Production of a novel class of polyreactive pathogenic autoantibodies in BXD2 mice causes glomerulonephritis and arthritis

Increased development of T-bet+CD11c+ B cells predisposes to lupus in females: Analysis in BXD2 mouse and genetic crosses

Cardinal features of lupus include elevated B cell activation and autoantibody production with a female sex preponderance. We quantified interactions of sex and genetic variation on the development of autoimmune B-cell phenotypes and autoantibodies in the BXD2 murine model of lupus using a cohort of backcrossed progeny (BXD2 x C57BL/6J) x BXD2. Sex was the key factor leading to increased total IgG, IgG2b, and autoantibodies. The percentage of T-bet+CD11c+ IgD+ activated naive B cells (aNAV) was higher in females and was associated with increased T-bet+CD11c+ IgD- age-related B cells, Fas+GL7+ germinal center B cells, Cxcr5-Icos+ peripheral T-helper cells, and Cxcr5+Icos+ follicular T-helper cells. IFN-β was elevated in females. Variation in aNAV cells was mapped to Chr 7 in a locus that shows significant interactions between the female sex and heterozygous B/D variant. Our results suggest that activation of naive B cells forms the basis for the female-predominant development of autoantibodies in lupus-susceptible BXD2 mice.

Host genetics but not commensal microbiota determines the initial development of systemic autoimmune disease in BXD2 mice

OBJECTIVE

To determine the extent of gut microbiome in influencing systemic autoimmunity, we generated germ-free (GF) BXD2 lupus mice, which otherwise develop spontaneous germinal centers (GCs) and high titers of serum autoantibodies.

METHODS

The GF status was confirmed by gut bacterial culture. The autoimmune phenotypes in 6- and 12-mo-old gnotobiotic GF BXD2 mice and specific pathogen-free (SPF) BXD2 mice were compared. Serum levels of autoantibody were measured using ELISA. Histologic sections of kidney and joints were evaluated. Flow cytometry was used to analyze GC and age-associated B cells (ABCs). CD4⁺ T cells were analyzed for PD-1⁺ ICOS⁺ activated T cells, follicular T-regulatory cells (Tfr, Foxp3⁺ CD25⁺ PD-1⁺ CXCR5⁺ ), and PMA/ionomycin stimulated IL-17A⁺ or interferon-gamma (IFN-&ip.gamma;)⁺ PD-1⁺ ICOS⁺ T cells.

RESULTS

At 6-mo of age, the GF status did not affect splenomegaly, GC B cells, ABCs or serum autoantibodies except for IgG anti-histone. GF BXD2 mice exhibited a significantly higher percent of Tfr cells, compared to the SPF counterpart. At 12-mo-old, however, there were significantly diminished IgG autoantibodies and a lower percent of GC B cells and ABCs in GF BXD2 mice. Following stimulation, PD-1⁺ ICOS⁺ CD4 T cells expressed significantly lower IL-17A but not IFN-&ip.gamma; in GF BXD2 mice, compared to SPF mice. Both SPF and GF BXD2 mice developed equivalent renal and joint disease with no significant differences in severity.

CONCLUSION

Our results suggest a model in which genetics play a dominant role in determining the initial development of autoimmunity. In contrast, gut microbiomes may regulate the persistence of certain aspects of systemic autoimmunity.

Patients with Proliferative Lupus Nephritis Have Autoantibodies That React to Moesin and Demonstrate Increased Glomerular Moesin Expression

Kidney involvement in systemic lupus erythematosus (SLE)—termed lupus nephritis (LN)—is a severe manifestation of SLE that can lead to end-stage kidney disease (ESKD). LN is characterized by immune complex deposition and inflammation in the glomerulus. We tested the hypothesis that autoantibodies targeting podocyte and glomerular cell proteins contribute to the development of immune complex formation in LN. We used Western blotting with SLE sera from patients with and without LN to identify target antigens in human glomerular and cultured human-derived podocyte membrane proteins. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identified the proteins in the gel regions corresponding to reactive bands observed with sera from LN patients. We identified 102 proteins that were present in both the podocyte and glomerular samples. We identified 10 high-probability candidates, including moesin, using bioinformatic analysis. Confirmation of moesin as a target antigen was conducted using immunohistochemical analysis (IHC) of kidney biopsy tissue and enzyme-linked immunosorbent assay (ELISA) to detect circulating antibodies. By IHC, biopsies from patients with proliferative lupus nephritis (PLN, class III/IV) demonstrated significantly increased glomerular expression of moesin (p < 0.01). By ELISA, patients with proliferative LN demonstrated significantly increased antibodies against moesin (p < 0.01). This suggests that moesin is a target glomerular antigen in lupus nephritis.

