Tsvetelina Batsalova

Breaking T Cell Tolerance Against Self Type II Collagen in HLA-DR4-Transgenic Mice and Development of Autoimmune Arthritis

OBJECTIVE To establish a new animal model in DRB1*0401 (DR4)-transgenic mice in which T cell tolerance to self type II collagen (CII) can be broken and allow for the development of autoimmune arthritis, to investigate the role of posttranslational modifications of the CII(259-273) epitope in the induction and breaking of tolerance of DR4-restricted T cells, and to characterize DR4-restricted T cell recognition of the immunodominant CII(259-273) epitope. METHODS DR4-transgenic mice expressing either the entire human CII protein (HuCII) or only the immunodominant T cell epitope of heterologous CII (MMC) in joint cartilage were established on different genetic backgrounds, and susceptibility to collagen-induced arthritis (CIA) was tested. RESULTS HuCII mice displayed stronger T cell tolerance to heterologous CII than did MMC mice. On the B10 background, arthritis developed only in MMC mice with a defective oxidative burst. However, MMC mice on the C3H background were susceptible to arthritis also with a functional oxidative burst. Significant recall responses in tolerized mice were detected only against the nonglycosylated CII(259-273) epitope. Recognition of the CII(259-273) epitope was heterogeneous, but the majority of T cells in DR4 mice specifically recognized the nonglycosylated side chain of lysine at position 264. CONCLUSION It is possible to break tolerance to self CII and induce arthritis in DR4 mice. However, arthritis susceptibility is tightly controlled by the genetic background and by the source of the transgenic element for expressing the heterologous CII peptide as a self CII protein in the joint. In contrast to CIA in A(q)-expressing mice, the nonglycosylated CII(259-273) epitope is clearly immunodominant in both tolerized and nontolerized DR4 mice.

Oxazole-modified glycopeptides that target arthritis-associated class II MHC Aq and DR4 proteins

The glycopeptide CII259-273, a fragment from type II collagen (CII), can induce tolerance in mice susceptible to collagen-induced arthritis (CIA), which is a validated disease model for rheumatoid arthritis (RA). Here, we describe the design and synthesis of a small series of modified CII259-273 glycopeptides with oxazole heterocycles replacing three potentially labile peptide bonds. These glycopeptidomimetics were evaluated for binding to murine CIA-associated A(q) and human RA-associated DR4 class II major histocompatibility complex (MHC) proteins. The oxazole modifications drastically reduced or completely abolished binding to A(q). Two of the glycopeptidomimetics were, however, well tolerated in binding to DR4 and they also induced strong responses by one or two DR4-restricted T-cell hybridomas. This work contributes to the development of an altered glycopeptide for inducing immunological tolerance in CIA, with the long-term goal of developing a therapeutic vaccine for treatment of RA.

Design of Glycopeptides Used to Investigate Class II MHC Binding and T-Cell Responses Associated with Autoimmune Arthritis

The glycopeptide fragment CII259–273 from type II collagen (CII) binds to the murine Aq and human DR4 class II Major Histocompatibility Complex (MHC II) proteins, which are associated with development of murine collagen-induced arthritis (CIA) and rheumatoid arthritis (RA), respectively. It has been shown that CII259–273 can be used in therapeutic vaccination of CIA. This glycopeptide also elicits responses from T-cells obtained from RA patients, which indicates that it has an important role in RA as well. We now present a methodology for studies of (glyco)peptide-receptor interactions based on a combination of structure-based virtual screening, ligand-based statistical molecular design and biological evaluations. This methodology included the design of a CII259–273 glycopeptide library in which two anchor positions crucial for binding in pockets of Aq and DR4 were varied. Synthesis and biological evaluation of the designed glycopeptides provided novel structure-activity relationship (SAR) understanding of binding to Aq and DR4. Glycopeptides that retained high affinities for these MHC II proteins and induced strong responses in panels of T-cell hybridomas were also identified. An analysis of all the responses revealed groups of glycopeptides with different response patterns that are of high interest for vaccination studies in CIA. Moreover, the SAR understanding obtained in this study provides a platform for the design of second-generation glycopeptides with tuned MHC affinities and T-cell responses.

(E)-Alkene and Ethylene Isosteres Substantially Alter the Hydrogen-Bonding Network in Class II MHC Aq/Glycopeptide Complexes and Affect T-Cell Recognition

