Antigen processing and presentation of a naturally glycosylated protein elicits major histocompatibility complex class II-restricted, carbohydrate-specific T cells

Paradoxical Duel Role of Collagen in Rheumatoid Arthritis: Cause of Inflammation and Treatment

In biology, collagen-biomaterial regulates several signaling mechanisms of bone and immune cells involved in tissue repair and any imbalance in collagen turnover may affect the homeostasis of cells, becoming a major cause of several complications. In this case, the administration of oral collagen may play a potential role in returning cells to their normal function. For several decades, the beneficial effects of collagen have been explored widely, and thus many commercial products are available in cosmetics, food, and biomedical fields. For instance, collagen-based-products have been widely used to treat the complications of cartilage-related-disorders. Many researchers are reporting the anti-arthritogenic properties of collagen-based materials. In contrast, collagen, especially type-II collagen (CII), has been widely used to induce arthritis by immunization in an animal-model with or without adjuvants, and the potentially immunogenic-properties of collagen have been continuously reported for a long time. Additionally, the immune tolerance of collagen is mainly regulated by the T-lymphocytes and B-cells. This controversial hypothesis is getting more and more evidence nowadays from both sides to support its mechanism. Therefore, this review links the gap between the arthritogenic and anti-arthritogenic effects of collagen and explored the actual mechanism to understand the fundamental concept of collagen in arthritis. Accordingly, this review opens-up several unrevealed scientific knots of collagen and arthritis and helps the researchers understand the potential use of collagen in therapeutic applications.

Mapping the SARS-CoV-2 spike glycoprotein-derived peptidome presented by HLA class II on dendritic cells

Understanding and eliciting protective immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an urgent priority. To facilitate these objectives, we profile the repertoire of human leukocyte antigen class II (HLA-II)-bound peptides presented by HLA-DR diverse monocyte-derived dendritic cells pulsed with SARS-CoV-2 spike (S) protein. We identify 209 unique HLA-II-bound peptide sequences, many forming nested sets, which map to sites throughout S including glycosylated regions. Comparison of the glycosylation profile of the S protein to that of the HLA-II-bound S peptides reveals substantial trimming of glycan residues on the latter, likely induced during antigen processing. Our data also highlight the receptor-binding motif in S1 as a HLA-DR-binding peptide-rich region and identify S2-derived peptides with potential for targeting by cross-protective vaccine-elicited responses. Results from this study will aid analysis of CD4⁺ T cell responses in infected individuals and vaccine recipients and have application in next-generation vaccine design.

Mapping the SARS-CoV-2 spike glycoprotein-derived peptidome presented by HLA class II on dendritic cells

Understanding and eliciting protective immune responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an urgent priority. To facilitate these objectives, we have profiled the repertoire of human leukocyte antigen class II (HLA-II)-bound peptides presented by HLA-DR diverse monocyte-derived dendritic cells pulsed with SARS-CoV-2 spike (S) protein. We identify 209 unique HLA-II-bound peptide sequences, many forming nested sets, which map to sites throughout S including glycosylated regions. Comparison of the glycosylation profile of the S protein to that of the HLA-II-bound S peptides revealed substantial trimming of glycan residues on the latter, likely introduced during antigen processing. Our data also highlight the receptor-binding motif in S1 as a HLA-DR-binding peptide-rich region. Results from this study have application in vaccine design, and will aid analysis of CD4+ T cell responses in infected individuals and vaccine recipients.

Nitroxidized-Albumin Advanced Glycation End Product and Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease whose major clinical consequence is inflammation of small joints and contiguous structures. Oxidative and nitrosative stress along with increased formation of advanced glycation end products (AGEs) play an important role in the disease process. Generation of reactive species during glycation of proteins further adds to the oxidative and nitrosative stress. Albumin, being the most abundant plasma protein, is frequently targeted by different oxidizing and nitrating agents, including peroxynitrite (OONO-) anion. Albumin is also targeted and modified by dicarbonyl metabolites (glyoxal and methylglyoxal) which are formed in oxidative and non-oxidative processes during the synthesis of AGEs. The endogenously formed OONO- and dicarbonyls may modify plasma albumin including those albumin that have travelled or migrated to synovial cells and caused nitration, oxidation, and glycation. These modifications may produce crosslinks, aggregate in albumin and confer immunogenicity. Simultaneous modification of albumin by OONO- and dicarbonyls may generate nitroxidized-AGE-albumin which may persist in circulation for a longer duration compared to native albumin. Nitroxidized-AGE-albumin level (or serum autoantibodies against nitroxidized- AGE-albumin) along with other pre-clinical features may help predict the likely onset of RA.

Targeting IgG in Arthritis: Disease Pathways and Therapeutic Avenues

Rheumatoid arthritis (RA) is a polygenic and multifactorial syndrome. Many complex immunological and genetic interactions are involved in the final outcome of the clinical disease. Autoantibodies (rheumatoid factors, anti-citrullinated peptide/protein antibodies) are present in RA patients' sera for a long time before the onset of clinical disease. Prior to arthritis onset, in the autoantibody response, epitope spreading, avidity maturation, and changes towards a pro-inflammatory Fc glycosylation phenotype occurs. Genetic association of epitope specific autoantibody responses and the induction of inflammation dependent and independent changes in the cartilage by pathogenic autoantibodies emphasize the crucial contribution of antibody-initiated inflammation in RA development. Targeting IgG by glyco-engineering, bacterial enzymes to specifically cleave IgG/alter N-linked Fc-glycans at Asn 297 or blocking the downstream effector pathways offers new avenues to develop novel therapeutics for arthritis treatment.

T cells specific for post-translational modifications escape intrathymic tolerance induction

Establishing effective central tolerance requires the promiscuous expression of tissue-restricted antigens by medullary thymic epithelial cells. However, whether central tolerance also extends to post-translationally modified proteins is not clear. Here we show a mouse model of autoimmunity in which disease development is dependent on post-translational modification (PTM) of the tissue-restricted self-antigen collagen type II. T cells specific for the non-modified antigen undergo efficient central tolerance. By contrast, PTM-reactive T cells escape thymic selection, though the PTM variant constitutes the dominant form in the periphery. This finding implies that the PTM protein is absent in the thymus, or present at concentrations insufficient to induce negative selection of developing thymocytes and explains the lower level of tolerance induction against the PTM antigen. As the majority of self-antigens are post-translationally modified, these data raise the possibility that T cells specific for other self-antigens naturally subjected to PTM may escape central tolerance induction by a similar mechanism.