IL-23 Promotes a Coordinated B Cell Germinal Center Program for Class-Switch Recombination to IgG2b in BXD2 Mice

IL-23 promotes autoimmune disease, including Th17 CD4 T cell development and autoantibody production. In this study, we show that a deficiency of the p19 component of IL-23 in the autoimmune BXD2 (BXD2-p19^-/- ) mouse leads to a shift of the follicular T helper cell program from follicular T helper (Tfh)-IL-17 to Tfh-IFN-γ. Although the germinal center (GC) size and the number of GC B cells remained the same, BXD2-p19^-/- mice exhibited a lower class-switch recombination (CSR) in the GC B cells, leading to lower serum levels of IgG2b. Single-cell transcriptomics analysis of GC B cells revealed that whereas Ifngr1, Il21r, and Il4r genes exhibited a synchronized expression pattern with Cxcr5 and plasma cell program genes, Il17ra exhibited a synchronized expression pattern with Cxcr4 and GC program genes. Downregulation of Ighg2b in BXD2-p19^-/- GC B cells was associated with decreased expression of CSR-related novel base excision repair genes that were otherwise predominantly expressed by Il17ra ⁺ GC B cells in BXD2 mice. Together, these results suggest that although IL-23 is dispensable for GC formation, it is essential to promote a population of Tfh-IL-17 cells. IL-23 acts indirectly on Il17ra ⁺ GC B cells to facilitate CSR-related base excision repair genes during the dark zone phase of GC B cell development.

Preferential recognition of epitopes on peroxynitrite-modified alpha-2-macroglobulin by circulating autoantibodies in rheumatoid arthritis patients

Autoimmune responses against post-translationally modified antigens are a hallmark of several autoimmune diseases. In this work, we have studied the changes in alpha-2-macroglobulin (α₂M) upon modification by peroxynitrite. Furthermore, we have evaluated the immunogenicity of modified α₂M in experimental rabbits and rheumatoid arthritis (RA) patients. Peroxynitrite-modified α₂M showed disturbed microenvironment and altered aromatic residues under UV and fluorescence studies. Aggregation, reduction in β-sheet content, production of nitrotyrosine and shift in amide I and II bands were observed in the modified α₂M by polyacrylamide gel electrophoresis besides CD and FTIR spectroscopic analysis. The exposure of hydrophobic clusters and changes in contact positions were observed in ANS and ThT binding assays. Immunological studies using ELISA showed peroxynitrite-modified α₂M as highly immunogenic producing high titre of specific antibodies in immunized rabbits. Cross-reactivity studies revealed the polyspecificity of the elicited antibodies. Direct binding ELISA and competitive inhibition studies confirmed the presence of circulating antibodies in the sera of RA patients having high specificity towards the peroxynitrite-modified α₂M as compared to the native α₂M. Sera from healthy (normal) human subjects showed lower binding with the native and modified protein. This study confirms that peroxynitrite induces structural modifications in α₂M and makes it immunogenic. The presence of neo-antigenic determinants on modified α₂M with enhanced binding for circulating autoantibodies in RA patients could offer new possibilities for diagnosis and etiopathology of the disease. Communicated by Ramaswamy H. Sarma.

Dysregulation of T Follicular Helper Cells in Lupus

Although multiple and overlapping mechanisms are ultimately responsible for the immunopathology observed in patients with systemic lupus erythematosus, autoreactive Abs secreted by autoreactive plasma cells (PCs) are considered to play a critical role in disease progression and immunopathology. Given that PCs derive from the germinal centers (GC), long-term dysregulated GC reactions are often associated with the development of spontaneous autoantibody responses and immunopathology in systemic lupus erythematosus patients. In this review, we summarize the emerging evidence concerning the roles of T follicular helper cells in regulating pathogenic GC and autoreactive PC responses in lupus.

Autoreactive B cells in SLE, villains or innocent bystanders?

