The Pol II preinitiation complex (PIC) influences Mediator binding but not promoter-enhancer looping

Knowledge of how Mediator and TFIID cross-talk contributes to promoter-enhancer (P-E) communication is important for elucidating the mechanism of enhancer function. We conducted an shRNA knockdown screen in murine embryonic stem cells to identify the functional overlap between Mediator and TFIID subunits on gene expression. Auxin-inducible degrons were constructed for TAF12 and MED4, the subunits eliciting the greatest overlap. Degradation of TAF12 led to a dramatic genome-wide decrease in gene expression accompanied by destruction of TFIID, loss of Pol II preinitiation complex (PIC) at promoters, and significantly decreased Mediator binding to promoters and enhancers. Interestingly, loss of the PIC elicited only a mild effect on P-E looping by promoter capture Hi-C (PCHi-C). Degradation of MED4 had a minor effect on Mediator integrity but led to a consistent twofold loss in gene expression, decreased binding of Pol II to Mediator, and decreased recruitment of Pol II to the promoters, but had no effect on the other PIC components. PCHi-C revealed no consistent effect of MED4 degradation on P-E looping. Collectively, our data show that TAF12 and MED4 contribute mechanistically in different ways to P-E communication but neither factor appears to directly control P-E looping, thereby dissociating P-E communication from physical looping.

Promoter-Enhancer Communication Occurs Primarily within Insulated Neighborhoods

Metazoan chromosomes are sequentially partitioned into topologically associating domains (TADs) and then into smaller sub-domains. One class of sub-domains, insulated neighborhoods, are proposed to spatially sequester and insulate the enclosed genes through self-association and chromatin looping. However, it has not been determined functionally whether promoter-enhancer interactions and gene regulation are broadly restricted to within these loops. Here, we employed published datasets from murine embryonic stem cells (mESCs) to identify insulated neighborhoods that confine promoter-enhancer interactions and demarcate gene regulatory regions. To directly address the functionality of these regions, we depleted estrogen-related receptor β (Esrrb), which binds the Mediator co-activator complex, to impair enhancers of genes within 222 insulated neighborhoods without causing mESC differentiation. Esrrb depletion reduces Mediator binding, promoter-enhancer looping, and expression of both nascent RNA and mRNA within the insulated neighborhoods without significantly affecting the flanking genes. Our data indicate that insulated neighborhoods represent functional regulons in mammalian genomes.

Escherichia coli infection induces autoimmune cholangitis and anti-mitochondrial antibodies in non-obese diabetic (NOD).B6 (Idd10/Idd18) mice

Several epidemiological studies have demonstrated that patients with primary biliary cirrhosis (PBC) have a higher incidence of urinary tract infections (UTI) and there is significant homology of the immunodominant mitochondrial autoantigen, the E2 component of the pyruvate dehydrogenase complex (PDC-E2), between mammals and bacteria. Previous work has demonstrated that non-obese diabetic (NOD).B6 Idd10/Idd18 infected with Novosphingobium aromaticivorans developed liver lesions similar to human PBC. It was postulated that the biliary disease was dependent upon the presence of the unique N. aro glycosphingolipids in activating natural killer T (NK T) cells. To address this issue, we infected NOD.B6 Idd10/Idd18 mice with either Escherichia coli, N. aro or use of a phosphate-buffered saline (PBS) vehicle control and serially followed animals for the appearance of liver pathology and anti-mitochondrial autoantibodies (AMA). Of striking importance, the biliary disease of E. coli-infected mice was more severe than N. Aro-infected mice and the titre of AMA was higher in E. coli-infected mice. Furthermore, the immunopathology did not correlate with the ability of bacterial extracts to produce antigen-dependent activation of NK T cells. Our data suggest that the unique glycosphingolipids of N. aro are not required for the development of autoimmune cholangitis. Importantly, the data highlight the clinical significance of E. coli infection in a genetically susceptible host, and we suggest that the appearance of autoimmune cholangitis is dependent upon molecular mimicry. These data highlight that breach of tolerance to PDC-E2 is probably the first event in the natural history of PBC in genetically susceptible hosts.

Regulatory T-cell stability and plasticity in mucosal and systemic immune systems

Regulatory T cells (Treg) express the forkhead box p3 (Foxp3) transcription factor and suppress pathological immune responses against self and foreign antigens, including commensal microorganisms. Foxp3 has been proposed as a master key regulator for Treg, required for their differentiation, maintenance, and suppressive functions. Two types of Treg have been defined. Natural Treg (nTreg) are usually considered to be a separate sublineage arising during thymus differentiation. Induced Treg (iTreg) originate upon T cell receptor (TCR) stimulation in the presence of tumor growth factor beta. Although under homeostatic conditions most Treg in the periphery are nTreg, special immune challenges in the intestine promote more frequently the generation of iTreg. Furthermore, recent observations have challenged the notion that Treg are a stable sublineage, and they suggest that, particularly under lymphopenic and/or inflammatory conditions, Treg may lose Foxp3 and/or acquire diverse effector functions, especially in the intestine, which may contribute to uncontrolled inflammation.

Carbohydrate Moieties as Vaccine Candidates: meeting summary

In September 2007, a meeting entitled 'Carbohydrate Moieties as Vaccine Candidates' was held at the National Institutes of Health (Bethesda, MD). This meeting brought together scientists from a number of disciplines to address issues concerning carbohydrate moieties as targets for vaccines for a variety of pathogens and tumors. In addition, the meeting participants addressed fundamental topics of glycoimmunology including the recognition of glycotopes by B and T lymphocytes, the ontogeny of anti-carbohydrate immune responses, peptide mimicry, carbohydrate antigen processing pathways and adjuvants. One session reported progress in the development of new tools such as computational algorithms, glycan arrays and oligosaccharide synthesis and their application to carbohydrate vaccine research. The session titles were: (1) immune response to bacterial carbohydrate antigens; (2) immune response to glycolipids; (3) immune response to carbohydrate antigens on other microbes and on tumors; (4) novel vaccine approaches; (5) novel tools in carbohydrate vaccine research; (6) bench to bedside: carbohydrate moieties as vaccine immunopotentiators.

