Role of toll-like receptors in primary Sjögren’s syndrome with a special emphasis on B-cell maturation within exocrine tissues

TRAF3 regulation of proximal TLR signaling in B cells

Toll-like receptors are pattern recognition receptors that bridge the innate and adaptive immune responses and are critical for host defense. Most studies of Toll-like receptors have focused upon their roles in myeloid cells. B lymphocytes express most Toll-like receptors and are responsive to Toll-like receptor ligands, yet Toll-like receptor-mediated signaling in B cells is relatively understudied. This is an important knowledge gap, as Toll-like receptor functions can be cell type specific. In striking contrast to myeloid cells, TRAF3 inhibits TLR-mediated functions in B cells. TRAF3-deficient B cells display enhanced IRF3 and NFκB activation, cytokine production, immunoglobulin isotype switching, and antibody production in response to Toll-like receptors 3, 4, 7, and 9. Here, we address the question of how TRAF3 impacts initial B-cell Toll-like receptor signals to regulate downstream activation. We found that TRAF3 in B cells associated with proximal Toll-like receptor 4 and 7 signaling proteins, including MyD88, TRAF6, and the tyrosine kinase Syk. In the absence of TRAF3, TRAF6 showed a greater association with several Toll-like receptor signaling proteins, suggesting that TRAF3 may inhibit TRAF6 access to Toll-like receptor signaling complexes and thus early Toll-like receptor signaling. In addition, our results highlight a key role for Syk in Toll-like receptor signaling in B cells. In the absence of TRAF3, Syk activation was enhanced in response to ligands for Toll-like receptors 4 and 7, and Syk inhibition reduced downstream Toll-like receptor-mediated NFκB activation and proinflammatory cytokine production. This study reveals multiple mechanisms by which TRAF3 serves as a key negative regulator of early Toll-like receptor signaling events in B cells.

Metformin-induced activation of Ca2+ signaling prevents immune infiltration/pathology in Sjogren's syndrome-prone mouse models

Immune cell infiltration and glandular dysfunction are the hallmarks of autoimmune diseases such as primary Sjogren's syndrome (pSS), however, the mechanism(s) is unknown. Our data show that metformin-treatment induces Ca2+ signaling that restores saliva secretion and prevents immune cell infiltration in the salivary glands of IL14α-transgenic mice (IL14α), which is a model for pSS. Mechanistically, we show that loss of Ca2+ signaling is a major contributing factor, which is restored by metformin treatment, in IL14α mice. Furthermore, the loss of Ca2+ signaling leads to ER stress in salivary glands. Finally, restoration of metformin-induced Ca2+ signaling inhibited the release of alarmins and prevented the activation of ER stress that was essential for immune cell infiltration. These results suggest that loss of metformin-mediated activation of Ca2+ signaling prevents ER stress, which inhibited the release of alarmins that induces immune cell infiltration leading to salivary gland dysfunction observed in pSS.

Dysregulated translational factors and epigenetic regulations orchestrate in B cells contributing to autoimmune diseases

B cells play a crucial role in antigen presentation, antibody production and pro-/anti-inflammatory cytokine secretion in adaptive immunity. Several translational factors including transcription factors and cytokines participate in the regulation of B cell development, with the cooperation of epigenetic regulations. Autoimmune diseases are generally characterized with autoreactive B cells and high-level pathogenic autoantibodies. The success of B cell depletion therapy in mouse model and clinical trials has proven the role of B cells in pathogenesis of autoimmune diseases. The failure of B cell tolerance in immune checkpoints results in accumulated autoreactive naïve B (B_N) cells with aberrant B cell receptor signaling and dysregulated B cell response, contributing to self-antibody-mediated autoimmune reaction. Dysregulation of translational factors and epigenetic alterations in B cells has been demonstrated to correlate with aberrant B cell compartment in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren's syndrome, multiple sclerosis, diabetes mellitus and pemphigus. This review is intended to summarize the interaction of translational factors and epigenetic regulations that are involved with development and differentiation of B cells, and the mechanism of dysregulation in the pathogenesis of autoimmune diseases.

Marginal zone B cells: From housekeeping function to autoimmunity?

