Antigen recognition by H-2-restricted T cells. I. Cell-free antigen processing

MHC heterozygosity limits T cell receptor variability in CD4 T cells

αβ T cell receptor (TCR) V(D)J genes code for billions of TCR combinations. However, only some appear on peripheral T cells in any individual because, to mature, thymocytes must react with low affinity but not high affinity with thymus expressed major histocompatibility (MHC)/peptides. MHC proteins are very polymorphic. Different alleles bind different peptides. Therefore, any individual might express many different MHC alleles to ensure that some peptides from an invader are bound to MHC and activate T cells. However, most individuals express limited numbers of MHC alleles. To explore this, we compared the TCR repertoires of naïve CD4 T cells in mice expressing one or two MHC alleles. Unexpectedly, the TCRs in heterozygotes were less diverse that those in the sum of their MHC homozygous relatives. Our results suggest that thymus negative selection cancels out the advantages of increased thymic positive selection in the MHC heterozygotes.

A Plausible Framework Reveals Potential Similarities in the Regulation of Immunity against Some Cancers and Some Infectious Agents: Implications for Prevention and Treatment

Different frameworks, which are currently employed to understand how immune responses are regulated, can account for different observations reported in the classical literature. I have argued that the predominant frameworks, employed over the last two/three decades to analyze the circumstances that determine whether an immune response is generated or this potential is ablated, and that determine the class of immunity an antigen induces, are inconsistent with diverse classical observations. These observations are "paradoxical" within the context of these frameworks and, consequently, tend to be ignored by most contemporary researchers. One such observation is that low and high doses of diverse types of antigen result, respectively, in cell-mediated and IgG antibody responses. I suggest these paradoxes render these frameworks implausible. An alternative framework, The Threshold Hypothesis, accounts for the paradoxical observations. Some frameworks are judged more plausible when found to be valuable in understanding findings in fields beyond their original compass. I explore here how the Threshold Hypothesis, initially based on studies with chemically well-defined and "simple antigens", most often a purified protein, can nevertheless shed light on diverse classical and more recent observations in the fields of immunity against cancer and against infectious agents, thus revealing common, immune mechanisms. Most cancers and some pathogens are best contained by cell-mediated immunity. The success of the Threshold Hypothesis has encouraged me to employ it as a basis for proposing strategies to prevent and to treat cancer and those infectious diseases caused by pathogens best contained by a cell-mediated attack.

DCs at the center of help: Origins and evolution of the three-cell-type hypothesis

Last year was the 10th anniversary of Ralph Steinman's Nobel Prize awarded for his discovery of dendritic cells (DCs), while next year brings the 50th anniversary of that discovery. Current models of anti-viral and anti-tumor immunity rest solidly on Steinman's discovery of DCs, but also rely on two seemingly unrelated phenomena, also reported in the mid-1970s: the discoveries of "help" for cytolytic T cell responses by Cantor and Boyse in 1974 and "cross-priming" by Bevan in 1976. Decades of subsequent work, controversy, and conceptual changes have gradually merged these three discoveries into current models of cell-mediated immunity against viruses and tumors.

Development of a filter device for the prevention of aquatic bacterial disease using a single-chain variable fragment (scFv)-conjugated affinity silk

Infectious disease is one of the most serious problems in the aquaculture industry for ornamental or edible fish. This study attempted to develop a new device for preventing an aquatic bacterial disease, ulcer disease, caused by Aeromonas salmonicida (As), using “affinity silk”. Affinity silk is a silk protein-containing fibroin L-chain (FibL) fused to the single-chain variable fragment (scFv). It can be easily processed into different formats such as fibers, gels, sponges, or films. A transgenic silkworm that could express a cDNA construct containing FibL fused to an scFv derived from a monoclonal antibody (MAb) against As was successfully generated. An enzyme-linked immunosorbent assay was used to detect As by employing 96-well plates coated with scFv-conjugated affinity silk. As could be captured efficiently by glass wool coated with affinity silk in the column. Furthermore, the air-lift water filter equipped with the affinity silk-coated wool could considerably reduce the concentration of As in water and was estimated to have sufficient ability to trap a lethal dose of As. These findings show that the “affinity silk filter” is a potential device for the prophylaxis of aquatic animal diseases.

50 Years of structural immunology

Fifty years ago, the first landmark structures of antibodies heralded the dawn of structural immunology. Momentum then started to build toward understanding how antibodies could recognize the vast universe of potential antigens and how antibody-combining sites could be tailored to engage antigens with high specificity and affinity through recombination of germline genes (V, D, J) and somatic mutation. Equivalent groundbreaking structures in the cellular immune system appeared some 15 to 20 years later and illustrated how processed protein antigens in the form of peptides are presented by MHC molecules to T cell receptors. Structures of antigen receptors in the innate immune system then explained their inherent specificity for particular microbial antigens including lipids, carbohydrates, nucleic acids, small molecules, and specific proteins. These two sides of the immune system act immediately (innate) to particular microbial antigens or evolve (adaptive) to attain high specificity and affinity to a much wider range of antigens. We also include examples of other key receptors in the immune system (cytokine receptors) that regulate immunity and inflammation. Furthermore, these antigen receptors use a limited set of protein folds to accomplish their various immunological roles. The other main players are the antigens themselves. We focus on surface glycoproteins in enveloped viruses including SARS-CoV-2 that enable entry and egress into host cells and are targets for the antibody response. This review covers what we have learned over the past half century about the structural basis of the immune response to microbial pathogens and how that information can be utilized to design vaccines and therapeutics.

T Cell Epitope Predictions

Throughout the body, T cells monitor MHC-bound ligands expressed on the surface of essentially all cell types. MHC ligands that trigger a T cell immune response are referred to as T cell epitopes. Identifying such epitopes enables tracking, phenotyping, and stimulating T cells involved in immune responses in infectious disease, allergy, autoimmunity, transplantation, and cancer. The specific T cell epitopes recognized in an individual are determined by genetic factors such as the MHC molecules the individual expresses, in parallel to the individual's environmental exposure history. The complexity and importance of T cell epitope mapping have motivated the development of computational approaches that predict what T cell epitopes are likely to be recognized in a given individual or in a broader population. Such predictions guide experimental epitope mapping studies and enable computational analysis of the immunogenic potential of a given protein sequence region.

PD-1 Imposes Qualitative Control of Cellular Transcriptomes in Response to T Cell Activation

Targeted blockade of programmed cell death 1 (PD-1), an immune-checkpoint receptor that inhibits T cell activation, provides clinical benefits in various cancers. However, how PD-1 modulates gene expression in T cells remains enigmatic. Here we investigated how PD-1 affects transcriptome changes induced by T cell receptor (TCR) activation. Intriguingly, we identified a huge variance in PD-1 sensitivity among TCR-inducible genes. When we quantified the half maximal effective concentration (EC₅₀) as the relationship between change in gene expression and TCR signal strength, we found that genes associated with survival and proliferation were efficiently expressed upon TCR activation and resistant to PD-1-mediated inhibition. Conversely, genes encoding cytokines and effector molecules were expressed less efficiently and sensitive to PD-1-mediated inhibition. We further demonstrated that transcription factor binding motifs and CpG frequency in the promoter region affect EC₅₀ and thus the PD-1 sensitivity of genes. Our findings explain how PD-1, dependent on the TCR signal strength, calibrates cellular transcriptomes to shape functional properties of T cell populations.

