fas and perforin dependent cytotoxicity. We also hypothesize that at least one of the type 1 diabetes associated HLA-DR molecules that bind and present wheat-derived peptide(s) also bind and present an islet cell antigen(s), activating plasma cell synthesis of islet cell autoantibodies and irrevocable, complement-dependent destruction of islet cells. Our final two hypotheses state that type 1 diabetes morbidity is reduced in those areas of globe where genetically susceptible individuals get adequate amounts of vitamin D, in the diet and/or through exposure to sunlight, and in areas where people are exposed to bacterial, viral, or parasitic infections in early childhood.

The immunoregulatory effects of gangliosides involve immune deviation favoring type-2 T cell responses

Gangliosides, sialic acid-containing glycosphingolipids present in most cell membranes, are thought to participate in the maintenance of immune privilege and tumor-induced immunosuppression. However, the mechanisms responsible for their immunomodulatory activity remain poorly understood. The purpose of this study was to investigate whether gangliosides are able to modulate the balance of type-1/type-2 T cell responses and to characterize the cellular mechanisms involved. The effects of different gangliosides on anti-CD3-stimulated murine splenocytes and purified T cells were studied. The presence of gangliosides during T cell activation reduced the expression of interferon-gamma (IFN-gamma) and enhanced that of interleukin (IL)-4, suggesting a shift toward a type-2 response. Intracellular cytokine staining demonstrated that gangliosides inhibited IFN-gamma production in CD4+, CD8+, and natural killer (NK)1.1+ cell populations and enhanced IL-4 in CD4+ T cells. The ganglioside-mediated enhancement in IL-4 production was independent of changes in endogenous IFN-gamma, did not occur with cells from CD1d-deficient mice, and was partially inhibited by anti-CD1d antibodies. The inhibitory effects on IFN-gamma were independent of endogenous IL-4 or the presence of NKT cells and were unaffected by anti-CD1d antibodies. These results suggest that gangliosides may modify the immunological environment by promoting immune deviation in favor of type-2 T cell responses.

NK T Cell Activation PromotesChlamydia trachomatisInfection In Vivo

We used two approaches to examine the role of NK T cells (NKT) in an intracellular bacterial (Chlamydia trachomatis mouse pneumonitis (C. muridarum)) infection. One is to use CD1 gene knockout (KO) mice, which lack NKT, and the other is to activate NKT using alpha-galactosylceramide (alpha-GalCer), a natural ligand of these cells. The data showed a promoting effect of NKT activation on Chlamydia lung infection. Specifically, CD1 KO mice exhibited significantly lower levels of body weight loss, less severe pathological change and lower chlamydial in vivo growth than wild-type mice. Immunological analysis showed that CD1 KO mice exhibited significantly lower C. muridarum-specific IL-4 and serum IgE Ab responses as well as more pronounced delayed-type hypersensitivity response compared with wild-type controls. In line with the finding in KO mice, the in vivo stimulation of NKT using alpha-GalCer enhanced chlamydial growth in vivo, which were correlated with reduced delayed-type hypersensitivity response and increased C. muridarum-driven IL-4/IgE production. Moreover, neutralization of IL-4 activity in the alpha-GalCer-treated BALB/c mice significantly reduced the promoting effect of alpha-GalCer treatment on chlamydial growth in vivo. These data provide in vivo evidence for the involvement of NKT in a bacterial pathogenesis and its role in promoting Th2 responses during infection.

BCR targeting of biotin-α-galactosylceramide leads to enhanced presentation on CD1d and requires transport of BCR to CD1d-containing endocytic compartments

CD1d is a non-polymorphic MHC class I-related protein that binds and presents glycolipid antigens to T cell antigen receptors expressed by NK-like T (NKT) cells. CD1d-dependent immune responses play critical roles in infectious disease, autoimmunity, allergy and cancer. We tested the hypothesis that B cell antigen receptor (BCR) targeting of a biotin-modified version of the CD1d-binding antigen alpha-galactosylceramide (biotin-alpha-GalCer) results in enhanced murine CD1d-mediated presentation as compared with presentation of non-targeted biotin-alpha-GalCer. Presentation of BCR-targeted antigen to NKT cells was enhanced 100- to 1000-fold compared with non-targeted antigen. CD1d presentation of BCR-targeted antigen was observed after 4 h treatment, consistent with a requirement for endosomal trafficking. Furthermore, unlike non-targeted antigen, BCR-targeted antigen was not loaded directly onto cell-surface CD1d. Blocking BCR signaling with the Syk tyrosine kinase inhibitor piceatannol inhibited presentation of BCR-targeted antigen but not non-targeted antigen. Piceatannol blocked transport of the BCR to CD1d-containing endosomes, showing that intersection of BCR-targeted antigen with endosomes is required for enhanced mCD1d antigen presentation. Our data suggest that the BCR facilitates capture of low quantities of mCD1d antigens to enhance CD1d-dependent immune responses.