Marginal zone (MZ) B cells comprise a subset of innate-like B cells found predominantly in the spleen, but also in lymph nodes and blood. Their principal functions are participation in quick responses to blood-borne pathogens and secretion of natural antibodies. The latter is important for housekeeping functions such as clearance of apoptotic cell debris. MZ B cells have B cell receptors with low poly-/self-reactivity, but they are not pathogenic at steady state. However, if simultaneously stimulated with self-antigen and pathogen- and/or damage-associated molecular patterns (PAMPs/DAMPs), MZ B cells may participate in the initial steps towards breakage of immunological tolerance. This review summarizes what is known about the role of MZ B cells in autoimmunity, both in mouse models and human disease. We cover factors important for shaping the MZ B cell compartment, how the functional properties of MZ B cells may contribute to breaking tolerance, and how MZ B cells are being regulated.

Molecular Evidence for Precursors of Sjögren's Foci in Histologically Normal Lacrimal Glands

Understanding the formation of Sjogren’s lymphocytic infiltrates could permit earlier diagnosis and better outcomes. We submitted gene transcript abundances in histologically normal rabbit lacrimal glands to principal component analysis. The analysis identified a cluster of transcripts associated with Sjögren’s foci, including messenger RNAs (mRNAs) for C–X–C motif chemokine ligand 13 (CXCL13) and B-cell activating factor (BAFF), which dominated the major principal component. We interpreted the transcript cluster as the signature of a cluster of integrally functioning cells. Pregnancy and dryness increased the likelihood that the cluster would develop to high levels, but responses were subject to high levels of stochasticity. Analyzing microdissected samples from high- and low-cluster-level glands, we found that certain transcripts, including mRNAs for C–C motif chemokine ligand 21 (CCL21), CXCL13, cluster of differentiation 4 (CD4), CD28, CD25, BAFF, and interleukin 18 (IL-18) were significantly more abundant in immune cell clusters (ICs) from the high-cluster-level gland; mRNAs for CCL2, CD25, and IL-1RA were significantly more abundant in acinus-duct axis samples; mRNAs for CCL4, BAFF, IL-6, and IL-10 were more abundant in some acinus-duct samples; cells with high prolactin immunoreactivity were more frequent in interacinar spaces. In conclusion, integrated functional networks comprising Sjögren’s infiltrates, such as ICs, acinar cells, ductal cells, and interacinar cells, can form in histologically normal glands, and it is feasible to detect their molecular signatures.

Toll-like receptors in the pathogenesis of autoimmune diseases: recent and emerging translational developments

Autoinflammatory diseases are defined as the loss of self-tolerance in which an inflammatory response to self-antigens occurs, which are a significant global burden. Toll-like receptors are key pattern recognition receptors, which integrate signals leading to the activation of transcription factors and ultimately proinflammatory cytokines. Recently, it has become apparent that these are at the nexus of autoinflammatory diseases making them viable and attractive drug targets. The aim of this review was to evaluate the role of innate immunity in autoinflammatory conditions alongside the role of negative regulation while suggesting possible therapeutic targets.

A case for IL-6, IL-17A, and nitric oxide in the pathophysiology of Sjögren's syndrome

Sjögren's syndrome (SS) is an autoimmune epithelitis characterized by mononuclear cell (MNC) infiltration of the lacrimal and salivary glands (SG), as well as the presence of serum autoantibodies. This condition is a growing public health concern in Algeria. Herein, we sought to determine if the levels of interleukin (IL)-6, IL-17A, and nitric oxide (NO), were correlated with the extent of MNC infiltration. The expression of inducible NO synthase (NOS2) and CD68 was measured in the SG of all patients, but not in those of the normal controls (NCs). We included 44 primary Sjögren's syndrome (pSS) patients and 15 NCs in this study; we found that the expression of NOS2 and CD68 was elevated in all of the SG of SS patients. Additionally, the serum and saliva levels of IL-6, IL-17A, and NO were higher in the pSS patients, compared with the NCs. Furthermore, the NOS2-induced excess NO was associated with the extent of the MNC infiltration, and thereby with tissue injury. It is also important to note that there were correlations between the levels of IL-6, IL-17A, and NO. Such findings indicate that through the effects of NO, IL-17A participates in the pathophysiology of the disease. With the purpose of improving both the diagnosis and prognosis, IL-6, IL-17A, and NO should be assayed in the serum and saliva of patients suspected of SS.