The current concepts for development of autoreactive B cells in SLE (systemic lupus erythematosus) focus on extrinsic stimuli and factors that provoke B cells into tolerance loss. Traditionally, major tolerance loss pathways are thought to be regulated by factors outside the B cell including autoantigen engagement of the B-cell receptor (BCR) with simultaneous type I interferon (IFN) produced by dendritic cells, especially plasmacytoid dendritic cells (pDCs). Later, in autoreactive follicles, B-cells encounter T-follicular helper cells (Tfh) that produce interleukin (IL)-21, IL-4 and pathogenic cytokines, IL-17 and IFN gamma (IFNɣ). This review discusses these mechanisms and also highlights recent advances pointing to the peripheral transitional B-cell stage as a major juncture where transient autocrine IFNβ expression by developing B-cells imprints a heightened susceptibility to external factors favoring differentiation into autoantibody-producing plasmablasts. Recent studies highlight transitional B-cell heterogeneity as a determinant of intrinsic resistance or susceptibility to tolerance loss through the shaping of B-cell responsiveness to cytokines and other environment factors.

Alpha-1 microglobulin as a potential therapeutic candidate for treatment of hypertension and oxidative stress in the STOX1 preeclampsia mouse model

Preeclampsia is a human placental disorder affecting 2–8% of pregnancies worldwide annually, with hypertension and proteinuria appearing after 20 weeks of gestation. The underlying cause is believed to be incomplete trophoblast invasion of the maternal spiral arteries during placentation in the first trimester, resulting in oxidative and nitrative stress as well as maternal inflammation and organ alterations. In the Storkhead box 1 (STOX1) preeclampsia mouse model, pregnant females develop severe and early onset manifestations as seen in human preeclampsia e.g. gestational hypertension, proteinuria, and organ alterations. Here we aimed to evaluate the therapeutic potential of human recombinant alpha-1 microglobulin (rA1M) to alleviate the manifestations observed. Human rA1M significantly reduced the hypertension during gestation and significantly reduced the level of hypoxia and nitrative stress in the placenta. In addition, rA1M treatment reduced cellular damage in both placenta and kidneys, thereby protecting the tissue and improving their function. This study confirms that rA1M has the potential as a therapeutic drug in preeclampsia, and likely also in other pathological conditions associated with oxidative stress, by preserving normal organ function.

3β-Acetyloxy-oleanolic Acid Attenuates Pristane-Induced Lupus Nephritis by Regulating Th17 Differentiation

Th17 activity has been implicated in systemic lupus erythematosus (SLE), which is a systemic autoimmune disease with a typical clinical manifestation of lupus nephritis (LN). Retinoic acid receptor-related orphan receptor gamma t (RORγt) has been shown to be important for Th17 differentiation. In this study, we evaluated the inhibition of RORγt activity by 3β-acetyloxy-oleanolic acid (AOA), a small molecule isolated from the root of Symplocos laurina, a traditional herb belonging to South China. We demonstrated that AOA can inhibit RORγt activity and prevent SLE pathogenesis in a pristane-induced LN model. The results showed that AOA decreased RORγt transcription activity in a reporter assay and prevented Th17 differentiation in vitro. In vivo studies showed that AOA treatment decreased serum anti-dsDNA antibody and alleviated renal pathologic damage as well as antibody complex accumulation in the pristane-induced LN model. These results demonstrated that AOA can improve the clinical manifestation of LN, indicating potential application in SLE therapy.

T Cell Migration in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation in joints, associated with synovial hyperplasia and with bone and cartilage destruction. Although the primacy of T cell-related events early in the disease continues to be debated, there is strong evidence that autoantigen recognition by specific T cells is crucial to the pathophysiology of rheumatoid synovitis. In addition, T cells are key components of the immune cell infiltrate detected in the joints of RA patients. Initial analysis of the cytokines released into the synovial membrane showed an imbalance, with a predominance of proinflammatory mediators, indicating a deleterious effect of Th1 T cells. There is nonetheless evidence that Th17 cells also play an important role in RA. T cells migrate from the bloodstream to the synovial tissue via their interactions with the endothelial cells that line synovial postcapillary venules. At this stage, selectins, integrins, and chemokines have a central role in blood cell invasion of synovial tissue, and therefore in the intensity of the inflammatory response. In this review, we will focus on the mechanisms involved in T cell attraction to the joint, the proteins involved in their extravasation from blood vessels, and the signaling pathways activated. Knowledge of these processes will lead to a better understanding of the mechanism by which the systemic immune response causes local joint disorders and will help to provide a molecular basis for therapeutic strategies.