The structural basis for antigen presentation by class II major histocompatibility complex (MHC) proteins to CD4(+) T-cells is important for understanding and possibly treating autoimmune diseases. In the work described in this paper, (E)-alkene and ethylene amide-bond isosteres were used to investigate the effect of removing hydrogen-bonding possibilities from the CII259-270 glycopeptide, which is bound by the arthritis-associated murine A(q) class II MHC protein. The isostere-modified glycopeptides showed varying and unexpectedly large losses of A(q) binding that could be linked to the dynamics of the system. Molecular dynamics (MD) simulations revealed that the backbone of CII259-270 and the A(q) protein are able to form up to 11 hydrogen bonds, but fewer than this number are present at any one time. Most of the strong hydrogen-bond interactions were formed by the N-terminal part of the glycopeptide, i.e., in the region where the isosteric replacements were made. The structural dynamics also revealed that hydrogen bonds were strongly coupled to each other; the loss of one hydrogen-bond interaction had a profound effect on the entire hydrogen-bonding network. The A(q) binding data revealed that an ethylene isostere glycopeptide unexpectedly bound more strongly to A(q) than the corresponding (E)-alkene, which is in contrast to the trend observed for the other isosteres. Analysis of the MD trajectories revealed that the complex conformation of this ethylene isostere was structurally different and had an altered molecular interaction pattern compared to the other A(q)/glycopeptide complexes. The introduced amide-bond isosteres also affected the interactions of the glycopeptide/A(q) complexes with T-cell receptors. The dynamic variation of the patterns and strengths of the hydrogen-bond interactions in the class II MHC system is of critical importance for the class II MHC/peptide/TCR signaling system.

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 Aq. 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.

Visualization and phenotyping of proinflammatory antigen-specific T cells during collagen-induced arthritis in a mouse with a fixed collagen type II-specific transgenic T-cell receptor β-chain

IntroductionThe Vβ12-transgenic mouse was previously generated to investigate the role of antigen-specific T cells in collagen-induced arthritis (CIA), an animal model for rheumatoid arthritis. This mouse expresses a transgenic collagen type II (CII)-specific T-cell receptor (TCR) β-chain and consequently displays an increased immunity to CII and increased susceptibility to CIA. However, while the transgenic Vβ12 chain recombines with endogenous α-chains, the frequency and distribution of CII-specific T cells in the Vβ12-transgenic mouse has not been determined. The aim of the present report was to establish a system enabling identification of CII-specific T cells in the Vβ12-transgenic mouse in order to determine to what extent the transgenic expression of the CII-specific β-chain would skew the response towards the immunodominant galactosylated T-cell epitope and to use this system to monitor these cells throughout development of CIA.MethodsWe have generated and thoroughly characterized a clonotypic antibody, which recognizes a TCR specific for the galactosylated CII(260-270) peptide in the Vβ12-transgenic mouse. Hereby, CII-specific T cells could be quantified and followed throughout development of CIA, and their phenotype was determined by combinatorial analysis with the early activation marker CD154 (CD40L) and production of cytokines.ResultsThe Vβ12-transgenic mouse expresses several related but distinct T-cell clones specific for the galactosylated CII peptide. The clonotypic antibody could specifically recognize the majority (80%) of these. Clonotypic T cells occurred at low levels in the naïve mouse, but rapidly expanded to around 4% of the CD4+ T cells, whereupon the frequency declined with developing disease. Analysis of the cytokine profile revealed an early Th1-biased response in the draining lymph nodes that would shift to also include Th17 around the onset of arthritis. Data showed that Th1 and Th17 constitute a minority among the CII-specific population, however, indicating that additional subpopulations of antigen-specific T cells regulate the development of CIA.ConclusionsThe established system enables the detection and detailed phenotyping of T cells specific for the galactosylated CII peptide and constitutes a powerful tool for analysis of the importance of these cells and their effector functions throughout the different phases of arthritis.

Comparative analysis of collagen type II-specific immune responses during development of collagen-induced arthritis in two B10 mouse strains

IntroductionImmune responses against collagen type II (CII) are crucial for the development of collagen-induced arthritis (CIA). The aim of the present study was to evaluate and compare the CII-directed T cell and antibody specificity at different time points in the course of CIA using two mouse strains on the B10 genetic background - B10.Q, expressing Aq MHC class II molecules, and B10.DR4.Ncf1*/*, expressing human rheumatoid arthritis-associated MHC II DR4 molecules (DRA*0101/DRB*0401).MethodsB10.Q and B10.DR4.Ncf1*/* mice were immunized with CII emulsified in adjuvant and development of CIA was assessed. T cells from draining lymph nodes were restimulated in vitro with CII peptides and interferon-gamma (IFN-γ) levels in culture supernatants were evaluated by ELISA. CII-specific antibody levels in serum samples were measured by ELISA.ResultsAt four different CIA time points we analyzed T cell specificity to the immunodominant CII epitope 259-273 (CII259-273) and several posttranslationally modified forms of CII259-273 as well as antibody responses to three B cell immunodominant epitopes on CII (C1, U1, J1). Our data show that CII-specific T and B cell responses increase dramatically after disease onset in both strains and are sustained during the disease course. Concerning anti-CII antibody fine specificity, during all investigated stages of CIA the B10.Q mice responded predominantly to the C1 epitope, whereas the B10.DR4.Ncf1*/* mice also recognized the U1 epitope. In the established disease phase, T cell reactivity toward the galactosylated CII259-273 peptide was similar between the DR4- and the Aq-expressing strains whereas the response to the non-modified CII peptide was dramatically enhanced in the DR4 mice compared with the B10.Q. In addition, we show that the difference in the transgenic DR4-restricted T cell specificity to CII259-273 is not dependent on the degree of glycosylation of the collagen used for immunization.ConclusionsThe present study provides important evaluation of CII-specific immune responses at different phases during CIA development as well as a comparative analysis between two CIA mouse models. We indicate significant differences in CII T cell and antibody specificities between the two strains and highlight a need for improved humanized B10.DR4 mouse model for rheumatoid arthritis.