Toll-like receptors and B cells: functions and mechanisms

Numerous reports have described Toll-like receptor (TLR) functions in myeloid cells such as dendritic cells (DCs) and macrophages, but relatively fewer studies have examined TLR responses in B lymphocytes. B cells express a wide variety of TLRs and are highly activated after TLR ligation, leading to enhancements in B cell survival, surface molecule expression, cytokine and antibody production, and antigen presentation. During an immune response, B cells can receive signals through TLRs as well as the B cell antigen receptor (BCR) and/or CD40. TLR ligation synergizes with signals through these receptors and augments both innate and adaptive immune functions of B lymphocytes. Additionally, targeting B cell TLRs may provide new therapies against certain types of cancer as well as autoimmune diseases. Here, we summarize TLR expression and contributions to both normal and pathogenic functions in mouse and human B cells.

The Link between Autoimmunity and Lymphoma: Does NOTCH Signaling Play a Contributing Role?

An association between certain autoimmune conditions and increased risk of developing lymphoma is well documented. Recent evidence points to NOTCH signaling as a strong driver of autoimmunity. Furthermore, a role for NOTCH in various lymphomas, including classical Hodgkin lymphoma, non-Hodgkin lymphoma, and T cell lymphoma has also been described. In this mini-review, we will outline what is known about involvement of NOTCH signaling in those autoimmune conditions, such as rheumatoid arthritis and primary Sjörgren’s syndrome, which show an increased risk for subsequent diagnosis of lymphoma. Furthermore, we will detail what is known about the lymphomas associated with these autoimmune conditions and how aberrant or sustained NOTCH signaling in the immune cells that mediate these diseases may contribute to lymphoma.

Evaluation of Germinal Center-like Structures and B Cell Clonality in Patients with Primary Sjögren Syndrome with and without Lymphoma

Objective.

Germinal center (GC)-like structures have previously been observed in minor salivary glands (MSG) of patients with primary Sjögren syndrome (pSS). The aim of our study was to explore the prevalence and features of GC-like structures and B cell clonality in patients with pSS with and without lymphoma.

Methods.

Based on a nationwide survey in Norway, we included 21 patients with pSS and with a concomitant lymphoma from whom MSG and/or lymphoma biopsies were available. Tonsil biopsies and MSG from 28 patients with pSS without lymphoma were used as controls. The presence of GC-like structures was investigated with H&E staining and double staining for CD21/IgD and CD38/IgD. B cell clonality in MSG and tumors were investigated with analysis of immunoglobulin gene rearrangements.

Results.

H&E labeling of MSG revealed GC-like structures in 17/40 (43%) of the patients: 4/12 (33%) with and 13/28 (46%) without lymphoma. Staining for CD21/CD38/IgD demonstrated CD21+ networks in 27/40 (68%) of the patients. CD21+/CD38– infiltrates were seen in 25/40 (63%) of the patients, and 16 of these were IgD+ within the infiltrate. Five percent (2/40) of the patients presented with CD21+/CD38+ infiltrates resembling tonsillar GC. Monoclonal B cell infiltration in MSG was present in 5/12 patients (42%) with and 5/28 patients (18%) without lymphoma (p = 0.12). In 2/10 (20%) of cases where both MSG and lymphoma biopsies were available, identical clonal rearrangements were detected.

Conclusion.

GC-like structures seen in H&E-stained MSG may represent various subtypes of CD21+ infiltrates. We were unable to detect a clear association between cellular infiltrates, B cell clonality, and lymphoma development.

The histopathology of labial salivary glands in primary Sjögren's syndrome: focusing on follicular helper T cells in the inflammatory infiltrates

Recently, we revealed the importance of follicular helper T cells (T(FH)) in the pathogenesis of primary Sjögren's syndrome (pSS). In the present study, we focused on the site of the inflammation and determined the composition of lymphocyte infiltration in labial salivary gland (LSG) biopsies with special emphasis on T(FH) and germinal center B cells. We selected tissue blocks obtained from ten patients at the time of disease onset. Detection of cell specific markers was performed with immunohistochemical and immunofluorescence stainings. We evaluated patients' clinical and laboratory features retrospectively and assessed the relation between disease course and early histopathological findings. LSG biopsies were graded based on the extension and arrangement level of periductal inflammatory cell infiltrates. T(FH) cell markers (CD84, PD-1, and Bcl-6) occurred predominantly in more organized structures with higher focus scores. The coexpression of CD3 and Bcl-6 markers clearly identified T(FH) cells close to Bcl-6(+) B cells with the typical formation of germinal centers. Systemic features were developed later in the disease course only in patients with highly structured infiltrates and the presence of T(FH) cells. Our observations suggest that the presence of T(FH) cells in LSGs at the disease onset may predict a more pronounced clinical course of pSS.

