Balancing immunity and tolerance: deleting and tuning lymphocyte repertoires

Deep immunophenotyping reveals that autoimmune and autoinflammatory disorders are spread along two immunological axes capturing disease inflammation levels and types

OBJECTIVES

Based on genetic associations, McGonagle and McDermott suggested a classification of autoimmune and autoinflammatory diseases as a continuum ranging from purely autoimmune to purely autoinflammatory diseases and comprising diseases with both components. We used deep immunophenotyping to identify immune cell populations and molecular targets characterising this continuum.

METHODS

We collected blood from 443 patients with one of 15 autoimmune or autoinflammatory diseases and 71 healthy volunteers. Deep phenotyping was performed using 13 flow cytometry panels characterising over 600 innate and adaptive cell populations. Unsupervised and supervised analyses were conducted to identify disease clusters with their common and specific cell parameters.

RESULTS

Unsupervised clustering categorised these diseases into five clusters. Principal component analysis deconvoluted this clustering into two immunological axes. The first axis was driven by the ratio of LAG3+ to ICOS+ in regulatory T lymphocytes (Tregs), and segregated diseases based on their inflammation levels. The second axis was driven by activated Tregs and type 3 innate lymphoid cells (ILC3s), and segregated diseases based on their types of affected tissues. We identified a signature of 23 cell populations that accurately characterised the five disease clusters.

CONCLUSIONS

We have refined the monodimensional continuum of autoimmune and autoinflammatory diseases as a continuum characterised by both disease inflammation levels and targeted tissues. Such classification should be helpful for defining therapies. Our results call for further investigations into the role of the LAG3+/ICOS+ balance in Tregs and the contribution of ILC3s in autoimmune and autoinflammatory diseases.

TRIAL REGISTRATION NUMBER

NCT02466217.

Peripheral memory B cells in multiple sclerosis vs. double negative B cells in neuromyelitis optica spectrum disorder: disease driving B cell subsets during CNS inflammation

B cells are fundamental players in the pathophysiology of autoimmune diseases of the central nervous system, such as multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). A deeper understanding of disease-specific B cell functions has led to the differentiation of both diseases and the development of different treatment strategies. While NMOSD is strongly associated with pathogenic anti-AQP4 IgG antibodies and proinflammatory cytokine pathways, no valid autoantibodies have been identified in MS yet, apart from certain antigen targets that require further evaluation. Although both diseases can be effectively treated with B cell depleting therapies, there are distinct differences in the peripheral B cell subsets that influence CNS inflammation. An increased peripheral blood double negative B cells (DN B cells) and plasmablast populations has been demonstrated in NMOSD, but not consistently in MS patients. Furthermore, DN B cells are also elevated in rheumatic diseases and other autoimmune entities such as myasthenia gravis and Guillain-Barré syndrome, providing indirect evidence for a possible involvement of DN B cells in other autoantibody-mediated diseases. In MS, the peripheral memory B cell pool is affected by many treatments, providing indirect evidence for the involvement of memory B cells in MS pathophysiology. Moreover, it must be considered that an important effector function of B cells in MS may be the presentation of antigens to peripheral immune cells, including T cells, since B cells have been shown to be able to recirculate in the periphery after encountering CNS antigens. In conclusion, there are clear differences in the composition of B cell populations in MS and NMOSD and treatment strategies differ, with the exception of broad B cell depletion. This review provides a detailed overview of the role of different B cell subsets in MS and NMOSD and their implications for treatment options. Specifically targeting DN B cells and plasmablasts in NMOSD as opposed to memory B cells in MS may result in more precise B cell therapies for both diseases.

Kidins220 regulates the development of B cells bearing the λ light chain

The ratio between κ and λ light chain (LC)-expressing B cells varies considerably between species. We recently identified Kinase D-interacting substrate of 220 kDa (Kidins220) as an interaction partner of the BCR. In vivo ablation of Kidins220 in B cells resulted in a marked reduction of λLC-expressing B cells. Kidins220 knockout B cells fail to open and recombine the genes of the Igl locus, even in genetic scenarios where the Igk genes cannot be rearranged or where the κLC confers autoreactivity. Igk gene recombination and expression in Kidins220-deficient B cells is normal. Kidins220 regulates the development of λLC B cells by enhancing the survival of developing B cells and thereby extending the time-window in which the Igl locus opens and the genes are rearranged and transcribed. Further, our data suggest that Kidins220 guarantees optimal pre-BCR and BCR signaling to induce Igl locus opening and gene recombination during B cell development and receptor editing.

Chimeric antigen receptor Treg therapy in transplantation

In the quest for more precise and effective organ transplantation therapies, chimeric antigen receptor (CAR) regulatory T cell (Treg) therapies represent a potential cutting-edge advance. This review comprehensively analyses CAR Tregs and how they may address important drawbacks of polyclonal Tregs and conventional immunosuppressants. We examine a growing body of preclinical findings of CAR Treg therapy in transplantation, discuss CAR Treg design specifics, and explore established and attractive new targets in transplantation. In addition, we explore present impediments where future studies will be necessary to determine the efficacy of CAR Tregs in reshaping alloimmune responses and transplant microenvironments to reduce reliance on chemical immunosuppressants. Overall, ongoing studies and trials are crucial for understanding the full scope of CAR Treg therapy in transplantation.

TLR9 ligand sequestration by chemokine CXCL4 negatively affects central B cell tolerance

Central B cell tolerance is believed to be regulated by B cell receptor signaling induced by the recognition of self-antigens in immature B cells. Using humanized mice with defective MyD88, TLR7, or TLR9 expression, we demonstrate that TLR9/MYD88 are required for central B cell tolerance and the removal of developing autoreactive clones. We also show that CXCL4, a chemokine involved in systemic sclerosis (SSc), abrogates TLR9 function in B cells by sequestering TLR9 ligands away from the endosomal compartments where this receptor resides. The in vivo production of CXCL4 thereby impedes both TLR9 responses in B cells and the establishment of central B cell tolerance. We conclude that TLR9 plays an essential early tolerogenic function required for the establishment of central B cell tolerance and that correcting defective TLR9 function in B cells from SSc patients may represent a novel therapeutic strategy to restore B cell tolerance.

DNA origami: Interrogating the nano-landscape of immune receptor activation

The immune response is orchestrated by elaborate protein interaction networks that interweave ligand-mediated receptor reorganization with signaling cascades. While the biochemical processes have been extensively investigated, delineating the biophysical principles governing immune receptor activation has remained challenging due to design limitations of traditional ligand display platforms. These constraints have been overcome by advances in DNA origami nanotechnology, enabling unprecedented control over ligand geometry on configurable scaffolds. It is now possible to systematically dissect the independent roles of ligand stoichiometry, spatial distribution, and rigidity in immune receptor activation, signaling, and cooperativity. In this review, we highlight pioneering efforts in manipulating the ligand presentation landscape to understand immune receptor triggering and to engineer functional immune responses.