Modular Polymer Antigens To Optimize Immunity

Subunit vaccines can have excellent safety profiles, but their ability to give rise to robust immune responses is often compromised. For glycan-based vaccines, insufficient understanding of B and T cell epitope combinations that yield optimal immune activation hinders optimization. To determine which antigen features promote desired IgG responses, we synthesized epitope-functionalized polymers using ring-opening metathesis polymerization (ROMP) and assessed the effect of B and T cell epitope loading. The most robust responses were induced by polymers with a high valency of B and T cell epitopes. Additionally, IgG responses were greater for polymers with T cell epitopes that are readily liberated upon endosomal processing. Combining these criteria, we used ROMP to generate a nontoxic, polymeric antigen that elicited stronger antibody responses than a comparable protein conjugate. These findings highlight principles for designing synthetic antigens that elicit strong IgG responses against inherently weak immune targets such as glycans.

PD-1 Primarily Targets TCR Signal in the Inhibition of Functional T Cell Activation

Cancer-immunotherapy targeting programmed cell death 1 (PD-1) activates tumor-specific T cells and provides clinical benefits in various cancers. However, the molecular basis of PD-1 function is still enigmatic. Especially, it is unclear which signaling pathway PD-1 primarily targets. Besides, the capacity of PD-1 to inhibit the T cell receptor (TCR)-dependent activation of T cells in the presence of co-stimulation is also controversial. Here we used co-culture systems of T cells and antigen-presenting cells with targeted deletion and overexpression of co-receptors and ligands and examined the inhibitory potency of PD-1 against T cell activation upon TCR stimulation with CD28 and ICOS co-stimulation. As an unambiguous criterion of T cell activation, we used the acquisition of cytokine production capacity, which represents one of the most important functions of T cells. PD-1 inhibited functional T cell activation upon TCR stimulation in the absence as well as in the presence of CD28 co-stimulation, indicating that PD-1 can directly inhibit TCR signal. Notably, CD28 co-stimulation rather attenuated the efficiency of PD-1 in inhibiting TCR-dependent functional T cell activation. In addition, PD-1 inhibited TCR-dependent functional T cell activation with ICOS co-stimulation as efficiently as that with CD28 co-stimulation. Furthermore, we found that the maintenance of antigen-induced follicular helper T (T_FH) cells that required ICOS co-stimulation was persistently restrained by PD-1 in vivo. These findings indicate that PD-1 primarily targets TCR signal in the inhibition of functional T cell activation. Thus, PD-1 functions as the rheostat of T cell activation rather than an inhibitor of a specific stimulatory co-receptor.

Bioengineered Nanocage from HBc Protein for Combination Cancer Immunotherapy

Protein nanocages are promising multifunctional platforms for nanomedicine owing to the ability to decorate their surfaces with multiple functionalities through genetic and/or chemical modification to achieve desired properties for therapeutic and diagnostic purposes. Here, we describe a model antigen (OVA peptide) that was conjugated to the surface of a naturally occurring hepatitis B core protein nanocage (HBc NC) by genetic modification. The engineered OVA-HBc nanocages (OVA-HBc NCs), displaying high density repetitive array of epitopes in a limited space by self-assembling into symmetrical structure, not only can induce bone marrow derived dendritic cells (BMDC) maturation effectively but also can be enriched in the draining lymph nodes. Naïve C57BL/6 mice immunized with OVA-HBc NCs are able to generate significant and specific cytotoxic T lymphocyte (CTL) responses. Moreover, OVA-HBc NCs as a robust nanovaccine can trigger preventive antitumor immunity and significantly delay tumor growth. When combined with a low-dose chemotherapy drug (paclitaxel), OVA-HBc NCs could specifically inhibit progression of an established tumor. Our findings support HBc-based nanocages with modularity and scalability as an attractive nanoplatform for combination cancer immunotherapy.

Development and validation of scFv-conjugated affinity silk protein for specific detection of carcinoembryonic antigen

The production costs for monoclonal antibodies (MAbs) utilized in medical diagnostic kits are inevitably high because the MAbs are mostly obtained from hybridoma cell culture. Here, we report the development and validation of a novel affinity silk protein produced by transgenic silkworm technology as a possible alternative diagnostic tool for cancers. We generated a transgenic silkworm expressing a cDNA construct containing fibroin L-chain fused to a single-chain variable fragment (scFv) derived from a MAb against carcinoembryonic antigen (CEA). The transgenic cocoons were dissolved in aqueous lithium bromide solution, applied to 96-well plates, and analysed by enzyme-linked immunosorbent assay. The scFv-conjugated affinity silk protein specifically recognized CEA as well as the parental MAb. The binding activity was retained after several months of storage in coated plates or concentrated solution. Thus, the scFv-conjugated affinity silk protein provides a potentially useful alternative to conventional MAbs in medical diagnostic kits.

The somatically generated portion of T cell receptor CDR3α contributes to the MHC allele specificity of the T cell receptor

Mature T cells bearing αβ T cell receptors react with foreign antigens bound to alleles of major histocompatibility complex proteins (MHC) that they were exposed to during their development in the thymus, a phenomenon known as positive selection. The structural basis for positive selection has long been debated. Here, using mice expressing one of two different T cell receptor β chains and various MHC alleles, we show that positive selection-induced MHC bias of T cell receptors is affected both by the germline encoded elements of the T cell receptor α and β chain and, surprisingly, dramatically affected by the non germ line encoded portions of CDR3 of the T cell receptor α chain. Thus, in addition to determining specificity for antigen, the non germline encoded elements of T cell receptors may help the proteins cope with the extremely polymorphic nature of major histocompatibility complex products within the species.

Feature selection using a one dimensional naïve Bayes' classifier increases the accuracy of support vector machine classification of CDR3 repertoires

Motivation

Somatic DNA recombination, the hallmark of vertebrate adaptive immunity, has the potential to generate a vast diversity of antigen receptor sequences. How this diversity captures antigen specificity remains incompletely understood. In this study we use high throughput sequencing to compare the global changes in T cell receptor β chain complementarity determining region 3 (CDR3β) sequences following immunization with ovalbumin administered with complete Freund’s adjuvant (CFA) or CFA alone.

Results

The CDR3β sequences were deconstructed into short stretches of overlapping contiguous amino acids. The motifs were ranked according to a one-dimensional Bayesian classifier score comparing their frequency in the repertoires of the two immunization classes. The top ranking motifs were selected and used to create feature vectors which were used to train a support vector machine. The support vector machine achieved high classification scores in a leave-one-out validation test reaching >90% in some cases.