Sjögren's syndrome: another facet of the autoimmune/inflammatory syndrome induced by adjuvants (ASIA)

Recently, a new syndrome, namely the "Autoimmune/inflammatory syndrome induced by adjuvants" (ASIA) has been defined. In this syndrome different conditions characterized by common signs and symptoms and induced by the presence of an adjuvant are included. The adjuvant is a substance capable of boosting the immune response and of acting as a trigger in the development of autoimmune diseases. Post-vaccination autoimmune phenomena represent a major issue of ASIA. Indeed, despite vaccines represent a mainstay in the improvement of human health, several of these have been implicated as a potential trigger for autoimmune diseases. Sjogren's Syndrome (SjS) is a systemic chronic autoimmune inflammatory disease characterized by the presence of an inflammatory involvement of exocrine glands accompanied by systemic manifestations. Own to the straight association between infectious agents exposure (mainly viruses) and sicca syndrome development, the possible link between vaccine and SjS is not surprising. Indeed, a few cases of SjS following vaccine delivery have been reported. At the same extent, the induction of SjS following silicone exposure has been described too. Thus, the aim of this review was to focus on SjS and its possible development following vaccine or silicone exposure in order to define another possible facet of the ASIA syndrome.

Interleukin-7 and Toll-like receptor 7 induce synergistic B cell and T cell activation

Objectives

To investigate the potential synergy of IL-7-driven T cell-dependent and TLR7-mediated B cell activation and to assess the additive effects of monocyte/macrophages in this respect.

Methods

Isolated CD19 B cells and CD4 T cells from healthy donors were co-cultured with TLR7 agonist (TLR7A, Gardiquimod), IL-7, or their combination with or without CD14 monocytes/macrophages (T/B/mono; 1 : 1 : 0,1). Proliferation was measured using ³H-thymidine incorporation and Ki67 expression. Activation marker (CD19, HLA-DR, CD25) expression was measured by FACS analysis. Immunoglobulins were measured by ELISA and release of cytokines was measured by Luminex assay.

Results

TLR7-induced B cell activation was not associated with T cell activation. IL-7-induced T cell activation alone and together with TLR7A synergistically increased numbers of both proliferating (Ki67⁺) B cells and T cells, which was further increased in the presence of monocytes/macrophages. This was associated by up regulation of activation markers on B cells and T cells. Additive or synergistic induction of production of immunoglobulins by TLR7 and IL-7 was associated by synergistic induction of T cell cytokines (IFNγ, IL-17A, IL-22), which was only evident in the presence of monocytes/macrophages.

Conclusions

IL-7-induced CD4 T cell activation and TLR7-induced B cell activation synergistically induce T helper cell cytokine and B cell immunoglobulin production, which is critically dependent on monocytes/macrophages. Our results indicate that previously described increased expression of IL-7 and TLR7 together with increased numbers of macrophages at sites of inflammation in autoimmune diseases like RA and pSS significantly contributes to enhanced lymphocyte activation.

TLR9 expressed on plasma membrane acts as a negative regulator of human B cell response

Toll-like receptors (TLRs) are positioned at the interface between innate and adaptive immunity. Unlike others, those such as TLR9, that recognize nucleic acids, are confined to the endosomal compartment and are scarce on the cell surface. Here, we present evidence for TLR9 expression on the plasma membrane of B cells. In contrast to endosomal TLR9, cell surface TLR9 does not bind CpG-B oligodeoxynucleotides. After B cell-receptor (BCR) stimulation, TLR9 was translocated into lipid rafts with the BCR, suggesting that it could serve as a co-receptor for BCR. Nevertheless, stimulation of B cells with anti-TLR9 antibodies did not modify the BCR-induced responses despite up-regulation of tyrosine phosphorylation of proteins. However, CpG-B activation of B cells, acting synergistically with BCR signals, was inhibited by anti-TLR9 stimulation. Induction of CD25 expression and proliferation of B cells were thus down-regulated by the engagement of cell surface TLR9. Overall, our results indicate that TLR9 expressed on the plasma membrane of B cells might be a negative regulator of endosomal TLR9, and could provide a novel control by which activation of autoreactive B cells is restrained.

