Toll-like receptor 7 (TLR7)-driven accumulation of a novel CD11c⁺ B-cell population is important for the development of autoimmunity

Complement in basic processes of the cell

The complement system is reemerging in the last few years not only as key element of innate immunity against pathogens, but also as a main regulator of local adaptive responses, affecting dendritic cells as well as T and B lymphocytes. We review data showing that leucocytes are capable of significant autocrine synthesis of complement proteins, and express a large range of complement receptors, which in turn regulate their differentiation and effector functions while cross talking with other innate receptors such as Toll-like receptors. Other unconventional roles of complement proteins are reviewed, including their impact in non-leukocytes and their intracellular cleavage by vesicular proteases, which generate critical cues required for T cell function. Thus, leucocytes are very much aware of complement-derived information, both extracellular and intracellular, to elaborate their responses, offering rich avenues for therapeutic intervention and new hypothesis for conserved major histocompatibility complex complotypes.

T Cell Production of IFNγ in Response to TLR7/IL-12 Stimulates Optimal B Cell Responses to Viruses

Knowledge of the processes that underlie IgG subclass switching could inform strategies designed to counteract infections and autoimmunity. Here we show that TLR7 ligands induce subsets of memory CD4 and CD8 T cells to secrete interferon γ (IFNγ) in the absence of antigen receptor stimulation. In turn, TLR ligation and IFNγ cause B cells to express the transcription factor, T-bet, and to switch immunoglobulin production to IgG2a/c. Absence of TLR7 in T cells leads to the impaired T-bet expression in B cells and subsequent inefficient IgG2a isotype switching both in vitro and during the infection with Friend virus in vivo. Our results reveal a surprising mechanism of antiviral IgG subclass switching through T-cell intrinsic TLR7/IL-12 signaling.

Age-Associated B Cells with Proinflammatory Characteristics Are Expanded in a Proportion of Multiple Sclerosis Patients

Immune aging occurs in the elderly and in autoimmune diseases. Recently, IgD^-CD27^- (double negative, DN) and CD21^-CD11c⁺ (CD21^low) B cells were described as age-associated B cells with proinflammatory characteristics. This study investigated the prevalence and functional characteristics of DN and CD21^low B cells in multiple sclerosis (MS) patients. Using flow cytometry, we demonstrated a higher proportion of MS patients younger than 60 y with peripheral expansions of DN (8/41) and CD21^low (9/41) B cells compared with age-matched healthy donors (1/33 and 2/33, respectively), which indicates an increase in age-associated B cells in MS patients. The majority of DN B cells had an IgG⁺ memory phenotype, whereas CD21^low B cells consisted of a mixed population of CD27^- naive, CD27⁺ memory, IgG⁺, and IgM⁺ cells. DN B cells showed similar (MS patients) or increased (healthy donors) MHC-II expression as class-switched memory B cells and intermediate costimulatory molecule expression between naive and class-switched memory B cells, indicating their potential to induce (proinflammatory) T cell responses. Further, DN B cells produced proinflammatory and cytotoxic cytokines following ex vivo stimulation. Increased frequencies of DN and CD21^low B cells were found in the cerebrospinal fluid of MS patients compared with paired peripheral blood. In conclusion, a proportion of MS patients showed increased peripheral expansions of age-associated B cells. DN and CD21^low B cell frequencies were further increased in MS cerebrospinal fluid. These cells could contribute to inflammation by induction of T cell responses and the production of proinflammatory cytokines.

Leukocyte arrest: Biomechanics and molecular mechanisms of β2 integrin activation

Integrins are a group of heterodimeric transmembrane receptors that play essential roles in cell-cell and cell-matrix interaction. Integrins are important in many physiological processes and diseases. Integrins acquire affinity to their ligand by undergoing molecular conformational changes called activation. Here we review the molecular biomechanics during conformational changes of integrins, integrin functions in leukocyte biorheology (adhesive functions during rolling and arrest) and molecules involved in integrin activation.

The transcriptional repressor Gfi1 prevents lupus autoimmunity by restraining TLR7 signaling

The transcriptional repressor growth factor independence 1 (Gfi1) is important in myeloid and lymphoid differentiation. In the current study we evaluated the involvement of Gfi1 in systemic lupus erythematosus (SLE). We found that Genista mice, which carry a hypomorphic mutation in the gfi1 gene or Gfi1-deficient (Gfi1^-/- ) mice develop signs of spontaneous lupus autoimmunity, including increased serum levels of IgM and IgG2a, autoantibodies against RNA and DNA, glomerular immunodeposits and increased frequencies of plasmablasts, germinal center (GC) B cells and age-associated B cells (ABCs). On the contrary, Genista mice deprived of TLR7 did not show any of these phenotypes, suggesting that the observed lupus autoimmunity in Genista mice is TLR7-dependent. Moreover, Genista mice showed an increased activation of dendritic cells (DCs), B and T cells that was dependent on TLR7 for DCs and B cells, but not for T cells. Upon TLR7 or TLR4 stimulation Genista DCs produced increased amounts of TNF, IL-6 and IFN-β and showed increased NF-κB phosphorylation and IRF7 nuclear translocation, suggesting that Gfi1 controls the NF-κB and type I IFN signaling pathway downstream of TLRs. Our data reveal that Gfi1 plays a critical role in the prevention of spontaneous lupus autoimmunity by negatively regulating TLR7 signaling.

Aged B cells alter immune regulation of allografts in mice

Organ transplantation in older people is increasing, but how aging impacts B-cell responses to organ transplantation is still unknown. Here, we show that the depletion of B cells with anti-CD20 antibodies has disparate effects depending on recipient age. In young murine recipients, anti-CD20 treatment impaired the ability of immune modulation to extend skin allograft survival. In contrast, anti-CD20 treatment extended allograft survival in aged recipients treated with immune modulation. Although regulatory B-cell function and the numbers of marginal and follicular B cells were similar between age groups, a subpopulation of B cells, termed age-associated B cells (ABCs), accumulated upon aging. ABCs isolated from aged mice exhibited upregulation of CD73, CD80, CD106, and TLR2 and an increased capacity to augment T-cell alloimmunity compared to ABCs from young mice. Importantly, ABCs from aged, but not young, mice impaired the ability of immune modulation to enhance allograft survival after adoptive transfer into young transplant recipients. Our study indicates that ABCs impair the immune regulation of allografts. Thus, recipient age needs to be considered when proposing B-cell-depleting immune therapy.

Sex differences in immune responses

Males and females differ in their immunological responses to foreign and self-antigens and show distinctions in innate and adaptive immune responses. Certain immunological sex differences are present throughout life, whereas others are only apparent after puberty and before reproductive senescence, suggesting that both genes and hormones are involved. Furthermore, early environmental exposures influence the microbiome and have sex-dependent effects on immune function. Importantly, these sex-based immunological differences contribute to variations in the incidence of autoimmune diseases and malignancies, susceptibility to infectious diseases and responses to vaccines in males and females. Here, we discuss these differences and emphasize that sex is a biological variable that should be considered in immunological studies.