Interferon-induced mechanosensing defects impede apoptotic cell clearance in lupus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease that is associated with increased circulating apoptotic cell autoantigens (AC-Ags) as well as increased type I IFN signaling. Here, we describe a pathogenic mechanism in which follicular translocation of marginal zone (MZ) B cells in the spleens of BXD2 lupus mice disrupts marginal zone macrophages (MZMs), which normally clear AC debris and prevent follicular entry of AC-Ags. Phagocytosis of ACs by splenic MZMs required the megakaryoblastic leukemia 1 (MKL1) transcriptional coactivator-mediated mechanosensing pathway, which was maintained by MZ B cells through expression of membrane lymphotoxin-α1β2 (mLT). Specifically, type I IFN-induced follicular shuttling of mLT-expressing MZ B cells disengaged interactions between these MZ B cells and LTβ receptor-expressing MZMs, thereby downregulating MKL1 in MZMs. Loss of MKL1 expression in MZMs led to defective F-actin polymerization, inability to clear ACs, and, eventually, MZM dissipation. Aggregation of plasmacytoid DCs in the splenic perifollicular region, follicular translocation of MZ B cells, and loss of MKL1 and MZMs were also observed in an additional murine lupus model and in the spleens of patients with SLE. Collectively, the results suggest that lupus might be interrupted by strategies that maintain or enhance mechanosensing signaling in the MZM barrier to prevent follicular entry of AC-Ags.

General Approach for Tetramer-Based Identification of Autoantigen-Reactive B Cells: Characterization of La- and snRNP-Reactive B Cells in Autoimmune BXD2 Mice

Autoreactive B cells are associated with the development of several autoimmune diseases, including systemic lupus erythematosus and rheumatoid arthritis. The low frequency of these cells represents a major barrier to their analysis. Ag tetramers prepared from linear epitopes represent a promising strategy for the identification of small subsets of Ag-reactive immune cells. This is challenging given the requirement for identification and validation of linear epitopes and the complexity of autoantibody responses, including the broad spectrum of autoantibody specificities and the contribution of isotype to pathogenicity. Therefore, we tested a two-tiered peptide microarray approach, coupled with epitope mapping of known autoantigens, to identify and characterize autoepitopes using the BXD2 autoimmune mouse model. Microarray results were verified through comparison with established age-associated profiles of autoantigen specificities and autoantibody class switching in BXD2 and control (C57BL/6) mice and high-throughput ELISA and ELISPOT analyses of synthetic peptides. Tetramers were prepared from two linear peptides derived from two RNA-binding proteins (RBPs): lupus La and 70-kDa U1 small nuclear ribonucleoprotein. Flow cytometric analysis of tetramer-reactive B cell subsets revealed a significantly higher frequency and greater numbers of RBP-reactive marginal zone precursor, transitional T3, and PDL-2(+)CD80(+) memory B cells, with significantly elevated CD69 and CD86 observed in RBP(+) marginal zone precursor B cells in the spleens of BXD2 mice compared with C57BL/6 mice, suggesting a regulatory defect. This study establishes a feasible strategy for the characterization of autoantigen-specific B cell subsets in different models of autoimmunity and, potentially, in humans.

Regulation of autoimmune germinal center reactions in lupus-prone BXD2 mice by follicular helper T cells

BXD2 mice spontaneously develop autoantibodies and subsequent glomerulonephritis, offering a useful animal model to study autoimmune lupus. Although initial studies showed a critical contribution of IL-17 and Th17 cells in mediating autoimmune B cell responses in BXD2 mice, the role of follicular helper T (Tfh) cells remains incompletely understood. We found that both the frequency of Th17 cells and the levels of IL-17 in circulation in BXD2 mice were comparable to those of wild-type. By contrast, the frequency of PD-1+ CXCR5+ Tfh cells was significantly increased in BXD2 mice compared with wild-type mice, while the frequency of PD-1+ CXCR5+ Foxp3+ follicular regulatory T (Tfr) cells was reduced in the former group. The frequency of Tfh cells rather than that of Th17 cells was positively correlated with the frequency of germinal center B cells as well as the levels of autoantibodies to dsDNA. More importantly, CXCR5+ CD4+ T cells isolated from BXD2 mice induced the production of IgG from naïve B cells in an IL-21-dependent manner, while CCR6+ CD4+ T cells failed to do so. These results together demonstrate that Tfh cells rather than Th17 cells contribute to the autoimmune germinal center reactions in BXD2 mice.

