Dendritic cells: In the forefront of immunopathogenesis and vaccine development – A review

Dendritic cellls (DCs) comprise an essential component of the immune system. These cells, as antigen presenting cells (APCs) to na?ve T cells, are crucial in the initiation of antigen specific immune responses. In the past years, several DC subsets have been identified in different organs which exert different effects in order to elicit adaptive immune responses. Thus, identification of such DC subsets has led to a better understanding of their distribution and function in the body. In this review, several key properties of the immunobiology, immunopathogenesis and vaccine strategies using DCs will be discussed.     

Analysis of the toxicity of gold nano particles on the immune system: effect on dendritic cell functions

The effect of manufactured gold nanoparticles (NPs) on the immune system was analysed through their ability to perturb the functions of dendritic cells (DCs), a major actor of both innate and acquired immune responses. For this purpose, DCs were produced in culture from mouse bone marrow progenitors. The analysis of the viability of the cells after their incubation in the presence of gold NPs shows that these NPs are not cytotoxics even at high concentration. Furthermore, the phenotype of the DC is unchanged after the addition of NPs, indicating that there is no activation of the DC. However, the analysis of the cells at the intracellular level reveals important amounts of gold NPs amassing in endocytic compartments. Furthermore, the secretion of cytokines is significantly modified after such internalisation indicating a potential perturbation of the immune response.     

Identification of proteases employed by dendritic cells in the processing of protein purified derivative (PPD)

Dendritic cells (DC) are known to present exogenous protein Ag effectively to T cells. In this study we sought to identify the proteases that DC employ during antigen processing. The murine epidermal-derived DC line Xs52, when pulsed with PPD, optimally activated the PPD-reactive Th1 clone LNC.2F1 as well as the Th2 clone LNC.4k1, and this activation was completely blocked by chloroquine pretreatment. These results validate the capacity of XS52 DC to digest PPD into immunogenic peptides inducing antigen specific T cell immune responses. XS52 DC, as well as splenic DC and DCs derived from bone marrow degraded standard substrates for cathepsins B, C, D/E, H, J, and L, tryptase, and chymases, indicating that DC express a variety of protease activities. Treatment of XS52 DC with pepstatin A, an inhibitor of aspartic acid proteases, completely abrogated their capacity to present native PPD, but not trypsin-digested PPD fragments to Th1 and Th2 cell clones. Pepstatin A also inhibited cathepsin D/E activity selectively among the XS52 DC-associated protease activities. On the other hand, inhibitors of serine proteases (dichloroisocoumarin, DCI) or of cystein proteases (E-64) did not impair XS52 DC presentation of PPD, nor did they inhibit cathepsin D/E activity. Finally, all tested DC populations (XS52 DC, splenic DC, and bone marrow-derived DC) constitutively expressed cathepsin D mRNA. These results suggest that DC primarily employ cathepsin D (and perhaps E) to digest PPD into antigenic peptides.     

Design of Gold Nanoparticles in Dendritic Cell‐Based Vaccines

The design of effective cancer vaccines must be able to activate dendritic cells (DCs) of the innate immune system in order to induce immunity to pathogens and cancer. DCs patrol the body and once they encounter antigens, they orchestrate a complex mechanism of events and signals that can alert the adaptive immune system to action. However, DC‐based vaccines remain a challenge in part because the source and quality of antigens, the DC targeting molecule, type of adjuvant, and delivery vehicle must be optimized to induce a robust immune response. Gold nanoparticles (AuNPs) have now entered clinical trials as carriers due to their ease of functionalization with antigens, adjuvants, and targeting molecules. This progress report discusses how AuNPs can influence DC activation and maturation, as well as their potential impact on T helper (Th) differentiation. Ultimately, successful AuNP‐based DC vaccines are able to induce phagocytosis, activation/maturation, migration, T cell costimulation, and cytokine secretion, which is named AuNP‐induced DC tuning (AuNP‐DC tuning). Although at its infancy, understanding the processes of AuNP‐DC tuning will give a better understanding of how best to engineer AuNPs and will redefine the next generation of DC‐based vaccines.     