Redefined clinical features and diagnostic criteria in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare primary immunodeficiency disorder typically caused by homozygous AIRE mutations. It classically presents with chronic mucocutaneous candidiasis and autoimmunity that primarily targets endocrine tissues; hypoparathyroidism and adrenal insufficiency are most common. Developing any two of these classic triad manifestations establishes the diagnosis. Although widely recognized in Europe, where nonendocrine autoimmune manifestations are uncommon, APECED is less defined in patients from the Western Hemisphere. We enrolled 35 consecutive American APECED patients (33 from the US) in a prospective observational natural history study and systematically examined their genetic, clinical, autoantibody, and immunological characteristics. Most patients were compound heterozygous; the most common AIRE mutation was c.967_979del13. All but one patient had anti-IFN-ω autoantibodies, including 4 of 5 patients without biallelic AIRE mutations. Urticarial eruption, hepatitis, gastritis, intestinal dysfunction, pneumonitis, and Sjögren's-like syndrome, uncommon entities in European APECED cohorts, affected 40%-80% of American cases. Development of a classic diagnostic dyad was delayed at mean 7.38 years. Eighty percent of patients developed a median of 3 non-triad manifestations before a diagnostic dyad. Only 20% of patients had their first two manifestations among the classic triad. Urticarial eruption, intestinal dysfunction, and enamel hypoplasia were prominent among early manifestations. Patients exhibited expanded peripheral CD4+ T cells and CD21loCD38lo B lymphocytes. In summary, American APECED patients develop a diverse syndrome, with dramatic enrichment in organ-specific nonendocrine manifestations starting early in life, compared with European patients. Incorporation of these new manifestations into American diagnostic criteria would accelerate diagnosis by approximately 4 years and potentially prevent life-threatening endocrine complications.

Rheumatoid Arthritis, Immunosenescence and the Hallmarks of Aging

Age is the most important risk factor for the development of infectious diseases, cancer and chronic inflammatory diseases including rheumatoid arthritis (RA). The very act of living causes damage to cells. A network of molecular, cellular and physiological maintenance and repair systems creates a buffering capacity against these damages. Aging leads to progressive shrinkage of the buffering capacity and increases vulnerability. In order to better understand the complex mammalian aging processes, nine hallmarks of aging and their interrelatedness were recently put forward.

RA is a chronic autoimmune disease affecting the joints. Although RA may develop at a young age, the incidence of RA increases with age. It has been suggested that RA may develop as a consequence of premature aging (immunosenescence) of the immune system. Alternatively, premature aging may be the consequence of the inflammatory state in RA. In an effort to answer this chicken and egg conundrum, we here outline and discuss the nine hallmarks of aging, their contribution to the pre-aged phenotype and the effects of treatment on the reversibility of immunosenescence in RA.

Cutting Edge: IL-4, IL-21, and IFN-γ Interact To Govern T-bet and CD11c Expression in TLR-Activated B Cells

T-bet and CD11c expression in B cells is linked with IgG2c isotype switching, virus-specific immune responses, and humoral autoimmunity. However, the activation requisites and regulatory cues governing T-bet and CD11c expression in B cells remain poorly defined. In this article, we reveal a relationship among TLR engagement, IL-4, IL-21, and IFN-γ that regulates T-bet expression in B cells. We find that IL-21 or IFN-γ directly promote T-bet expression in the context of TLR engagement. Further, IL-4 antagonizes T-bet induction. Finally, IL-21, but not IFN-γ, promotes CD11c expression independent of T-bet. Using influenza virus and Heligmosomoides polygyrus infections, we show that these interactions function in vivo to determine whether T-bet(+) and CD11c(+) B cells are formed. These findings suggest that T-bet(+) B cells seen in health and disease share the common initiating features of TLR-driven activation within this circumscribed cytokine milieu.

Antigen presenting cell abnormalities in the Cln3(-/-) mouse model of juvenile neuronal ceroid lipofuscinosis

Mutations of the CLN3 gene lead to juvenile neuronal ceroid lipofuscinosis (JNCL), an autosomal recessive lysosomal storage disorder that causes progressive neurodegeneration in children and adolescents. There is evidence of immune system involvement in pathology that has been only minimally investigated. We characterized bone marrow stem cell-derived antigen presenting cells (APCs), peritoneal macrophages, and leukocytes from spleen and blood, harvested from the Cln3(-/-) mouse model of JNCL. We detected dramatically elevated CD11c surface levels and increased total CD11c protein in Cln3(-/-) cell samples compared to wild type. This phenotype was specific to APCs and also to a loss of CLN3, as surface levels did not differ from wild type in other leukocyte subtypes nor in cells from two other NCL mouse models. Subcellularly, CD11c was localized to lipid rafts, indicating that perturbation of surface levels is attributable to derangement of raft dynamics, which has previously been shown in Cln3 mutant cells. Interrogation of APC function revealed that Cln3(-/-) cells have increased adhesiveness to CD11c ligands as well as an abnormal secretory pattern that closely mimics what has been previously reported for Cln3 mutant microglia. Our results show that CLN3 deficiency alters APCs, which can be a major contributor to the autoimmune response in JNCL.

Nodal marginal zone B cells in mice: a novel subset with dormant self-reactivity

Marginal zone (MZ) B cells, representing a distinct subset of innate-like B cells, mount rapid T-independent responses to blood-borne antigens. They express low-affinity polyreactive antigen receptors that recognize both foreign and self-structures. The spleen is considered the exclusive site for murine MZ B cells. However, we have here identified B cells with a MZ B-cell phenotype in the subcapsular sinuses of mouse lymph nodes. The nodal MZ (nMZ) B cells display high levels of IgM, costimulators and TLRs, and are represented by naïve and memory cells. The frequency of nMZ B cells is about 1–6% of nodal B cells depending on mouse strain, with higher numbers in older mice and a trend of increased numbers in females. There is a significant expansion of nMZ B cells following immunization with an autoantigen, but not after likewise immunization with a control protein or with the adjuvant alone. The nMZ B cells secrete autoantibodies upon activation and can efficiently present autoantigen to cognate T cells in vitro, inducing T-cell proliferation. The existence of self-reactive MZ B cells in lymph nodes may be a source of autoantigen-presenting cells that in an unfortunate environment may activate T cells leading to autoimmunity.

CD21(-/low) B cells in human blood are memory cells

The complement receptor 2 (CR2, CD21) is part of a complex (CD21/CD19/CD81) acting as a co-receptor to the B cell receptor (BCR). Simultaneous triggering of the BCR and CD21 lowers the threshold for B cell activation. Although CD21 is important, B cells that express low amounts or lack surface CD21 (CD21(-/low) ) are increased in conditions with chronic inflammation, e.g. autoimmune diseases. However, little is known about the CD21(-/low) B cell subset in peripheral blood from healthy donors. Here, we show that CD21(-/low) cells represent approximately 5% of B cells in peripheral blood from adults but are barely detectable in cord blood, after excluding transitional B cells. The CD21(-/low) subset can be divided into CD38(-) 24(+) and CD38(-) 24(low) cells, where most of the CD38(-) 24(+) are CD27(+) immunoglobulin (Ig)M(+) IgD(+) and the CD38(-) 24(low) are switched CD27(-) . Expression levels of additional markers, e.g. CD95 and CD62L, are similar to those on classical memory B cells. In contrast to naive cells, the majority of CD21(-/low) cells lack expression of the ABCB1 transporter. Stimulation with a combination of BCR, Toll-like receptor (TLR)-7/8 and interleukin (IL)-2 induces proliferation and differentiation of the CD21(-/low) B cells comparable to CD21(+) CD27(+) memory B cells. The response excluding BCR agonist is not on par with that of classical memory B cells, although clearly above that of naive B cells. This is ascribed to a weaker response by the CD38(-) 24(low) subset, implying that some memory B cells require not only TLR but also BCR triggering. We conclude that the CD21(-/low) cells in healthy donors are memory B cells.