Post-translational modifications are associated with autoimmune diseases but definitive evidence of their contribution to escape from central tolerance mechanisms is needed. Here, the authors show that T cells specific for post-translational modifications of type II collagen escape intrathymic tolerance induction in a mouse model of rheumatoid arthritis.

Identification and Characterization of Complex Glycosylated Peptides Presented by the MHC Class II Processing Pathway in Melanoma

The MHC class II (MHCII) processing pathway presents peptides derived from exogenous or membrane-bound proteins to CD4+ T cells. Several studies have shown that glycopeptides are necessary to modulate CD4+ T cell recognition, though glycopeptide structures in these cases are generally unknown. Here, we present a total of 93 glycopeptides from three melanoma cell lines and one matched EBV-transformed line with most found only in the melanoma cell lines. The glycosylation we detected was diverse and comprised 17 different glycoforms. We then used molecular modeling to demonstrate that complex glycopeptides are capable of binding the MHC and may interact with complementarity determining regions. Finally, we present the first evidence of disulfide-bonded peptides presented by MHCII. This is the first large scale study to sequence glyco- and disulfide bonded MHCII peptides from the surface of cancer cells and could represent a novel avenue of tumor activation and/or immunoevasion.

A Bitter Sweet Symphony: Immune Responses to Altered O-glycan Epitopes in Cancer

The appearance of aberrant glycans on the tumor cell surface is one of the emerging hallmarks of cancer. Glycosylation is an important post-translation modification of proteins and lipids and is strongly affected by oncogenesis. Tumor-associated glycans have been extensively characterized regarding their composition and tumor-type specific expression patterns. Nevertheless whether and how tumor-associated glycans contribute to the observed immunomodulatory actions by tumors has not been extensively studied. Here, we provide a detailed overview of the current knowledge on how tumor-associated O-glycans affect the anti-tumor immune response, thereby focusing on truncated O-glycans present on epithelial tumors and mucins. These tumor-associated O-glycans and mucins bind a variety of lectin receptors on immune cells to facilitate the subsequently induction of tolerogenic immune responses. We, therefore, postulate that tumor-associated glycans not only support tumor growth, but also actively contribute to immune evasion.

Mice producing less reactive oxygen species are relatively resistant to collagen glycopeptide vaccination against arthritis

The bottleneck for the induction of collagen-induced arthritis in mice is the recognition of immunodominant type II collagen (CII) peptide (CII259-273) bound to the MHC class II molecule A(q). We have shown previously that the posttranslationally glycosylated lysine at position 264 in this epitope is of great importance for T cell recognition and tolerance induction to CII as well as for arthritis development. The Ncf1 gene, controlling oxidative burst, has been shown to play an important role for immune tolerance to CII. To investigate the effect of oxidation on the efficiency of immune-specific vaccination with MHC class II/glycosylated-CII peptide complexes, we used Ncf1 mutated mice. We demonstrate that normal reactive oxygen species (ROS) levels contribute to the establishment of tolerance and arthritis protection, because only mice with a functional oxidative burst were completely protected from arthritis after administration of the glycosylated CII259-273 peptide in complex with MHC class II. Transfer of T cells from vaccinated mice with functional Ncf1 protein resulted in strong suppression of clinical signs of arthritis in B10.Q mice, whereas the Ncf1 mutated mice as recipients had a weaker suppressive effect, suggesting that ROS modified the secondary rather than the primary immune response. A milder but still significant effect was also observed in ROS deficient mice. During the primary vaccination response, regulatory T cells, upregulation of negative costimulatory molecules, and increased production of anti-inflammatory versus proinflammatory cytokines in both Ncf1 mutated and wild type B10.Q mice was observed, which could explain the vaccination effect independent of ROS.

Bridging innate and adaptive antitumor immunity targeting glycans

Effective immunotherapy for cancer depends on cellular responses to tumor antigens. The role of major histocompatibility complex (MHC) in T-cell recognition and T-cell receptor repertoire selection has become a central tenet in immunology. Structurally, this does not contradict earlier findings that T-cells can differentiate between small hapten structures like simple glycans. Understanding T-cell recognition of antigens as defined genetically by MHC and combinatorially by T cell receptors led to the “altered self” hypothesis. This notion reflects a more fundamental principle underlying immune surveillance and integrating evolutionarily and mechanistically diverse elements of the immune system. Danger associated molecular patterns, including those generated by glycan remodeling, represent an instance of altered self. A prominent example is the modification of the tumor-associated antigen MUC1. Similar examples emphasize glycan reactivity patterns of antigen receptors as a phenomenon bridging innate and adaptive but also humoral and cellular immunity and providing templates for immunotherapies.

Critical role of glycosylation in determining the length and structure of T cell epitopes

Background

Using a combined in silico approach, we investigated the glycosylation of T cell epitopes and autoantigens. The present systems biology analysis was made possible by currently available databases (representing full proteomes, known human T cell epitopes and autoantigens) as well as glycosylation prediction tools.

Results

We analyzed the probable glycosylation of human T cell epitope sequences extracted from the ImmuneEpitope Database. Our analysis suggests that in contrast to full length SwissProt entries, only a minimal portion of experimentally verified T cell epitopes is potentially N- or O-glycosylated (2.26% and 1.22%, respectively). Bayesian analysis of entries extracted from the Autoantigen Database suggests a correlation between N-glycosylation and autoantigenicity. The analysis of random generated sequences shows that glycosylation probability is also affected by peptide length. Our data suggest that the lack of peptide glycosylation, a feature that probably favors effective recognition by T cells, might have resulted in a selective advantage for short peptides to become T cell epitopes. The length of T cell epitopes is at the intersection of curves determining specificity and glycosylation probability. Thus, the range of length of naturally occurring T cell epitopes may ensure the maximum specificity with the minimal glycosylation probability.

Conclusion

The findings of this bioinformatical approach shed light on fundamental factors that might have shaped adaptive immunity during evolution. Our data suggest that amino acid sequence-based hypo/non-glycosylation of certain segments of proteins might be substantial for determining T cell immunity/autoimmunity.