Summary

The study describes a novel two-stage classification strategy combining a one-dimensional Bayesian classifier with a support vector machine. Using this approach we demonstrate that the frequency of a small number of linear motifs three amino acids in length can accurately identify a CD4 T cell response to ovalbumin against a background response to the complex mixture of antigens which characterize Complete Freund’s Adjuvant.

Availability and implementation

The sequence data is available at www.ncbi.nlm.nih.gov/sra/?term¼SRP075893. The Decombinator package is available at github.com/innate2adaptive/Decombinator. The R package e1071 is available at the CRAN repository https://cran.r-project.org/web/packages/e1071/index.html.

Supplementary information

Supplementary data are available at Bioinformatics online.

The elucidation of non-classical MHC class II antigen processing through the study of viral antigens

By convention, CD4+ T cells are activated predominantly by Major Histocompatibility Complex class II-bound peptides derived from extracellular (exogenous) antigens. It has been known for decades that alternative sources of antigen, particularly those synthesized within the antigen-presenting cell, can also supply peptides but the impact on TCD4+ responses, sometimes considerable, has only recently become appreciated. This review focuses on the contributions that studies of viral antigen have made to this shift in perspective, concluding with discussions of relevance to rational vaccine design, autoimmunity and cancer immunotherapy.

Multivalent Antigens for Promoting B and T Cell Activation

Efficacious vaccines require antigens that elicit productive immune system activation. Antigens that afford robust antibody production activate both B and T cells. Elucidating the antigen properties that enhance B-T cell communication is difficult with traditional antigens. We therefore used ring-opening metathesis polymerization to access chemically defined, multivalent antigens containing both B and T cell epitopes to explore how antigen structure impacts B cell and T cell activation and communication. The bifunctional antigens were designed so that the backbone substitution level of each antigenic epitope could be quantified using (19)F NMR. The T cell peptide epitope was appended so that it could be liberated in B cells via the action of the endosomal protease cathepsin D, and this design feature was critical for T cell activation. Antigens with high BCR epitope valency induce greater BCR-mediated internalization and T cell activation than did low valency antigens, and these high-valency polymeric antigens were superior to protein antigens. We anticipate that these findings can guide the design of more effective vaccines.

64Cu antibody-targeting of the T-cell receptor and subsequent internalization enables in vivo tracking of lymphocytes by PET

T cells are key players in inflammation, autoimmune diseases, and immunotherapy. Thus, holistic and noninvasive in vivo characterizations of the temporal distribution and homing dynamics of lymphocytes in mammals are of special interest. Herein, we show that PET-based T-cell labeling facilitates quantitative, highly sensitive, and holistic monitoring of T-cell homing patterns in vivo. We developed a new T-cell receptor (TCR)-specific labeling approach for the intracellular labeling of mouse T cells. We found that continuous TCR plasma membrane turnover and the endocytosis of the specific (64)Cu-monoclonal antibody (mAb)-TCR complex enables a stable labeling of T cells. The TCR-mAb complex was internalized within 24 h, whereas antigen recognition was not impaired. Harmful effects of the label on the viability, DNA-damage and apoptosis-necrosis induction, could be minimized while yielding a high contrast in in vivo PET images. We were able to follow and quantify the specific homing of systemically applied (64)Cu-labeled chicken ovalbumin (cOVA)-TCR transgenic T cells into the pulmonary and perithymic lymph nodes (LNs) of mice with cOVA-induced airway delayed-type hypersensitivity reaction (DTHR) but not into pulmonary and perithymic LNs of naïve control mice or mice diseased from turkey or pheasant OVA-induced DTHR. Our protocol provides consequent advancements in the detection of small accumulations of immune cells in single LNs and specific homing to the sites of inflammation by PET using the internalization of TCR-specific mAbs as a specific label of T cells. Thus, our labeling approach is applicable to other cells with constant membrane receptor turnover.

Antigen processing and presentation to T cells

In this article Howard Grey and Robert Chesnut describe recent insights into the mechanism of antigen presentation and discuss the needfor antigen processing in the stimulation of T cells.

Transcriptional regulation of kinases downstream of the T cell receptor: another immunomodulatory mechanism of glucocorticoids

BACKGROUND

Glucocorticoids affect peripheral immune responses, including modulation of T-cell activation, differentiation, and apoptosis. The quantity and quality of T-cell receptor (TCR)-triggered intracellular signals modulate T-cell function. Thus, glucocorticoids may affect T cells by interfering with the TCR signaling cascade. The purpose of the study was to search for glucocorticoid-modulated kinases downstream of the TCR.

METHODS

Gene modulation in lymphoid cells either treated with glucocorticoids or from glucocorticoid-treated mice was studied using a RNase protection assay, real-time PCR, and western blotting. The sensitivity of genetically modified thymocytes to glucocorticoid-induced apoptosis was studied by performing hypotonic propidium iodide staining and flow cytometry. The Student's t-test was employed for statistical evaluation.

RESULTS

We found that transcription of Itk, a non-receptor tyrosine kinase of the Tec family, was up-regulated in a mouse T-cell hybridoma by the synthetic glucocorticoid dexamethasone. In contrast, dexamethasone down-regulated the expression of Txk, a Tec kinase that functions redundantly with Itk, and Lck, the Src kinase immediately downstream of the TCR. We investigated the expression of Itk, Txk, and Lck in thymocytes and mature lymphocytes following in vitro and in vivo dexamethasone treatment at different time points and doses. Kinase expression was differentially modulated and followed distinct kinetics. Itk was up-regulated in all cell types and conditions tested. Txk was strongly up-regulated in mature lymphocytes but only weakly up-regulated or non-modulated in thymocytes in vitro or in vivo, respectively. Conversely, Lck was down-regulated in thymocytes, but not modulated or up-regulated in mature lymphocytes in the different experimental conditions. This complex behaviour correlates with the presence of both positive and negative glucocorticoid responsive elements (GRE and nGRE, respectively) in the Itk, Txk and Lck genes. To investigate the function associated with Itk up-regulation, dexamethasone-induced apoptosis of thymocytes from Itk-deficient mice was evaluated. Our results demonstrated that Itk deficiency causes increased sensitivity to dexamethasone but not to other pro-apoptotic stimuli.

CONCLUSIONS

Modulation of Itk, Txk, and Lck in thymocytes and mature lymphocytes is another mechanism by which glucocorticoids modulate T-cell activation and differentiation. Itk up-regulation plays a protective role in dexamethasone-treated thymocytes.