CTLA-4 blockade during dendritic cell based booster vaccination influences dendritic cell survival and CTL expansion

Dendritic cells (DCs) are potent antigen-presenting cells and critical for the priming of CD8+ T cells. Therefore the use of these cells as adjuvant cells has been tested in a large number of experimental and clinical vaccination studies, in particular cancer vaccine studies. A number of protocols are emerging that combine vaccination with CTL expanding strategies, such as e.g. blockade of CTLA-4 signalling. On the other hand, the lifespan and in vivo survival of therapeutic DCs have only been addressed in a few studies, although this is of importance for the kinetics of CTL induction during vaccination. We have previously reported that DCs loaded with specific antigens are eliminated by antigen specific CTLs in vivo and that this elimination affects the potential for in vivo CTL generation. We now show that CTLA-4 blockade increases the number of DC vaccine induced LCMV gp33 specific CTLs and the lysis of relevant in vivo targets. However, the CTLA-4 blockage dependent expansion of CTLs also affect DC survival during booster DC injections and our data suggest that during a booster DC vaccine, the largest increase in CTL levels is already obtained during the first vaccination.     

Cross-reactivity of T lymphocytes in infection and autoimmunity

T helper (Th) lymphocytes mediate critical effector and regulatory functions in infectious, allergic, or autoimmune diseases. Th cells possess clonal receptors that recognize antigenic peptides that are complexed with self-molecules of the major histocompatibility complex (MHC) on the surface of antigen presenting cells. An organism's repertoire of T cell receptors must be broad enough to recognize any possible microbial antigen. At the same time, tissue destruction resulting from the attack of autoreactive T lymphocytes that recognize self-peptides must be avoided. It was therefore believed that the immune system could distinguish between self and non-self antigens. This hypothesis was supported by several lines of evidence, including the seemingly exquisite specificity of immune responses. What, then, triggers autoaggressive attacks by the immune system? Clinical and epidemiological observations strongly suggest a link between infection and autoimmunity. A popular hypothesis considers autoimmunity as a side effect of antimicrobial immune responses. Cross-reactive T cells, capable of recognizing both microbial and self-peptides, have been prime suspects as instigators of autoimmunity ever since computerized data base searches revealed astonishing sequence homologies between microbial and self-peptides. Here we review recent data that show a previously unexpected degeneracy of antigen recognition by T cells. It has become clear that each individual T cell receptor can recognize a large number of different ligands. Furthermore, structural criteria rather than sequence homology dictate the antigen recognition process. Thus, the idea that cross-reactivity per se would cause autoimmune disease is most likely too simple. Instead, a variety of different molecularmechanisms dictate the immunological outcome of ligand recognition by T cells.     

Restricted dislocation motion in crystals of colloidal dimer particles

At high area fractions, monolayers of colloidal dimer particles form a degenerate crystal (DC) structure in which the particle lobes occupy triangular lattice sites while the particles are oriented randomly along any of the three lattice directions. We report that dislocation glide in DCs is blocked by certain particle orientations. The mean number of lattice constants between such obstacles is Z[over](exp)=4.6+/-0.2 in experimentally observed DC grains and Z[over](sim)=6.18+/-0.01 in simulated monocrystalline DCs. Dislocation propagation beyond these obstacles is observed to proceed through dislocation reactions. We estimate that the energetic cost of dislocation pair separation via such reactions in an otherwise defect free DC grows linearly with final separation, hinting that the material properties of DCs may be dramatically different from those of 2-D crystals of spheres.     