Multivalent Scaffolds to Promote B cell Tolerance

Autoimmune diseases are characterized by aberrant immune responses toward self-antigens. Current treatments lack specificity, promoting adverse effects by broadly suppressing the immune system. Therapies that specifically target the immune cells responsible for disease are a compelling strategy to mitigate adverse effects. Multivalent formats that display numerous binding epitopes off a single scaffold may enable selective immunomodulation by eliciting signals through pathways unique to the targeted immune cells. However, the architecture of multivalent immunotherapies can vary widely, and there is limited clinical data with which to evaluate their efficacy. Here, we set forth to review the architectural properties and functional mechanisms afforded by multivalent ligands and evaluate four multivalent scaffolds that address autoimmunity by altering B cell signaling pathways. First, we address both synthetic and natural polymer backbones functionalized with a variety of small molecule, peptide, and protein ligands for probing the effects of valency and costimulation. Then, we review nanoparticles composed entirely from immune signals which have been shown to be efficacious. Lastly, we outline multivalent liposomal nanoparticles capable of displaying high numbers of protein antigens. Taken together, these examples highlight the versatility and desirability of multivalent ligands for immunomodulation and illuminate strengths and weaknesses of multivalent scaffolds for treating autoimmunity.

First-degree relatives of patients with systemic lupus erythematosus: Autoreactivity but not autoimmunity?

BACKGROUND

Systemic lupus erythematosus (SLE) is a disorder with a complex immunopathogenesis. It is well known that the disease begins with immunological alterations and autoantibody appearance in the serum years before clinical onset. As SLE has a strong tendency to familial aggregation, first-degree relatives (FDRs) constitute a group at elevated risk. The current understanding is that external risk factors trigger underlying immune dysregulations, leading to overt disease in those with elevated genetic risk.

OBJECTIVE

This cross-sectional study investigates the degree to which clinical features, external risk factors, and immunological profiles differ in SLE FDRs from healthy individuals and SLE patientts.

METHODS

Three groups were studied: Lupus patient FDRs (n = 56), healthy controls (n = 20), and SLE patients (n = 20). FDRs and healthy participants completed a detailed clinical questionnaire that included questions regarding smoking and estrogen drug history. All participants were tested for the presence of the following antinuclear autoantibodies (ANAs) against: nRNP/Sm, Sm, Ro60, Ro-52, La, Scl-70, PM-Scl, PM- Scl, Jo-1, CENP B, PCNA, dsDNA, nucleosomes, histones, RibP, AMA M2, DFS70, and eight soluble cytokines, including transforming growth factor-β (TGF-β), vitamin D levels, and antibodies against Epstein-Barr virus (EBV).

RESULTS

Compared with the healthy controls, FDRs had higher titers of ANA, more specific staining immunofluorescent patterns, and more autoantibody specificities. Furthermore, FDRs differed significantly in their TGF-β levels from the other two groups. In FDRs, some clinical features (hair loss, skin, and oral ulcer-like lesions) were associated with higher ANA titers and some (oral ulcer-like lesions) with the anti-Ro60-specific antibody. Interestingly, there was an association between ANA titers and levels of antibodies against EBV only in the FDR group.

CONCLUSION

First-degree relatives display unique clinical and immunological profiles, placing them between healthy individuals and SLE patients, with a balance between compensated immune dysregulation and disease-developing potential. A possible association between ANA titer and the number of clinical complaints is observed, which needs to be confirmed in more extensive studies.

Bioinformatics and Connectivity Map Analysis Suggest Viral Infection as a Critical Causative Factor of Hashimoto's Thyroiditis

Hashimoto's thyroiditis (HT) is a common autoimmune disease, and its prevalence is rapidly increasing. Both genetic and environmental risk factors contribute to the development of HT. Recently, viral infection has been suggested to act as a trigger of HT by eliciting the host immune response and subsequent autoreactivity. We analyzed the features of HT through bioinformatics analysis so as to identify the markers of HT development. We accessed public microarray data of HT patients from the Gene Expression Omnibus (GEO) and obtained differentially expressed genes (DEGs) under HT. Gene Ontology (GO) and KEGG-pathway-enrichment analyses were performed for functional clustering of our protein-protein interaction (PPI) network. Utilizing ranked gene lists, we performed a Gene Set Enrichment Analysis (GSEA) by using the clusterprofiler R package. By comparing the expression signatures of the huge perturbation database with the queried rank-ordered gene list, a connectivity map (CMap) analysis was performed to screen potential therapeutic targets and agents. The gene expression profile of the HT group was in line with the general characteristics of HT. Biological processes related to the immune response and viral infection pathways were obtained for the upregulated DEGs. The GSEA results revealed activation of autoimmune-disease-related pathways and several viral-infection pathways. Autoimmune-disease and viral-infection pathways were highly interconnected by common genes, while the HLA genes, which are shared by both, were significantly upregulated. The CMap analysis suggested that perturbagens, including SRRM1, NLK, and CCDC92, have the potential to reverse the HT expression profile. Several lines of evidence suggested that viral infection and the host immune response are activated during HT. Viral infection is suspected to act as a key trigger of HT by causing autoimmunity. SRRM1, an alternative splicing factor which responds to viral activity, might serve as potential marker of HT.

Autoimmunity in Anti-Glomerular Basement Membrane Disease: A Review of Mechanisms and Prospects for Immunotherapy

Anti-glomerular basement membrane (anti-GBM) disease is an organ-specific autoimmune disorder characterized by autoantibodies against the glomerular and alveolar basement membranes, leading to rapidly progressive glomerulonephritis and severe alveolar hemorrhage. The noncollagenous domain of the α3 chain of type IV collagen, α3(IV)NC1, contains the main target autoantigen in this disease. Epitope mapping studies of α3(IV)NC1 have identified several nephritogenic epitopes and critical residues that bind to autoantibodies and trigger anti-GBM disease. The discovery of novel target antigens has revealed the heterogeneous nature of this disease. In addition, both epitope spreading and mimicry have been implicated in the pathogenesis of anti-GBM disease. Epitope spreading refers to the development of autoimmunity to new autoepitopes, thus worsening disease progression, whereas epitope mimicry, which occurs via sharing of critical residues with microbial peptides, can initiate autoimmunity. An understanding of these autoimmune responses may open opportunities to explore potential new therapeutic approaches for this disease. We review how current advances in epitope mapping, identification of novel autoantigens, and the phenomena of epitope spreading and mimicry have heightened the understanding of autoimmunity in the pathogenesis of anti-GBM disease, and we discuss prospects for immunotherapy.