Lymphocyte-based model systems for allergy research: a historic overview

During the last decades, a multitude of studies applying distinct in vitro and in vivo model systems have contributed greatly to our better understanding of the initiation and regulation of inflammatory processes leading to allergic diseases. Over the years, it has become evident that among lymphocytes, not only IgE-producing B cells and allergy-orchestrating CD4(+) helper cells but also cytotoxic CD8(+) T cells, γδ-T cells and innate lymphoid cells, as well as regulatory lymphocytes, might critically shape the immune response towards usually innocuous allergens. In this review, we provide a historic overview of pioneering work leading to the establishment of important lymphocyte-based model systems for allergy research. Moreover, we contrast the original findings with our currently more refined knowledge to appreciate the actual validity of the respective models and to reassess the conclusions obtained from them. Conflicting studies and interpretations are identified and discussed. The tables are intended to provide an easy overview of the field not only for scientists newly entering the field but also for the broader readership interested in updating their knowledge. Along those lines, herein we discuss in vitro and in vivo approaches to the investigation of lymphocyte effector cell activation, polarization and regulation, and describe depletion and adoptive transfer models along with gene knockout and transgenic (tg) methodologies. In addition, novel attempts to establish humanized T cell antigen receptor tg mouse models for allergy research are described and discussed.

Podosomes of dendritic cells facilitate antigen sampling

Dendritic cells sample the environment for antigens and play an important role in establishing the link between innate and acquired immunity. Dendritic cells contain mechanosensitive adhesive structures called podosomes that consist of an actin-rich core surrounded by integrins, adaptor proteins and actin network filaments. They facilitate cell migration via localized degradation of extracellular matrix. Here, we show that podosomes of human dendritic cells locate to spots of low physical resistance in the substrate (soft spots) where they can evolve into protrusive structures. Pathogen recognition receptors locate to these protrusive structures where they can trigger localized antigen uptake, processing and presentation to activate T-cells. Our data demonstrate a novel role in antigen sampling for the podosomes of dendritic cells.

Toward a Network Model of MHC Class II-Restricted Antigen Processing

The standard model of Major Histocompatibility Complex class II (MHCII)-restricted antigen processing depicts a straightforward, linear pathway: internalized antigens are converted into peptides that load in a chaperone dependent manner onto nascent MHCII in the late endosome, the complexes subsequently trafficking to the cell surface for recognition by CD4(+) T cells (TCD4+). Several variations on this theme, both moderate and radical, have come to light but these alternatives have remained peripheral, the conventional pathway generally presumed to be the primary driver of TCD4+ responses. Here we continue to press for the conceptual repositioning of these alternatives toward the center while proposing that MHCII processing be thought of less in terms of discrete pathways and more in terms of a network whose major and minor conduits are variable depending upon many factors, including the epitope, the nature of the antigen, the source of the antigen, and the identity of the antigen-presenting cell.

Single domain intrabodies against WASP inhibit TCR-induced immune responses in transgenic mice T cells

Intrabody technology provides a novel approach to decipher the molecular mechanisms of protein function in cells. Single domains composed of only the variable regions (V_H or V_L) of antibodies are the smallest recombinant antibody fragments to be constructed thus far. In this study, we developed transgenic (Tg) mice expressing the V_H or V_L single domains derived from a monoclonal antibody raised against the N-terminal domain of Wiskott–Aldrich syndrome protein (WASP), which is an adaptor molecule in immune cells. In T cells from anti-WASP V_H and V_L single domain Tg mice, interleukin-2 production induced by T cell receptor (TCR) stimulation were impaired, and specific interaction between the WASP N-terminal domain and the Fyn SH3 domain was strongly inhibited by masking the binding sites in WASP. These results strongly suggest that the V_H/V_L single domain intrabodies are sufficient to knockdown the domain function of target proteins in the cytosol.

T cells and their eons-old obsession with MHC

T cells bearing receptors made up of α and β chains (TCRs) usually react with peptides bound to major histocompatibility complex proteins (MHC). This bias could be imposed by positive selection, the phenomenon that selects thymocytes to mature into T cells only if the TCRs they bear react with low but appreciable affinity with MHC + peptide combinations in the thymus cortex. However, it is also possible that the polypeptides of TCRs themselves do not have random specificities but rather are biased toward reaction with MHC. Evolution would therefore have selected for a collection of TCR variable elements that are prone to react with MHC. If this were to be so, positive selection would act on thymocytes bearing a pre biased collection of TCRs to pick out those that react to some extent, but not too well, with self MHC + self-peptides. A problem with studies of this evolutionary idea is the fact that there are many TCR variable elements and that these differ considerably in the amino acids with which they contact MHC. However, recent experiments by our group and others suggest that one group of TCR variable elements, those related to the mouse Vβ8 family, has amino acids in their CDR2 regions that consistently bind a particular site on an MHC α-helix. Other groups of variable elements may use different patterns of amino acids to achieve the same goal. Mutation of these amino acids reduces the ability of T cells and thymocytes to react with MHC. These amino acids are present in the variable regions of distantly related species such as sharks and human. Overall the data indicate that TCR elements have indeed been selected by evolution to react with MHC proteins. Many mysteries about TCRs remain to be solved, including the nature of auto-recognition, the basis of MHC allele specificity, and the very nature and complexity of TCRs on mature T cells.

Structural insights into activation of antiviral NK cell responses

Natural killer (NK) cells are key components of innate immune responses, providing surveillance against cells undergoing tumorigenesis or infection, by viruses or internal pathogens. NK cells can directly eliminate compromised cells and regulate downstream responses of the innate and acquired immune systems through the release of immune modulators (cytokines, interferons). The importance of the role NK cells play in immune defense was demonstrated originally in herpes viral infections, usually mild or localized, which become severe and life threatening in NK-deficient patients . NK cell effector functions are governed by balancing opposing signals from a diverse array of activating and inhibitory receptors. Many NK receptors occur in paired activating and inhibitory isoforms and recognize major histocompatibility complex (MHC) class I proteins with varying degrees of peptide specificity. Structural studies have made considerable inroads into understanding the molecular mechanisms employed to broadly recognize multiple MHC ligands or specific pathogen-associated antigens and the strategies employed by viruses to thwart these defenses. Although many details of NK development, signaling, and integration remain mysterious, it is clear that NK receptors are key components of a system exquisitely tuned to sense any dysregulation in MHC class I expression, or the expression of certain viral antigens, resulting in the elimination of affected cells.