TCR-mediated recognition of glycolipid CD1 complexes

Populations of unconventional T lymphocytes that express alpha beta T cell antigen receptors (TCRs) have been characterized, including T cells reactive to glycolipids presented by CD1 molecules. The CD1 molecules have a structure broadly similar to major histocompatibility complex (MHC) class I and class II proteins, but because the antigens CD 1 presents are so different from peptides, it is possible that glycolipid reactive TCRs have properties that distinguish them from TCRs expressed by conventional T cells. Consistent with this possibility, CD1-reactive T cells have an unrestrained pattern of co-receptor expression, as they include CD4+, CD8+, and double-negative cells. Furthermore, unlike peptide-reactive T cells, there are populations of glycolipid-reactive T cells with invariant alpha chain TCRs that are conserved across species. There are also glycolipid reactive populations with more variable TCRs, however, suggesting that it may be difficult to make categorical generalizations about glycolipid reactive TCRs. Among the glycolipid reactive TCRs, the invariant TCR expressed by CD1d reactive NKT cells has been by far the most thoroughly studied, and in this article we emphasize the unique features of this antigen recognition system, including repertoire formation, fine specificity, TCR affinity, and TCR structure.

Visualizing levels of osteoblast differentiation by a two-color promoter-GFP strategy: Type I collagen-GFPcyan and osteocalcin-GFPtpz

A 3.9 kb DNA fragment of human osteocalcin promoter and 3.6 kb DNA fragment of the rat collagen type1a1 promoter linked with visually distinguishable GFP isomers, topaz and cyan, were used for multiplex analysis of osteoblast lineage progression. Three patterns of dual transgene expression can be appreciated in primary bone cell cultures derived from the transgenic mice and by histology of their corresponding bones. Our data support the interpretation that strong pOBCol3.6GFPcyan alone is found in newly formed osteoblasts, while strong pOBCol3.6GFPcyan and hOC-GFPtpz are present in osteoblasts actively making a new matrix. Osteoblasts expressing strong hOC-GFPtpz and weak pOBCol3.6GFPcyan are also present and may or may not be producing mineralized matrix. This multiplex approach reveals the heterogeneity within the mature osteoblast population that cannot be appreciated by current histological methods. It should be useful to identify and isolate populations of cells within an osteoblast lineage as they progress through stages of differentiation.

beta7 Integrin expression is not required for the localization of T cells to the intestine and colitis pathogenesis

beta7 Integrins have been shown to have an important role in the localization of T cells to the intestine. Utilizing two different experimental mouse models of inflammatory bowel disease (IBD), this study was undertaken to determine if beta7 integrin expression is critical for T cell localization to the intestine and colitis pathogenesis. Transfer of CD4+ CD45RBhigh cells into immunodeficient mice results in colitis. To examine the role of beta7 integrins, donor cells were obtained from beta7 integrin gene-deficient animals and disease induction was examined following transfer into severe combined immunodeficiency (SCID) mice. Additionally, beta7 integrin gene-deficient animals were crossed to IL-2-deficient mice and the onset of spontaneous colitis that normally occurs in IL-2-deficient animals was examined. No differences in the onset or severity of spontaneous colitis was noted in animals that were deficient in both beta7 integrin and IL-2. In contrast, the onset of colitis in recipients of T cells from beta7 integrin-deficient donors was delayed significantly. In mice receiving beta7 integrin negative cells, the initial lack of colitis appeared to correlate with fewer numbers of CD3+beta7 integrin -/- donor lymphocytes present in the host colon. The eventual development of disease, however, was associated with increased numbers of donor beta7 integrin -/- lymphocytes. These results show that beta7 integrin expression is not absolutely required for T cell localization to the intestine and colitis pathogenesis.

Activation of natural killer T cells potentiates or prevents experimental autoimmune encephalomyelitis

Natural killer (NK) T cells recognize lipid antigens in the context of the major histocompatibility complex (MHC) class 1-like molecule CD1 and rapidly secrete large amounts of the cytokines interferon (IFN)-gamma and interleukin (IL)-4 upon T cell receptor (TCR) engagement. We have asked whether NK T cell activation influences adaptive T cell responses to myelin antigens and their ability to cause experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. While simultaneous activation of NK T cells with the glycolipid alpha-galactosylceramide (alpha-GalCer) and myelin-reactive T cells potentiates EAE in B10.PL mice, prior activation of NK T cells protects against disease. Exacerbation of EAE is mediated by an enhanced T helper type 1 (Th1) response to myelin basic protein and is lost in mice deficient in IFN-gamma. Protection is mediated by immune deviation of the anti-myelin basic protein (MBP) response and is dependent upon the secretion of IL-4. The modulatory effect of alpha-GalCer requires the CD1d antigen presentation pathway and is dependent upon the nature of the NK T cell response in B10.PL or C57BL/6 mice. Because CD1 molecules are nonpolymorphic and remarkably conserved among different species, modulation of NK T cell activation represents a target for intervention in T cell-mediated autoimmune diseases.