Tissue transglutaminase enhances collagen type II-induced arthritis and modifies the immunodominant T-cell epitope CII260-270

The calcium-dependent enzyme tissue transglutaminase (tTG) is associated with diverse biological functions, such as induction of apoptosis, modeling of the extracellular matrix, receptor-mediated endocytosis, cell growth and differentiation, cell adhesion and signal transduction. Also, it may deamidate glutamine residues to glutamic acid and catalyze cross-linking of proteins. In this study, we have investigated the impact of tTG for posttranslational modifications and cross-linking of the immunodominant T-cell epitope CII260-270 and their effects on the collagen-induced arthritis, an animal model for rheumatoid arthritis. By using mass spectrometry analysis and hybridoma assays, we have demonstrated that tTG could perform both types of modifications (deamidation and cross-link formation) on the immunodominant T-cell epitope CII259-273. Replacement of the glutamine at position 267 with glutamic acid leads to a decreased binding affinity to MHC II. T cells recognized both non-modfied (Q(267)) and modified (E(267)) CII259-273-peptides. We also show that administration of tTG leads to increased incidence, severity and histopathological manifestations of collagen-induced arthritis in mice. Moreover, we conclude that both processes, deamidation and cross-linking, are involved in the tTG-catalyzed reactions, and in vivo administration of tTG enhances arthritis severity and joint destruction in mice.

Impact of glycans on T-cell tolerance to glycosylated self-antigens

There is now substantial evidence that antigen post-translational modifications are recognized by T cells, and alterations in epitope modification has been linked to a number of autoimmune diseases. An estimated one third of the MHC ligands contain post-translational modification of epitopes. A common post-translational modification of proteins is glycosylation and it is predicted on theoretical grounds that approximately 1-5% of MHC ligands may bear a glycan. From numerous studies over the past 15 years it is clear that glycans can influence T cell responses either by contribution to the structure of the epitope or by influencing the profile of peptide epitopes presented by APCs. The influence of glycans on antigen processing and T cell recognition has particular relevance to the induction of tolerance to self-antigens. Here we discuss the potential impact of glycans on the profile of self-epitopes presented by APCs and the consequence of changes in glycosylation to generate neo self-epitopes resulting in the loss of tolerance and the development of autoimmune diseases. With the recent developments in profiling T cell epitopes, and with strategies for modulating glycosylation in vivo, it is now feasible to directly examine the global influence of glycans on self-tolerance and autoimmunity.

Quantitative Structure−Activity Relationship of Peptides Binding to the Class II Major Histocompatibility Complex Molecule Aq Associated with Autoimmune Arthritis

Presentation of (glyco)peptides by the class II major histocompatibility complex molecule Aq to T cells plays a central role in collagen-induced arthritis, an animal model for the autoimmune disease rheumatoid arthritis. A peptide library was designed using statistical molecular design in amino acid space in which five positions in the minimal mouse collagen type II binding epitope CII260-267 were varied. A substantially reduced peptide library of 24 peptides with diverse and representative molecular characteristics was selected, synthesized, and evaluated for the binding strength to Aq. A multivariate QSAR model was established by correlating calculated descriptors, compressed to its principle properties, with the binding data using partial least-square regression. The model was successfully validated by an external test set. Interpretation of the model provided a molecular property binding motif for peptides interacting with Aq. The information may be useful in future research directed toward new treatments of rheumatoid arthritis.

T cell surface redox levels determine T cell reactivity and arthritis susceptibility

Rats and mice with a lower capacity to produce reactive oxygen species (ROS) because of allelic polymorphisms in the Ncf1 gene (which encodes neutrophil cytosolic factor 1) are more susceptible to develop severe arthritis. These data suggest that ROS are involved in regulating the immune response. We now show that the lower capacity to produce ROS is associated with an increased number of reduced thiol groups (-SH) on T cell membrane surfaces. Artificially increasing the number of reduced thiols on T cells from animals with arthritis-protective Ncf1 alleles by glutathione treatment lowered the threshold for T cell reactivity and enhanced proliferative responses in vitro and in vivo. Importantly, T cells from immunized congenic rats with an E3-derived Ncf1 allele (DA.Ncf1E3 rats) that cannot transfer arthritis to rats with an arthritis-associated Dark Agouti (DA)-derived mutated Ncf1 allele (DA.Ncf1DA rats) became arthritogenic after increasing cell surface thiol levels. This finding was confirmed by the reverse experiment, in which oxidized T cells from DA.Ncf1DA rats induced less severe arthritis compared with controls. Therefore, we conclude that ROS production as controlled by Ncf1 is important in regulating surface redox levels of T cells and thereby suppresses autoreactivity and arthritis development.

Side-chain and backbone amide bond requirements for glycopeptide stimulation of T-cells obtained in a mouse model for rheumatoid arthritis

Collagen induced arthritis (CIA) is the most studied animal model for rheumatoid arthritis and is associated with the MHC class II molecule Aq. T-cell recognition of a peptide from type II collagen, CII256-270, bound to Aq is a requirement for development of CIA. Lysine 264 is the major T-cell recognition site of CII256-270 and CIA is in particular associated with recognition of lysine 264 after posttranslational hydroxylation and subsequent attachment of a beta-D-galactopyranosyl moiety. In this paper we have studied the structural requirements of collagenous glycopeptides required for T-cell stimulation, as an extension of earlier studies of the recognition of the galactose moiety. Synthesis and evaluation of alanine substituted glycopeptides revealed that there are T-cells that only recognise the galactosylated hydroxylysine 264, and no other amino acid side chains in the peptide. Other T-cells also require glutamic acid 266 as a T-cell contact point. Introduction of a methylene ether isostere instead of the amide bond between residues 260 and 261 allowed weaker recognition by some, but not all, of the T-cells. Altogether, these results allowed us to propose a model for glycopeptide recognition by the T-cells, where recognition from one or the other side of the galactose moiety could explain the different binding patterns of the T-cells.

Expression of aberrantly glycosylated tumor mucin-1 on human DC after transduction with a fiber-modified adenoviral vector

BACKGROUND

DC-presenting tumor Ag are currently being developed to be used as a vaccine in human cancer immunotherapy. To increase chances for successful therapy it is important to deliver full-length tumor Ag instead of loading single peptides.

METHODS

In this study we used a fiber-modified adenoviral vector (rAd5F35) containing full-length tumor Ag cDNA to transduce human monocyte (Mo)-derived DC in vitro. Cells were efficiently transduced and survived for at least 3 days after adenoviral transduction. Phenotype and function after maturation of Mo-DC were not impaired by infection with adenovirus particles. Expression of the tumor-associated Ag mucin-1 (MUC1) was detected using MAb defining different MUC1 glycoforms.