B cells in the balance: Offsetting self-reactivity avoidance with protection against foreign

Antibodies are theoretically limitless in their diversity and specificity to foreign antigens; however they are constrained by the need to avoid binding to self. Germinal centers (GC) allow diversification and maturation of the antibody response towards the foreign antigen. While self-tolerance mechanisms controlling self-reactivity during B cell maturation are well recognized, the mechanisms by which GCs balance self-tolerance and foreign binding especially in the face of cross-reactivity between self and foreign, remain much less well defined. In this review we explore the extent to which GC self-tolerance restricts affinity maturation. We present studies suggesting that the outcome is situationally dependent, affected by affinity and avidity to self-antigen, and the extent to which self-binding and foreign-binding are interdependent. While auto-reactive GC B cells can mutate away from self while maturing towards the foreign antigen, if no mutational trajectories allow for self-reactive redemption, self-tolerance prevails and GC responses to the foreign pathogen are restricted, except when self-tolerance checkpoints are relaxed. Finally, we consider whether polyreactivity is subject to the same level of restriction in GC responses, especially if polyreactivity is linked to an increase in foreign protection, as occurs in certain broadly neutralizing antibodies. Overall, the outcomes for GC B cells that bind self-antigen can range from redemption, transient relaxation in self-tolerance or restriction of the antibody response to the foreign pathogen.

Dual Effect of Immune Cells within Tumour Microenvironment: Pro- and Anti-Tumour Effects and Their Triggers

Our body is constantly exposed to pathogens or external threats, but with the immune response that our body can develop, we can fight off and defeat possible attacks or infections. Nevertheless, sometimes this threat comes from an internal factor. Situations such as the existence of a tumour also cause our immune system (IS) to be put on alert. Indeed, the link between immunology and cancer is evident these days, with IS being used as one of the important targets for treating cancer. Our IS is able to eliminate those abnormal or damaged cells found in our body, preventing the uncontrolled proliferation of tumour cells that can lead to cancer. However, in several cases, tumour cells can escape from the IS. It has been observed that immune cells, the extracellular matrix, blood vessels, fat cells and various molecules could support tumour growth and development. Thus, the developing tumour receives structural support, irrigation and energy, among other resources, making its survival and progression possible. All these components that accompany and help the tumour to survive and to grow are called the tumour microenvironment (TME). Given the importance of its presence in the tumour development process, this review will focus on one of the components of the TME: immune cells. Immune cells can support anti-tumour immune response protecting us against tumour cells; nevertheless, they can also behave as pro-tumoural cells, thus promoting tumour progression and survival. In this review, the anti-tumour and pro-tumour immunity of several immune cells will be discussed. In addition, the TME influence on this dual effect will be also analysed.

COVID-19, varying genetic resistance to viral disease and immune tolerance checkpoints

Coronavirus disease 2019 (COVID‐19) is a zoonosis like most of the great plagues sculpting human history, from smallpox to pandemic influenza and human immunodeficiency virus. When viruses jump into a new species the outcome of infection ranges from asymptomatic to lethal, historically ascribed to “genetic resistance to viral disease.” People have exploited these differences for good and bad, for developing vaccines from cowpox and horsepox virus, controlling rabbit plagues with myxoma virus and introducing smallpox during colonization of America and Australia. Differences in resistance to viral disease are at the core of the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) crisis, yet our understanding of the mechanisms in any interspecies leap falls short of the mark. Here I review how the two key parameters of viral disease are countered by fundamentally different genetic mechanisms for resistance: (1) virus transmission, countered primarily by activation of innate and adaptive immune responses; and (2) pathology, countered primarily by tolerance checkpoints to limit innate and adaptive immune responses. I discuss tolerance thresholds and the role of CD8 T cells to limit pathological immune responses, the problems posed by tolerant superspreaders and the signature coronavirus evasion strategy of eliciting only short‐lived neutralizing antibody responses. Pinpointing and targeting the mechanisms responsible for varying pathology and short‐lived antibody were beyond reach in previous zoonoses, but this time we are armed with genomic technologies and more knowledge of immune checkpoint genes. These known unknowns must now be tackled to solve the current COVID‐19 crisis and the inevitable zoonoses to follow.

Tracing Self-Reactive B Cells in Normal Mice

BCR transgenic mice dominate studies of B cell tolerance; consequently, tolerance in normal mice expressing diverse sets of autoreactive B cells is poorly characterized. We have used single B cell cultures to trace self-reactivity in BCR repertoires across the first and second tolerance checkpoints and in tolerized B cell compartments of normal mice. This approach reveals affinity "setpoints" that define each checkpoint and a subset of tolerized, autoreactive B cells that is long-lived. In normal mice, the numbers of B cells avidly specific for DNA fall significantly as small pre-B become immature and transitional-1 B cells, revealing the first tolerance checkpoint. By contrast, DNA reactivity does not significantly change when immature and transitional-1 B cells become mature follicular B cells, showing that the second checkpoint does not reduce DNA reactivity. In the spleen, autoreactivity was high in transitional-3 (T3) B cells, CD93⁺IgM^-/loIgD^hi anergic B cells, and a CD93^- anergic subset. Whereas splenic T3 and CD93⁺ anergic B cells are short-lived, CD93^-IgM^-/loIgD^hi B cells have half-lives comparable to mature follicular B cells. B cell-specific deletion of proapoptotic genes, Bak and Bax, resulted in increased CD93^-IgM^-/loIgD^hi B cell numbers but not T3 B cell numbers, suggesting that apoptosis regulates differently persistent and ephemeral autoreactive B cells. The self-reactivity and longevity of CD93^-IgM^-/loIgD^hi B cells and their capacity to proliferate and differentiate into plasmacytes in response to CD40 activation in vitro lead us to propose that this persistent, self-reactive compartment may be the origin of systemic autoimmunity and a potential target for vaccines to elicit protective Abs cross-reactive with self-antigens.

Immunological Paradigms, Mechanisms, and Models: Conceptual Understanding Is a Prerequisite to Effective Modeling

Most mathematical models that describe the individual or collective actions of cells aim at creating faithful representations of limited sets of data in a self-consistent manner. Consistency with relevant physiological rules pertaining to the greater picture is rarely imposed. By themselves, such models have limited predictive or even explanatory value, contrary to standard claims. Here I try to show that a more critical examination of currently held paradigms is necessary and could potentially lead to models that pass the test of time. In considering the evolution of paradigms over the past decades I focus on the “smart surveillance” theory of how T cells can respond differentially, individually and collectively, to both self- and foreign antigens depending on various “contextual” parameters. The overall perspective is that physiological messages to cells are encoded not only in the biochemical connections of signaling molecules to the cellular machinery but also in the magnitude, kinetics, and in the time- and space-contingencies, of sets of stimuli. By rationalizing the feasibility of subthreshold interactions, the “dynamic tuning hypothesis,” a central component of the theory, set the ground for further theoretical and experimental explorations of dynamically regulated immune tolerance, homeostasis and diversity, and of the notion that lymphocytes participate in nonclassical physiological functions. Some of these efforts are reviewed. Another focus of this review is the concomitant regulation of immune activation and homeostasis through the operation of a feedback mechanism controlling the balance between renewal and differentiation of activated cells. Different perspectives on the nature and regulation of chronic immune activation in HIV infection have led to conflicting models of HIV pathogenesis—a major area of research for theoretical immunologists over almost three decades—and can have profound impact on ongoing HIV cure strategies. Altogether, this critical review is intended to constructively influence the outlook of prospective model builders and of interested immunologists on the state of the art and to encourage conceptual work.