The endosome-lysosome pathway and information generation in the immune system

For a long time the lysosomal pathway was thought to be exclusively one for catabolism and recycling of material taken up by endocytosis from the external milieu or from the cytosol by autophagy. At least in the immune system it is clear now that endo/lysosomal proteolysis generates crucially important information, in particular peptides that bind class II MHC molecules to create ligands for survey by the diverse antigen receptors of the T lymphocyte system. This process of antigen processing and presentation is used to display not only foreign but also self peptides and therefore is important for 'self' tolerance as well as immunity to pathogens. Some cells, macrophages and particularly dendritic cells can load peptides on class I MHC molecules in the endosome system through the important, though still not fully characterised, pathway of cross-presentation. Here I try to provide a brief review of how this area developed focussing to some extent our own contributions to understanding the class II MHC pathway. I also mention briefly recent work of others showing that proteolysis along this pathway turns out to regulate immune signalling events in the innate immune system such as the activation of some members of the Toll-like receptor family. Finally, our recent work on the endo/lysosome targeted protease inhibitor cystatin F, suggests that auto-regulation of protease activity in some immune cells occurs. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Analysis of detergent-free lipid rafts isolated from CD4+ T cell line: interaction with antigen presenting cells promotes coalescing of lipid rafts

Background

Lipid rafts present on the plasma membrane play an important role in spatiotemporal regulation of cell signaling. Physical and chemical characterization of lipid raft size and assessment of their composition before, and after cell stimulation will aid in developing a clear understanding of their regulatory role in cell signaling. We have used visual and biochemical methods and approaches for examining individual and lipid raft sub-populations isolated from a mouse CD4⁺ T cell line in the absence of detergents.

Results

Detergent-free rafts were analyzed before and after their interaction with antigen presenting cells. We provide evidence that the average diameter of lipid rafts isolated from un-stimulated T cells, in the absence of detergents, is less than 100 nm. Lipid rafts on CD4⁺ T cell membranes coalesce to form larger structures, after interacting with antigen presenting cells even in the absence of a foreign antigen.

Conclusions

Findings presented here indicate that lipid raft coalescence occurs during cellular interactions prior to sensing a foreign antigen.

Rhoh deficiency reduces peripheral T-cell function and attenuates allogenic transplant rejection

Rhoh is a hematopoietic system-specific GTPase. Rhoh-deficient T cells have been shown to have a defect in TCR signaling manifested during their thymic development. Our aims were to investigate the phenotype of peripheral Rhoh-deficient T cells and to explore in vivo the potential benefit of Rhoh deficiency in a clinically relevant situation, in which T-cell inhibition is desirable. In murine allogenic kidney transplantation, Rhoh deficiency caused a significant 75% reduction of acute and chronic transplant rejection accompanied by 75% lower alloantigen-specific antibody levels and significantly better graft function. This effect was independent of the lower T-cell numbers in Rhoh-deficient recipients, because injection of equal numbers of Rhoh-deficient or control T cells into kidney transplanted mice with SCID led again to a significant 60% reduction of rejection. Mixed lymphocyte reaction revealed that the weaker alloreactivity was associated with a 85% lower cytotoxicity and a 50-80% lower cytokine release in Rhoh-deficient T cells without an influence on the secretion itself. Antigen uptake and presentation in DC were unaffected by Rhoh deficiency. These findings stress the importance of Rhoh for the function of peripheral T cells.

Peroxisome proliferator-activated receptor (PPAR)gamma can inhibit chronic renal allograft damage

Chronic inflammation and fibrosis are the leading causes of chronic allograft failure. The nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma is a transcription factor known to have antidiabetogenic and immune effects, and PPARgamma forms obligate heterodimers with the retinoid X receptor (RXR). We have reported that a retinoic acid (RAR)/RXR-agonist can potently influence the course of renal chronic allograft dysfunction. In this study, in a Fischer to Lewis rat renal transplantation model, administration of the PPARgamma-agonist, rosiglitazone, independent of dose (3 or 30 mg/kgBW/day), lowered serum creatinine, albuminuria, and chronic allograft damage with a chronic vascular damage score as follows: 35.0 +/- 5.8 (controls) vs. 8.1 +/- 2.4 (low dose-Rosi; P < 0.05); chronic tubulointerstitial damage score: 13.6 +/- 1.8 (controls) vs. 2.6 +/- 0.4 (low dose-Rosi; P < 0.01). The deposition of extracellular matrix proteins (collagen, fibronectin, decorin) was strikingly lower. The expression of transforming growth factor-beta1 was inhibited, whereas that of bone morphogenic protein-7 (BMP-7) was increased. Intragraft mononuclear cells and activated fibroblast numbers were reduced by 50%. In addition, the migratory and proliferative activity of these cells was significantly inhibited in vitro. PPARgamma activation diminished the number of cells expressing the proinflammatory and fibrogenic proteoglycan biglycan. In macrophages its secretion was blocked by rosiglitazone in a predominantly PPARgamma-dependent manner. The combination of PPARgamma- and RAR/RXR-agonists resulted in additive effects in the inhibition of fibrosis. In summary, PPARgamma activation was potently immunosuppressive and antifibrotic in kidney allografts, and these effects were enhanced by a RAR/RXR-agonist.

MHC class II epitope predictive algorithms

SUMMARY

Major histocompatibility complex class II (MHC-II) molecules sample peptides from the extracellular space, allowing the immune system to detect the presence of foreign microbes from this compartment. To be able to predict the immune response to given pathogens, a number of methods have been developed to predict peptide-MHC binding. However, few methods other than the pioneering TEPITOPE/ProPred method have been developed for MHC-II. Despite recent progress in method development, the predictive performance for MHC-II remains significantly lower than what can be obtained for MHC-I. One reason for this is that the MHC-II molecule is open at both ends allowing binding of peptides extending out of the groove. The binding core of MHC-II-bound peptides is therefore not known a priori and the binding motif is hence not readily discernible. Recent progress has been obtained by including the flanking residues in the predictions. All attempts to make ab initio predictions based on protein structure have failed to reach predictive performances similar to those that can be obtained by data-driven methods. Thousands of different MHC-II alleles exist in humans. Recently developed pan-specific methods have been able to make reasonably accurate predictions for alleles that were not included in the training data. These methods can be used to define supertypes (clusters) of MHC-II alleles where alleles within each supertype have similar binding specificities. Furthermore, the pan-specific methods have been used to make a graphical atlas such as the MHCMotifviewer, which allows for visual comparison of specificities of different alleles.

Diverse regulatory roles for lysosomal proteases in the immune response

The innate and adaptive immune system utilise endocytic protease activity to promote functional immune responses. Cysteine and aspartic proteases (cathepsins) constitute a subset of endocytic proteases, the immune function of which has been described extensively. Although historically these studies have focused on their role in processes such as antigen presentation and zymogen processing within the endocytic compartment, recent discoveries have demonstrated a critical role for these proteases in other intracellular compartments, and within the extracellular milieu. It has also become clear that their pattern of expression and substrate specificities are more diverse than was first envisaged. Here, we discuss recent advances addressing the role of lysosomal proteases in various aspects of the immune response. We pay attention to reports demonstrating cathepsin activity outside of its canonical endosome/lysosome microenvironment.