B-cell hyperactivity in primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is characterized by mononuclear inflammatory infiltrates and IgG plasma cells in salivary and lacrimal glands which lead to irreversible destruction of the glandular tissue and is accompanied by sensation of dryness of mouth and eyes. B cells play a central role in the immunopathogenesis and exhibit signs of hyperactivity. Hyperactivity of B cells is the consequence of the coordinated and integrated action of stimulation of the B-cell receptor, CD40 and toll-like receptors in the presence of appropriate cytokines. As discussed, overexpression of type I IFN and BAFF on one hand and IL-6 and IL-21 on the other hand are critically involved in the enhanced plasma cell formation in pSS patients. Hyperactivity of B cells results in secretion of autoantibodies and production of various cytokines. These insights in the role of B cells in the pathogenetic process of pSS offer ample targets for successful therapeutical intervention in pSS.

The future of B cell-targeted therapies in Sjögren's syndrome

Primary Sjögren's syndrome is a systemic autoimmune disease characterized by progressive exocrine gland destruction, resulting clinically in eyes and mouth dryness. To date, no treatment has been proven effective to modify the course of this slow-evolving disease. B cells are now considered to play a central role in the pathogenesis of primary Sjögren's syndrome because their functions are not restrained to antibody production. Thus, several B-cell targeting therapies are under clinical investigation. Rituximab, a monoclonal antibody directed to CD20 and leading to transient blood B-cell depletion, has shown partial improvements in subjective and objective sicca symptoms in small studies. However, the results of two large controlled trials are awaited before considering its use in large populations of patients. Several other therapeutic strategies are being studied, targeting other B-cell surface proteins (epratuzumab and anti-CD22) or major cytokines of B-cell homeostasis (e.g., BAFF, IL-6 and lymphotoxin-β). Although great hope is generated by the trials of these specific therapies, another challenge for clinical researchers is the development of reliable tools to assess the activity of Sjögren's syndrome and its response to treatment.

Differentiation of follicular helper T cells by salivary gland epithelial cells in primary Sjögren's syndrome

Follicular helper T cells (Tfh), which play a pivotal role in B cell activation and differentiation in lymphoid structures, secrete IL-21 whose augmented secretion is a hallmark of several autoimmune diseases. To decipher the cellular and molecular interactions occurring in salivary glands of patients suffering from primary Sjögren's syndrome (pSS), we investigated whether salivary gland epithelial cells (SGECs) were capable to induce Tfh differentiation. Co-cultures of naïve CD4(+) T cells and SGECs from both patients with pSS and controls were performed. Here, we report that IL-6 and ICOSL expression by SGECs contributes to naïve CD4(+) T differentiation into Tfh cells, as evidenced by their acquisition of a specific phenotype, characterized by Bcl-6, ICOS and CXCR5 expression and IL-21 secretion, but also but by their main functional feature: the capacity to enhance B lymphocytes survival. We demonstrated an increase of serum IL-21 with systemic activity. Finally, we analyzed the potential occurrence of a genetic association between IL-21 or IL-21R gene polymorphisms and pSS or elevated IL-21 secretion. This study, which demonstrates a direct induction of Tfh differentiation by SGECs, emphasizes a yet unknown pathogenic role of SGECs and suggests that Tfh and IL-21 might be relevant biomarkers and/or therapeutic targets in primary Sjögren's syndrome.