Virus-like particles for vaccination against cancer

Active immunotherapy of cancer aims to treat the disease by inducing effective cellular and humoral immune responses. Virus‐like particle‐based vaccines have evolved dramatically over the last few decades, greatly reducing morbidity and mortality of several infectious diseases and expectedly preventing cervical cancer caused by human papilloma virus. In contrast to these broad successes of disease prevention, therapeutic cancer vaccines remain to demonstrate clinical benefit. Yet, several preclinical and clinical trials have revealed promising results and are paving the way for medical breakthroughs. This study reviews and discusses the recent preclinical development and clinical trials in this field.

This article is categorized under:

Biology‐Inspired Nanomaterials > Protein and Virus‐Based Structures

Nanotechnology Approaches to Biology > Nanoscale Systems in Biology

Self-tolerance curtails the B cell repertoire to microbial epitopes

Immunological tolerance removes or inactivates self-reactive B cells, including those that also recognize cross-reactive foreign antigens. Whereas a few microbial pathogens exploit these "holes" in the B cell repertoire by mimicking host antigens to evade immune surveillance, the extent to which tolerance reduces the B cell repertoire to foreign antigens is unknown. Here, we use single-cell cultures to determine the repertoires of human B cell antigen receptors (BCRs) before (transitional B cells) and after (mature B cells) the second B cell tolerance checkpoint in both healthy donors and in patients with systemic lupus erythematosus (SLE) . In healthy donors, the majority (~70%) of transitional B cells that recognize foreign antigens also bind human self-antigens (foreign+self), and peripheral tolerance halves the frequency of foreign+self-reactive mature B cells. In contrast, in SLE patients who are defective in the second tolerance checkpoint, frequencies of foreign+self-reactive B cells remain unchanged during maturation of transitional to mature B cells. Patterns of foreign+self-reactivity among mature B cells from healthy donors differ from those of SLE patients. We propose that immune tolerance significantly reduces the scope of the BCR repertoire to microbial pathogens and that cross-reactivity between foreign and self epitopes may be more common than previously appreciated.

Non-receptor tyrosine kinase signaling in autoimmunity and therapeutic implications

Autoimmune diseases are characterized by impaired immune tolerance towards self-antigens, leading to enhanced immunity to self by dysfunctional B cells and/or T cells. The activation of these cells is controlled by non-receptor tyrosine kinases (NRTKs), which are critical mediators of antigen receptor and cytokine receptor signaling pathways. NRTKs transduce, amplify and sustain activating signals that contribute to autoimmunity, and are counter-regulated by protein tyrosine phosphatases (PTPs). The function of and interaction between NRTKs and PTPs during the development of autoimmunity could be key points of therapeutic interference against autoimmune diseases. In this review, we summarize the current state of knowledge of the functions of NRTKs and PTPs involved in B cell receptor (BCR), T cell receptor (TCR), and cytokine receptor signaling pathways that contribute to autoimmunity, and discuss their targeting for therapeutic approaches against autoimmune diseases.

Modulation of B cell activation threshold mediated by BCR/CD40 costimulation by targeting Cbl-b for ubiquitination

It has been shown that CD40 is required for optimal B cell activation. Casitas-B-lineage lymphoma-b (Cbl-b), a RING finger E3 ubiquitin ligase, inhibits B cell activation. In this report, we demonstrate that CD40 stimulation markedly enhances IgM-induced B cell proliferation in wild-type (WT) mice, whereas this cell proliferation was reduced in CD40-deficient (Cd40 ^-/-) mice. Interestingly, CD40 ligation strongly augments IgM-induced Cbl-b ubiquitination and degradation in primary mouse B cells, which closely correlates with their proliferation capacity. Cbl-b deficiency uncouples BCR-induced B cell proliferation from CD40 costimulation. Our results indicate that Cbl-b negatively regulates costimulation of BCR and CD40, possibly by setting the threshold for B cell activation via controlling Cbl-b expression.

BCR affinity differentially regulates colonization of the subepithelial dome and infiltration into germinal centers within Peyer's patches

Gut-derived antigens trigger immunoglobulin A (IgA) immune responses that are initiated by cognate B cells in Peyer's patches (PPs). These cells colonize the subepithelial domes (SEDs) of the PPs and subsequently infiltrate pre-existing germinal centers (GCs). Here we defined the pre-GC events and the micro-anatomical site at which affinity-based B cell selection occurred in PPs. Using whole-organ imaging, we showed that the affinity of the B cell antigen receptor (BCR) regulated the infiltration of antigen-specific B cells into GCs but not clonal competition in the SED. Follicular helper-like T cells resided in the SED and promoted its B cell colonization, independently of the magnitude of BCR affinity. Imaging and immunoglobulin sequencing indicated that selective clonal expansion ensued during infiltration into GCs. Thus, in contrast to the events in draining lymph nodes and spleen, in PPs, T cells promoted mainly the population expansion of B cells without clonal selection during pre-GC events. These findings have major implications for the design of oral vaccines.

Anti-Insulin B Cells Are Poised for Antigen Presentation in Type 1 Diabetes

Early breaches in B cell tolerance are central to type 1 diabetes progression in mouse and man. Conventional BCR transgenic mouse models (VH125.Tg NOD) reveal the power of B cell specificity to drive disease as APCs. However, in conventional fixed IgM models, comprehensive assessment of B cell development is limited. To provide more accurate insight into the developmental and functional fates of anti-insulin B cells, we generated a new NOD model (V_H125^SDNOD) in which anti-insulin VDJH125 is targeted to the IgH chain locus to generate a small (1-2%) population of class switch-competent insulin-binding B cells. Tracking of this rare population in a polyclonal repertoire reveals that anti-insulin B cells are preferentially skewed into marginal zone and late transitional subsets known to have increased sensitivity to proinflammatory signals. Additionally, IL-10 production, characteristic of regulatory B cell subsets, is increased. In contrast to conventional models, class switch-competent anti-insulin B cells proliferate normally in response to mitogenic stimuli but remain functionally silent for insulin autoantibody production. Diabetes development is accelerated, which demonstrates the power of anti-insulin B cells to exacerbate disease without differentiation into Ab-forming or plasma cells. Autoreactive T cell responses in V_H125^SDNOD mice are not restricted to insulin autoantigens, as evidenced by increased IFN-γ production to a broad array of diabetes-associated epitopes. Together, these results independently validate the pathogenic role of anti-insulin B cells in type 1 diabetes, underscore their diverse developmental fates, and demonstrate the pathologic potential of coupling a critical β cell specificity to predominantly proinflammatory Ag-presenting B cell subsets.

The essential role of G protein-coupled receptor (GPCR) signaling in regulating T cell immunity

AIM

The aim of this paper is to clarify the critical role of GPCR signaling in T cell immunity.