Up-regulation of CD1d expression restores the immunoregulatory function of NKT cells and prevents autoimmune diabetes in nonobese diabetic mice

The immunoregulatory function of NKT cells is crucial for prevention of autoimmunity. The prototypical NKT cell Ag alpha-galactosylceramide is not present in mammalian cells, and little is known about the mechanism responsible for NKT cell recruitment and activation. Up-regulation of CD1d, the NKT cell restriction molecule, expressed on mononuclear cells infiltrating the target organ, could represent the physiological trigger for NKT cells to self-contain T cell immunity and to prevent autoimmune disease. Recognition of CD1d, either by itself or bound to self-ligands (selfCD1d), could drive NKT cells toward an immunoregulatory phenotype. Hence, ineffective NKT cell-mediated immunoregulation in autoimmune-prone individuals including nonobese diabetic (NOD) mice could be related to defective signals that regulate CD1d expression at time and site of autoimmunity. To test this hypothesis, we transgenically overexpressed CD1d molecules under the control of the insulin promoter within the pancreatic islets of NOD mice (insCD1d). Recognition of overexpressed CD1d molecules rescued NKT cell immunoregulatory function and prevented autoimmune diabetes in insCD1d transgenic NOD mice. Protection from diabetes was associated with a biased IL-4-secreting cytokine phenotype of NKT cells and alteration of the cytokine microenvironment in the pancreatic lymph nodes of transgenic mice. The net effect was a reduced development of the autoimmune T cell repertoire. Our findings suggest that up-regulation of CD1d expression during inflammation is critical to maintain T cell homeostasis and to prevent autoimmunity.

Presentation of alpha-galactosylceramide by murine CD1d to natural killer T cells is facilitated by plasma membrane glycolipid rafts

CD1 molecules are non-polymorphic major histocompatibility complex class I-related proteins that bind and present glycolipid antigens to T-cell antigen receptors (TCR) expressed by alphabeta T cells or natural killer-like T cells (NKT). Anti-metastatic properties of NKT cells reactive to the CD1d-binding antigen alpha-galactosylceramide (alpha-GalCer) are now being explored as a contributor to tumour cell killing. In this study, we tested the hypothesis that presentation of alpha-GalCer by murine CD1d (mCD1d) to mCD1d-restricted NKT cells was facilitated by plasma membrane glycolipid rafts. Confocal microscopy of mCD1d-transfected A20 B cells (A20mCD1d) demonstrated that mCD1d was raft-localized. This observation was confirmed by immunoblotting of raft fractions isolated on sucrose density gradients. Raft disruption by the cholesterol-binding agent nystatin, or short-chain ceramides, inhibited presentation of low concentrations of alpha-GalCer to NKT cells. Inhibition of antigen presentation was reversed by treatment of A20mCD1d cells with higher alpha-GalCer concentrations, or removal of raft-disrupting agents. These data indicate that partitioning of mCD1d into membrane rafts increases the capacity of antigen-presenting cells to present limiting quantities of glycolipid antigens, perhaps by stabilizing mCD1d/antigen structures on the plasma membrane and optimizing TCR engagement on NKT cells.

Effect of Mycobacterium bovis BCG vaccination on Mycobacterium-specific cellular proliferation and tumor necrosis factor alpha production from distinct guinea pig leukocyte populations

In this study, we focused on three leukocyte-rich guinea pig cell populations, bronchoalveolar lavage (BAL) cells, resident peritoneal cells (PC), and splenocytes (SPC). BAL cells, SPC, and PC were stimulated either with live attenuated Mycobacterium tuberculosis H37Ra or with live or heat-killed virulent M. tuberculosis H37Rv (multiplicity of infection of 1:100). Each cell population was determined to proliferate in response to heat-killed virulent H37Rv, whereas no measurable proliferative response could be detected upon stimulation with live mycobacteria. Additionally, this proliferative capacity (in SPC and PC populations) was significantly enhanced upon prior vaccination with Mycobacterium bovis BCG. Accordingly, in a parallel set of experiments we found a strong positive correlation between production of antigen-specific bioactive tumor necrosis factor alpha (TNF-alpha) and prior vaccination with BCG. A nonspecific stimulus, lipopolysaccharide, failed to induce this effect on BAL cells, SPC, and PC. These results showed that production of bioactive TNF-alpha from mycobacterium-stimulated guinea pig cell cultures positively correlates with the vaccination status of the host and with the virulence of the mycobacterial strain.