Virus Infections Incite Pain Hypersensitivity by Inducing Indoleamine 2,3 Dioxygenase

Increased pain sensitivity is a comorbidity associated with many clinical diseases, though the underlying causes are poorly understood. Recently, chronic pain hypersensitivity in rodents treated to induce chronic inflammation in peripheral tissues was linked to enhanced tryptophan catabolism in brain mediated by indoleamine 2,3 dioxygenase (IDO). Here we show that acute influenza A virus (IAV) and chronic murine leukemia retrovirus (MuLV) infections, which stimulate robust IDO expression in lungs and lymphoid tissues, induced acute or chronic pain hypersensitivity, respectively. In contrast, virus-induced pain hypersensitivity did not manifest in mice lacking intact IDO1 genes. Spleen IDO activity increased markedly as MuLV infections progressed, while IDO1 expression was not elevated significantly in brain or spinal cord (CNS) tissues. Moreover, kynurenine (Kyn), a tryptophan catabolite made by cells expressing IDO, incited pain hypersensitivity in uninfected IDO1-deficient mice and Kyn potentiated pain hypersensitivity due to MuLV infection. MuLV infection stimulated selective IDO expression by a discreet population of spleen cells expressing both B cell (CD19) and dendritic cell (CD11c) markers (CD19+ DCs). CD19+ DCs were more susceptible to MuLV infection than B cells or conventional (CD19neg) DCs, proliferated faster than B cells from early stages of MuLV infection and exhibited mature antigen presenting cell (APC) phenotypes, unlike conventional (CD19neg) DCs. Moreover, interactions with CD4 T cells were necessary to sustain functional IDO expression by CD19+ DCs in vitro and in vivo. Splenocytes from MuLV-infected IDO1-sufficient mice induced pain hypersensitivity in uninfected IDO1-deficient recipient mice, while selective in vivo depletion of DCs alleviated pain hypersensitivity in MuLV-infected IDO1-sufficient mice and led to rapid reduction in splenomegaly, a hallmark of MuLV immune pathogenesis. These findings reveal critical roles for CD19+ DCs expressing IDO in host responses to MuLV infection that enhance pain hypersensitivity and cause immune pathology. Collectively, our findings support the hypothesis elevated IDO activity in non-CNS due to virus infections causes pain hypersensitivity mediated by Kyn. Previously unappreciated links between host immune responses to virus infections and pain sensitivity suggest that IDO inhibitors may alleviate heightened pain sensitivity during infections.

IDO2 Modulates T Cell-Dependent Autoimmune Responses through a B Cell-Intrinsic Mechanism

Mechanistic insight into how adaptive immune responses are modified along the self-nonself continuum may offer more effective opportunities to treat autoimmune disease, cancer, and other sterile inflammatory disorders. Recent genetic studies in the KRN mouse model of rheumatoid arthritis demonstrate that the immunomodulatory molecule IDO2 modifies responses to self-antigens; however, the mechanisms involved are obscure. In this study, we show that IDO2 exerts a critical function in B cells to support the generation of autoimmunity. In experiments with IDO2-deficient mice, adoptive transplant experiments demonstrated that IDO2 expression in B cells was both necessary and sufficient to support robust arthritis development. IDO2 function in B cells was contingent on a cognate, Ag-specific interaction to exert its immunomodulatory effects on arthritis development. We confirmed a similar requirement in an established model of contact hypersensitivity, in which IDO2-expressing B cells are required for a robust inflammatory response. Mechanistic investigations showed that IDO2-deficient B cells lacked the ability to upregulate the costimulatory marker CD40, suggesting IDO2 acts at the T-B cell interface to modulate the potency of T cell help needed to promote autoantibody production. Overall, our findings revealed that IDO2 expression by B cells modulates autoimmune responses by supporting the cross talk between autoreactive T and B cells.

Fc Receptor-like 5 Expression Distinguishes Two Distinct Subsets of Human Circulating Tissue-like Memory B Cells

Fc receptor-like (FCRL) 5 is a novel IgG binding protein expressed on B cells, with the capacity to regulate Ag receptor signaling. We assessed FCRL5 expression on circulating B cells from healthy donors and found that FCRL5(+) cells are most enriched among atypical CD21(-/lo)/CD27(-) tissue-like memory (TLM) B cells, which are abnormally expanded in several autoimmune and infectious diseases. Using multicolor flow cytometry, FCRL5(+) TLM cells were found to express more CD11c and several inhibitory receptors than did the FCRL5(-) TLM subset. The homing receptor profiles of the two TLM subsets shared features consistent with migration away from lymphoid tissues, but they also displayed distinct differences. Analysis of IgH V regions in single cells indicated that although both subsets are diverse, the FCRL5(+) subset accumulated significantly more somatic mutations. Furthermore, the FCRL5(+) subset had more switched isotype expression and more extensive proliferative history. Microarray analysis and quantitative RT-PCR demonstrated that the two TLM subsets possess distinct gene expression profiles, characterized by markedly different CD11c, SOX5, T-bet, and RTN4R expression, as well as differences in expression of inhibitory receptors. Functional analysis revealed that the FCRL5(+) TLM subset responds poorly to multiple stimuli compared with the FCRL5(-) subset, as reflected by reduced calcium mobilization and blunted cell proliferation. We propose that the FCRL5(+) TLM subset, but not the FCRL5(-) TLM subset, underwent Ag-driven development and is severely dysfunctional. The present study elucidates the heterogeneity of TLM B cells and provides the basis to dissect their roles in the pathogenesis of inflammatory and infectious diseases.

Cutting Edge: BAFF Promotes Autoantibody Production via TACI-Dependent Activation of Transitional B Cells

Mice overexpressing B cell activating factor of the TNF family (BAFF) develop systemic autoimmunity characterized by class-switched anti-nuclear Abs. Transmembrane activator and CAML interactor (TACI) signals are critical for BAFF-mediated autoimmunity, but the B cell developmental subsets undergoing TACI-dependent activation in settings of excess BAFF remain unclear. We report that, although surface TACI expression is usually limited to mature B cells, excess BAFF promotes the expansion of TACI-expressing transitional B cells. TACI(+) transitional cells from BAFF-transgenic mice are characterized by an activated, cycling phenotype, and the TACI(+) cell subset is specifically enriched for autoreactivity, expresses activation-induced cytidine deaminase and T-bet, and exhibits evidence of somatic hypermutation. Consistent with a potential contribution to BAFF-mediated humoral autoimmunity, TACI(+) transitional B cells from BAFF-transgenic mice spontaneously produce class-switched autoantibodies ex vivo. These combined findings highlight a novel mechanism through which BAFF promotes humoral autoimmunity via direct, TACI-dependent activation of transitional B cells.