RESULTS

Non-transduced mature Mo-DC express endogenous MUC1 with normal glycosylation. After transduction with the rAd5F35-MUC1 adenoviral vector, Mo-DC also expressed MUC1 with tumor-associated glycosylation (Tn and T glycoforms), although no changes in mRNA levels of relevant glycosyltransferases could be demonstrated.

DISCUSSION

The presence of aberrantly glycosylated MUC1 may influence Ag presentation of the tumor glycoforms of MUC1 to immune cells, affecting tumor cell killing. These findings could be highly relevant to developing strategies for cancer immunotherapy based on DC vaccines using MUC1 as tumor Ag.

Therapeutic vaccination of active arthritis with a glycosylated collagen type II peptide in complex with MHC class II molecules

In both collagen-induced arthritis (CIA) and rheumatoid arthritis, T cells recognize a galactosylated peptide from type II collagen (CII). In this study, we demonstrate that the CII259-273 peptide, galactosylated at lysine 264, in complex with Aq molecules prevented development of CIA in mice and ameliorated chronic relapsing disease. In contrast, nonglycosylated CII259-273/Aq complexes had no such effect. CIA dependent on other MHC class II molecules (Ar/Er) was also down-regulated, indicating a bystander vaccination effect. T cells could transfer the amelioration of CIA, showing that the protection is an active process. Thus, a complex between MHC class II molecules and a posttranslationally modified peptide offers a new possibility for treatment of chronically active autoimmune inflammation such as rheumatoid arthritis.

Synthesis of a C-Glycoside Analogue of β-d-Galactosyl Hydroxylysine and Incorporation in a Glycopeptide from Type II Collagen

A stereoselective synthesis of the C-glycoside analogue of beta-D-galactosyl-(5R,2S)-hydroxylysine (1) has been achieved starting from tetra-O-benzyl-D-galactopyranosyl lactone. The synthesis involved establishment of three stereogenic centers in an unambiguous manner. A facially selective Grignard reaction followed by a silane reduction was used for the anomeric position of the C-galactose residue. An Evans allylation established the configuration of the delta-aminomethylene group of the hydroxylysine moiety, whereas an asymmetric hydrogenation utilizing Burk's catalyst was used for the alpha-amino acid moiety itself. The synthesis was completed in 17 steps with an overall yield of 18%, resulting in the most complex and functionalized C-glycoside analogue of a naturally occurring glycosylated amino acid prepared to date. In addition, amino acid 1 was incorporated in a glycopeptide from type II collagen known to be crucial for the response of autoimmune T cells obtained in models of rheumatoid arthritis. A preliminary immunological study revealed that four out of five members in a panel of T cell hybridomas were able to recognize this C-linked glycopeptide when presented by A(q) class II MHC molecules.

The major T cell epitope on type II collagen is glycosylated in normal cartilage but modified by arthritis in both rats and humans

Type II collagen (CII) is a target for autoreactive T cells in both rheumatoid arthritis and the murine model collagen-induced arthritis. The determinant core of CII has been identified as CII260-270, and the alteration of this T cell epitope by posttranslational modifications is known to be critical for development of arthritis in mice. Using CII-specific T cell hybridomas we have now shown that the immunodominant T cell epitope in the normal (healthy) human and rat joint cartilage is O-glycosylated at the critical T cell receptor recognition position 264 with a mono- or di-saccharide attached to a hydroxylysine. In contrast, in the arthritic human and rat joint cartilage there are both glycosylated and non-glycosylated CII forms. Glycosylated CII from normal cartilage could not be recognized by T cells reactive to peptides having only lysine or hydroxylysine at position 264, showing that antigen-presenting cells could not degrade the O-linked carbohydrate. Thus, the variable forms of the glycosylated epitope are determined by the structures present in cartilage, and these vary during the disease course. We conclude that the chondrocyte determines the structures presented to the immune system and that these structures are different in normal versus arthritic states.

Identification of the minimal glycopeptide core recognized by T cells in a model for rheumatoid arthritis

Collagen induced arthritis (CIA) is a common mouse model for rheumatoid arthritis. Two sets of truncated peptides derived from type II collagen have been prepared and tested for binding to A(q), a MHC-II molecule associated with development of CIA. Binding to A(q) correlated well with predictions from a computer-based model. T-cell hybridomas, obtained in CIA, were also used to study the ability of A(q) bound peptides to trigger a T-cell response. The minimal peptide epitope required for binding, as well as for giving a T-cell response, was determined to be CII260-267. In collagen this epitope is often glycosylated at hydroxylysine 264 and glycosylation has been shown to be an immunodominant feature in CIA. Synthesis and evaluation of CII260-267 carrying a beta-D-galactosyl moiety at position 264 revealed that this glycopeptide stimulated representative members from a panel of carbohydrate-specific T-cell hybridomas obtained in CIA.

Influence of saccharide size on the cellular immune response to glycopeptides

Glycopeptides that bind to MHC molecules on antigen presenting cells may elicit carbohydrate selective T cells. In order to investigate how the cellular immune response depends on the size of the carbohydrate moiety, a trigalactosylated derivative of an immunogenic peptide from hen egg-white lysozyme (HEL52-61) was prepared. Synthesis was accomplished by assembly of an alpha-1,4-linked trigalactose peracetate which was coupled to Fmoc serine. After activation as a pentafluorophenyl ester the resulting building block was used in solid-phase synthesis In contrast to the corresponding mono- and digalactosylated derivatives of HEL52-61, the trigalactosylated HEL52-61 was not immunogenic. Somewhat surprisingly, this was found to be because the trigalactosyl derivative bound approximately two orders of magnitude weaker to I-Ak MHC molecules than the mono- and digalactosyl peptides. Our observation suggests an explanation for previous findings, which show that glycopeptides isolated from MHC molecules in nature usually carry small saccharides.