Sorting out self and microbial lipid antigens for CD1

CD1 proteins mediate T cell activation in response to self and foreign lipids, including lipid antigens from the intracellular pathogen Mycobacterium tuberculosis. During natural infections, myeloid cells migrate to sites of infection and use microbial pattern recognition receptors to internalize live bacteria and lipid antigens into the endosomal network. New studies show that certain CD1 proteins are particularly receptive to binding lipid antigens in the low pH environment of endosomes. Therefore, the endosomal network may represent a depot for concentrating and then selectively presenting exogenous foreign lipid antigens to T cells.

Regulation of human beta 2-microglobulin transactivation in hematopoietic cells

beta(2)-Microglobulin (beta(2)m) is a chaperone of major histocompatibility complex (MHC) class I (-like) molecules that play a central role in antigen presentation, immunoglobulin transport, and iron metabolism. It is therefore of importance that beta(2)m is adequately expressed in cells that perform these functions, such as hematopoietic cells. In this study, we investigated the transcriptional regulation of beta(2)m in lymphoid and myeloid cell lines through a promoter containing a putative E box, Ets/interferon-stimulated response element (ISRE), and kappa B site. Here we show that upstream stimulatory factor 1 (USF1) and USF2 bind to the E box and regulate beta(2)m transactivation. The nuclear factor kappa B (NF-kappa B) subunits p50 and p65 bind to the kappa B box and p65 transactivates beta(2)m. Interferon regulatory factor 1 (IRF1), IRF2, IRF4, and IRF8, but not PU.1, bind to the Ets/ISRE, and IRF1 and IRF3 are strong transactivators of beta(2)m. Together, all 3 boxes are important for the constitutive and cytokine-induced levels of beta(2)m expression in lymphoid and myeloid cell types. As such, beta(2)m transactivation is under the control of important transcriptional pathways, which are activated during injury, infection, and inflammation.

Self glycosphingolipids: new antigens recognized by autoreactive T lymphocytes

T cells may recognize glycolipids and lipids of bacterial and self origin associated with the CD1 antigen-presenting molecules. Understanding the mechanisms governing CD1-self glycolipid interaction will provide information on the molecular rules of glycolipid presentation and suggest new approaches to immunotherapy.

DNA repair enzymes and cytotoxic effects of temozolomide: comparative studies between tumor cells and normal cells of the immune system

O6-alkylguanine-DNA alkyltransferase (OGAT) and the mismatch repair system (MRS) play a crucial role in the susceptibility of tumor cells to the cytotoxic effects of agents that generate O6-methylguanine in DNA, including the triazene compound temozolomide (TMZ). Studies performed with peripheral blood mononuclear cells (MNC) showed that TMZ was scarcely active on lymphocyte functions not dependent on cell proliferation (e.g. NK activity and cytokine-mediated induction of CD1b molecule in adherent MNC). In contrast, TMZ depressed proliferation and lymphokine activated killer (LAK) cell generation in response to IL-2. In this case, a reasonably good inverse relationship was found between OGAT levels of MNC and their susceptibility to TMZ. This study also analyzed the ratio of the toxic effect of TMZ on MNC and on tumor cells (i.e. "Tumor-Immune Function Toxicity Index", TIFTI). A particularly favorable TIFTI can be obtained when OGAT levels are extremely high in MNC and markedly low in tumor cells. This holds true for MRS-proficient neoplastic cells, but not for MRS-deficient tumors. In conclusion, strategies aimed at modulating OGAT and MRS may improve the clinical response to TMZ. However, the use of OGAT inhibitors to potentiate the antitumor activity of TMZ might result in a concomitant increase of the immunosuppressive effects of the drug, thus reducing the relative TIFTI.

Synthesis and characterization of a dianionic carbohydrate-based phospholipid

A novel carbohydrate-based phospholipid containing a phosphatidic acid head group, bis-(2,3-lauroyl)-1-methoxy-5-ribo-phosphatidic acid (DLRPA), was synthesized and characterized by 1H NMR, 13C NMR, and 31P NMR. This molecule is an analog of dilauroyl phosphatidic acid (DLPA). The T(m) of DLRPA decreases with increasing pH in a similar pattern to DLPA, as determined by MDSC. From this thermotropic behavior, the apparent pK(a)s of DLRPA are estimated to be 4 and 8.

The CD1 family and T cell recognition of lipid antigens

For many years it was thought that T lymphocytes recognized only peptide antigens presented by MHC class I or class II molecules. Recently, it has become clear that a wide variety of lipids and glycolipids are also targets of the T cell response. This novel form of cell-mediated immune recognition is mediated by a family of lipid binding and presenting molecules known as CD1. The CD1 proteins represent a small to moderate sized family of beta2-microglobulin-associated transmembrane proteins that are distantly related to MHC class I and class II molecules. They are conserved in most or all mammals, and control the development and function of T cell populations that participate in innate and adaptive immune responses through the recognition of self and foreign lipid antigens. Here we review the current state of our understanding of the structure and function of CD1 proteins, and the role of CD1-restricted T cell responses in the immune system.