Age-Associated B Cells: A T-bet-Dependent Effector with Roles in Protective and Pathogenic Immunity

A newly discovered B cell subset, age-associated B cells, expresses the transcription factor T-bet, has a unique surface phenotype, and accumulates progressively with age. Moreover, B cells with these general features are associated with viral infections and autoimmunity in both mice and humans. In this article, we review current understanding of the characteristics, origins, and functions of these cells. We also suggest that the protective versus pathogenic actions of these cells reflect appropriate versus aberrant engagement of regulatory mechanisms that control the Ab responses to nucleic acid-containing Ags.

CD21 -/low B cells: A Snapshot of a Unique B Cell Subset in Health and Disease

B cells represent one of the cellular components of the immune system that protects the individual from invading pathogens. In response to the invader, these cells differentiate into plasma cells and produce large amounts of antibodies that bind to and eliminate the pathogen. A hallmark of autoimmune diseases is the production of autoantibodies i.e. antibodies that recognize self. Those that are considered pathogenic can damage tissues and organs, either by direct binding or when deposited as immune complexes. For decades, B cells have been considered to play a major role in autoimmune diseases by antibody production. However, as pathogenic autoantibodies appear to derive mainly from T cell dependent responses, T cells have been the focus for many years. The successful treatment of patients with autoimmune diseases with either B cell depletion therapy (rituximab) or inhibition of B cell survival (belimumab), suggested that not only the autoantibodies but also other B cell features are important. This has caused a surge of interest in B cells and their biology resulting in the identification of various subsets e.g. regulatory B cells, several memory B cell subsets etc. Also, in other conditions such as chronic viral infections and primary immunodeficiency, several B cell subsets with unique characteristics have been identified. In this review, we will discuss one of these subsets, a subset that is expanded in conditions characterized by chronic immune stimulation. This B cell subset lacks, or expresses low, surface levels of the complement receptor 2 (CD21) and has therefore been termed CD21(-/low) B cells.

Immunosenescence in renal transplantation: a changing balance of innate and adaptive immunity

PURPOSE OF REVIEW

With global demographic changes and an overall improved healthcare, more older end-stage renal disease (ESRD) patients receive kidney transplants. At the same time, organs from older donors are utilized more frequently. Those developments have and will continue to impact allocation, immunosuppression and efforts improving organ quality.

RECENT FINDINGS

Findings mainly outside the field of transplantation have provided insights into mechanisms that drive immunosenescence and immunogenicity, thus providing a rationale for an age-adapted immunosuppression and relevant clinical trials in the elderly. With fewer rejections in the elderly, alloimmune responses appear to be characterized by a decline in effectiveness and an augmented unspecific immune response.

SUMMARY

Immunosenescence displays broad and ambivalent effects in elderly transplant recipients. Those changes appear to compensate a decline in allospecific effectiveness by a shift towards an augmented unspecific immune response. Immunosuppression needs to target those age-specific changes to optimize outcomes in elderly transplant recipients.

Predominant Role of Plasmacytoid Dendritic Cells in Stimulating Systemic Autoimmunity

Plasmacytoid dendritic cells (pDCs), which are prominent type I interferon (IFN-I)-producing immune cells, have been extensively implicated in systemic lupus erythematosus (SLE). However, whether they participate critically in lupus pathogenesis remains unknown. Recent studies using various genetic and cell type-specific ablation strategies have demonstrated that pDCs play a pivotal role in the development of autoantibodies and the progression of lupus under diverse experimental conditions. The findings of several investigations highlight a notion that pDCs operate critically at the early stage of lupus development. In particular, pDCs have a profound effect on B-cell activation and humoral autoimmunity in vivo. This deeper understanding of the vital role of pDCs in lupus pathogenesis supports the therapeutic targeting of the pDC-IFN-I pathway in SLE.

Genetic Interaction between Lyn, Ets1, and Btk in the Control of Antibody Levels

Tight control of B cell differentiation into plasma cells (PCs) is critical for proper immune responses and the prevention of autoimmunity. The Ets1 transcription factor acts in B cells to prevent PC differentiation. Ets1(-/-) mice accumulate PCs and produce autoantibodies. Ets1 expression is downregulated upon B cell activation through the BCR and TLRs and is maintained by the inhibitory signaling pathway mediated by Lyn, CD22 and SiglecG, and SHP-1. In the absence of these inhibitory components, Ets1 levels are reduced in B cells in a Btk-dependent manner. This leads to increased PCs, autoantibodies, and an autoimmune phenotype similar to that of Ets1(-/-) mice. Defects in inhibitory signaling molecules, including Lyn and Ets1, are associated with human lupus, although the effects are more subtle than the complete deficiency that occurs in knockout mice. In this study, we explore the effect of partial disruption of the Lyn/Ets1 pathway on B cell tolerance and find that Lyn(+/-)Ets1(+/-) mice demonstrate greater and earlier production of IgM, but not IgG, autoantibodies compared with Lyn(+/-) or Ets1(+/-) mice. We also show that Btk-dependent downregulation of Ets1 is important for normal PC homeostasis when inhibitory signaling is intact. Ets1 deficiency restores the decrease in steady state PCs and Ab levels observed in Btk(-/-) mice. Thus, depending on the balance of activating and inhibitory signals to Ets1, there is a continuum of effects on autoantibody production and PC maintenance. This ranges from full-blown autoimmunity with complete loss of Ets1-maintaining signals to reduced PC and Ab levels with impaired Ets1 downregulation.

CD11c-Expressing B Cells Are Located at the T Cell/B Cell Border in Spleen and Are Potent APCs

In addition to the secretion of Ag-specific Abs, B cells may play an important role in the generation of immune responses by efficiently presenting Ag to T cells. We and other investigators recently described a subpopulation of CD11c(+) B cells (Age/autoimmune-associated B cells [ABCs]) that appear with age, during virus infections, and at the onset of some autoimmune diseases and participate in autoimmune responses by secreting autoantibodies. In this study, we assessed the ability of these cells to present Ag and activate Ag-specific T cells. We demonstrated that ABCs present Ag to T cells, in vitro and in vivo, better than do follicular B cells (FO cells). Our data indicate that ABCs express higher levels of the chemokine receptor CCR7, have higher responsiveness to CCL21 and CCL19 than do FO cells, and are localized at the T/B cell border in spleen. Using multiphoton microscopy, we show that, in vivo, CD11c(+) B cells form significantly more stable interactions with T cells than do FO cells. Together, these data identify a previously undescribed role for ABCs as potent APCs and suggest another potential mechanism by which these cells can influence immune responses and/or the development of autoimmunity.