Complex carbohydrates are not removed during processing of glycoproteins by dendritic cells: processing of tumor antigen MUC1 glycopeptides for presentation to major histocompatibility complex class II-restricted T cells

In contrast to protein antigens, processing of glycoproteins by dendritic cells (DCs) for presentation to T cells has not been well studied. We developed mouse T cell hybridomas to study processing and presentation of the tumor antigen MUC1 as a model glycoprotein. MUC1 is expressed on the surface as well as secreted by human adenocarcinomas. Circulating soluble MUC1 is available for uptake, processing, and presentation by DCs in vivo and better understanding of how that process functions in the case of glycosylated antigens may shed light on antitumor immune responses that could be initiated against this glycoprotein. We show that DCs endocytose MUC1 glycopeptides, transport them to acidic compartments, process them into smaller peptides, and present them on major histocompatability complex (MHC) class II molecules without removing the carbohydrates. Glycopeptides that are presented on DCs are recognized by T cells. This suggests that a much broader repertoire of T cells could be elicited against MUC1 and other glycoproteins than expected based only on their peptide sequences.

Glycosylation of type II collagen is of major importance for T cell tolerance and pathology in collagen-induced arthritis

Type II collagen (CII) is a candidate cartilage-specific autoantigen, which can become post-translationally modified by hydroxylation and glycosylation. T cell recognition of CII is essential for the development of murine collagen-induced arthritis (CIA) and also occurs in rheumatoid arthritis (RA). The common denominator of murine CIA and human RA is the presentation of an immunodominant CII-derived glycosylated peptide on murine Aq and human DR4 molecules, respectively. To investigate the importance of T cell recognition of glycosylated CII in CIA development after immunization with heterologous CII, we treated neonatal mice with different heterologous CII-peptides (non-modified, hydroxylated and galactosylated). Treatment with the galactosylated peptide (galactose at position 264) was superior in protecting mice from CIA. Protection was accompanied by a reduced antibody response to CII and by an impaired T cell response to the glycopeptide. To investigate the importance of glycopeptide recognition in an autologous CIA model, we treated MMC-transgenic mice, which express the heterologous CII epitope with a glutamic acid in position 266 in cartilage, with CII-peptides. Again, a strong vaccination potential of the glycopeptide was seen. Hence CII-glycopeptides may be the optimal choice of vaccination target in RA, since humans share the same epitope as the MMC mouse.

Identification of the advanced glycation end products N(epsilon)-carboxymethyllysine in the synovial tissue of patients with rheumatoid arthritis

BACKGROUND

Generation of advanced glycation end products (AGEs) is an inevitable process in vivo and can be accelerated under pathological conditions such as oxidative stress. In serum and synovial fluid of patients with rheumatoid arthritis (RA) raised AGE levels have been found.

OBJECTIVE

To determine the presence of N(epsilon)-carboxymethyllysine (CML; marker of oxidative stress) in RA synovial tissue by immunohistology.

METHODS

Frozen synovial tissue samples from 10 patients with RA and eight controls (four patients without joint disease and four patients with osteoarthritis (OA)) were treated with rabbit-anti-CML-IgG and goat-antirabbit-IgG. Immunostaining was visualised by streptavidine-alkaline phosphatase (chromogen fuchsin). Cell differentiation was performed with antibodies against CD68, CD45RO, and CD20.

RESULTS

CML was detected in the synovial lining, sublining, and endothelium in 10/10 RA and 4/4 OA synovial specimens. In RA some macrophages (CD68+) and T cells (CD45RO+) showed positive immunostaining for CML, whereas B cells were negative. Staining in OA synovial sublining was weak compared with RA.

CONCLUSIONS

CML was detected for the first time in RA and OA synovial tissue. Different patterns of immunostaining in RA and OA and the presence of CML on macrophages and T cells, suggest a role for CML in the pathogenesis of RA. This might be due to presentation of new epitopes which can maintain or even trigger an autoimmune response.

Immunization of rats with homologous type XI collagen leads to chronic and relapsing arthritis with different genetics and joint pathology than arthritis induced with homologous type II collagen

The most commonly used animal model for rheumatoid arthritis (RA) is collagen-induced arthritis (CIA), induced by immunization with type II collagen (CII), a cartilage restricted protein. In this work we show that type XI collagen (CXI), which is a minor component in cartilage, induces a different form of erosive and chronic relapsing polyarthritis in rats. Using a series of inbred rat strains involving various genetic backgrounds (DA, LEW, E3), and congenic MHC regions (a, u, f, n, c, d), we found that CXI induced arthritis (C(XI)IA) is associated with the RT1f haplotype in contrast to CII induced arthritis (C(II)IA), which is associated with the RT1a and RT1u haplotypes. The C(XI)IA follows a chronic disease course affecting peripheral joints with both progression and relapses, which appear not to cease (occurring >800 days). Susceptible strains showed a sustained antibody response to CXI with time indicating that the autoimmune response was self-perpetuated. Microscopic analysis of the joints at different stages demonstrated the severe destruction of bone and cartilage by pannus tissue consisting of activated macrophages and T cells. The main difference to joints from rats with C(II)IA was larger numbers of infiltrating lymphocytes and these tended to form follicle-like aggregates. Surprisingly, males were more susceptible to C(XI)IA than females whereas the opposite has been observed in other rat arthritis models, including C(II)IA. Taken together, C(XI)IA is a chronic relapsing and erosive polyarthritis that is MHC associated, which in fact fulfills the criteria for diagnosis of RA. Thus the C(XI)IA model will be useful as a novel and relevant animal model for RA.

Characterization of T cell hybridomas raised against a glycopeptide containing the tumor-associated T antigen, (betaGal (1-3) alphaGalNAc-O/Ser)

T cell hybridomas were raised against the glycopeptide S(72) (Core-1) containing the tumor-associated disaccharide betaGal (1-3) alphaGalNAc (Core-1) O-linked to serine at position 72 in the mouse hemoglobin derived decapeptide Hb (67-76). All hybridomas recognized the glycopeptide S(72) (Core-1). Two of the selected hybridomas responded, however, much better to the S(72) (Tn) glycopeptide containing the monosaccharide alphaGalNAc O-linked to serine. In addition, one hybridoma cross-responded to the glycopeptide T(72) (Core-1) having a threonine at position 72 instead of a serine. No cross-responses were found to other glycopeptides consisting of the same hemoglobin peptide with different glycans attached or to the unglycosylated peptides. The T cell receptor Valpha and Vbeta usage was clearly diverse. The CDR3alpha regions demonstrated moreover a predominance of small polar amino acid side chains, and three hybridomas contained a common sequence motif. All the sequenced CDR3beta regions contained furthermore a conserved proline-glycine motif. In conclusion, immunization with the disaccharide containing glycopeptides S(72) (Core-1) created a heterogeneous population of glycopeptide specific T cells with the ability of cross-responding toward related glycopeptides.