Tetramers reveal IL-17-secreting CD4+ T cells that are specific for U1-70 in lupus and mixed connective tissue disease

Antigen-specific CD4(+) T cells are implicated in the autoimmune disease systemic lupus erythematosus (SLE), but little is known about the peptide antigens that they recognize and their precise function in disease. We generated a series of MHC class II tetramers of I-E(k)-containing peptides from the spliceosomal protein U1-70 that specifically stain distinct CD4(+) T-cell populations in MRL/lpr mice. The T-cell populations recognize an epitope differing only by the presence or absence of a single phosphate residue at position serine(140). The frequency of CD4(+) T cells specific for U1-70(131-150):I-E(k) (without phosphorylation) correlates with disease severity and anti-U1-70 autoantibody production. These T cells also express RORγt and produce IL-17A. Furthermore, the U1-70-specific CD4(+) T cells that produce IL-17A are detected in a subset of patients with SLE and are significantly increased in patients with mixed connective tissue disease. These studies provide tools for studying antigen-specific CD4(+) T cells in lupus, and demonstrate an antigen-specific source of IL-17A in autoimmune disease.

Interleukin-21 promotes germinal center reaction by skewing the follicular regulatory T cell to follicular helper T cell balance in autoimmune BXD2 mice

OBJECTIVE

Follicular regulatory T (Tfr) cells act as the regulatory counterpart of follicular helper T (Tfh) cells to suppress germinal center (GC) B cell differentiation. We recently showed that interleukin-21 (IL-21) promoted Tfh cell differentiation in autoimmune BXD2 mice that develop spontaneous GCs. This study was undertaken to determine the modulatory effects of IL-21 on Tfr cells and the Tfr cell to Tfh cell balance in BXD2 mice.

METHODS

The percentage and phenotype of Tfr cells were determined in BXD2 and BXD2-IL21(-/-) mice. The effects of IL-21 on Tfr cells and the Tfr cell:Tfh cell ratio were evaluated. Sorted Tfr cells from BXD2-IL21(-/-) mice were cocultured with Tfh cells and B cells, or transferred into BXD2 mice to determine their function.

RESULTS

The percentages and numbers of GC B cells and Tfh cells were significantly reduced, but the percentage of Tfr cells was 2-fold higher in BXD2-IL21(-/-) mice than in wild-type BXD2 mice. Administration of AdIL-21 to BXD2-IL21(-/-) mice decreased the percentages and numbers of Tfr cells and the Tfr cell:Tfh cell ratio but increased the number of GC B cells in the spleen. Recombinant murine IL-21 suppressed FoxP3 and significantly reduced Tgfb1, Il2, and Gitr but enhanced Il21, Il6, Pd1, Cxcr5, and Icos expression in Tfr cells. IL-21 also counteracted Tfr cell-mediated inhibition of antibody secretion in the Tfh cell-B cell coculture system. Transfer of Tfr cells into young BXD2 mice reduced GC size and decreased the numbers of autoantibody-producing B cells.

CONCLUSION

Our findings indicate that high levels of IL-21 selectively enhance Tfh cell differentiation but inhibit Tfr cell commitment and the suppressive function of Tfr cells on Tfh cells and B cells, suggesting that IL-21 skews the balance from Tfr cells to Tfh cells to promote autoreactive GC reactions in BXD2 mice.

Oxidative and Nitrosative Stress and Immune-Inflammatory Pathways in Patients with Myalgic Encephalomyelitis (ME)/Chronic Fatigue Syndrome (CFS)

Myalgic Encephalomyelitis (ME) / Chronic Fatigue Syndrome (CFS) has been classified as a disease of the central nervous system by the WHO since 1969. Many patients carrying this diagnosis do demonstrate an almost bewildering array of biological abnormalities particularly the presence of oxidative and nitrosative stress (O&NS) and a chronically activated innate immune system. The proposal made herein is that once generated chronically activated O&NS and immune-inflammatory pathways conspire to generate a multitude of self-sustaining and self-amplifying pathological processes which are associated with the onset of ME/CFS. Sources of continuous activation of O&NS and immune-inflammatory pathways in ME/CFS are chronic, intermittent and opportunistic infections, bacterial translocation, autoimmune responses, mitochondrial dysfunctions, activation of the Toll-Like Receptor Radical Cycle, and decreased antioxidant levels. Consequences of chronically activated O&NS and immune-inflammatory pathways in ME/CFS are brain disorders, including neuroinflammation and brain hypometabolism / hypoperfusion, toxic effects of nitric oxide and peroxynitrite, lipid peroxidation and oxidative damage to DNA, secondary autoimmune responses directed against disrupted lipid membrane components and proteins, mitochondrial dysfunctions with a disruption of energy metabolism (e.g. compromised ATP production) and dysfunctional intracellular signaling pathways. The interplay between all of these factors leads to self-amplifying feed forward loops causing a chronic state of activated O&NS, immune-inflammatory and autoimmune pathways which may sustain the disease.