Constitutive expression of LIGHT on T cells leads to lymphocyte activation, inflammation, and tissue destruction

LIGHT, a member of the TNF family of cytokines (homologous to lymphotoxin, exhibits inducible expression and competes with HSV glycoprotein D for herpesvirus entry mediator, a receptor expressed on T cells), is induced on activated T cells and mediates costimulatory and antitumor activity in vitro. Relatively little information is available on the in vivo effects of LIGHT expression, particularly within the T cell compartment. In this work, we describe transgenic mice that express human LIGHT under the control of the CD2 promoter, resulting in constitutive transgene expression in cells of the T lymphocyte lineage. LIGHT-transgenic animals exhibit abnormalities in both lymphoid tissue architecture and the distribution of lymphocyte subsets. They also show signs of inflammation that are most severe in the intestine, along with tissue destruction of the reproductive organs. These LIGHT-mediated effects were recapitulated when immune-deficient mice were reconstituted with bone marrow from LIGHT-transgenic donor mice. T cells in the LIGHT-transgenic mice have an activated phenotype and mucosal T cells exhibit enhanced Th1 cytokine activity. The results indicate that LIGHT may function as an important regulator of T cell activation, and implicate LIGHT signaling pathways in inflammation focused on mucosal tissues.

T cell responses modulated through interaction between CD8alphaalpha and the nonclassical MHC class I molecule, TL

The thymus leukemia antigen (TL) is a nonclassical class I molecule, expressed abundantly on intestinal epithelial cells. We show that, in contrast to other major histocompatibility complex (MHC) class I molecules that bind CD8alphabeta, TL preferentially binds the homotypic form of CD8alpha (CD8alphaalpha). Thus, TL tetramers react specifically to CD8alphaalpha-expressing cells, including most intestinal intraepithelial lymphocytes. Compared with CD8alphabeta, which recognizes the same MHC as the T cell receptor (TCR) and thus acts as a TCR coreceptor, high-affinity binding of CD8alphaalpha to TL modifies responses mediated by TCR recognition of antigen presented by distinct MHC molecules. These findings define a novel mechanism of lymphocyte regulation through CD8alphaalpha and MHC class I.

Natural killer T cells reactive to a single glycolipid exhibit a highly diverse T cell receptor beta repertoire and small clone size

CD1d-restricted natural killer (NK) T cells reactive with the glycolipid alpha-galactosylceramide (alpha-GalCer) are a distinct lymphocyte sublineage. They express an invariant Valpha14-Jalpha18 T cell receptor (TcR), but the role of the beta chain has been controversial. Here, we have used CD1d tetramers to identify and isolate NK T cells based on their antigen specificity. In mice lacking germline Vbeta8, most of the alpha-GalCer-reactive T cells express either Vbeta2 or Vbeta7, strong Vbeta selection being revealed by the lack of an increase in other Vbeta regions. By contrast to the selection for complementarity determining region (CDR) 3beta sequences in some anti-peptide responses, alpha-GalCer-reactive T cells have polyclonal CDR3beta sequences. There is little CDR3beta sequence redundancy between organs or individual mice, and, surprisingly, there also is no evidence for organ-specific CDR3beta sequence motifs. These data argue against a T cell receptor-mediated self-reactivity for tissue-specific CD1d-bound ligands. Each NKT clone is represented by only 5-10 cells. This clone size is similar to naive conventional T cells, and much lower than that reported for memory T cells, although NK T cells have an activated/memory phenotype.

NKT cells derive from double-positive thymocytes that are positively selected by CD1d

CD1d-reactive NKT cells are a separate T cell sublineage. Instructive models propose that NKT cells branch off the mainstream developmental pathway because of their T cell antigen receptor specificity, whereas stochastic models would propose that they develop from precursor cells committed to this sublineage before variable-gene rearrangement. We show here that immature double-positive (DP) thymocytes form the canonical rearranged Valpha gene of NKT cells at nearly equivalent frequencies in the presence or absence of CD1d expression. After interacting with CD1d in the thymus, these cells give rise to expanded populations of NKT cells-including both CD4+ and double-negative lymphocytes in the thymus and periphery-that express this alpha chain. These results confirm the existence of a DP intermediate for CD1d-reactive NKT cells. They also show that the early developmental stages of these T cells are not governed by a distinct mechanism, which is consistent with the TCR-instructive model of differentiation.

Human NKT cells mediate antitumor cytotoxicity directly by recognizing target cell CD1d with bound ligand or indirectly by producing IL-2 to activate NK cells

alpha-Galactosylceramide (alphaGalCer) stimulates NKT cells and has antitumor activity in mice. Murine NKT cells may directly kill tumor cells and induce NK cell cytotoxicity, but the mechanisms are not well defined. Newly developed human CD1d/alphaGalCer tetrameric complexes were used to obtain highly purified human alphaGalCer-reactive NKT cell lines (>99%), and the mechanisms of NKT cell cytotoxicity and activation of NK cells were investigated. Human NKT cells were cytotoxic against CD1d(-) neuroblastoma cells only when they were rendered CD1d(+) by transfection and pulsed with alphaGalCer. Four other CD1d(-) tumor cell lines of diverse origin were resistant to NKT cells, whereas Jurkat and U937 leukemia cell lines, which are constitutively CD1d(+), were killed. Killing of the latter was greatly augmented in the presence of alphaGalCer. Upon human CD1d/alphaGalCer recognition, NKT cells induced potent cytotoxicity of NK cells against CD1d(-) neuroblastoma cell lines that were not killed directly by NKT cells. NK cell activation depended upon NKT cell production of IL-2, and was enhanced by secretion of IFN-gamma. These data demonstrate that cytotoxicity of human NKT cells can be CD1d and ligand dependent, and that TCR-stimulated NKT cells produce IL-2 that is required to induce NK cell cytotoxicity. Thus, NKT cells can mediate potent antitumor activity both directly by targeting CD1d and indirectly by activating NK cells.