A novel method to identify and characterise peptide mimotopes of heat shock protein 70-associated antigens

The heat shock protein, Hsp70, has been shown to play an important role in tumour immunity. Vaccination with Hsp70-peptide complexes (Hsp70-PCs), isolated from autologous tumour cells, can induce protective immune responses. We have developed a novel method to identify synthetic mimic peptides of Hsp70-PCs and to test their ability to activate T-cells. Peptides (referred to as "recognisers") that bind to Hsp70-PCs from the human breast carcinoma cell line, MDA-MB-231, were identified by bio-panning a random peptide M13 phage display library. Synthetic recogniser peptides were subsequently used as bait in a reverse bio-panning experiment to identify potential Hsp70-PC mimic peptides. The ability of the recogniser and mimic peptides to prime human lymphocyte responses against tumour cell antigens was tested by stimulating lymphocytes with autologous peptide-loaded monocyte-derived dendritic cells (DCs). Priming and subsequent stimulation with either the recogniser or mimic peptide resulted in interferon-γ (IFN-γ) secretion by the lymphocytes. Furthermore, DCs loaded with Hsp70, Hsp70-PC or the recogniser or the mimic peptide primed the lymphocytes to respond to soluble extracts from breast cells. These results highlight the potential application of synthetic peptide-mimics of Hsp70-PCs, as modulators of the immune response against tumours.     

Tumor-infiltrating effector cells of alpha-galactosylceramide-induced antitumor immunity in metastatic liver tumor

BACKGROUND: alpha-Galactosylceramide (alpha-GalCer) can be presented by CD1d molecules of antigen-presenting cells, and is known to induce a potent NKT cell-dependent cytotoxic response against tumor cells. However, the main effector cells in alpha-GalCer-induced antitumor immunity are still controversial. METHODS: In order to elucidate the cell phenotype that plays the most important role in alpha-GalCer-induced antitumor immunity, we purified and analyzed tumor-infiltrating leukocytes (TILs) from liver metastatic nodules of a colon cancer cell line (Colon26), comparing alpha-GalCer- and control vehicle-treated mice. Flow cytometry was performed to analyze cell phenotype in TILs and IFN-gamma ELISA was performed to detect antigen-specific immune response. RESULTS: Flow cytometry analysis showed a significantly higher infiltration of NK cells (DX5+, T cell receptor alphabeta (TCR)-) into tumors in alpha-GalCer-treated mice compared to vehicle-treated mice. The DX5+TCR+ cell population was not significantly different between these two groups, indicating that these cells were not the main effector cells. Interestingly, the CD8+ T cell population was increased in TILs of alpha-GalCer-treated mice, and the activation level of these cells based on CD69 expression was higher than that in vehicle-treated mice. Moreover, the number of tumor-infiltrating dendritic cells (DCs) was increased in alpha-GalCer-treated mice. IFN-gamma ELISA showed stronger antigen-specific response in TILs from alpha-GalCer-treated mice compared to those from vehicle-treated mice, although the difference between these two groups was not significant. CONCLUSIONS: In alpha-GalCer-induced antitumor immunity, NK cells seem to be some of the main effector cells and both CD8+ T cells and DCs, which are related to acquired immunity, might also play important roles in this antitumor immune response. These results suggest that alpha-GalCer has a multifunctional role in modulation of the immune response.     

The effect of CpG-ODN on antigen presenting cells of the foal

Background  

Cytosine-phosphate-guanosine oligodeoxynucleotide (CpG-ODN) has been used successfully to induce immune responses against viral and intracellular organisms in mammals. The main objective of this study was to test the effect of CpG-ODN on antigen presenting cells of young foals.     

Synthetic and biogenic magnetite nanoparticles for tracking of stem cells and dendritic cells

Accurate delivery of cells to target organs is critical for success of cell-based therapies with stem cells or immune cells such as antigen-presenting dendritic cells (DC). Labeling with contrast agents before implantation provides a powerful means for monitoring cellular migration using magnetic resonance imaging (MRI). In this study, we investigated the uptake of fully synthesized or bacterial magnetic nanoparticles (MNPs) into hematopoietic Flt3⁺ stem cells and DC from mouse bone marrow. We show that (i) uptake of both synthetic and biogenic nanoparticles into cells endow magnetic activity and (ii) low numbers of MNP-loaded cells are readily detected by MRI.     