Extension of the germinal center stage of B cell development promotes autoantibodies in BXD2 mice

OBJECTIVE

Regulator of G protein signaling (RGS) proteins inhibit chemokine signaling by desensitizing G protein-coupled receptor signals. This study was undertaken to determine the mechanisms by which RGS13 promotes the generation of pathogenic autoantibodies in germinal centers (GCs), using BXD2-Rgs13-/- mice.

METHODS

Confocal and light microscopy imaging techniques were used to determine the location of cells that express RGS13 and activation-induced cytidine deaminase (AID) in the mouse spleen, and the number of plasmablasts. The levels of GC and plasma cell program transcripts in GC B cells were determined by real-time quantitative polymerase chain reaction (qPCR). Differential interleukin-17 (IL-17)-mediated expression of RGS13 in GC versus non-GC B cells was analyzed using A20 and 70Z/3 B cells.

RESULTS

In the spleens of BXD2 mice, RGS13 was mainly expressed by GC B cells and was stimulated by IL-17 but not IL-21. IL-17 up-regulated RGS13 in A20 GC cells but not 70Z/3 non-GC B cells. BXD2- Rgs13-/- mice exhibited smaller GCs and lower AID levels, suggesting lower somatic hypermutation and affinity maturation. However, GC B cells from BXD2- Rgs13-/- mice showed increased levels of IgMbright plasmablasts, up-regulation of the genes encoding plasma program, including interferon regulatory factor 4, B lymphocyte-induced maturation protein 1, and X-box binding protein 1 and the p-CREB target genes Fosb and Obf1, and down-regulation of the GC program genes Aid, Pax5, and Bach2 compared to BXD2 mice. BXD2-Rgs13-/- mice had lower titers of IgG autoantibodies and IgG deposits in the glomeruli, suggesting reduced autoantibody pathogenicity.

CONCLUSION

RGS13 deficiency is associated with a reduction in GC program genes and the exit of fewer pathogenic IgM plasmablasts in BXD2 mice. Our findings indicate that prolonged GC program, mediated by up-regulation of RGS13, enhances AID expression and enables the generation of pathogenic autoantibodies in autoreactive GCs.

IL-17RA is essential for optimal localization of follicular Th cells in the germinal center light zone to promote autoantibody-producing B cells

Germinal centers (GCs) provide a microenvironment that promotes and regulates the interactions of B cells with follicular Th (TFH) cells. In this study, we show that there are significantly higher frequencies of CXCR5(+)ICOS(+) TFH cells in autoimmune BXD2 mice, and these cells express both IL-21R and IL-17RA. Although IL-17 and IL-21 are both important for the formation of spontaneous GCs and development of pathogenic autoantibodies, IL-21, but not IL-17, is required for the proper development of TFH cells in BXD2 mice. The total numbers of TFH cells and their ability to induce B cell responses in vitro were not affected by a deficiency of IL-17RA in BXD2-Il17ra(-/-) mice, the majority of CXCR5(+) TFH cells from BXD2-Il17ra(-/-) mice were, however, not localized in the GC light zone (LZ). Interruption of IL-17 signaling, either acutely by AdIL-17R:Fc or chronically by Il17ra(-/-), disrupted TFH-B interactions and abrogated the generation of autoantibody-forming B cells in BXD2 mice. IL-17 upregulated the expression of regulator of G-protein signaling 16 (RGS16) to promote the ability of TFH to form conjugates with B cells, which was abolished in TFH cells from BXD2-Rgs16(-/-) mice. The results suggests that IL-17 is an extrinsic stop signal that it acts on postdifferentiated IL-17RA(+) TFH to enable its interaction with responder B cells in the LZ niche. These data suggest a novel concept that TFH differentiation and its stabilization in the LZ are two separate checkpoints and that IL-21 and IL-17 act at each checkpoint to enable pathogenic GC development.