METHODS

The G protein-coupled receptors (GPCRs) are the most common targets in current pharmaceutical industry, and represent the largest and most versatile family of cell surface communicating molecules. GPCRs can be activated by a diverse array of ligands including neurotransmitters, chemokines as well as sensory stimuli. Therefore, GPCRs are involved in many key cellular and physiological processes, such as sense of light, taste and smell, neurotransmission, metabolism, endocrine and exocrine secretion. In recent years, GPCRs have been found to play an important role in immune system. T cell is an important type of immune cell, which plays a central role in cell-mediated immunity. A variety of GPCRs and their signaling mediators (RGS proteins, GRKs and β-arrestin) have been found to express in T cells and involved T cell-mediated immunity. We will summarize the role of GPCR signaling and their regulatory molecules in T cell activation, homeostasis and function in this article.

RESULTS

GPCR signaling plays an important role in T cell activation, homeostasis and function.

CONCLUSION

GPCR signaling is critical in regulating T cell immunity.

Accommodation and related conditions in vascularized composite allografts

PURPOSE OF REVIEW

The outcome of vascularized composite allografts (VCA) often appear unrelated to the presence of donor-specific antibodies (DSA) in blood of the recipient or deposition of complement in the graft. The attenuation of injury and the absence of rejection in other types of grafts despite manifest donor-specific immunity have been explained by accommodation (acquired resistance to immune-mediated injury), adaptation (loss of graft antigen) and/or enhancement (antibody-mediated antigen blockade). Whether and how accommodation, adaptation and/or enhancement impact on the outcome of VCA is unknown. Here we consider how recent observations concerning accommodation in organ transplants might advance understanding and resolve uncertainties about the clinical course of VCA.

RECENT FINDINGS

Investigation of the mechanisms through which kidney allografts avert antibody-mediated injury and rejection provide insights potentially applicable to VCA. Interaction of DSA can facilitate replacement of donor by recipient endothelial cells, modulate or decrease synthesis of antigen, mobilize antigen that in turn blocks further immune recognition and limit the amount of bound antibody, allowing accommodation to ensue. These processes also can explain the apparent dissociation between the presence and levels of DSA in blood, deposition of C4d in grafts and antibody-mediated rejection. Over time the processes might also explain the inception of chronic graft changes.

SUMMARY

The disrupted tissue in VCA and potential for repopulation by endothelial cells of the recipient establish conditions that potentially decrease susceptibility to acute antibody-mediated rejection. These conditions include clonal suppression of donor-specific B cells, and adaptation, enhancement and accommodation. This setting also potentially highlights heretofore unrecognized interactions between these 'protective' processes.

Pathogenic roles of B lymphocytes in systemic sclerosis

Systemic sclerosis (SSc) is a collagen disease characterized by autoimmunity and excessive extracellular matrix deposition in the skin and visceral organs. Although the pathogenic relationship between systemic autoimmunity and the clinical manifestations of SSc remains unknown, SSc patients show a variety of abnormal immune activation including the production of disease-specific autoantibodies and cytokine production. Many recent studies have demonstrated that immune cells, including T cells, B cells, and macrophages, have a variety of immunological abnormalities in SSc. So far, several groups and our group reported that B cells play a critical role in systemic autoimmunity and disease expression through various functions, such as cytokine production, lymphoid organogenesis, and induction of other immune cell activation in addition to autoantibody production. Recent studies show that B cells from SSc patients demonstrate an up-regulated CD19 expression, a crucial regulator of B cell activation, which induces chronic hyper-reactivity of memory B cells and SSc-specific autoantibody production and also causes fibrosis of several organs. Furthermore, in SSc-model mice, such as tight-skin mice, bleomycin-induced SSc model mice, and DNA topoisomerase I and complete Freund's adjuvant-induced SSc model mice, have abnormal B cell activation which associates with skin and lung fibrosis. Indeed, B cell depletion therapy using anti-CD20 Ab, Rituximab, is considered to one potential beneficial treatment for patients with SSc. However, there is no direct evidence which can explain how B cells, especially autoantigen-reactive B cells, progress or regulate disease manifestations of SSc. Collectively, B cell abnormalities in SSc is most likely participating in fibrosis and tissue damage of SSc. If the relationship between SSc-specific tissue damage and B cell abnormalities is revealed, these findings lead to novel effective therapy for SSc.

Antigen Density Dictates Immune Responsiveness following Red Blood Cell Transfusion

Although RBC transfusion can result in the development of anti-RBC alloantibodies that increase the probability of life-threatening hemolytic transfusion reactions, not all patients generate anti-RBC alloantibodies. However, the factors that regulate immune responsiveness to RBC transfusion remain incompletely understood. One variable that may influence alloantibody formation is RBC alloantigen density. RBC alloantigens exist at different densities on the RBC surface and likewise exhibit distinct propensities to induce RBC alloantibody formation. However, although distinct alloantigens reside on the RBC surface at different levels, most alloantigens also represent completely different structures, making it difficult to separate the potential impact of differences in Ag density from other alloantigen features that may also influence RBC alloimmunization. To address this, we generated RBCs that stably express the same Ag at different levels. Although exposure to RBCs with higher Ag levels induces a robust Ab response, RBCs bearing low Ag levels fail to induce RBC alloantibodies. However, exposure to low Ag-density RBCs is not without consequence, because recipients subsequently develop Ag-specific tolerance. Low Ag-density RBC-induced tolerance protects higher Ag-density RBCs from immune-mediated clearance, is Ag specific, and occurs through the induction of B cell unresponsiveness. These results demonstrate that Ag density can potently impact immune outcomes following RBC transfusion and suggest that RBCs with altered Ag levels may provide a unique tool to induce Ag-specific tolerance.

B lymphocytes in systemic sclerosis: Abnormalities and therapeutic targets

Systemic sclerosis (SSc) is a connective tissue disease characterized by excessive extracellular matrix deposition in the skin and visceral organs with an autoimmune background. Although the pathogenic relationship between systemic autoimmunity and the clinical manifestations remains unknown, SSc patients have immunological abnormalities including the production of disease-specific autoantibodies. Recent studies have demonstrated that B cells play a crucial role in systemic autoimmunity and disease expression via various functions in addition to autoantibody production. Recent studies show that B cells from SSc patients demonstrate an upregulated CD19 signaling pathway, which is a crucial regulator of B-cell activation, that induces SSc-specific autoantibody production in SSc. In addition, B cells from SSc patients exhibit an overexpression of CD19. Consistently, in CD19 transgenic mice, CD19 overexpression induces SSc-specific autoantibody production. SSc patients have also intrinsic B-cell abnormalities characterized by chronic hyperreactivity of memory B cells, possibly due to CD19 overexpression. Similarly, B cells from a tight-skin mouse, a genetic model of SSc, show augmented CD19 signaling and chronic hyperreactivity. Furthermore, in bleomycin-induced SSc model mice, endogenous ligands for Toll-like receptors, induced by bleomycin treatment, stimulate B cells to produce various fibrogenic cytokines and autoantibodies. Remarkably, CD19 loss results in inhibition of B-cell hyperreactivity and elimination of autoantibody production, which is associated with improvement of fibrosis. Taken together, altered B-cell function may result in tissue fibrosis, as well as autoimmunity, in SSc. Although further studies and greater understanding are needed, B cells are potential therapeutic target in SSc.