A HCMV pp65 polypeptide promotes the expansion of CD4+ and CD8+ T cells across a wide range of HLA specificities

Human cytomegalovirus (HCMV) can cause life-threatening disease in infected hosts. Immunization with human leukocyte antigen (HLA)-restricted immunodominant synthetic peptides and adoptive transfer of epitope-specific T cells have been envisaged to generate or boost HCMV-specific cellular immunity, thereby preventing HCMV infection or reactivation. However, induction or expansion of T cells effective against HCMV are limited by the need of utilizing peptides with defined HLA restrictions. We took advantage of a combination of seven predictive algorithms to identify immunogenic peptides of potential use in the prevention or treatment of HCMV infection or reactivation. Here we describe a pp65-derived peptide (pp65(340-355), RQYDPVAALFFFDIDL: RQY16-mer), characterized by peculiar features. First, RQY-16mer is able to stimulate HCMV pp65 specific responses in both CD4(+) and CD8(+) T cells, restricted by a wide range of HLA class I and II determinants. Second, RQY-16mer is able to induce an unusually wide range of effector functions in CD4(+) T cells, including proliferation, killing of autologous HCMV-infected target cells and cytokine production. Third, and most importantly, the RQY-16mer is able to stimulate CD4(+) and CD8(+) T-cell responses in pharmacologically immunosuppressed patients. These data suggest that a single reagent might qualify as synthetic immunogen for potentially large populations exposed to HCMV infection or reactivation.

Superantigen-presentation by rat major histocompatibility complex class II molecules RT1.Bl and RT1.Dl

Rat major histocompatibility complex (MHC) class II molecules RT1.B(l) (DQ-like) and RT1.D(l) (DR-like) were cloned from the LEW strain using reverse transcription-polymerase chain reaction and expressed in mouse L929 cells. The transduced lines bound MHC class II-specific monoclonal antibodies in an MHC-isotype-specific manner and presented peptide antigens and superantigens to T-cell hybridomas. The T-cell-hybridomas responded well to all superantigens presented by human MHC class II, whereas the response varied considerably with rat MHC class II-transduced lines as presenters. The T-cell hybridomas responded to the pyrogenic superantigens Staphylococcus enterotoxin B (SEB), SEC1, SEC2 and SEC3 only at high concentrations with RT1.B(l)-transduced and RT1.D(l)-transduced cells as presenters. The same was true for streptococcal pyrogenic exotoxin A (SPEA), but this was presented only by RT1.B(l) and not by RT1.D(l). SPEC was recognized only if presented by human MHC class II. Presentation of Yersinia pseudotuberculosis superantigen (YPM) showed no MHC isotype preference, while Mycoplasma arthritidis superantigen (MAS or MAM) was presented by RT1.D(l) but not by RT1.B(l). Interestingly, and in contrast to RT1.B(l), the RT1.D(l) completely failed to present SEA and toxic shock syndrome toxin 1 even after transduction of invariant chain (CD74) or expression in other cell types such as the surface MHC class II-negative mouse B-cell lymphoma (M12.4.1.C3). We discuss the idea that a lack of SEA presentation may not be a general feature of RT1.D molecules but could be a consequence of RT1.D(l)beta-chain allele-specific substitutions (arginine 80 to lysine, asparagine 82 to aspartic acid) in the extremely conserved region flanking the Zn(2+)-binding histidine 81, which is crucial for high-affinity SEA-binding.

Novel T-cell epitopes of ovalbumin in BALB/c mouse: potential for peptide-immunotherapy

The identification of food allergen T-cell epitopes provides a platform for the development of novel immunotherapies. Despite extensive knowledge of the physicochemical properties of hen ovalbumin (OVA), a major egg allergen, the complete T-cell epitope map of OVA has surprisingly not been defined in the commonly used BALB/c mouse model. In this study, spleen cells obtained from OVA-sensitized mice were incubated in the presence of 12-mer overlapping synthetic peptides, constructed using the SPOTS((R)) synthesis method. Proliferative activity was assessed by 72-h in vitro assays with use of the tetrazolium salt WST-1 and led to identification of four mitogenic sequences, i.e., A39R50, S147R158, K263E274, and A329E340. ELISA analyses of interferon (IFN)-gamma and interleukin (IL)-4 productions in cell culture supernatants upon stimulation with increasing concentrations of peptides confirmed their immunogenicity. Knowledge of the complete T-cell epitope map of OVA opens the way to a number of experimental investigations, including the exploration of peptide-based immunotherapy.

Optimized DNA vaccines to specifically induce therapeutic CD8 T cell responses against autochthonous breast tumors

BACKGROUND

Vaccines capable of inducing CD8 T cell responses to antigens expressed by tumor cells are considered as attractive choices for the treatment and prevention of malignant diseases. Our group has previously reported that immunization with synthetic peptide corresponding to a CD8 T cell epitope derived from the rat neu (rNEU) oncogene administered together with a Toll-like receptor agonist as adjuvant, induced immune responses that translated into prophylactic and therapeutic benefit against autochthonous tumors in an animal model of breast cancer (BALB-neuT mice). DNA-based vaccines offer some advantages over peptide vaccines, such as the possibility of including multiple CD8 T cell epitopes in a single construct.

MATERIALS AND METHODS

Plasmids encoding a fragment of rNEU were designed to elicit CD8 T cell responses but no antibody responses. We evaluated the use of the modified plasmids as DNA vaccines for their ability to generate effective CD8 T cell responses against breast tumors expressing rNEU.

RESULTS

DNA-based vaccines using modified plasmids were very effective in specifically stimulating tumor-reactive CD8 T cell responses. Moreover, vaccination with the modified DNA plasmids resulted in significant anti-tumor effects that were mediated by CD8 T cells without the requirement of generating antibodies to the product of rNEU.

CONCLUSIONS

DNA vaccination is a viable alternative to peptide vaccination to induce potent anti-tumor CD8 T cell responses that provide effective therapeutic benefit. These results bear importance for the design of DNA vaccines for the treatment and prevention of cancer.

Immunodominance of CD4 T cells to foreign antigens is peptide intrinsic and independent of molecular context: implications for vaccine design

Immunodominance refers to the restricted peptide specificity of T cells that are detectable after an adaptive immune response. For CD4 T cells, many of the mechanisms used to explain this selectivity suggest that events related to Ag processing play a major role in determining a peptide's ability to recruit CD4 T cells. Implicit in these models is the prediction that the molecular context in which an antigenic peptide is contained will impact significantly on its immunodominance. In this study, we present evidence that the selectivity of CD4 T cell responses to peptides contained within protein Ags is not detectably influenced by the location of the peptide in a given protein or the primary sequence of the protein that bears the test peptide. We have used molecular approaches to change the location of peptides within complex protein Ags and to change the flanking sequences that border the peptide epitope to now include a protease site, and find that immunodominance or crypticity of a peptide observed in its native protein context is preserved. Collectively, these results suggest immunodominance of peptides contained in complex Ags is due to an intrinsic factor of the peptide, based upon the affinity of that peptide for MHC class II molecules. These findings are discussed with regard to implications for vaccine design.