Thymic Selection of T Cells as Diffusion with Intermittent Traps

T cells orchestrate adaptive immune responses by recognizing short peptides derived from pathogens, and by distinguishing them from self-peptides. To ensure the latter, immature T cells (thymocytes) diffuse within the thymus gland, where they encounter an ensemble of self-peptides presented on (immobile) antigen presenting cells. Potentially autoimmune T cells are eliminated if the thymocyte binds sufficiently strongly with any such antigen presenting cell. We model thymic selection of T cells as a random walker diffusing in a field of immobile traps that intermittently turn “on” and “off”. The escape probability of potentially autoimmune T cells is equivalent to the survival probability of such a random walker. In this paper we describe the survival probability of a random walker on a d-dimensional cubic lattice with randomly placed immobile intermittent traps, and relate it to the result of a well-studied problem where traps are always “on”. Additionally, when switching between the trap states is slow, we find a peculiar caging effect for the survival probability.     

Fluorescent Probe ABM and Estimation of Immune State in Patients with Different Pathologies (Review Article)

The fluorescent probe ABM (3-aminobenzanthrone derivative) one of the fluorescent probes synthesized in Riga Technical University proved to be an excellent, independent model for studying cell membranes. In our work we have investigated the possibility of using the fluorescent probe ABM for detection of immune state in patients with different pathologies. There is a strong correlation among all studied ABM spectral parameters, immunological characteristics, clinical and laboratory investigations of the all observed patients groups. The obtained results suggest that ABM spectral parameters in cell suspension reflect the alterations of the cellular mechanisms of immunity. Therefore fluorescent method could be used as preliminary screening test in immune diagnostics instead of more expensive, time consuming methods (subset detection, radioisotope method etc.) used as routine in clinics. Spectral parameters of ABM reflect a wide range of interrelated (interdependent) characteristics of cells (physico-chemical state and microviscosity of membrane, proliferating and lipid metabolic activity of cells, distribution of cells among subsets). The observed change of the studied parameters reflects alterations of the cellular mechanisms of immunity which is a main focus for its application as preliminary screening test in immune diagnostics. The fluorescence based method is sensitive, less expensive and time consuming, technically simple and convenient.     

Sonochemiluminescence observation and acoustic detection of cavitation induced by pulsed HIFU at a tissue–fluid interface

The aim of this study is to investigate the mechanism of the erosion process induced by 1.2 MHz pulsed high-intensity focused ultrasound (pulsed HIFU). By using Sonochemiluminescence (SCL) photograph, the initiation and maintenance of active cavitation were observed. In order to understand the role of both inertial cavitation and stable cavitation, a passive cavitation detection (PCD) transducer was used. Since the exposure variables of HIFU are important in the controlled ultrasound tissue erosion, the influence of pulse length (PL) and duty cycle (DC, T_on:T_off) has been examined. The results of tissue hole, SCL observation and acoustic detection revealed that the erosion was highly efficient for shorter PL. For higher DCs, the area of SCL increased with increasing PL. For lower DCs, the area of SCL increased with increasing PL from 10 to 20 μs and then kept constant. For all PLs, the intensity of SCL decreased with lower DC. For all DCs, the intensity of SCL per unit area (the ratio of SCL intensity to SCL area) also decreased with increasing PL from 10 to 80 μs, which suggested that the higher the intensity of SCL is, the higher the efficiency of tissue erosion is. At DC of 1:10, the position of the maximum pixel in SCL pictures was distant from the tissue–fluid interface with the increasing PL because of shielding effect. By the comparison of inertial cavitation dose (ICD) and the stable cavitation dose (SCD), the mechanisms associated with inertial cavitation are very likely to be the key factor of the erosion process.     

The Influence of T Cell Development on Pathogen Specificity and Autoreactivity

T cells orchestrate adaptive immune responses upon activation. T cell activation requires sufficiently strong binding of T cell receptors on their surface to short peptides derived from foreign proteins bound to protein products of the major histocompatibility (MHC) gene products, which are displayed on the surface of antigen presenting cells. T?cells can also interact with peptide-MHC complexes, where the peptide is derived from host (self) proteins. A diverse repertoire of relatively self-tolerant T cell receptors is selected in the thymus. We study a model, computationally and analytically, to describe how thymic selection shapes the repertoire of T cell receptors, such that T cell receptor recognition of pathogenic peptides is both specific and degenerate. We also discuss the escape probability of autoimmune T cells from the thymus.     