Activation of natural killer T cells by alpha-galactosylceramide treatment prevents the onset and recurrence of autoimmune Type 1 diabetes

Type 1 diabetes (T1D) in non-obese diabetic (NOD) mice may be favored by immune dysregulation leading to the hyporesponsiveness of regulatory T cells and activation of effector T-helper type 1 (Th1) cells. The immunoregulatory activity of natural killer T (NKT) cells is well documented, and both interleukin (IL)-4 and IL-10 secreted by NKT cells have important roles in mediating this activity. NKT cells are less frequent and display deficient IL-4 responses in both NOD mice and individuals at risk for T1D (ref. 8), and this deficiency may lead to T1D (refs. 1,6-9). Thus, given that NKT cells respond to the alpha-galactosylceramide (alpha-GalCer) glycolipid in a CD1d-restricted manner by secretion of Th2 cytokines, we reasoned that activation of NKT cells by alpha-GalCer might prevent the onset and/or recurrence of T1D. Here we show that alpha-GalCer treatment, even when initiated after the onset of insulitis, protects female NOD mice from T1D and prolongs the survival of pancreatic islets transplanted into newly diabetic NOD mice. In addition, when administered after the onset of insulitis, alpha-GalCer and IL-7 displayed synergistic effects, possibly via the ability of IL-7 to render NKT cells fully responsive to alpha-GalCer. Protection from T1D by alpha-GalCer was associated with the suppression of both T- and B-cell autoimmunity to islet beta cells and with a polarized Th2-like response in spleen and pancreas of these mice. These findings raise the possibility that alpha-GalCer treatment might be used therapeutically to prevent the onset and recurrence of human T1D.

The natural killer T-cell ligand alpha-galactosylceramide prevents autoimmune diabetes in non-obese diabetic mice

Diabetes in non-obese diabetic (NOD) mice is mediated by pathogenic T-helper type 1 (Th1) cells that arise because of a deficiency in regulatory or suppressor T cells. V alpha 14-J alpha 15 natural killer T (NKT) cells recognize lipid antigens presented by the major histocompatibility complex class I-like protein CD1d (refs. 3,4). We have previously shown that in vivo activation of V alpha 14 NKT cells by alpha-galactosylceramide (alpha-GalCer) and CD1d potentiates Th2-mediated adaptive immune responses. Here we show that alpha-GalCer prevents development of diabetes in wild-type but not CD1d-deficient NOD mice. Disease prevention correlated with the ability of alpha-GalCer to suppress interferon-gamma but not interleukin-4 production by NKT cells, to increase serum immunoglobulin E levels, and to promote the generation of islet autoantigen-specific Th2 cells. Because alpha-GalCer recognition by NKT cells is conserved among mice and humans, these findings indicate that alpha-GalCer might be useful for therapeutic intervention in human diseases characterized by Th1-mediated pathology such as Type 1 diabetes.

The Crohn's disease-associated bacterial protein I2 is a novel enteric t cell superantigen

An aberrant T cell response to enteric bacteria is important in inflammatory bowel disease. However, the identity of relevant microbial antigens is unknown. Here, we report the presence of I2, a Crohn's disease-associated microbial gene, in the murine intestine. The I2 protein induced a proliferative and IL-10 response by CD4(+) T cells from unimmunized mice. The I2 response was dependent on MHC class II-mediated recognition but did not require antigen processing. Selective activation was observed for the TCR-Vbeta5 subpopulation. These findings indicate that the I2 protein is a new class of T cell superantigen and suggest that colonization by the I2 microorganism in susceptible hosts may provide a superantigenic stimulus pertinent to Crohn's disease pathogenesis.

Crucial amino acid residues of mouse CD1d for glycolipid ligand presentation to V(alpha)14 NKT cells

A novel lymphocyte, NKT cells bearing an invariant V(alpha)14 antigen receptor, specifically recognizes alpha-galactosylceramide (alpha-GalCer) exclusively presented by mouse CD1d (mCD1d). However, the precise molecular interaction remains unclear. For the basis of functional analyses, a docking model of alpha-GalCer with the crystal structure of mCD1d was constructed. Possible residues involved in the alpha-GalCer--mCD1d interaction were found to be Arg79, Glu83 and Asp80 for carbohydrate recognition, and Asp153 for interaction with the amide group on the fatty acyl chain. The alpha-GalCer-presenting ability of various transfectants expressing mutant mCD1d was completely abrogated if a single amino acid mutation was induced at positions 79, 80, 83 or 153, suggesting that the polar amino acids above the F' pocket are crucial for alpha-GalCer presentation to activate V(alpha)14 NKT cells. The possibility that Glu83 is a contact site for the NKT cell receptor is also discussed.

Transgenic expression of IL-10 in T cells facilitates development of experimental myasthenia gravis

Ab to the acetylcholine receptor (AChR) cause experimental myasthenia gravis (EMG). Th1 cytokines facilitate EMG, whereas Th2 cytokines might be protective. IL-10 inhibits Th1 responses but facilitates B cell proliferation and Ig production. We examined the role of IL-10 in EMG by using wild-type (WT) C57BL/6 mice and transgenic (TG) C57BL/6 mice that express IL-10 under control of the IL-2 promoter. We immunized the mice with doses of AChR that cause EMG in WT mice or with low doses ineffective at causing EMG in WT mice. After low-dose AChR immunization, WT mice did not develop EMG and had very little anti-AChR serum Ab, which were mainly IgG1, whereas TG mice developed EMG and had higher levels of anti-AChR serum Ab, which were mainly IgG2, in addition to IgG1. At the higher doses, TG mice developed EMG earlier and more frequently than WT mice and had more serum anti-AChR Ab. Both strains had similar relative serum concentrations of anti-AChR IgG subclasses and IgG and complement at the muscle synapses. CD8(+)-depleted splenocytes from all AChR-immunized mice proliferated in the presence of AChR and recognized a similar epitope repertoire. CD8(+)-depleted splenocytes from AChR-immunized TG mice stimulated in vitro with AChR secreted significantly more IL-10, but less of the prototypic Th1 cytokine IFN-gamma, than those from WT mice. They secreted comparable amounts of IL-4 and slightly but not significantly reduced amounts of IL-2. This suggests that TG mice had reduced activation of anti-Torpedo AChR Th1 cells, but increased anti-AChR Ab synthesis, that likely resulted from IL-10-mediated stimulation of anti-AChR B cells. Thus, EMG development is not strictly dependent on Th1 cell activity.