Presentation of a determinant by MHC class II can be prevented through competitive capture by a flanking determinant on a multideterminant peptide

Competitive capture is a process by which different determinants of an unfolding antigen compete for binding to the same MHC class II molecule. The "winning" determinant is then dominantly displayed. For self antigens, T cells with specificity for dominantly displayed determinants will be subject to strong tolerance induction. With this in mind we set out to characterize the determinant hierarchy of the junctional region of the Golli-MBP complex. Within this region the MBP 1-9 determinant is known to be a strong inducer of experimental autoimmune encephalomyelitis. We found that the Golli-MBP junctional region contains a triad of three overlapping determinants: LDVM1-5, MBP 1-9, and MBP 7-20. We demonstrate that these three determinants are unique and compete for binding to I-A(u) and that a determinant hierarchy exists with MBP 7-20 being the most dominantly displayed determinant. Because of the prevention of MBP1-9 access to MHC-II, the residual T cell repertoire to this determinant remains complete, thereby permitting its highest affinity members to drive the response, and to convert MBP1-9 into a dominant determinant, despite its poor MHC binding capacity.

A brief history of CD8 T cells

CD8 T cells comprise a powerful branch of the adaptive immune system, yet were not formally recognized until long after the discovery of antibody. CD8 T cells contribute to the eradication of intracellular infections and to the control of many chronic infections. There is tempered optimism that CD8 T cell memory elicited via vaccination may hold the key to manufacturing protective immunity against pathogens that cause chronic infections in humans. The specificity and destructive capabilities of CD8 T cells may also be harnessed for the eradication of tumors. However, CD8 T cells also contribute to a variety of clinical difficulties such as immune mediated pathology, rejection of organ transplants, and autoimmunity. Clearly, learning how to safely generate protective long-lived CD8 T cell memory and how to control or eliminate specific unwanted responses could deliver substantial clinical rewards, and there is a great need for continued research on the biology and therapeutic potential of these cells. Herein, we recount the historical developments leading to the discovery of CD8 T cells, highlight a few of the important discoveries that have followed, and discuss some of the critical issues on the horizon.

Activation of dendritic cells and induction of CD4(+) T cell differentiation by aluminum-containing adjuvants

Aluminum-containing adjuvants are widely used in licensed human and veterinary vaccines. However, the mechanism by which these adjuvants enhance the immune response and predominantly stimulate a T(H)2 humoral immune response is not well understood. In this study, the effects of aluminum hydroxide and aluminum phosphate adjuvants on antigen presentation, expression of costimulatory molecules and cytokines by mouse dendritic cells (DCs) and the ability of DCs to induce T helper cell differentiation were investigated. Dendritic cells pulsed with ovalbumin (OVA) adsorbed to aluminum-containing adjuvants activated antigen-specific T cells more effectively than DCs pulsed with OVA alone. Aluminum hydroxide adjuvant had a significantly stronger effect than aluminum phosphate adjuvant. Both aluminum-containing adjuvants significantly increased the expression of CD86 on DCs but only aluminum hydroxide adjuvant also induced moderate expression of CD80. Aluminum-containing adjuvants stimulated the release of IL-1beta and IL-18 from DCs via caspase-1 activation. DCs incubated with LPS and OVA induced T(H)1 differentiation of naïve CD4(+) T cells. In contrast, DCs incubated with aluminum/OVA activated CD4(+) T cells to secrete IL-4 and IL-5 as well as IFN-gamma. Addition of neutralizing anti-IL-1beta antibodies decreased IL-5 production and addition of anti-IL-18 antibodies decreased both IL-4 and IL-5 production. Inhibition of IL-1beta and IL-18 secretion by DCs via inhibition of caspase-1 also led to a marked decrease of IL-4 and IL-5 by CD4(+) T cells. These results indicate that aluminum-containing adjuvants activate DCs and influence their ability to direct T(H)1 and T(H)2 responses through the secretion of IL-1beta and IL-18.

Reconstruction of a pathway of antigen processing and class II MHC peptide capture

Endocytosed antigens are proteolytically processed and small amounts of peptides captured by class II MHC molecules. The details of antigen proteolysis, peptide capture and how destruction of T-cell epitopes is avoided are incompletely understood. Using the tetanus toxin antigen, we show that the introduction of 3-6 cleavage sites is sufficient to trigger a partially unfolded conformation able to bind to class II MHC molecules. The known locations of T-cell epitopes and protease cleavage sites predict that large domains of processed antigen (8-35 kDa) are captured under these conditions. Remarkably, when antigen is bound to the B-cell antigen receptor (BCR), processing can trigger a concerted 'hand-over' reaction whereby BCR-associated processed antigen is captured by neighbouring class II MHC molecules. Early capture of minimally processed antigen and confinement of the processing and class II MHC loading reaction to the membrane plane may improve the likelihood of T-cell epitope survival in the class II MHC pathway and may help explain the reciprocal relationships observed between B- and T-cell epitopes in many protein antigens and autoantigens.

Instant effect of soluble antigen on effector T cells in peripheral immune organs during immunotherapy of autoimmune encephalomyelitis

i.v. infusion of native autoantigen or its altered peptide variants is an important therapeutic option for the treatment of autoimmune diseases, because it selectively targets the disease-inducing T cells. To learn more about the mechanisms and kinetics of this approach, we visualized the crucial initial effects of i.v. infusion of peptides or intact protein on GFP-tagged autoaggressive CD4(+) effector T cells using live-video and two-photon in situ imaging of spleens in living animals. We found that the time interval between i.v. injection of intact protein to first changes in T cell behavior was extremely short; within 10 min after protein application, the motility of the T cells changed drastically. They slowed down and became tethered to local sessile stromal cells. A part of the cells aggregated to form clusters. Within the following 20 min, IFN-gamma mRNA was massively (>100-fold) up-regulated; surface IL-2 receptor and OX-40 (CD 134) increased 1.5 h later. These processes depleted autoimmune T cells in the blood circulation, trapping the cells in the peripheral lymphoid organs and thus preventing them from invading the CNS. This specific blockage almost completely abrogated CNS inflammation and clinical disease. These findings highlight the speed and efficiency of antigen recognition in vivo and add to our understanding of T cell-mediated autoimmunity.

Finding the groove

Envisioning how T cells might recognize antigen presented by major histocompatibility complex molecules proved to be a formidable challenge. Pamela Bjorkman describes her journey to provide structural insights into how such recognition is achieved.

CD44 differentially activates mouse NK T cells and conventional T cells

NK T (NKT) cells are an important component of the innate immune system and recognize the MHC class I-like CD1d molecule. NKT cells possess significant immunoregulatory activity due to their rapid secretion of large quantities of pro- and anti-inflammatory cytokines following CD1d-dependent stimulation. Because the innate immune system is programmed to respond to a multitude of diverse stimuli and must be able to quickly differentiate between pathogenic and endogenous signals, we hypothesized that, apart from stimulation via the TCR (e.g., CD1d-dependent activation), there must be multiple activation pathways that can be triggered through other cell surface receptors on NKT cells. Therefore, we analyzed the ability of CD44, a structurally diverse cell surface receptor expressed on most cells, to stimulate murine NKT cells, compared with conventional T cells. Stimulation of CD44 through Ab cross-linking or binding to its natural ligands hyaluronan and osteopontin induced NKT cells to secrete cytokines, up-regulate activation markers, undergo morphological changes, and resist activation-induced cell death, whereas conventional T cells only exhibited changes in morphology and protection from activation-induced cell death. This CD44-specific stimulation of NKT cells correlated with their ability to bind hyaluronan. Thus, fundamental differences in CD44 function between these lymphocyte subsets suggest an important biological role for CD44 in the innate immune response.