An accurate analysis for two-mode interferometer based Mach-Zehnder interferometers interleaver

By using a more accurate analysis, we investigate the effect of the mode coupling and radiation loss of a two-mode interferometer (TMI) which is employed in the design of Mach-Zehnder interferometer interleaver by considering different branching angles and index contrasts. Based on our study, we find that the transmission characteristics of a TMI in the interleaver design cannot always be treated as a simple zero gap directional coupler (DC), called pure model. Under certain conditions, its characteristics should be treated as a zero gap DC combined with two variable gap DCs, and correspondently called integrated model. The conditions under which a TMI is treated as pure model or integrated model are defined in terms of branching angle and index contrast. Our findings are confirmed with the experimental results.     

Dynamic nucleation of domain-chains in magnetic nanotracks

Most of the reported observations are about the dynamic properties of individual domain-walls in magnetic nanowires,but the properties of multiple stripe-domains have rarely been investigated.Here,we demonstrate a simple but efficient scenario for multiple domains injection in magnetic nanowires.The domain-chains(DCs),a cluster of multiple domains,can be dynamically generated with tunable static properties.It is found that the number of domains in a single DC can be dynamically adjusted by varying the frequency of microwave field(MF)and the period of spin-polarized current(SPC)intensity.The static properties of the DCs,i.e.,its length,spacing,and period between neighboring DCs,can be dynamically controlled by regulating the frequency of MF and the intensity of SPC.We have also discussed the possibility of using domain-chains as information carries,which provides a meaningful approach for flexible multi-bit information storage applications.     

Biocompatible Lipid‐Coated Persistent Luminescent Nanoparticles for In Vivo Imaging of Dendritic Cell Migration

Dendritic cell (DC)‐based vaccines for immunotherapy have already achieved promising results in the last decade. To further improve current treatment protocols and enhance the therapeutic outcome, noninvasive in vivo tracking of DCs remains of crucial importance. Persistent luminescent nanoparticles (PLNPs) are inorganic materials which show an afterglow for hours after the optical excitation has ceased. If the afterglow is in the near‐infrared, the emission of injected particles can be tracked in vivo. However, stability and toxicity issues limit the use of bare PLNPs for biological applications. Therefore, appropriate surface functionalization is needed to improve their biocompatibility. In this study, it is demonstrated that near‐infrared light emitting LiGa₅O₈:Cr³⁺ nanoparticles can be functionalized with a biocompatible lipid coating which provides them with outstanding stability in biological media. In vitro experiments show efficient uptake, absence of cytotoxicity even at very high particle concentrations, and no adverse effects on the maturation potential of DCs. DCs labeled with lipid‐coated LiGa₅O₈:Cr³⁺ nanoparticles injected in mice can be imaged over days, confirming efficient in vivo migration to the popliteal lymph node. Together the results show that lipid coated LiGa₅O₈:Cr³⁺ nanoparticles possess excellent possibilities for further use in research and development of DC based vaccines.     

Detection and recognition of cancer cells in vivo

A fundamentally new recognition method of bio-objects (e.g., cancer cells as the most important case of them) that escape the immune system supervision control is suggested. It is proposed to use a unified complex consisting of several molecular groups (e.g., antibodies or their fragments) bound with each other. Binding targets are localized on the surface of this bio-object. The choice of the targets is determined by antigen profiling being expressed on the surface of these bio-objects. The recognition efficiency appears to be notably higher than in a situation when molecular groups do not form a unified complex and act separately.     

<Emphasis Type="Italic">Ex vivo</Emphasis> development,expansion and <Emphasis Type="Italic">in vivo</Emphasis>analysis of a novel lineage of dendritic cells from hematopoietic stem cells

Dendritic cells (DCs) play a key role in innate and adaptive immunity but the access to sufficient amount of DCs for basic and translational research has been limited.