Immunization with a carbohydrate mimicking peptide augments tumor-specific cellular responses

The metastatic potential of some tumor cells is associated with the expression of the neolactoseries antigens sialyl-Lewis x (sLex) and sialyl-Lewis a (sLea) as they are ligands for selectins. We have recently shown that peptide mimetics of these antigens can potentiate IgG2a antibodies, which are associated with a Th1-type cellular response. As L-selectin is preferentially expressed on CD4+ Th1 and CD8+ T cell populations, specific induction of these phenotypes could augment a response to L-selectin ligand-expressing tumor cells. Here we demonstrate that immunization with a multiple antigen peptide (MAP) mimetic of sugar constituents of neolactoseries antigens induces a MHC-dependent peptide-specific cellular response that triggers IFN-gamma production upon peptide stimulation, correlating with IgG2a induction. Surprisingly, T lymphocytes from peptide-immunized animals were activated in vitro by sLex, also triggering IFN-gamma production in a MHC-dependent manner. Stimulation by peptide or carbohydrate resulted in loss of L-selectin on CD4+ T cells confirming a Th1 phenotype. We also observed an enhancement in cytotoxic T lymphocyte (CTL) activity in vitro against sLex-expressing Meth A cells using effector cells from Meth A-primed/peptide-boosted animals. CTL activity was inhibited by both anti-MHC class I and anti-L-selectin antibodies. These results further support a role for L-selectin in tumor rejection along with the engagement by the TCR for most likely processed tumor-associated glycopeptides, focusing on peptide mimetics as a means to induce carbohydrate reactive cellular responses.

Pleiotropic effects of post-translational modifications on the fate of viral glycopeptides as cytotoxic T cell epitopes

The fate of viral glycopeptides as cytotoxic T lymphocyte (CTL) epitopes is unclear. We have dissected the mechanisms of antigen presentation and CTL recognition of the peptide GP392-400 (WLVTNGSYL) from the lymphocytic choriomeningitis virus (LCMV) and compared them with those of the previously reported GP92-101 antigen (CSANNSHHYI). Both GP392-400 and GP92-101 bear a glycosylation motif, are naturally N-glycosylated in the mature viral glycoproteins, bind to major histocompatibility complex H-2D(b) molecules, and are immunogenic. However, post-translational modifications differentially affected GP92-101 and GP392-400. Upon N-glycosylation or de-N-glycosylation, a marked decrease in major histocompatibility complex binding was observed for GP392-400 but not for GP92-101. Further, under its N-glycosylated or de-N-glycosylated form, GP392-400 then lost its initial ability to generate a CTL response in mice, whereas GP92-101 was still immunogenic under the same conditions. The genetically encoded form of GP392-400, which on the basis of its immunogenicity could still be presented with H-2D(b) during the course of LCMV infection, does not in fact appear at the surface of LCMV-infected cells. Our results show that post-translational modifications of viral glycopeptides can have pleiotropic effects on their presentation to and recognition by CTL that contribute to either creation of neo-epitopes or destruction of potential epitopes.

Role of glycopeptide-specific T cells in collagen-induced arthritis: an example how post-translational modification of proteins may be involved in autoimmune disease

Immunization of mice with type II collagen (CII), a cartilage-restricted protein, leads to collagen-induced arthritis (CIA), a model for rheumatoid arthritis (RA). CIA symptoms consist of an erosive joint inflammation caused by an autoimmune attack, mediated by both T and B lymphocytes. CD4+ alphabeta T cells play a central role in CIA, both by helping B cells to produce anti-CII antibodies, and by interacting with other cells in the joints, eg macrophages. In H-2q mice, most CII-specific CD4+ T cells recognize the CII(256-270) peptide presented on the major histocompatibility complex (MHC) class II Aq molecule. Post-translational modifications (hydroxylation and variable glycosylation) of the lysine residue at position 264 of CII generate at least four different T-cell determinants that are specifically recognized by distinct T-cell subsets. Most T cells recognize CII(256-270) glycosylated with the monosaccharide galactose, which is consequently immunodominant in CIA. Recent studies indicate that the arthritogenic T cells in CIA are glycopeptide-specific, suggesting that induction of self-tolerance may be rendered more difficult by glycosylation of CII. These data open the possibility that outoimmune disease may be caused by the creation of new epitopes by posttranslational modification of proteins under circumstances such as trauma, inflammation or ageing.

N-linked carbohydrates in tyrosinase are required for its recognition by human MHC class II-restricted CD4(+) T cells

Glycosylation of mammalian proteins is known to influence their intracellular trafficking, half life, and susceptibility to enzymatic degradation. Rare instances of natural T cell epitopes dependent upon glycosylation for recognition have been described. We report here on human CD4(+) T lymphocyte cultures and clones from two melanoma patients that recognize the melanoma-associated Ag tyrosinase in the context of HLA-DR4 and -DR8. These T cells recognize tyrosinase, normally a heavily glycosylated molecule, when expressed constitutively in melanoma cells or in COS-7 transfectants pulsed as lysates onto autologous APC. However, these T cells fail to recognize tyrosinase expressed in bacteria, nor do they react with overlapping peptides covering full-length tyrosinase, suggesting a critical role for glycosylation in the processing and / or composition of the stimulatory epitopes. The requirement for glycosylation was demonstrated by the failure of tyrosinase-specific CD4(+) T cells to recognize tyrosinase synthesized in the presence of glycosylation inhibitors, or deglycosylated enzymatically. Site-directed mutagenesis of each of seven potential N-glycosylation sites showed that four sites were required to generate forms of tyrosinase that could be recognized by individual T cell clones. These data indicate that certain carbohydrate moieties are required for processing the tyrosinase peptides recognized by CD4(+) T cells. Post-translational modifications of human tumor-associated proteins such as tyrosinase could be a critical factor for the development of antitumor immune responses.