Fate mapping of dendritic cells

Dendritic cells (DCs) are a heterogeneous group of mononuclear phagocytes with versatile roles in immunity. They are classified predominantly based on phenotypic and functional properties, namely their stellate morphology, expression of the integrin CD11c, and major histocompatibility class II molecules, as well as their superior capacity to migrate to secondary lymphoid organs and stimulate naïve T cells. However, these attributes are not exclusive to DCs and often change within inflammatory or infectious environments. This led to debates over cell identification and questioned even the mere existence of DCs as distinct leukocyte lineage. Here, we review experimental approaches taken to fate map DCs and discuss how these have shaped our understanding of DC ontogeny and lineage affiliation. Considering the ontogenetic properties of DCs will help to overcome the inherent shortcomings of purely phenotypic- and function-based approaches to cell definition and will yield a more robust way of DC classification.

Expression of FcRL4 defines a pro-inflammatory, RANKL-producing B cell subset in rheumatoid arthritis

OBJECTIVES

The success of B cell targeting therapies has highlighted the importance of B cells in rheumatoid arthritis pathogenesis. We have previously shown that B cells in the RA synovium are capable of producing pro-inflammatory and bone-destructive cytokines including RANKL. Here we sought to characterise the nature and functional relevance of the RANKL-producing B cell subset in the RA synovium.

METHODS

Synovial fluid and peripheral blood B cells from patients with RA were analysed by flow cytometry for markers of B cell differentiation and activation and for chemokine receptors. FcRL4(+) and FcRL4(-) B cells sorted from synovial fluid were analysed for cytokine expression using Taqman low-density arrays. Synovial tissue biopsies obtained from patients with RA were analysed by immunofluorescence for CD20, RANKL and FcRL4. FCRL4 mRNA expression was determined in synovial tissue of RA patients and non-inflammatory control subjects by real-time PCR.

RESULTS

RANKL-producing B cells in RA synovial tissue and fluid were identified as belonging to a distinct subset of B cells defined by expression of the transmembrane protein FcRL4. FcRL4+ B cells express a distinct combination of cytokines and surface proteins indicating a function distinct from that of FcRL4- B cells. Notably, FcRL4+ B cells expressed high levels of TNF-α and RANKL mRNA.

CONCLUSIONS

We have identified a novel pro-inflammatory B cell population in the RA synovium which is defined by expression of FcRL4 and responsible for RANKL production. This B cell population expresses high levels of CD20, and its removal by rituximab may contribute to the anti-inflammatory effect of this drug.

Sexual dimorphism in autoimmunity

Autoimmune diseases occur when the immune system attacks and destroys the organs and tissues of its own host. Autoimmunity is the third most common type of disease in the United States. Because there is no cure for autoimmunity, it is extremely important to study the mechanisms that trigger these diseases. Most autoimmune diseases predominantly affect females, indicating a strong sex bias. Various factors, including sex hormones, the presence or absence of a second X chromosome, and sex-specific gut microbiota can influence gene expression in a sex-specific way. These changes in gene expression may, in turn, lead to susceptibility or protection from autoimmunity, creating a sex bias for autoimmune diseases. In this Review we discuss recent findings in the field of sex-dependent regulation of gene expression and autoimmunity.

B-cell exhaustion in HIV infection: the role of immune activation

PURPOSE OF REVIEW

To discuss a component of the pathogenic mechanisms of HIV infection in the context of phenotypic and functional alterations in B cells that are due to persistent viral replication leading to aberrant immune activation and cellular exhaustion. We explore how B-cell exhaustion arises during persistent viremia and how it compares with T-cell exhaustion and similar B-cell alterations in other diseases.

RECENT FINDINGS

HIV-associated B-cell exhaustion was first described in 2008, soon after the demonstration of persistent virus-induced T-cell exhaustion, as well as the identification of a subset B cells in tonsil tissues with immunoregulatory features similar to those observed in T-cell exhaustion. Our understanding of B-cell exhaustion has since expanded in two important areas: the role of inhibitory receptors in the unresponsiveness of exhausted B cells and the increasing evidence that similar B cells are found in other diseases that are associated with aberrant immune activation and inflammation.

SUMMARY

The phenomenon of B-cell exhaustion is now well established in HIV infection and other diseases characterized by immune activation. Over the coming years, it will be important to understand how cellular exhaustion affects the capacity of the immune system to respond to persisting primary pathogens, as well as to other microbial antigens, whether encountered as secondary infections or following immunization.

Persistently elevated abnormal B-cell subpopulations and anti-core antibodies in patients co-infected with HIV/HCV who relapse

Hepatitis C (HCV) treatment for patients coinfected with human immunodeficiency virus (HIV) and HCV is associated with modest rates of sustained virologic response (SVR) and an increased rate of relapse when compared to HCV monoinfected patients. As patients who attain SVR and patients who relapse are clinically indistinguishable during treatment, where both groups have fully suppressed HCV viral load, it has not been possible to identify in advance those who will relapse. Biomarkers that may distinguish patients with differential treatment response may be clinically useful and provide insight into mechanisms of relapse. In this retrospective study, serum and PBMCs were obtained from 41 HIV/HCV co-infected patients and 17 healthy volunteers. Changes in antibody titers to various regions of the HCV proteome during treatment for HCV were determined using a novel luciferase immunoprecipitation assay. Changes in B-cell subtypes in patients with differential treatment response as well as healthy volunteers were compared. This study demonstrates that elevated anti-HCV core antibody titers persisted during HCV treatment in patients who relapsed when compared to those who attained SVR. Furthermore, characterization of B cells in patients who relapsed demonstrated an abnormal B-cell phenotype distribution characterized by elevated frequencies of exhausted B cells among relapsers at baseline, which persisted despite suppression of HCV viremia at 24 weeks, along with increased frequencies of plasmablasts. These data suggest that anti-HCV specific B cells may be responding to ongoing subclinical HCV replication in patients who will relapse.

TLR7, IFNγ, and T-bet: their roles in the development of ABCs in female-biased autoimmunity

The majority of autoimmune diseases have a strong gender bias, affecting mostly females. Gender-specific factors like sex-hormones, the presence or absence of a second X chromosome, and gender-specific gut microbiota may contribute to this bias. In this review we will discuss the role of the X chromosome encoded toll-like receptor 7 (TLR7) and interferon gamma (IFNγ) in the development of autoimmunity. We will also review recent data indicating how these factors may affect an immune response in a gender-dependent manner.

Early-onset Evans syndrome, immunodeficiency, and premature immunosenescence associated with tripeptidyl-peptidase II deficiency

Autoimmune cytopenia is a frequent manifestation of primary immunodeficiencies. Two siblings presented with Evans syndrome, viral infections, and progressive leukopenia. DNA available from one patient showed a homozygous frameshift mutation in tripeptidyl peptidase II (TPP2) abolishing protein expression. TPP2 is a serine exopeptidase involved in extralysosomal peptide degradation. Its deficiency in mice activates cell death programs and premature senescence. Similar to cells from naïve, uninfected TPP2-deficient mice, patient cells showed increased major histocompatibility complex I expression and most CD8(+) T-cells had a senescent CCR7-CD127(-)CD28(-)CD57(+) phenotype with poor proliferative responses and enhanced staurosporine-induced apoptosis. T-cells showed increased expression of the effector molecules perforin and interferon-γ with high expression of the transcription factor T-bet. Age-associated B-cells with a CD21(-) CD11c(+) phenotype expressing T-bet were increased in humans and mice, combined with antinuclear antibodies. Moreover, markers of senescence were also present in human and murine TPP2-deficient fibroblasts. Telomere lengths were normal in patient fibroblasts and granulocytes, and low normal in lymphocytes, which were compatible with activation of stress-induced rather than replicative senescence programs. TPP2 deficiency is the first primary immunodeficiency linking premature immunosenescence to severe autoimmunity. Determination of senescent lymphocytes should be part of the diagnostic evaluation of children with refractory multilineage cytopenias.