Ragweed-allergic subjects have decreased serum levels of chemokines CCL2, CCL3, CCL4 and CCL5 out of the pollen season

CC-chemokines are important mediators of the allergic responses and regulate the cell trafficking. The aim of this study was to examine the serum levels of CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β and CCL5/RANTES, and to determine whether there are differences between ragweed-allergic subjects and healthy individuals out of the pollen season. Peripheral blood samples were collected from 24 subjects allergic to ragweed pollen and 12 healthy controls. Serum concentrations of chemokines/cytokines were measured by an enzyme-linked immunosorbent assay. We observed significantly decreased concentrations of CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β and CCL5/RANTES in the sera of ragweed-allergic patients compared to the healthy individuals (32.2 vs. 106.4 pg/ml, 89.5 vs. 135.7 pg/ml, 63.4 vs. 119.2 pg/ml and 11.2 vs. 18.1 ng/ml, respectively, p < 0.01). In contrast to the CC-chemokines, the serum levels of IL-8/CXCL8 showed a significant increase (p < 0.05) in the allergic group compared to the non-allergic subjects. Interleukin 4 levels were similar in both groups. In the sera of allergic patients, we have also detected significantly elevated levels of ragweed-specific IgE and IgG. However, decreased serum concentrations of the four CC-chemokines and elevated levels of IL-8/CXCL8 can be used as biomarkers for more accurate evaluation of the allergic status of patients with pollen allergy out of the season, to study the mechanisms for activation/inhibition of the subclinical allergic responses and for development of therapeutic strategies.

Outer membrane efflux protein (OMEP) is a suitable molecular marker for resolving the phylogeny and taxonomic status of closely related cyanobacteria: OMEP as a phylogenetic marker

Taxonomy of Cyanobacteria, the oldest phototrophic prokaryotes, is problematic for many years due to their simple morphology, high variability and adaptability to diverse ecological niches. After introduction of the polyphasic approach, which is based on the combination of several criteria (molecular sequencing, morphological and ecological), the whole classification system of these organisms is subject to reorganization. The aim of this study was to evaluate whether the outer membrane efflux protein (OMEP) sequences can be used as a molecular marker for resolving the phylogeny and taxonomic status of closely related cyanobacteria. We have performed phylogenetic analyses based on the amino acid sequences of the OMEP and the DNA sequences of the 16S rRNA gene from 86 cyanobacterial species/strains with completely sequenced genomes. Phylogenetic trees based on the OMEP showed that most of the cyanobacterial species/strains belonging to different genera are clustered in separate clades supported by high bootstrap values. Comparing the OMEP trees with the 16S rDNA tree clearly showed that the OMEP is more suitable marker in resolving phylogenetic relationships within Cyanobacteria at generic and species level.

In Vitro Cytotoxicity and Antioxidative Potential of Nostoc Microscopicum (Nostocales, Cyanobacteria)

Many cyanobacterial species (cyanoprokaryotes, blue-green algae) are potent producers of various secondary metabolites with low molecular weight and diverse biological activities (antitumor, antimycotic, antiviral, antimicrobial, immunomodulatory, enzyme inhibition, cytotoxic activity). They have the potential to serve as convenient source of active substances for new medications and other commercial products. Therefore, cyanobacteria have become an object of intense scientific interest. New findings have shown that different cyanoprokaryotic species produce compounds with antioxidant activity. Also, there are reports for successful clinical trials using antitumor agents that contain active substances isolated from these organisms. On the other hand, it is well known that certain cyanobacteria produce toxins that could harm plants, animals and humans. Some cyanotoxins induce severe injuries even by contact with polluted water while washing or swimming. Hence, cyanotoxins production must be analyzed for all widely distributed cyanoprokaryotic species as well as those with potential application in medical practice. Certain species of the genus Nostoc are well known producers of substances with antitumor, enzyme inhibition, immunomodulatory, antioxidant or cytotoxic activities. However, little is known about the species Nostoc microscopicum. Therefore, the aim of the present study was to evaluate the antioxidant activity and potential cytotoxic effects of Nostoc microscopicum using extracts derived with different solvents. We show a moderate antioxidant activity of different Nostoc microscopicum extracts and prominent cytotoxic activity against several human cell lines (HeLa, FL, A549). Our results determine Nostoc microscopicum as interesting source of active compounds for pharmacology and biotechnology. In addition, this report presents for the first time an evidence for saxitoxins and microcystins production by Nostoc microscopicum and highlights the toxicological importance of this cyanobacterial species.