Synthesis of a C-glycoside analogue of beta-D-galactosyl hydroxynorvaline and its use in immunological studies

A C-linked isostere of beta-D-galactosylated hydroxynorvaline has been prepared in eight steps from per-O-benzylated galactopyranolactone. Addition of a homoallylic Grignard reagent to the lactone, reduction of the resulting hemiacetal with triethylsilane, and a Wittig reaction with Garner's aldehyde were key steps in this synthesis. The C-linked building block was then incorporated at position 264 into the fragment CII(256--270) from typeII collagen by solid-phase synthesis using a combination of the tert-butoxycarbonyl (Boc) and 9-fluorenylmethoxycarbonyl (Fmoc) protective group strategies. Deprotection of the benzylated C-linked galactosyl moiety was achieved simultaneously with cleavage of the glycopeptide from the solid phase by using triethylsilyl trifluoromethanesulfonate in TFA. Helper T-cell hybridomas obtained in a mouse model for rheumatoid arthritis responded to the C-linked glycopeptide when presented by classII MHC molecules. However, 10- to 20-fold higher concentrations were required as compared to when O-linked beta-D-galactosylated hydroxynorvaline or hydroxylysine (Hyl) were present at position 264 of CII(256--270). Thus, replacement of a single oxygen atom by a methylene group in the carbohydrate moiety of a glycopeptide antigen had a substantial influence on the T-cell response. This reveals that T cells are able to recognize the carbohydrate moiety of glycopeptide antigens with high specificity. Finally, the results suggest that structural modifications of beta-D-Gal-Hyl(264) in CII(256--270) may give altered peptide ligands that can be used for induction of tolerance in autoimmune rheumatoid arthritis.

T cells that are naturally tolerant to cartilage-derived type II collagen are involved in the development of collagen-induced arthritis

The immunodominant T-cell epitope that is involved in collagen-induced arthritis (CIA) is the glycosylated type II collagen (CII) peptide 256-270. In CII transgenic mice, which express the immunodominant CII 256-270 epitope in cartilage, the CII-specific T cells are characterized by a partially tolerant state with low proliferative activity in vitro, but with maintained effector functions, such as IFN-gamma secretion and ability to provide B cell help. These mice were still susceptible to CIA. The response was mainly directed to the glycosylated form of the CII 256-270 peptide, rather than to the nonglycosylated peptide. Tolerance induction was rapid; transferred T cells encountered CII within a few days. CII immunization several weeks after thymectomy of the mice did not change their susceptibility to arthritis or the induction of partial T-cell tolerance, excluding a role for recent thymic emigrants. Thus, partially tolerant CII autoreactive T cells are maintained and are crucial for the development of CIA.

Phosphorylated Peptides Can Be Transported by TAP Molecules, Presented by Class I MHC Molecules, and Recognized by Phosphopeptide-Specific CTL

CTL recognize short peptide fragments presented by class I MHC molecules. In this study, we examined the effect of phosphorylation on TAP transport, binding to class I MHC molecules, and recognition by CTL of peptide fragments from known phosphorylated oncogene proteins or virus phosphoproteins. We show that phosphopeptides can be efficiently transported from the cytosol to the endoplasmic reticulum by the TAP. Furthermore, we show that phosphorylation can have a neutral, negative, or even a positive effect on peptide binding to class I MHC. Finally, we have generated phosphopeptide-specific CTL that discriminate between the phosphorylated and the nonphosphorylated versions of the peptide. We conclude that phosphopeptide-specific CTL responses are likely to constitute a subset of the class I MHC-restricted CTL repertoire in vivo.

Transgenic mouse models of rheumatoid arthritis

A combined analysis of data available in the literature has demonstrated that the strongest association in rheumatoid arthritis (RA) is with DR genes rather than DQ or DP genes. Functional and structural data of RA-associated DR molecules suggest that selective binding of peptides is the molecular basis for this association. The establishment of functional transgenic mice expressing RA-associated HLA class II molecules has proven to be useful in the delineation of the role of these molecules in immune responses possibly related to RA and in the development of humanized models for this disease. Such humanized mice develop arthritis upon immunization with type II collagen (CII), which shows similarities with RA. Interestingly, the immunodominant T-cell determinant in CII is derived from positions 261-273, which overlap with a previously identified CII T-cell epitope restricted by the mouse Aq molecule, which is associated with collagen-induced arthritis. Studies in collagen transgenic mice have shown that recognition of this peptide may lead either to T-cell tolerance or to an arthritogenic response. It is therefore proposed that the T-cell recognition of the CII peptide bound by DR molecules is one of the molecular interactions of critical importance in the development of RA and accordingly also an important target for prevention and treatment of this disease.

Epitope glycosylation plays a critical role for T cell recognition of type II collagen in collagen-induced arthritis

Immunization of mice with type II collagen (CII) leads to collagen-induced arthritis (CIA), a model for rheumatoid arthritis. T cell recognition of CII is believed to be a critical step in CIA development. We have analyzed the T cell determinants on CII and the TCR used for their recognition, using twenty-nine T cell hybridomas derived from C3H.Q and DBA/1 mice immunized with rat CII. All hybridomas were specific for the CII(256-270) segment. However, posttranslational modifications (hydroxylation and variable O-linked glycosylation) of the lysine at position 264 generated five T cell determinants that were specifically recognized by different T cell hybridoma subsets. TCR sequencing indicated that each of the five T cell epitopes selected its own TCR repertoire. The physiological relevance of this observation was shown by in vivo antibody-driven depletion of TCR Valpha2-positive T cells, which resulted in an inhibition of the T cell proliferative response in vitro towards the non-modified CII(256-270), but not towards the glycosylated epitope. Most hybridomas (20/29) specifically recognized CII(256-270) glycosylated with a monosaccharide (beta-D-galactopyranose). We conclude that this glycopeptide is immunodominant in CIA and that posttranslational modifications of CII create new T cell determinants that generate a diverse TCR repertoire.

Intranasal administration of denatured type II collagen and its fragments can delay the onset of collagen-induced arthritis

Collagen-induced arthritis (CIA) is an autoimmune animal model for some types of human rheumatoid arthritis (RA). We have evaluated the effectiveness of intranasal administration of antigen in inhibiting CIA in DBA/1 mice. The intranasal administration of heat-denatured or trypsin-digested bovine type II collagen (CII) before immunization with CII strongly delayed the onset of CIA, whereas administration of native CII did not do so. The mice administered denatured or digested CII possessed much lower titers of anti-CII IgG2a than the control mice, whereas titers of anti-CII IgG1 and IgG2b were unchanged or slightly decreased. Responding to CII and peptides containing immunodominant T cell determinants, lymph node cells from mice administered denatured CII produced less IFN-gamma. These results suggest that intranasal administration of antigen downregulated preferentially Th1-type responses, whereas an enhanced Th2-type response was not observed. We demonstrate that the methods shown here are a possible treatment for rheumatoid arthritis.