Transfection of drug-specific T-cell receptors into hybridoma cells: tools to monitor drug interaction with T-cell receptors and evaluate cross-reactivity to related compounds

In the context of drug hypersensitivity, our group has recently proposed a new model based on the structural features of drugs (pharmacological interaction with immune receptors; p-i concept) to explain their recognition by T cells. According to this concept, even chemically inert drugs can stimulate T cells because certain drugs interact in a direct way with T-cell receptors (TCR) and possibly major histocompatibility complex molecules without the need for metabolism and covalent binding to a carrier. In this study, we investigated whether mouse T-cell hybridomas transfected with drug-specific human TCR can be used as an alternative to drug-specific T-cell clones (TCC). Indeed, they behaved like TCC and, in accordance with the p-i concept, the TCR recognize their specific drugs in a direct, processing-independent, and dose-dependent way. The presence of antigen-presenting cells was a prerequisite for interleukin-2 production by the TCR-transfected cells. The analysis of cross-reactivity confirmed the fine specificity of the TCR and also showed that TCR transfectants might provide a tool to evaluate the potential of new drugs to cause hypersensitivity due to cross-reactivity. Recombining the alpha- and beta-chains of sulfanilamide- and quinolone-specific TCR abrogated drug reactivity, suggesting that both original alpha- and beta-chains were involved in drug binding. The TCR-transfected hybridoma system showed that the recognition of two important classes of drugs (sulfanilamides and quinolones) by TCR occurred according to the p-i concept and provides an interesting tool to study drug-TCR interactions and their biological consequences and to evaluate the cross-reactivity potential of new drugs of the same class.

Mannose-pepstatin conjugates as targeted inhibitors of antigen processing

The molecular details of antigen processing, including the identity of the enzymes involved, their intracellular location and their substrate specificity, are still incompletely understood. Selective inhibition of proteolytic antigen processing enzymes such as cathepsins D and E, using small molecular inhibitors such as pepstatin, has proven to be a valuable tool in investigating these pathways. However, pepstatin is poorly soluble in water and has limited access to the antigen processing compartment in antigen presenting cells. We have synthesised mannose-pepstatin conjugates, and neomannosylated BSA-pepstatin conjugates, as tools for the in vivo study of the antigen processing pathway. Conjugation to mannose and to neomannosylated BSA substantially improved the solubility of the conjugates relative to pepstatin. The mannose-pepstatin conjugates showed no reduction in inhibition of cathepsin E, whereas the neomannosylated BSA-pepstatin conjugates showed some loss of inhibition, probably due to steric factors. However, a neomannosylated BSA-pepstatin conjugate incorporating a cleavable disulfide linkage between the pepstatin and the BSA showed the best uptake to dendritic cells and the best inhibition of antigen processing.

T cell-mediated hypersensitivity to quinolones: mechanisms and cross-reactivity

BACKGROUND

Quinolones are widely used, broad spectrum antibiotics that can induce immediate- and delayed-type hypersensitivity reactions, presumably either IgE or T cell mediated, in about 2-3% of treated patients.

OBJECTIVE

To better understand how T cells interact with quinolones, we analysed six patients with delayed hypersensitivity reactions to ciprofloxacin (CPFX), norfloxacin (NRFX) or moxifloxacin (MXFX).

METHODS

We confirmed the involvement of T cells in vivo by patch test and in vitro by means of the lymphocyte proliferation test (LTT). The nature of the drug-T cell interaction as well as the cross-reactivity with other quinolones were investigated through the generation and analysis (flow cytometry and proliferation assays) of quinolone-specific T cell clones (TCC).

RESULTS

The LTT confirmed the involvement of T cells because peripheral blood mononuclear cells (PBMC) mounted an enhanced in vitro proliferative response to CPFX and/or NRFX or MXFX in all patients. Patch tests were positive after 24 and 48 h in three out of the six patients. From two patients, CPFX- and MXFX-specific CD4(+)/CD8(+) T cell receptor (TCR) alphabeta(+) TCC were generated to investigate the nature of the drug-T cell interaction as well as the cross-reactivity with other quinolones. The use of eight different quinolones as antigens (Ag) revealed three patterns of cross-reactivity: clones exclusively reacting with the eliciting drug, clones with a limited cross-reactivity and clones showing a broad cross-reactivity. The TCC recognized quinolones directly without need of processing and without covalent association with the major histocompatability complex (MHC)-peptide complex, as glutaraldehyde-fixed Ag-presenting cells (APC) could present the drug and washing quinolone-pulsed APC removed the drug, abrogating the reactivity of quinolone-specific TCC.

CONCLUSION

Our data show that T cells are involved in delayed immune reactions to quinolones and that cross-reactivity among the different quinolones is frequent.

Intrabodies against the EVH1 domain of Wiskott-Aldrich syndrome protein inhibit T cell receptor signaling in transgenic mice T cells

Intracellularly expressed antibodies (intrabodies) have been used to inhibit the function of various kinds of protein inside cells. However, problems with stability and functional expression of intrabodies in the cytosol remain unsolved. In this study, we show that single-chain variable fragment (scFv) intrabodies constructed with a heavy chain variable (V(H)) leader signal sequence at the N-terminus were translocated from the endoplasmic reticulum into the cytosol of T lymphocytes and inhibited the function of the target molecule, Wiskott-Aldrich syndrome protein (WASP). WASP resides in the cytosol as a multifunctional adaptor molecule and mediates actin polymerization and interleukin (IL)-2 synthesis in the T-cell receptor (TCR) signaling pathway. It has been suggested that an EVH1 domain in the N-terminal region of WASP may participate in IL-2 synthesis. In transgenic mice expressing anti-EVH1 scFvs derived from hybridoma cells producing WASP-EVH1 mAbs, a large number of scFvs in the cytosol and binding between anti-EVH1 scFvs and native WASP in T cells were detected by immunoprecipitation analysis. Furthermore, impairment of the proliferative response and IL-2 production induced by TCR stimulation which did not affect TCR capping was demonstrated in the scFv transgenic T cells. We previously described the same T-cell defects in WASP transgenic mice overexpressing the EVH1 domain. These results indicate that the EVH1 intrabodies inhibit only the EVH1 domain function that regulates IL-2 synthesis signaling without affecting the overall domain structure of WASP. The novel procedure presented here is a valuable tool for in vivo functional analysis of cytosolic proteins.