Clonal redemption of autoantibodies by somatic hypermutation away from self-reactivity during human immunization

Clonal anergy is an enigmatic self-tolerance mechanism because no apparent purpose is served by retaining functionally silenced B cells bearing autoantibodies. Human autoantibodies with IGHV4-34*01 heavy chains bind to poly-N-acetyllactosamine carbohydrates (I/i antigen) on erythrocytes and B lymphocytes, cause cold agglutinin disease, and are carried by 5% of naive B cells that are anergic. We analyzed the specificity of three IGHV4-34*01 IgG antibodies isolated from healthy donors immunized against foreign rhesus D alloantigen or vaccinia virus. Each IgG was expressed and analyzed either in a hypermutated immune state or after reverting each antibody to its unmutated preimmune ancestor. In each case, the preimmune ancestor IgG bound intensely to normal human B cells bearing I/i antigen. Self-reactivity was removed by a single somatic mutation that paradoxically decreased binding to the foreign immunogen, whereas other mutations conferred increased foreign binding. These data demonstrate the existence of a mechanism for mutation away from self-reactivity in humans. Because 2.5% of switched memory B cells use IGHV4-34*01 and >43% of these have mutations that remove I/i binding, clonal redemption of anergic cells appears efficient during physiological human antibody responses.

Ikaros limits follicular B cell activation by regulating B cell receptor signaling pathways

The Ikaros transcription factor is essential for early B cell development, but its effect on mature B cells is debated. We show that Ikaros is required to limit the response of naive splenic B cells to B cell receptor signals. Ikaros deficient follicular B cells grow larger and enter cell cycle faster after anti-IgM stimulation. Unstimulated mutant B cells show deregulation of positive and negative regulators of signal transduction at the mRNA level, and constitutive phosphorylation of ERK, p38, SYK, BTK, AKT and LYN. Stimulation results in enhanced and prolonged ERK and p38 phosphorylation, followed by hyper-proliferation. Pharmacological inhibition of ERK and p38 abrogates the increased proliferative response of Ikaros deficient cells. These results suggest that Ikaros functions as a negative regulator of follicular B cell activation.

Activation-Induced Cytidine Deaminase Expression in Human B Cell Precursors Is Essential for Central B Cell Tolerance

Activation-induced cytidine deaminase (AID), the enzyme-mediating class-switch recombination (CSR) and somatic hypermutation (SHM) of immunoglobulin genes, is essential for the removal of developing autoreactive B cells. How AID mediates central B cell tolerance remains unknown. We report that AID enzymes were produced in a discrete population of immature B cells that expressed recombination-activating gene 2 (RAG2), suggesting that they undergo secondary recombination to edit autoreactive antibodies. However, most AID+ immature B cells lacked anti-apoptotic MCL-1 and were deleted by apoptosis. AID inhibition using lentiviral-encoded short hairpin (sh)RNA in B cells developing in humanized mice resulted in a failure to remove autoreactive clones. Hence, B cell intrinsic AID expression mediates central B cell tolerance potentially through its RAG-coupled genotoxic activity in self-reactive immature B cells.

Reprint of: B cells in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) continues to be a common complication of allogeneic hematopoietic stem cell transplantation. Unlike acute graft-versus-host disease, which is mediated almost entirely by donor T cells, the immune pathology of cGVHD is more complex and donor B cells have also been found to play an important role. Recent studies from several laboratories have enhanced our understanding of how donor B cells contribute to this clinical syndrome and this has led to new therapeutic opportunities. Here, Dr Sarantopoulos reviews some of the important mechanisms responsible for persistent B cell activation and loss of B cell tolerance in patients with cGVHD. Dr Blazar describes recent studies in preclinical models that have identified novel B cell-directed agents that may be effective for prevention or treatment of cGVHD. Some B cell-directed therapies have already been tested in patients with cGVHD and Dr Cutler reviews the results of these studies documenting the potential efficacy of this approach. Supported by mechanistic studies in patients and preclinical models, new B cell-directed therapies for cGVHD will now be evaluated in clinical trials.

Dynamic tuning of lymphocytes: physiological basis, mechanisms, and function

Dynamic tuning of cellular responsiveness as a result of repeated stimuli improves the ability of cells to distinguish physiologically meaningful signals from each other and from noise. In particular, lymphocyte activation thresholds are subject to tuning, which contributes to maintaining tolerance to self-antigens and persisting foreign antigens, averting autoimmunity and immune pathogenesis, but allowing responses to strong, structured perturbations that are typically associated with acute infection. Such tuning is also implicated in conferring flexibility to positive selection in the thymus, in controlling the magnitude of the immune response, and in generating memory cells. Additional functional properties are dynamically and differentially tuned in parallel via subthreshold contact interactions between developing or mature lymphocytes and self-antigen-presenting cells. These interactions facilitate and regulate lymphocyte viability, maintain their functional integrity, and influence their responses to foreign antigens and accessory signals, qualitatively and quantitatively. Bidirectional tuning of T cells and antigen-presenting cells leads to the definition of homeostatic set points, thus maximizing clonal diversity.

Abnormal B lymphocyte activation and function in systemic sclerosis

Systemic sclerosis (SSc) is characterized by tissue fibrosis and autoimmunity. Although the pathogenic relationship between autoimmunity and clinical manifestations of SSc remains unknown, SSc patients display abnormal immune responses including the production of disease-specific autoantibodies. Previous studies have demonstrated that B cells play a critical role in systemic autoimmunity and disease expression through various functions such as induction of the activation of other immune cells in addition to autoantibody production. CD19 is a crucial regulator of B cell activation. Recent studies demonstrated that B cells from SSc patients showed an up-regulated CD19 signaling pathway that induced SSc-specific autoantibody production in SSc mouse models. CD19 transgenic mice lost tolerance for autoantigen and generated autoantibodies spontaneously. B cells from SSc patients exhibited an overexpression of CD19 that induced SSc-specific autoantibody production in transgenic mice. Moreover, SSc patients displayed intrinsic B cell abnormalities characterized by chronic hyper-reactivity of memory B cells, which was possibly due to CD19 overexpression. Similarly, B cells from a tight-skin mouse, a genetic model of SSc, showed augmented CD19 signaling. In bleomycin-induced SSc mouse models, endogenous ligands for toll-like receptor 4 induced by bleomycin stimulated B cells to produce various fibrogenic cytokines and autoantibodies. Remarkably, the loss of CD19 resulted in the inhibition of B cell hyper-reactivity and autoantibody production, which are associated with improvements in fibrosis and a parallel decrease in fibrogenic cytokine production by B cells. Taken together, the findings suggest that altered B cell function may result in tissue fibrosis as well as autoimmunity in SSc.