The A' and F' pockets of human CD1b are both required for optimal presentation of lipid antigens to T cells

CD1 proteins are unique in their ability to present lipid Ags to T cells. Human CD1b shares significant amino acid homology with mouse CD1d1, which contains an unusual putative Ag-binding groove formed by two large hydrophobic pockets, A' and F'. We investigated the function of the amino acid residues that line the A' and F' pockets of CD1b by engineering 36 alanine-substitution mutants and analyzing their ability to present mycobacterial glycolipid Ags. Two lipid Ags presented by CD1b were studied, a naturally occurring glucose monomycolate (GMM) isolated from mycobacteria, which contains two long alkyl chains (C54-C62 and C22-C24) and synthetic GMM (sGMM), which includes two short alkyl chains (C18 and C14). We identified eight residues in both the A' and F' pockets that were involved in the presentation of both GMM and sGMM to T cells. Interestingly, four additional residues located in the distal portion of the A' pocket were required for the optimal presentation of GMM, but not sGMM. Conversely, nine residues located between the center of the groove and the F' pocket were necessary for the optimal presentation of sGMM, but not GMM. These data indicate that both the A' and F' pockets of human CD1b are required for the presentation of lipid Ags to T cells.

Presentation of self and microbial lipids by CD1 molecules

CD1 molecules present both self lipids and microbial lipids. Recent studies have elucidated novel antigenic structures that can be presented by CD1 for T cell stimulation, as well as new pathways for lipid-antigen presentation. Additionally, the development of lipid-CD1 tetramers now permits the tracking of CD1-reactive T cells during immune responses. Despite this, the roles of CD1-reactive T cells in both host defense and immune regulation remain to be unequivocally defined.

Glycolipid antigen processing for presentation by CD1d molecules

The requirement for processing glycolipid antigens in T cell recognition was examined with mouse CD1d-mediated responses to glycosphingolipids (GSLs). Although some disaccharide GSL antigens can be recognized without processing, the responses to three other antigens, including the disaccharide GSL Gal(alpha1-->2)GalCer (Gal, galactose; GalCer, galactosylceramide), required removal of the terminal sugars to permit interaction with the T cell receptor. A lysosomal enzyme, alpha-galactosidase A, was responsible for the processing of Gal(alpha1-->2)GalCer to generate the antigenic monosaccharide epitope. These data demonstrate a carbohydrate antigen processing system analogous to that used for peptides and an ability of T cells to recognize processed fragments of complex glycolipids.

Molecular biology of NK T cell specificity and development

NK T cells recognize a glycosphingolipid, alpha -galactosyl ceramide, presented by CD1d. CD1d is capable of binding a variety of lipids, however, and the hydrophilic groups of the antigen contribute relatively little to CD1d binding. Amino acids in the CD1d groove and the top of the alpha helices are involved in lipid antigen presentation, suggesting a conventional mode of presentation and antigen recognition. NK T cells also have unique requirements for their differentiation, as suggested by the analysis of a number of mouse germline mutations. For example, the development of NK T cells, unlike conventional T lymphocytes, is highly lymphotoxin dependent.

Structural requirements for antigen presentation by mouse CD1

The structural basis for the T cell response to glycolipid antigens (Ags) remains poorly understood. T lymphocytes autoreactive for mouse CD1 (mCD1.1) or reactive for the glycosphingolipid alphagalactosylceramide (alpha-GalCer) presented by mCD1.1 have been described previously. In this paper it is shown that mutations at the top of the alpha helices and in the bottom of the Ag-binding groove can disrupt both mCD1.1 autoreactivity and alpha-GalCer recognition. The locations of the positions that affect T cell responses indicate that recognition of mCD1.1 is not likely to be unconventional or superantigen-like. Furthermore, the effects of the bottom of the pocket mutation suggest that the autoreactive response could require an autologous ligand, and they indicate that alpha-GalCer binds to the groove of mCD1.1, most likely with the shorter 18-carbon hydrophobic chain in the A' pocket. Natural killer T cell hybridomas with identical T cell antigen receptor (TCR) alpha chains and different beta chains respond differently to alpha-GalCer presented by mCD1.1 mutants. This finding indicates a role for TCR beta in defining natural killer T cell specificity, despite the more restricted diversity of the alpha chains in these cells. Overall, the data are consistent with a mode of lipoglycan recognition similar to that proposed for glycopeptides, in which the TCR alpha and beta chains survey a surface composed of both mCD1.1 and the carbohydrate portion of alpha-GalCer.

The alphabeta T cell response to self-glycolipids shows a novel mechanism of CD1b loading and a requirement for complex oligosaccharides

The structural basis for the T cell recognition of lipoglycans remains to be elucidated. We have described autoreactive T cells responsive to GM1 ganglioside presented by CD1b. We show that glycosphingolipids bind to CD1b on the cell surface at neutral pH and are recognized without internalization or processing. Furthermore, soluble GM-CD1b complexes stimulate specific T cells. Oligosaccharide groups containing five or more sugars are required to build a minimal epitope for TCR recognition. This suggests a mechanism for T cell recognition of glycosphingolipids in which much of the CD1b-bound ligand is exposed. Binding to CD1b is a highly reversible process and other ceramide-containing glycosphingolipids displace GM1. These nonantigenic compounds act as blockers and may prevent harmful autoreactivity in vivo.