Only Selected Light Chains Combine with a Given Heavy Chain to Confer Specificity for a Model Glycopeptide Antigen

The M and N human blood group glycopeptide Ags are carried on RBCs by glycophorin A. Previous results suggested that the murine humoral immune response against the N, but not the M, Ag is restricted. In addition, these results suggested that particular highly homologous heavy chains might be able to combine promiscuously with various light chains to yield anti-N specificity. To examine this, the current study used Fab phage methodology to couple an array of light chains, obtained from cDNA libraries isolated from immunized mice, to single Fd obtained from N61, N92, and 425/2B hybridomas. Interestingly, for the chimeric Fab to retain M or N specificity, the new light chains needed to belong to the same Vk gene family as the light chain from the parental, hybridoma-derived mAb. In some cases the new light chains modified the Fab affinity and fine specificity. For example, library-derived light chains coupled with the N92 Fd yielded chimeric Fab with increased affinity. In particular, the affinity of these univalent chimeric Fab for the N Ag was equivalent to that of the bivalent parental IgG mAb. Taken together, these results demonstrate that particular structures formed by the light chain V region are required to cooperate with a particular heavy chain V region to create a functional binding site for these glycopeptide Ags. They also demonstrate a lack of heavy chain promiscuity in the formation of murine anti-M and anti-N Abs.

The structural basis of MHC control of collagen-induced arthritis; binding of the immunodominant type II collagen 256-270 glycopeptide to H-2Aq and H-2Ap molecules

The Aq major histocompatibility complex (MHC) class II molecule is associated with susceptibility to murine collagen-induced arthritis (CIA), whereas the closely related H-2Ap molecule is not. To understand the molecular basis for this difference, we have analyzed the ability of H-2Aq and H-2Ap molecules (referred to as Aq and Ap) to bind and present collagen type II (CII)-derived glycosylated and non-glycosylated peptides. T cell clones specific for the immunodominant CII 256-270 peptide and restricted to both Aq and Ap molecules were identified. When these clones were incubated with CII protein and either Aq- or Ap-expressing antigen-presenting cells (APC), only Aq-expressing APC were able to induce stimulation. With the use of A(beta) transgenic mice this could be shown to be solely dependent on the MHC class II molecule itself and to be independent of other MHC- or non-MHC genes. Peptide binding studies were performed using affinity-purified MHC class II molecules. The CII 256-270 peptide bound with lower affinity to the Ap molecule than to the Aq molecule. Using a set of alanine-substituted CII 256-270 peptides, MHC class II and T cell receptor (TCR) contacts were identified. Mainly the side chains of isoleucine 260 and phenylalanine 263 were used for binding both the Aq and Ap molecule, i.e. the peptide was orientated similarly in the binding clefts. The major TCR contact amino acids were lysine 264, which can be posttranslationally modified, and glutamic acid 266, which is the only amino acid in the heterologous peptide which differs from the mouse sequence. Glycosylation at positions 264 and 270 of the CII 256-270 peptide did not change the anchor positions used for binding to the Aq or Ap molecules. The autologous form of the peptide (with aspartic acid at position 266) bound with lower affinity to the Aq molecule as compared with the heterologous peptide. The variable affinity displayed by the immunodominant CII 256-270 peptide for different MHC class II molecules, the identification of MHC and TCR contacts and the significance of glycosylation of these have important implications for the understanding of the molecular basis for inherited MHC class II-associated susceptibility to CIA and in turn, for development of novel treatment strategies in this disease.

Synthetic methods of glycopeptide assembly, and biological analysis of glycopeptide products

The technology of glycopeptide synthesis has recently developed into a fully mature science capable of creating diverse glycopeptides of biological interest, even in combinatorial displays. This has allowed biochemists to investigate substrate specificity in the biosynthetic processing and immunology of various protein glycoforms. The construction of all the mucin core structures and a variety of cancer-related glycopeptides has facilitated detailed analysis of the interaction between MHC-bound glycopeptides and T cell receptors. Novel dendritic neoglycopeptide ligands have been shown to demonstrate high affinity for carbohydrate receptors and these interactions are highly dendrimer specific. Large complex N-linked oligosaccharides have been introduced into glycopeptides using synthetic or chemoenzymatic procedures, both methods affording pure glycopeptides corresponding to a single glycoform in preparative quantities. The improved availability of glycosyl transferases has led to increased use of chemoenzymatic synthesis. Chemical ligation has been introduced as a method of attaching glycans to peptide templates. Combinatorial synthesis and the analysis of resin-bound glycopeptide libraries have been successfully carried out by applying the ladder synthesis principle. Direct quantitative glycosylation of peptide templates on solid phase has paved the way for the synthesis of templated glycopeptide mixtures as libraries of libraries.

Immunogenicity of bacterial carbohydrates: cholera toxin modulates the immune response against dextran B512

Native dextran B512 is a T-cell-independent (TI) antigen. By conjugating low molecular weight (MW) dextran to protein, a T-cell-dependent (TD) response against dextran can be obtained. We have previously reported the effects of native dextran and two different protein-dextran conjugates on the immune system. While one type of conjugate induced an optimal TD response, the other conjugate ('suboptimal') evoked a response more similar to that induced by native dextran, i.e. with little immunoglobulin class switch and with a secondary response of similar magnitude to the primary response. In order to investigate if it was possible to augment the anti-dextran response we examined the effects of cholera toxin (CT) in our dextran model system. CT is a potent mucosal, as well as systemic, adjuvant with effects on T cells, B cells and antigen-presenting cells. We show that CT is a very efficient adjuvant for both the TD and TI forms of dextran. A major increase in IgM and IgG anti-dextran antibody production was detected after administration of CT together with the conjugates compared with a conventional alum adjuvant. The effect was most pronounced for the suboptimal TD conjugate. CT was also able partially to abrogate the unresponsiveness to dextran in the TI type 2 (TI-2) non-responder strain CBA/N. CT was also found to be a very potent adjuvant for native dextran, secondary IgM levels were enhanced eightfold by the co-administration of CT. Furthermore CTB-Dx, which is a conjugate of the non-toxic part of CT and low MW, non-immunogenic dextran, elicited an anti-dextran response in nude mice. Collectively, our data show that it is possible to improve the immunogenicity of both TD and TI forms of a carbohydrate by co-administration of CT. This is indicative of two components of the adjuvant effect, one could enhance antigen presentation and costimulation of T cells and the other could have a direct stimulatory effect on B cells.