Liver auto-immunology: the paradox of autoimmunity in a tolerogenic organ

The study of the liver as a lymphoid organ is a growing field fueled by our better knowledge of the different component of the immune system and how they orchestrate an immune-related response. The liver have highly specialized mechanisms of immune tolerance, mainly because is continuously exposed to microbial and environmental antigens, and dietary components from the gut. Accordingly, the liver contains specialized lymphoid subpopulations acting as antigen-presenting cells. Growing evidences show that the liver is also associated with obesity-associated diseases because of its immune-related capacity to sense metabolic stress induced by nutritional surplus. Finally, the liver produces a pletora of neo-antigens being the primary metabolic organ of the body. Common immune mechanisms play a key pathogenetic role in most of acute and chronic liver diseases and in the rejection of liver allografts. Any perturbations of liver-related immune functions have important clinical implications. This issue of the Journal of Autoimmunity is focused on the more recent advances in our knowledge related to the loss of liver tolerance, a paradox for a tolerogenic organ, that leads to overactivation of the innate and adaptive immune response and the development of autoimmune liver diseases, such as autoimmune hepatitis, primary biliary cirrhosis, and primary sclerosing cholangitis. The invited expert review articles capture the underlying immunomolecular mechanisms of the development and progression of autoimmune liver diseases, the novel field of the immune-related "liver-gut" axis influences to the development of liver autoimmunity, the predominant role of genetic factors, and the increasingly effective immuno-therapeutic possibilities.

T helper subsets in Sjögren's syndrome and IgG4-related dacryoadenitis and sialoadenitis: a critical review

IgG4-related disease (IgG4-RD) is a systemic disease characterized by the elevation of serum IgG4 and infiltration of IgG4-positive plasma cells in multiple target organs, including the pancreas, kidney, biliary tract and salivary glands. In contrast, Mikulicz's disease (MD) has been considered a subtype of Sjögren's syndrome (SS) based on histopathological similarities. However, it is now recognized that MD is an IgG4-RD distinguishable from SS and called as IgG4-related dacryoadenitis and sialoadenitis (IgG4-DS). Regarding immunological aspects, it is generally accepted that CD4+ T helper (Th) cells play a crucial role in the pathogenesis of SS. Since it is well known that IgG4 is induced by Th2 cytokines such as interleukin (IL)-4 and IL-13, IgG4-DS is speculated to be a unique inflammatory disorder characterized by Th2 immune reactions. However, the involvement of Th cells in the pathogenesis of IgG4-DS remains to be clarified. Exploring the role of Th cell subsets in IgG4-DS is a highly promising field of investigation. In this review, we focus on the selective localization and respective functions of Th cell subsets and discuss the differences between SS and IgG4-DS to clarify the pathogenic mechanisms of these diseases.

[Regulatory lymphocytes: a new cooperation between T and B cells for a better control of the immune response]

Mechanims of peripheral tolerance include molecular controls and the presence of regulatory lymphocytes. Regulatory T lymphocytes (Tregs) correspond to different sub-populations of T cells that control immune responses due to the production of cytokines, such as IL-10 and with direct cell-to-cell contacts. Tregs targets are antigen presenting cells, such as dendritic cells, effector CD4(+) and CD8(+) lymphocytes but also effector antibody-producing B lymphocytes. Regulatory B lymphocytes (Bregs) have been more recently described and likely represent different sub-populations of B cells that control the development of autoimmune and inflammatory diseases due to the production of IL-10 and using intercellular contacts. Bregs targets encompass all the cells involved in the immune responses which are thus under a dual control by regulatory lymphocytes. Development and efficient activity of Tregs appear dependent of Bregs for a better regulation of autoimmune reactions, of anti-infectious reactions, but also of anti-tumor reactions.

Are the B cells cast with the leading part in the Sjogren's syndrome scenario?

The autoimmune exocrinopathy Sjögren's syndrome (SS) is characterized by mononuclear cell (MNC) infiltrates of exocrine glands and overactivity of B lymphocytes. Although T cells have long been perceived as the prime effectors, increasing evidence indicates that the key role is rather served by B cells. Among related abnormalities are rheumatoid factor (RF), anti-SSA/Ro, and anti-SSB/La antibodies (Ab). Also, supporting this view is our finding of an increase in the number of circulating naïve mature B (Bm) cells, with a reciprocal decrease in that of memory B cells. Furthermore, a ratio of Bm2-plus-Bm2' cells to early Bm5-plus-late Bm5 above 5 is diagnostic. This variation partly reflects the migration of active memory B cells into the exocrine glands of the patients, as well as into their skin. More recently, the B-cell-activating factor of the TNF family (BAFF) has been endorsed with a pivotal role in B-cell survival and hence implicated in the pathogenesis of autoimmunity. In practice, B cells have turned quite attractive as a target for biotherapy. For example, treatment with anti-CD20 Ab has afforded some benefits in this disease, while BAFF blockers are still on the way, but should expand our armamentarium for treating SS. With such B-cell-directed biotherapies in mind, we delineate herein the distinguishing traits of B lymphocytes in SS.