The effect of the autoimmunity-associated gene, PTPN22, on a BXSB-derived model of lupus

A single nucleotide polymorphism in PTPN22 is linked to increased disease susceptibility in a range of autoimmune diseases including systemic lupus erythematosus (SLE). PTPN22 encodes the Lyp phosphatase that dampens TCR signaling and is necessary for signaling downstream of toll-like receptors in myeloid cells. To understand these dual functions in disease, we examined the impact of deficiency in PTPN22 on a spontaneous murine model of SLE. Male PTPN22 KO mice carrying BXSB chromosome 1 and the Yaa disease accelerating factor developed disease at a similar rate and severity as PTPN22 WT. In contrast, although female mice showed no differences in survival in the absence of PTPN22, autoantibody production was significantly increased and splenic populations associated with pathogenesis in this model were expanded in the PTPN22 KO group. These findings support the notion that when coupled with other predisposing autoimmunity genes, PTPN22 deficiency contributes to a predisposition to lupus pathogenesis.

Aberrant presentation of self-lipids by autoimmune B cells depletes peripheral iNKT cells

Invariant natural killer T (iNKT) cells provide cognate help via CD1d to lipid antigen-presenting B cells for antibody production, but whether B cells reciprocally regulate iNKT cells remains largely unexplored. Here, we found peripheral, but not thymic, iNKT cells to be numerically reduced in autoimmune mice lacking Fas specifically in B cells. The residual iNKT cells were antigenically overstimulated, had altered cytokine production, and manifested enhanced proliferation and apoptosis. B cell-specific ablation of CD1d ameliorated these iNKT defects, suggesting that inappropriate presentation of CD1d-restricted self-lipids by autoimmune B cell-depleted peripheral iNKT cells. CD1d(+) autoimmune B cells have reduced α-galactosidase A expression and, as revealed by lipidomic profiling, altered lipidome with aberrant accumulation of certain self-lipids and reduction of others. These findings unveil a critical link between autoimmunity, B cell lipidome, and the maintenance of peripheral iNKT cells and highlight an essential homeostatic function of B cells beyond antibody production.

Deletion of the antiphospholipid syndrome autoantigen β2 -glycoprotein I potentiates the lupus autoimmune phenotype in a Toll-like receptor 7-mediated murine model

OBJECTIVE

The BXSB.Yaa mouse strain is a model of systemic lupus erythematosus that is dependent on duplication of the Toll-like receptor 7 gene. The objective of this study was to systematically describe the amplified autoimmune phenotype observed when the soluble plasma protein β2 -glycoprotein I (β2 GPI) gene was deleted in male BXSB.Yaa mice.

METHODS

We generated BXSB.Yaa and NZW mouse strains in which the β2 GPI gene had been knocked out by backcrossing the wild-type strains with C57BL/6 β2 GPI(-/-) mice for 10 generations. Sex- and age-matched mice of the various strains were housed under identical conditions and were killed at fixed time intervals. Serum and tissue specimens were collected at various time points. Lupus-associated autoantibodies, inflammatory cytokines, and the type I interferon (IFN) gene signature were measured. Flow cytometric analyses of lymphocyte populations were performed. The severity of glomerulonephritis was graded by 2 independent renal histopathologists.

RESULTS

Male BXSB.Yaa β2 GPI(-/-) mice developed significant lymphadenopathy and splenomegaly compared with age-matched controls. Male BXSB.Yaa β2 GPI(-/-) mice also had significantly higher levels of autoantibodies, increased levels of inflammatory cytokines including tumor necrosis factor α, interleukin-6, and BAFF, and more severe glomerulonephritis. The type I IFN gene signature in male BXSB.Yaa β2 GPI(-/-) mice was significantly higher than that in control mice. Male BXSB.Yaa β2 GPI(-/-) mice also had marked dysregulation of various B cell and T cell populations in the spleens and lymph nodes and a disturbance in apoptotic cell clearance.

CONCLUSION

Deletion of β2 GPI accelerates and potentiates the autoimmune phenotype in male BXSB.Yaa mice.

Early, transient depletion of plasmacytoid dendritic cells ameliorates autoimmunity in a lupus model

Plasmacytoid dendritic cells (pDCs) have long been implicated in the pathogenesis of lupus. However, this conclusion has been largely based on a correlative link between the copious production of IFN-α/β by pDCs and the IFN-α/β "signature" often seen in human lupus patients. The specific contribution of pDCs to disease in vivo has not been investigated in detail. For this reason, we generated a strain of BXSB lupus-prone mice in which pDCs can be selectively depleted in vivo. Early, transient ablation of pDCs before disease initiation resulted in reduced splenomegaly and lymphadenopathy, impaired expansion and activation of T and B cells, reduced antibodies against nuclear autoantigens and improved kidney pathology. Amelioration of pathology coincided with decreased transcription of IFN-α/β-induced genes in tissues. PDC depletion had an immediate impact on the activation of immune cells, and importantly, the beneficial effects on pathology were sustained even though pDCs later recovered, indicating an early pDC contribution to disease. Together, our findings demonstrate a critical function for pDCs during the IFN-α/β-dependent initiation of autoimmune lupus and point to pDCs as an attractive therapeutic target for the treatment of SLE.

Inbred mouse strains reveal biomarkers that are pro-longevity, antilongevity or role switching

Traditionally, biomarkers of aging are classified as either pro-longevity or antilongevity. Using longitudinal data sets from the large-scale inbred mouse strain study at the Jackson Laboratory Nathan Shock Center, we describe a protocol to identify two kinds of biomarkers: those with prognostic implication for lifespan and those with longitudinal evidence. Our protocol also identifies biomarkers for which, at first sight, there is conflicting evidence. Conflict resolution is possible by postulating a role switch. In these cases, high biomarker values are, for example, antilongevity in early life and pro-longevity in later life. Role-switching biomarkers correspond to features that must, for example, be minimized early, but maximized later, for optimal longevity. The clear-cut pro-longevity biomarkers we found reflect anti-inflammatory, anti-immunosenescent or anti-anaemic mechanisms, whereas clear-cut antilongevity biomarkers reflect inflammatory mechanisms. Many highly significant blood biomarkers relate to immune system features, indicating a shift from adaptive to innate processes, whereas most role-switching biomarkers relate to blood serum features and whole-body phenotypes. Our biomarker classification approach is applicable to any combination of longitudinal studies with life expectancy data, and it provides insights beyond a simplified scheme of biomarkers for long or short lifespan.

Impaired B lymphopoiesis in old age: a role for inflammatory B cells?