Membrane lymphotoxin is required for the development of different subpopulations of NK T cells

The development of lymphoid organs requires membrane-bound lymphotoxin (LT), a heterotrimer containing LTalpha and LTbeta, but the effects of LT on T cell function have not been characterized extensively. Upon TCR cross-linking in vitro, splenocytes from both LTalpha-/- and LTbeta-/- mice failed to produce IL-4 and IL-10 due to a reduction in NK T cells. Concordantly, LTalpha-/- and LTbeta-/- mice did not respond to the lipoglycan alpha-galactosylceramide, which is presented by mouse CD1 to Valpha14+ NK T cells. Interestingly, both populations of NK T cells, including those that are mouse CD1 dependent and alpha-galactosylceramide reactive and those that are not, were affected by disruption of the LTalpha and LTbeta genes. NK T cells were not affected, however, in transgenic mice in which LT signaling is blocked, beginning on day 3 after birth, by expression of a soluble decoy LTbeta receptor. This suggests that membrane-bound LT is critical for NK T cells early in ontogeny, but not for the homeostasis of mature cells.

CD1-mediated antigen presentation of glycosphingolipids

CD1 proteins are distinguished by their ability to present lipid antigens to T cells. Group II CD1 or CD1d molecules are recognized by the specialized NK T-cell subset, and this reactivity can be greatly augmented by alpha-galactosylceramide, a glycosphingolipid derived from a marine sponge. Human CD1b, which is only distantly related to the CD1d molecules, can present mammalian glycosphingolipids (gangliosides) to autoreactive T-cell clones derived from multiple sclerosis patients. Thus, CD1 responsive and glycosphingolipid-reactive cells may play an important immune regulatory role, in addition to their well-characterized role in the response to microbial lipids.

Systemic activation and antigen-driven oligoclonal expansion of T cells in a mouse model of colitis

Transfer of CD4+CD45RBhigh T cells into immunodeficient mice results in both the expansion of the transferred T cells and colitis. Here we show that colitis pathogenesis requires expression of MHC class II molecules by the immune-deficient host. Analysis of the TCRbeta repertoire of the cells found in the large intestine of diseased mice revealed a population with restricted TCR diversity. Furthermore, nucleotide sequence analysis demonstrated the selection for particular CDR3beta amino acid sequence motifs. Collectively, these data indicate that the expansion of T cells in the intestine and colitis pathogenesis are likely to require the activation of Ag-specific T cells, as opposed to nonspecific or superantigen-mediated events. There is relatively little overlap, however, when the TCR repertoires of different individuals are compared, suggesting that a number of Ags can contribute to T cell expansion and the generation of a T cell population in the intestine. Surprisingly, many of the expanded clones found in the large intestine also were found in the spleen and elsewhere, although inflammation is localized to the colon. Additionally, donor-derived T cells appear to be activated in both the intestine and the spleen at early time points after cell transfer. Together, these results strongly suggest that disease induction in this model involves either the early and systemic activation of antigen-specific T cells or the rapid dispersal of T cells activated at a particular site.

Specific inhibition of cyclooxygenase 2 restores antitumor reactivity by altering the balance of IL-10 and IL-12 synthesis

Cyclooxygenase-2 (COX-2), the enzyme at the rate-limiting step of prostanoid production, has been found to be overexpressed in human lung cancer. To evaluate lung tumor COX-2 modulation of antitumor immunity, we studied the antitumor effect of specific genetic or pharmacological inhibition of COX-2 in a murine Lewis lung carcinoma (3LL) model. Inhibition of COX-2 led to marked lymphocytic infiltration of the tumor and reduced tumor growth. Treatment of mice with anti-PGE2 mAb replicated the growth reduction seen in tumor-bearing mice treated with COX-2 inhibitors. COX-2 inhibition was accompanied by a significant decrement in IL-10 and a concomitant restoration of IL-12 production by APCs. Because the COX-2 metabolite PGE2 is a potent inducer of IL-10, it was hypothesized that COX-2 inhibition led to antitumor responses by down-regulating production of this potent immunosuppressive cytokine. In support of this concept, transfer of IL-10 transgenic T lymphocytes that overexpress IL-10 under control of the IL-2 promoter reversed the COX-2 inhibitor-induced antitumor response. We conclude that abrogation of COX-2 expression promotes antitumor reactivity by restoring the balance of IL-10 and IL-12 in vivo.

Highly conserved antigen-presenting function of CD1d molecules

The lack of polymorphism of nonclassical antigen-presenting molecules has led to the proposal that they may carry out some conserved and essential antigen-presenting function. Although this is a plausible hypothesis, the major histocompatibility complex has undergone dramatic expansions and contractions through evolution, and there is surprisingly little evidence for interspecies conservation of nonclassical class I molecules. The CD1d molecule, by contrast, shows an extremely high degree of functional conservation between mice and humans, with regard to its interaction with the relatively invariant TCRs that are expressed by NK T cells. This conservation for CD1d recognition is observed either in the absence of exogenous Ag or together with a lipoglycan antigen. The close functional and phenotypic conservation of NK T cells, in mammalian species separated by approximately 50 million years, suggests an essential role in the immune system for CD1d recognition by NK T cells.

T cell-derived IL-10 promotes lung cancer growth by suppressing both T cell and APC function

We have found previously that human lung cancers potently induce T lymphocyte IL-10 production in vitro. To assess the impact of enhanced T cell-derived IL-10 on antitumor immunity in vivo, we utilized transgenic mice expressing IL-10 under the control of the IL-2 promoter. We have shown previously that Lewis lung carcinoma cells (3LL) have more aggressive growth potential in IL-10 transgenic mice compared with control littermates. In this study, we show that transfer of T cells from IL-10 transgenic mice to control littermates transferred the IL-10 immunosuppressive effect and led to enhanced 3LL tumor growth. In addition to changes in T cell-mediated immunity, professional APC from IL-10 transgenic mice were found to have significantly suppressed capacity to induce MHC alloreactivity, CTL responses, and IL-12 production. Tumor Ag-pulsed dendritic cells from IL-10 transgenic mice also failed to generate antitumor reactivity. These results suggest that increased levels of T cell-derived IL-10 severely impair antitumor immunity in vivo, due to defects in both T cell and APC function.