Toll-like receptors as therapeutic targets for autoimmune connective tissue diseases

Autoimmune connective tissue diseases (ACTDs) are a family of consistent systemic autoimmune inflammatory disorders, including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), systemic sclerosis (SSc) and Sjögren's syndrome (SS). IL-1R-like receptors (TLRs) are located on various cellular membranes and sense exogenous and endogenous danger-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs), playing a critical role in innate immune responses. During the past decade, the investigation of TLRs in inflammatory autoimmune diseases has been fruitful. In this report, we review the significant biochemical, physiological and pathological studies of the key functions of TLRs in ACTDs. Several proteins in the TLR signaling pathways (e.g., IKK-2 and MyD88) have been identified as potential therapeutic targets for the treatment of ACTDs. Antibodies, oligodeoxyribonucleotides (ODNs) and small molecular inhibitors (SMIs) have been tested to modulate TLR signaling. Some drug-like SMIs of TLR signaling, such as RDP58, ST2825, ML120B and PHA-408, have demonstrated remarkable potential, with promising safety and efficacy profiles, which should warrant further clinical investigation. Nonetheless, one should bear in mind that all TLRs exert both protective and pathogenic functions; the function of TLR4 in inflammatory bowel disease represents such an example. Therefore, an important aspect of TLR modulator development involves the identification of a balance between the suppression of disease-inducing inflammation, while retaining the beneficiary host immune response.

B cells in Sjögren's syndrome: from pathophysiology to diagnosis and treatment

Primary Sjögren's syndrome (pSS) is a chronic autoimmune systemic disease, characterized by a lymphoplasmocytic infiltration and a progressive destruction of salivary and lachrymal glands, leading to ocular and mouth dryness. T cells were originally considered to play the initiating role in the autoimmune process, while B cells were restricted to autoantibody production. However, recent years have seen growing evidence that the roles of B cells in pSS pathophysiology are multiple, and that these cells may actually play a central role in the development of the disease. B cells are over-stimulated and produce excessive amounts of immunoglobulins and various autoantibodies. Peripheral blood and salivary-gland B-cell subset distribution is altered, leading to the constitution of ectopic germinal centers where auto-reactive clones may escape tolerance checkpoints. B cells control T-cell activation by different means: B effector cells guide Th1 or Th2 differentiation, whereas regulatory B cells inhibit T-cell proliferation. Several B-cell specific cytokines, such as BAFF or Flt-3L, are instrumental in the occurrence of B-cell dysfunction. Chronic and excessive stimulation of B cells may lead to the development of lymphoma in pSS patients. Autoantibodies and blood B-cell subset analysis are major contributors of a clinical diagnosis of pSS. These considerations led to the development of B-cell depletion therapies for the management of pSS. Rituximab, a monoclonal antibody to CD20, is the best studied biologics in pSS, but other treatments hold promise, targeting for example CD22 or BAFF. Thus, during the last 20 years, the understanding of the multifaceted roles of B cells in pSS has revolutionized the management of this complex disease.

TLR9 drives the development of transitional B cells towards the marginal zone pathway and promotes autoimmunity

Maturation of B cells depends on environmental stimuli. Peripheral immature B cells develop into follicular pathway when antigenic stimulation is combined with T cell signals. Here, we wished to identify stimuli contributing to the development into marginal zone B cells known to be involved in autoimmune response. We found that TLR9 stimulation of transitional B cells induces proliferation and specific maturation into CD24(-) CD38(+) CD21(high) CD23(low) IgM(high) IgD(low) and Notch2(high) B cells characteristics of marginal zone B cells. Terminal differentiation into antibody-secreting cell associated with isotype switch commitment is also triggered which leads to a striking production of autoantibodies. Interestingly, mature B cells do not differentiate into marginal zone pathway following TLR9 stimulation, nor do transitional B cells under antigenic and T cell combined signals. These results suggest that transitional B cells are specifically sensitive to TLR9 stimulation to produce autoreactive marginal zone B cells.