Continued generation of new B cells within the bone marrow is required throughout life. However, in old age, B lymphopoiesis is inhibited at multiple developmental stages from hematopoietic stem cells through the late stages of new B cell generation. While changes in B cell precursor subsets, as well as alterations in the supporting bone marrow microenvironment, in old age have been known for the last 20 years, only more recently have insights into the cellular and molecular mechanisms responsible become clarified. Our recent discovery that B cells in aged mice are pro-inflammatory and can diminish B cell generation within the bone marrow suggests a potential mechanism of inappropriate "B cell feedback" which contributes to a bone marrow microenvironment unfavorable to B lymphopoiesis. We hypothesize that the consequences of a pro-inflammatory microenvironment in old age are (1) reduced B cell generation and (2) alteration in the "read-out" of the antibody repertoire. Both of these likely ensue from reduced expression of the surrogate light chain (λ5 + VpreB) and consequently reduced expression of the pre-B cell receptor (preBCR), critical to pre-B cell expansion and Vh selection. In old age, B cell development may progressively be diverted into a preBCR-compromised pathway. These abnormalities in B lymphopoiesis likely contribute to the poor humoral immunity seen in old age.

Human regulatory B cells combine phenotypic and genetic hallmarks with a distinct differentiation fate

Regulatory B cells (B-reg) produce IL-10 and suppress inflammation in both mice and humans, but limited data on the phenotype and function of these cells have precluded detailed assessment of their contribution to host immunity. In this article, we report that human B-reg cannot be defined based on a phenotype composed of conventional B cell markers, and that IL-10 production can be elicited in both the CD27(+) memory population and naive B cell subset after only a brief stimulation in vitro. We therefore sought to obtain a better definition of IL-10-producing human B-regs using a multiparameter analysis of B cell phenotype, function, and gene expression profile. Exposure to CpG and anti-Ig are the most potent stimuli for IL-10 secretion in human B cells, but microarray analysis revealed that human B cells cotreated with these reagents resulted in only ∼0.7% of genes being differentially expressed between IL-10(+) and IL-10(-) cells. Instead, connectivity map analysis revealed that IL-10-secreting B cells are those undergoing specific differentiation toward a germinal center fate, and we identified a CD11c(+) B cell subset that was not capable of producing IL-10 even under optimal conditions. Our findings will assist in the identification of a broader range of human pro-B-reg populations that may represent novel targets for immunotherapy.

Accumulation of 4-1BBL+ B cells in the elderly induces the generation of granzyme-B+ CD8+ T cells with potential antitumor activity

Although the accumulation of highly-differentiated and granzyme B (GrB)-expressing CD8(+)CD28(-) T cells has been associated with aging, the mechanism for their enrichment and contribution to immune function remains poorly understood. Here we report a novel B-cell subset expressing 4-1BBL, which increases with age in humans, rhesus macaques, and mice, and with immune reconstitution after chemotherapy and autologous progenitor cell transplantation. These cells (termed 4BL cells) induce GrB(+)CD8(+) T cells by presenting endogenous antigens and using the 4-1BBL/4-1BB axis. We found that the 4BL cells increase antitumor responses in old mice, which may explain in part the paradox of retarded tumor growth in the elderly. 4BL cell accumulation and its capacity to evoke the generation of GrB(+)CD8(+) T cells can be eliminated by inducing reconstitution of B cells in old mice, suggesting that the age-associated skewed cellular immune responses are reversible. We propose that 4BL cells and the 4-1BBL signaling pathway are useful targets for improved effectiveness of natural antitumor defenses and therapeutic immune manipulations in the elderly.

Enhanced auto-antibody production and Mott cell formation in FcμR-deficient autoimmune mice

The IgM-Fc receptor (FcμR) is involved in IgM homeostasis as evidenced by increased pre-immune serum IgM and natural auto-antibodies of both IgM and IgG isotypes in Fcmr-deficient C57BL/6 (B6) mice. To determine the impact of Fcmr-ablation on autoimmunity, we introduced the Fcmr null mutation onto the Fas-deficient autoimmune-prone B6.MRL Fas (lpr/lpr) mouse background (B6/lpr). Both IgM and IgG auto-antibodies against dsDNA or chromatin appeared earlier in FcμR(-) B6/lpr than FcμR(+) B6/lpr mice, but this difference became less pronounced with age. Splenic B2 cells, which were 2-fold elevated in FcμR(+) B6/lpr mice, were reduced to normal B6 levels in FcμR(-) B6/lpr mice, whereas splenic B1 cells were comparable in both groups of B6/lpr mice. By contrast, marginal zone (MZ) B cells were markedly reduced in FcμR(-) B6/lpr mice compared with either FcμR(+) B6/lpr or wild type (WT) B6 mice. This reduction appeared to result from rapid differentiation of MZ B cells into plasma cells in the absence of FcμR, as IgM antibody to a Smith (Sm) antigen, to which MZ B cells are known to preferentially respond, was greatly increased in both groups (B6/lpr and B6) of FcμR(-) mice compared with FcμR(+) B6/lpr or B6 mice. Mott cells, aberrant plasma cells with intra-cytoplasmic inclusions, were also increased in the absence of FcμR. Despite these abnormalities, the severity of renal pathology and function and survival were all indistinguishable between FcμR(-) and FcμR(+) B6/lpr mice. Collectively, these findings suggest that FcμR plays important roles in the regulation of auto-antibody production, Mott cell formation and the differentiation of MZ B cells into plasma cells in B6.MRL Fas (lpr/lpr) mice.

Immune defects in the risk of infection and response to vaccination in monoclonal gammopathy of undetermined significance and multiple myeloma

The plasma cell proliferative disorders monoclonal gammopathy of undetermined significance (MGUS) and malignant multiple myeloma (MM) are characterized by an accumulation of transformed clonal plasma cells in the bone marrow and production of monoclonal immunoglobulin. They typically affect an older population, with median age of diagnosis of approximately 70 years. In both disorders, there is an increased risk of infection due to the immunosuppressive effects of disease and conjointly of therapy in MM, and response to vaccination to counter infection is compromised. The underlying factors in a weakened immune response in MGUS and MM are as yet not fully understood. A confounding factor is the onset of normal aging, which quantitatively and qualitatively hampers humoral immunity to affect response to infection and vaccination. In this review, we examine the status of immune alterations in MGUS and MM and set these against normal aging immune responses. We focus primarily on quantitative and functional aspects of B-cell immunity. Furthermore, we review the current knowledge relating to susceptibility to infectious disease in MGUS and MM, and how efficacy of conventional vaccination is affected by proliferative disease-related and therapy-related factors.