Cutting edge: TCR alpha beta+ CD8 alpha alpha+ T cells are found in intestinal intraepithelial lymphocytes of mice that lack classical MHC class I molecules

TCR alpha beta+ intestinal intraepithelial lymphocytes (IEL) can express either the typical CD8 alpha beta heterodimer or an unusual CD8 alpha alpha homodimer. Both types of CD8+ IEL require class I molecules for their differentiation, since they are absent in beta2m-/- mice. To gain insight into the role of class I molecules in forming TCR alpha beta+ CD8+ IEL populations, we have analyzed the IEL in mice deficient for either TAP, beta 2m, CD1, or K and D. We find that K-/-D-/- mice have TCR alpha beta+ CD8 alpha alpha+ IEL, although they are deficient for TCR alpha beta+ CD8 alpha beta+ cells. This indicates that at least some TCR alpha beta+ CD8 alpha alpha+ IEL require only nonclassical class I molecules for their development. Surprisingly, the TCR alpha beta+ CD8 alpha alpha+ IEL are significantly increased in K-/-D-/- mice, suggesting a complex interaction between CD8+ IEL and class I molecules that might include direct or indirect negative regulation by K and D, as well as positive effects mediated by nonclassical class I molecules.

Cutting edge: activation of NK T cells by CD1d and alpha-galactosylceramide directs conventional T cells to the acquisition of a Th2 phenotype

NK T cells recognize glycolipid Ags such as alpha-galactosylceramide (alpha-GalCer) presented by the MHC class I-like molecule CD1d. In this paper we have studied the in vivo effects of alpha-GalCer on the generation of adaptive immune responses. Treatment of mice with alpha-GalCer resulted in rapid activation of NK T cells and production of the cytokines IL-4 and IFN-gamma. However, after this initial stimulation, NK T cells became polarized for the production of IL-4. Further, as soon as 6 days after alpha-GalCer injection, a marked increase in serum IgE levels was observed. Administration of alpha-GalCer at the time of priming of mice with protein Ag resulted in the generation of Ag-specific Th2 cells and a profound increase in the production of IgE. Collectively, these findings indicate that alpha-GalCer may be useful for modulating immune responses toward a Th2 phenotype during prophylaxis and therapy.

Cutting edge: anti-CD1 monoclonal antibody treatment reverses the production patterns of TGF-beta 2 and Th1 cytokines and ameliorates listeriosis in mice

Protection against intracellular bacteria by T cells is regulated by Ag-presenting molecules, which comprise classical MHC class I molecules, MHC class II molecules, and nonclassical MHC class Ib molecules. The role of CD1 molecules, which are structurally similar to classical MHC class I gene products, but less polymorphic, is not understood so far. We show that CD1 surface expression increased on APC in Listeria-infected mice. The in vivo treatment with anti-CD1 mAb reduced TGF-beta 2 levels and concomitantly increased secretion of the proinflammatory cytokine TNF, the Th1 cell promoting cytokine IL-12, and the Th1 cell cytokine IFN-gamma at the onset of listerial infection. These findings point to a regulatory role of CD1-reactive cells in the immune response against listeriosis.

Mucosal immunity and inflammation. II. The yin and yang of T cells in intestinal inflammation: pathogenic and protective roles in a mouse colitis model

Inflammatory bowel disease (IBD) is a multifactorial immune disorder of uncertain etiology. The advent of several mouse models of mucosal inflammation that resemble IBD has provided insight into the mechanisms governing both normal and pathological mucosal immune function. In a widely used adoptive transfer model, the injection into immunodeficient mice of a subset of CD4(+) T lymphocytes, the CD4(+)CD45RBhigh cells, leads to inflammation of the intestine. Pathogenesis is due in part to the secretion of proinflammatory cytokines. The induction of colitis can be prevented by cotransfer of another CD4(+) subpopulation, the CD4(+)CD45RBlow T cells. This population behaves analogously to the CD4(+)CD45RBhigh population in terms of the acquisition of activation markers and homing to the host intestine. However, their lymphokine profile when activated is different, and anti-inflammatory cytokines secreted and/or induced by CD4(+)CD45RBlow T cells prevent colitis. In this themes article, a description of the adoptive transfer model is given, the factors that promote and prevent colitis pathogenesis are discussed, and some controversial aspects of the model are addressed.

An automated semiquantitative B and T cell clonality assay

BACKGROUND

Rearrangements of the antigen receptor genes in B and T cells generate products of unique length and sequence. Polymerase chain reaction (PCR) assays are routinely used to identify clonal lymphocyte populations by detecting clonal V-J rearrangements or chromosomal translocations within these antigen receptor loci. Multiple primer sets are, however, required to detect the majority of clonal B- and T-cell malignancies. Products from the individual reactions must be analyzed separately to avoid misinterpretation. Moreover, small clonal populations remain difficult to identify. To address these difficulties, we propose that an integrated fluorescence-based approach to clonal B- and T-cell detection would simultaneously identify both B- and T-cell neoplasia; increase amplicon resolution, analytic sensitivity, and assay throughput; produce more comprehensive and semiquantitative data useful for evaluation of hematologic malignancies; and eliminate labor intensive agarose and polyacrylamide gel electrophoresis.

METHODS AND RESULTS

Samples were genomic DNA and cDNA. Differentially labeled primers were used to amplify regions diagnostic for B- and T-cell clonality in a single plate with a single thermocycler program. Combined amplicon products underwent capillary electrophoresis for high resolution fractionation and differential fluorescence detection and quantification. Data were automatically analyzed and archived. In a comparative analysis of a variety of clinical samples, this automated and integrated B- and T-cell assay showed >94% agreement (33 of 35 results) with individual B- and T-cell PCR assays. Furthermore, this assay had an overall monoclonality detection rate of 100%, and as little as 100 ng of sample DNA yielded complete B- and T-cell clonality test results. The limit of detection was approximately 10-2 cells, and amplicons were sized to within 0.1 basepair. Serial dilutions of clonal B- and T-cell lines comprising a coded proficiency panel were identified and correctly ranked. Specificity was 100% as determined by analysis of 18 control samples that were all negative for B- and T-cell clonality.