B cells in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) continues to be a common complication of allogeneic hematopoietic stem cell transplantation. Unlike acute graft-versus-host disease, which is mediated almost entirely by donor T cells, the immune pathology of cGVHD is more complex and donor B cells have also been found to play an important role. Recent studies from several laboratories have enhanced our understanding of how donor B cells contribute to this clinical syndrome and this has led to new therapeutic opportunities. Here, Dr Sarantopoulos reviews some of the important mechanisms responsible for persistent B cell activation and loss of B cell tolerance in patients with cGVHD. Dr Blazar describes recent studies in preclinical models that have identified novel B cell-directed agents that may be effective for prevention or treatment of cGVHD. Some B cell-directed therapies have already been tested in patients with cGVHD and Dr Cutler reviews the results of these studies documenting the potential efficacy of this approach. Supported by mechanistic studies in patients and preclinical models, new B cell-directed therapies for cGVHD will now be evaluated in clinical trials.

In utero hematopoietic cell transplantation: induction of donor specific immune tolerance and postnatal transplants

In utero hematopoietic cell transplantation (IUHCT) is a non-myeloablative non-immunosuppressive transplant approach that allows for donor cell engraftment across immunologic barriers. Successful engraftment is associated with donor-specific tolerance. IUHCT has the potential to treat a large number of congenital hematologic, immunologic, and genetic diseases either by achieving high enough engraftment levels following a single IUHCT or by inducing donor specific tolerance to allow for non-toxic same-donor postnatal transplants. This review evaluates donor specific tolerance induction achieved by IUHCT. Specifically it addresses the need to achieve threshold levels of donor cell engraftment following IUHCT to consistently obtain immunologic tolerance. The mechanisms of tolerance induction including partial deletion of donor reactive host T cells by direct and indirect antigen presentation and the role of regulatory T cells in maintaining tolerance are reviewed. Finally, this review highlights the promising clinical potential of in utero tolerance induction to provide a platform on which postnatal cellular and organ transplants can be performed without myeloablative or immunosuppressive conditioning.

Chance, genetics, and the heterogeneity of disease and pathogenesis in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a remarkably complex and heterogeneous systemic autoimmune disease. Disease complexity within individuals and heterogeneity among individuals, even genetically identical individuals, is driven by stochastic execution of a complex inherited program. Genome-wide association studies (GWAS) have progressively improved understanding of which genes are most critical to the potential for SLE and provided illuminating insight about the immune mechanisms that are engaged in SLE. What initiates expression of the genetic program to cause SLE within an individual and how that program is initiated remains poorly understood. If we extrapolate from all of the different experimental mouse models for SLE, we can begin to appreciate why SLE is so heterogeneous and consequently why prediction of disease outcome is so difficult. In this review, we critically evaluate extrinsic versus intrinsic cellular functions in the clearance and elimination of cellular debris and how dysfunction in that system may promote autoimmunity to nuclear antigens. We also examine several mouse models genetically prone to SLE either because of natural inheritance or inheritance of induced mutations to illustrate how different immune mechanisms may initiate autoimmunity and affect disease pathogenesis. Finally, we describe the heterogeneity of disease manifestations in SLE and discuss the mechanisms of disease pathogenesis with emphasis on glomerulonephritis. Particular attention is given to discussion of how anti-DNA autoantibody initiates experimental lupus nephritis (LN) in mice.

B cell receptor signaling-based index as a biomarker for the loss of peripheral immune tolerance in autoreactive B cells in rheumatoid arthritis

This study examines the loss of peripherally induced B cell immune tolerance in Rheumatoid arthritis (RA) and establishes a novel signaling-based measure of activation in a subset of autoreactive B cells - the Induced tolerance status index (ITSI). Naturally occurring naïve autoreactive B cells can escape the “classical” tolerogenic mechanisms of clonal deletion and receptor editing, but remain peripherally tolerized through B cell receptor (BCR) signaling inhibition (postdevelopmental “receptor tuning” or anergy). ITSI is a statistical index that numerically determines the level of homology between activation patterns of BCR signaling intermediaries in B cells that are either tolerized or activated by auto antigen exposure, and thus quantifies the level of peripheral immune tolerance. The index is based on the logistic regression analysis of phosphorylation levels in a panel of BCR signaling proteins. Our results demonstrate a new approach to identifying autoreactive B cells based on their BCR signaling features.

Activation of Ras overcomes B-cell tolerance to promote differentiation of autoreactive B cells and production of autoantibodies

Newly generated immature B cells are selected to enter the peripheral mature B-cell pool only if they do not bind (or bind limited amount of) self-antigen. We previously suggested that this selection relies on basal extracellular signal-regulated kinase (Erk) activation mediated by tonic B-cell antigen receptor (BCR) signaling and that this signal can be replaced by an active rat sarcoma (Ras), which are small GTPase proteins. In this study we compared the activity of Ras and Erk in nonautoreactive and autoreactive immature B cells and investigated whether activation of Ras can break tolerance. Our results demonstrate lower levels of active Erk and Ras in autoreactive immature B cells, although this is evident only when these cells display medium/high avidity for self-antigen. Basal activation of Erk in immature B cells is proportional to surface IgM and dependent on sarcoma family kinases, whereas it is independent of B-cell activating factor, IFN, and Toll-like receptor signaling. Ectopic expression of the constitutively active mutant Ras form N-RasD12 in autoreactive cells raises active Erk, halts receptor editing via PI3 kinase, and promotes differentiation via Erk, breaking central tolerance. Moreover, when B cells coexpress autoreactive and nonautoreactive BCRs, N-RasD12 leads also to a break in peripheral tolerance with the production of autoantibodies. Our findings indicate that in immature B cells, basal activation of Ras and Erk are controlled by tonic BCR signaling, and that positive changes in Ras activity can lead to a break in both central and peripheral B-cell tolerance.

Actin cytoskeletal defects in immunodeficiency

The importance of the cytoskeleton in mounting a successful immune response is evident from the wide range of defects that occur in actin-related primary immunodeficiencies (PIDs). Studies of these PIDs have revealed a pivotal role for the actin cytoskeleton in almost all stages of immune system function, from hematopoiesis and immune cell development, through to recruitment, migration, intercellular and intracellular signaling, and activation of both innate and adaptive immune responses. The major focus of this review is the immune defects that result from mutations in the Wiskott-Aldrich syndrome gene (WAS), which have a broad impact on many different processes and give rise to clinically heterogeneous immunodeficiencies. We also discuss other related genetic defects and the possibility of identifying new genetic causes of cytoskeletal immunodeficiency.