Opposing impact of B cell-intrinsic TLR7 and TLR9 signals on autoantibody repertoire and systemic inflammation

Systemic lupus erythematosus is a multisystem autoimmune disease characterized by autoantibodies targeting nucleic acid-associated Ags. The endosomal TLRs TLR7 and TLR9 are critical for generation of Abs targeting RNA- or DNA-associated Ags, respectively. In murine lupus models, deletion of TLR7 limits autoimmune inflammation, whereas deletion of TLR9 exacerbates disease. Whether B cell or myeloid TLR7/TLR9 signaling is responsible for these effects has not been fully addressed. In this study, we use a chimeric strategy to evaluate the effect of B cell-intrinsic deletion of TLR7 versus TLR9 in parallel lupus models. We demonstrate that B cell-intrinsic TLR7 deletion prevents RNA-associated Ab formation, decreases production of class-switched Abs targeting nonnuclear Ags, and limits systemic autoimmunity. In contrast, B cell-intrinsic TLR9 deletion results in decreased DNA-reactive Ab, but increased Abs targeting a broad range of systemic autoantigens. Further, we demonstrate that B cell-intrinsic TLR9 deletion results in increased systemic inflammation and immune complex glomerulonephritis, despite intact TLR signaling within the myeloid compartment. These data stress the critical importance of dysregulated B cell-intrinsic TLR signaling in the pathogenesis of systemic lupus erythematosus.

Prevalence of anti-citrullinated protein antibodies (ACPA) in patients with diffuse large B-cell lymphoma (DLBCL): a case-control study

Background

Antibodies against citrullinated proteins (ACPA) have been recognised as the most specific serum marker for rheumatoid arthritis. However, serum autoantibodies such as anti-nuclear antibodies have also been detected in the sera of different lymphatic malignancies without accompanying rheumatologic disease. Therefore, we conducted a study to evaluate the prevalence of ACPA in diffuse large B-cell non-Hodgkin lymphoma (DLBCL).

Methods

Sera of 395 DLBCL patients and 258 age-matched healthy controls were investigated to evaluate the prevalence of ACPA and RF. ACPA-positive data were stratified into subgroups of RF positivity and established prognostic parameters for DLBCL, including overall survival. In addition, the ACPA serum concentrations levels were compared to an ACPA-positive RA cohort (n = 175). The statistics were performed with χ2 test and Mann- Whitney-U test; Kaplan-Meyer curves (log rank test) were used to analyse the overall survival. P-value <0.05 was statistically significant.

Results

ACPA, but not RF, occurred significantly more frequently in the sera of DLBCL patients than in healthy controls (3.5% versus 0.8%, p = 0.030). However, the ACPA serum concentration levels were significantly lower than in RA patients (median 10.4 versus 124.1 U/ml, p = 0.0001). After subgroup stratification, ACPA positivity in DLBCL was significantly associated with male gender (4.4% versus 0%, p = 0.022; odds ratio 1.046, CI 1.014–1.079) and with RF-IgM seropositivity (1.77% versus 0%, p = 0.043), but not with prognostic parameters for DLBCL.

Conclusions

DLBCL is associated with a significantly higher prevalence of ACPA, with an increased prevalence in male patients, and simultaneous RF-IgM positivity. However, ACPA is not prognostic for DLBCL. The prevalence of RF-IgM, -IgA, or -IgG did not differ from healthy controls.

CD80+ and CD86+ B cells as biomarkers and possible therapeutic targets in HTLV-1 associated myelopathy/tropical spastic paraparesis and multiple sclerosis

Background

Human T-cell lymphotropic virus (HTLV-1) is the causative agent of the incapacitating, neuroinflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Currently, there are no disease-modifying therapies with long-term clinical benefits or validated biomarkers for clinical follow-up in HAM/TSP. Although CD80 and CD86 costimulatory molecules play prominent roles in immune regulation and reflect disease status in multiple sclerosis (MS), data in HAM/TSP are lacking.

Methods

Using flow cytometry, we quantified ex vivo and in vitro expression of CD80 and CD86 in PBMCs of healthy controls, HTLV-1-infected individuals with and without HAM/TSP, and MS patients. We hypothesized ex vivo CD80 and CD86 expressions and their in vitro regulation by interferon (IFN)-α/β mirror similarities between HAM/TSP and MS and hence might reveal clinically useful biomarkers in HAM/TSP.

Results

Ex vivo expression of CD80 and CD86 in T and B cells increased in all HTLV-1 infected individuals, but with a selective defect for B cell CD86 upregulation in HAM/TSP. Despite decreased total B cells with increasing disease duration (p = 0.0003, r = −0.72), CD80⁺ B cells positively correlated with disease severity (p = 0.0017, r = 0.69) in HAM/TSP. B cell CD80 expression was higher in women with HAM/TSP, underscoring that immune markers can reflect the female predominance observed in most autoimmune diseases. In contrast to MS patients, CD80⁺ (p = 0.0001) and CD86⁺ (p = 0.0054) lymphocytes expanded upon in vitro culture in HAM/TSP patients. The expansion of CD80⁺ and CD86⁺ T cells but not B cells was associated with increased proliferation in HTLV-1 infection. In vitro treatment with IFN-β but not IFN-α resulted in a pronounced increase of B cell CD86 expression in healthy controls, as well as in patients with neuroinflammatory disease (HAM/TSP and MS), similar to in vivo treatment in MS.

Conclusions

We propose two novel biomarkers, ex vivo CD80⁺ B cells positively correlating to disease severity and CD86⁺ B cells preferentially induced by IFN-β, which restores defective upregulation in HAM/TSP. This study suggests a role for B cells in HAM/TSP pathogenesis and opens avenues to B cell targeting (with proven clinical benefit in MS) in HAM/TSP but also CD80-directed immunotherapy, unprecedented in both HAM/TSP and MS.

Genetic variations in Toll-like receptors (TLRs 3/7/8) are associated with systemic lupus erythematosus in a Taiwanese population

Toll-like receptors (TLRs), as innate immunity sensors, play critical roles in immune responses. Six SNPs of TLR3, TLR7, and TLR8 were genotyped to determine their associations with systemic lupus erythematosus (SLE) and clinical manifestations of SLE. TLR7 SNP rs3853839 was independently associated with SLE susceptibility in females (G vs. C: p = 0.0051). TLR7 rs3853839-G (G vs. C: p = 0.0100) and TLR8 rs3764880-G (recessive model: p = 0.0173; additive model: p = 0.0161) were associated with pericardial effusion in females relative to healthy females. Anti-SSA positive cases were more likely to have the dominant TLR7 rs179010-T allele than normal controls (p = 0.0435). TLR3 rs3775296-T was associated with photosensitivity (p = 0.0020) and anemia (p = 0.0082). The “G-G” haplotype of TLR7 rs3853839 and TLR8 rs3764880 increased risk of SLE in females (age adjusted p = 0.0032). These findings suggest that TLR variations that modify gene expression affect risk for SLE susceptibility, clinical phenotype development, and production of autoantibodies.

Pivotal Functions of Plasmacytoid Dendritic Cells in Systemic Autoimmune Pathogenesis

Plasmacytoid dendritic cells (pDCs) were initially identified as the prominent natural type I interferon-producing cells during viral infection. Over the past decade, the aberrant production of interferon α/β by pDCs in response to self-derived molecular entities has been critically implicated in the pathogenesis of systemic lupus erythematosus and recognized as a general feature underlying other autoimmune diseases. On top of imperative studies on human pDCs, the functional involvement and mechanism by which the pDC-interferon α/β pathway facilitates the progression of autoimmunity have been unraveled recently from investigations with several experimental lupus models. This article reviews correlating information obtained from human in vitro characterization and murine in vivo studies and highlights the fundamental and multifaceted contribution of pDCs to the pathogenesis of systemic autoimmune manifestation.