CONCLUSIONS

Our data show that this automated and integrated B- and T-cell clonality assay system is a sensitive and specific tool useful for rapid identification of clonal lymphocyte populations and will likely have broad clinical applications.

Immunization with alpha-galactosylceramide polarizes CD1-reactive NK T cells towards Th2 cytokine synthesis

We have compared the immune responses of mice immunized either with alpha-galactosylceramide (alpha-GalCer), capable of eliciting a CD1-metiated stimulation of V alpha14+ NK T cells, or with lipoarabinomannan (LAM), a glycophospholipid derived from mycobacteria which is known to be presented by CD1b in humans. Within 24 h, alpha-GalCer induces a burst of IFN-gamma secretion in vivo, and recall with antigen in vitro leads to the synthesis of IL-4 and IL-10 in addition to IFN-gamma. Associated with this in vivo cytokine release is a polyclonal activation of splenic B and T cells. CD1-reactive NK T lymphocytes mediate these events, because none of them are observed in alpha-GalCer-immunized CD1-/- mice. LAM immunization fails to promote similar early responses in vivo. Repeated exposure of mice to alpha-GalCer induces splenic T cells to secrete IL-4 and IL-10 but dramatically reduced levels of IFN-gamma. Such a bias in the cytokine balance triggered by NK T cells stimulated with multiple doses of alpha-GalCer suggests that this compound might be useful in the induction of Th2 immune responses and the prevention of chronic inflammatory conditions mediated by Th1 cytokines.

CD1-mediated immune responses to glycolipids

Major advances have recently been accomplished in understanding the biochemistry of interactions between lipid antigens and CD1. The diversity of lipid antigens loaded onto CD1 molecules in normal cells, the ligand requirements for CD1 recognition by autoreactive T cells, including NK T cells, and the significance of CD1-mediated autoreactivity, as opposed to pathogen reactivity, remain controversial issues.

Syntheses of biotinylated alpha-galactosylceramides and their effects on the immune system and CD1 molecules

A representative alpha-galactosylceramide (alpha-GalCer), KRN7000, has strong immunostimulatory and antitumor activity. Recent studies demonstrated that KRN7000-pulsed antigen-presenting cells (APC) can activate natural killer T (NKT) cells, a novel T-cell lineage, and CD1d molecules on APC play an important role in the activation of NKT cells. However, it remains unclear whether alpha-GalCers actually bind to CD1d molecules. To address this question, we synthesized three kinds of biotinylated alpha-GalCer and a biotinylated beta-GalCer and found that the biotinylated alpha-GalCers significantly stimulate the proliferation of murine spleen cells, but the biotinylated beta-GalCer does not and that all biotinylated compounds bind to CD1d molecules.

The murine nonclassical class I major histocompatibility complex-like CD1.1 molecule protects target cells from lymphokine-activated killer cell cytolysis

Classical class I major histocompatibility complex (MHC) molecules, as well as the nonclassical class I histocompatibility leukocyte antigen (HLA)-E molecule, can negatively regulate natural killer (NK) cell cytotoxicity through engagement of NK inhibitory receptors. We show that expression of murine (m)CD1.1, a nonpolymorphic nonclassical MHC class I-like molecule encoded outside the MHC, protects NK-sensitive RMA/S target cells from adherent lymphokine-activated killer cell (A-LAK) cytotoxicity. Passage of effector cells in recombinant interleukin (rIL)-2 enhanced protection by mCD1.1, suggesting an expansion of relevant A-LAK population(s) or modulation of A-LAK receptor expression. Murine CD1. 1 conferred protection from lysis by rIL-2-activated spleen cells of recombination activating gene (Rag)-1(-/-) mice, which lack B and T cells, demonstrating that mCD1.1 can protect RMA/S cells from lysis by NK cells. An antibody specific for mCD1.1 partially restored A-LAK lysis of RMA/S.CD1.1 transfectants, indicating that cell surface mCD1.1 can confer protection from lysis; therefore, mCD1.1 possibly acts through interaction with an NK inhibitory receptor. CD1.1 is by far the most divergent class I molecule capable of regulating NK cell activity. Finally, mCD1.1 expression rendered RMA/S cells resistant to lysis by A-LAK of multiple mouse strains. The conserved structure of mCD1.1 and pattern of mCD1.1 resistance from A-LAK lysis suggest that mCD1.1 may be a ligand for a conserved NK inhibitory receptor.

Presentation of peptide antigens by mouse CD1 requires endosomal localization and protein antigen processing

Mouse CD1(mCD1) molecules have been reported to present two types of antigens: peptides or proteins and the glycolipid alpha-galactosylceramide. Here, we demonstrate that a protein antigen, chicken ovalbumin (Ova), must be processed to generate peptides presented by mCD1 to CD8(+) T cells. The processing and mCD1-mediated presentation of chicken Ova depend on endosomal localization because inhibitors of endosomal acidification and endosomal recycling pathways block T cell reactivity. Furthermore, a cytoplasmic tail mutant of mCD1, which disrupts endosomal localization, has a greatly reduced capacity to present Ova to mCD1 restricted cells. Newly synthesized mCD1 molecules, however, are not required for Ova presentation, suggesting that molecules recycling from the cell surface are needed. Because of these data showing that mCD1 trafficks to endosomes, where it can bind peptides derived from exogenous proteins, we conclude that peptide antigen presentation by mCD1 is likely to be a naturally occurring phenomenon. In competition assays, alpha-galactosylceramide did not inhibit Ova presentation, and presentation of the glycolipid was not inhibited by excess Ova or the peptide epitope derived from it. This suggests that, although both lipid and peptide presentation may occur naturally, mCD1 may interact differently with these two types of antigens.