Mercury alters B-cell protein phosphorylation profiles

Environmental exposure to mercury is suggested to contribute to human immune dysfunction. To shed light on the mechanism, we identified changes in the phosphoproteomic profile of the WEHI-231 B cell line after intoxication with Hg(2+). These changes were compared to changes in the phosphoproteome that were induced by pervanadate or okadaic acid exposure. Both 250 μM HgCl2 and pervanadate, a known phosphotyrosine phosphatase inhibitor, caused an increase in the number of proteins identified after TiO2 affinity selection and LC-MS/MS analysis. Pervanadate treatment had a larger effect than Hg(2+) on the number of Scansite motifs that were tyrosine-phosphorylated, 17, and Ingenuity canonical signaling pathways activated, 4, with score >5.0. However, Hg(2+) had a more focused effect, primarily causing tyrosine-phosphorylation in src homology 2 domains in proteins that are in the B cell receptor signaling pathway. The finding that many of the changes induced by Hg(2+) overlap with those of pervanadate, indicates that at high concentrations Hg(2+) inhibits protein tyrosine phosphatases.

Age-specific mortality during the 1918 influenza pandemic: unravelling the mystery of high young adult mortality

The worldwide spread of a novel influenza A (H1N1) virus in 2009 showed that influenza remains a significant health threat, even for individuals in the prime of life. This paper focuses on the unusually high young adult mortality observed during the Spanish flu pandemic of 1918. Using historical records from Canada and the U.S., we report a peak of mortality at the exact age of 28 during the pandemic and argue that this increased mortality resulted from an early life exposure to influenza during the previous Russian flu pandemic of 1889-90. We posit that in specific instances, development of immunological memory to an influenza virus strain in early life may lead to a dysregulated immune response to antigenically novel strains encountered in later life, thereby increasing the risk of death. Exposure during critical periods of development could also create holes in the T cell repertoire and impair fetal maturation in general, thereby increasing mortality from infectious diseases later in life. Knowledge of the age-pattern of susceptibility to mortality from influenza could improve crisis management during future influenza pandemics.

Glycopolymer probes of signal transduction

Glycans are key participants in biological processes ranging from reproduction to cellular communication to infection. Revealing glycan roles and the underlying molecular mechanisms by which glycans manifest their function requires access to glycan derivatives that vary systematically. To this end, glycopolymers (polymers bearing pendant carbohydrates) have emerged as valuable glycan analogs. Because glycopolymers can readily be synthesized, their overall shape can be varied, and they can be altered systematically to dissect the structural features that underpin their activities. This review provides examples in which glycopolymers have been used to effect carbohydrate-mediated signal transduction. Our objective is to illustrate how these powerful tools can reveal the molecular mechanisms that underlie carbohydrate-mediated signal transduction.

[Auto-vaccines: an immunological alternative to gene silencing]

Auto-vaccination is a procedure that recently attracted the interest of a growing number of investigators as an alternative to gene inactivation for functional studies of cytokines or other mediators. It is based on the observation that autologous cytokines cross-linked to a foreign protein or peptide are recognized by self-reactive B cells that present foreign peptides, and by doing so attract illicit help from helper T cells that recognize the foreign peptide on the self-reactive B cell MHC Class II complex. This leads to the production of antibodies reacting with self-proteins and thus to neutralization of the targeted factor. Here, we summarize the different techniques that were successful in breaking this self-tolerance and provide several examples of the functional consequences of these auto-vaccines. An additional output of auto-vaccination is the production of mouse monoclonal antibodies against mouse factors. Such antibodies have obvious advantages for long-term use in vivo.

The molecular pathways underlying host resistance and tolerance to pathogens

Breeding livestock that are better able to withstand the onslaught of endemic- and exotic pathogens is high on the wish list of breeders and farmers world-wide. However, the defense systems in both pathogens and their hosts are complex and the degree of genetic variation in resistance and tolerance will depend on the trade-offs that they impose on host fitness as well as their life-histories. The genes and pathways underpinning resistance and tolerance traits may be distinct or intertwined as the outcome of any infection is a result of a balance between collateral damage of host tissues and control of the invading pathogen. Genes and molecular pathways associated with resistance are mainly expressed in the mucosal tract and the innate immune system and control the very early events following pathogen invasion. Resistance genes encode receptors involved in uptake of pathogens, as well as pattern recognition receptors (PRR) such as the toll-like receptor family as well as molecules involved in strong and rapid inflammatory responses which lead to rapid pathogen clearance, yet do not lead to immunopathology. In contrast tolerance genes and pathways play a role in reducing immunopathology or enhancing the host's ability to protect against pathogen associated toxins. Candidate tolerance genes may include cytosolic PRRs and unidentified sensors of pathogen growth, perturbation of host metabolism and intrinsic danger or damage associated molecules. In addition, genes controlling regulatory pathways, tissue repair and resolution are also tolerance candidates. The identities of distinct genetic loci for resistance and tolerance to infectious pathogens in livestock species remain to be determined. A better understanding of the mechanisms involved and phenotypes associated with resistance and tolerance should ultimately help to improve livestock health and welfare.

Mechanisms involved in the p62-73 idiopeptide-modulated delay of lupus nephritis in SNF(1) mice

The F(1) progeny of the (SWR × NZB) cross develop a lupus-like disease with high serum titers of autoantibodies, and increased frequency and severity of immune complex-mediated glomerulonephritis in females. In previous work, we found that an idiotypic peptide corresponding to aa62-73 (p62-73) of the heavy chain variable region of autoantibody 540 (Id(LN)F(1)) induced the proliferation of p62-73 idiotype-reactive T cell clones. Further, monthly immunization of pre-nephritic SNF(1) female mice with p62-73 resulted in decreased nephritis and prolonged life spans. Here we show that this treatment modulated proliferative responses to Id(LN)F(1) antigen, including a reduction in the population of idiopeptide-presenting antigen-presenting cells (APCs), as early as two weeks after immunization (10 weeks of age). Th1-type cytokine production was increased at 12 weeks of age. The incidence and severity of nephritis was reduced by 14 weeks compared to controls. Clinical indicators of nephritis, specifically histological evidence of glomerulonephritis and urine protein levels, were reduced by 20 weeks. Together these data suggest that events involved in the mechanism(s) whereby p62-73 immunization delayed nephritis occurred early after immunization, and involved modulation of APCs, B and T cell populations.

The Fas/CD95 Receptor Regulates the Death of Autoreactive B Cells and the Selection of Antigen-Specific B Cells

Cell death receptors have crucial roles in the regulation of immune responses. Here we review recent in vivo data confirming that the Fas death receptor (TNFSR6) on B cells is important for the regulation of autoimmunity since the impairment of only Fas function on B cells results in uncontrolled autoantibody production and autoimmunity. Fas plays a role in the elimination of the non-specific and autoreactive B cells in germinal center, while during the selection of antigen-specific B cells different escape signals ensure the resistance to Fas-mediated apoptosis. Antigen-specific survival such as BCR or MHCII signal or coreceptors (CD19) cooperating with BCR inhibits the formation of death inducing signaling complex. Antigen-specific survival can be reinforced by antigen-independent signals of IL-4 or CD40 overproducing the anti-apoptotic members of the Bcl-2 family proteins.