Cutting Edge: defective follicular exclusion of apoptotic antigens due to marginal zone macrophage defects in autoimmune BXD2 mice

Marginal zone macrophages (MZMs) act as a barrier to entry of circulating apoptotic debris into the follicles of secondary lymphoid organs. In autoimmune BXD2 mice, there is a progressive reduction in the function and numbers of MZMs. Absence of MZMs results in retention of apoptotic cell (AC) debris within the marginal zone (MZ) and increased loading of AC Ags on MZ B cells and MZ-precursor (MZ-P) B cells. The MZ-P B cells are capable of translocating the AC Ags to the follicular zone and stimulating T cells. Both MZMs and MZ-P B cells from BXD2 mice express low levels of tolerogenic signals and high levels of inflammatory signals. Thus, the current study suggests a multifaceted mechanism in which MZMs maintain tolerance to apoptotic autoantigens and suppress their translocation to follicles. Lack of clearance of apoptotic debris by MZMs drives follicular Ag-transportation by MZ-P B cells to stimulate an autoimmune response.

Modulatory function of invariant natural killer T cells in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disease with complex immunological and clinical manifestations. Multiple organ failure in SLE can be caused by immune dysfunction and deposition of autoantibodies. Studies of SLE-susceptible loci and the cellular and humoral immune responses reveal variable aberrations associated with this systemic disease. Invariant natural killer T (iNKT) cells are a unique subset of lymphocytes that control peripheral tolerance. Mounting evidence showing reductions in the proportion and activity of iNKT cells in SLE patients suggests the suppressive role of iNKT cells. Studies using murine lupus models demonstrate that iNKT cells participate in SLE progression by sensing apoptotic cells, regulating immunoglobulin production, and altering the cytokine profile upon activation. However, the dichotomy of iNKT cell actions in murine models implies complicated interactions within the body's milieu. Therefore, application of potential therapy for SLE using glycolipids to regulate iNKT cells should be undertaken cautiously.

The dysregulation of cytokine networks in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease associated with chronic immune activation and tissue damage. Organ damage in SLE results from the deposition of immune complexes and the infiltration of activated T cells into susceptible organs. Cytokines are intimately involved in every step of the SLE pathogenesis. Defective immune regulation and uncontrolled lymphocyte activation, as well as increased antigen presenting cell maturation are all influenced by cytokines. Moreover, expansion of local immune responses as well as tissue infiltration by pathogenic cells is instigated by cytokines. In this review, we describe the main cytokine abnormalities reported in SLE and discuss the mechanisms that drive their aberrant production as well as the pathogenic pathways that their presence promotes.

Inhibition of the catalytic function of activation-induced cytidine deaminase promotes apoptosis of germinal center B cells in BXD2 mice

OBJECTIVE

To determine whether functional suppression of the catalytic domain of activation-induced cytidine deaminase (AID) can suppress the hyperreactive germinal center (GC) responses in BXD2 mice.

METHODS

We generated transgenic BXD2 mice expressing a dominant-negative (DN) form of Aicda at the somatic hypermutation site (BXD2-Aicda-DN-transgenic mice). Real-time quantitative reverse transcriptase-polymerase chain reaction was used to determine the expression of Aicda and DNA damage/repair genes. Enzyme-linked immunosorbent assay was used to measure serum levels of autoantibodies and immune complexes (ICs). Development of GCs and antibody-containing ICs as well as numbers of proliferative and apoptotic cells were determined using flow cytometry and/or immunohistochemical analyses. Development of arthritis and kidney disease was evaluated histologically in 6-8-month-old mice.

RESULTS

Suppression of the somatic hypermutation function of AID resulted in a significant decrease in autoantibody production without affecting the expression of DNA damage-related genes in GC B cells of BXD2-Aicda-DN-transgenic mice. There was decreased proliferation, increased apoptosis, increased expression of caspase 9 messenger RNA in GC B cells, and lower numbers of GCs in the spleens of BXD2-Aicda-DN-transgenic mice. Decreased GC response was associated with lower levels of IgG-containing ICs. Anti-IgM- and anti-CD40 plus anti-Ig-induced B cell proliferative responses were decreased in BXD2-Aicda-DN-transgenic mice.

CONCLUSION

Inhibition of the AID somatic hypermutation function in BXD2 mice suppressed development of spontaneous GCs, generation of autoantibody-producing B cells, and autoimmunity in BXD2 mice. Suppression of AID catalytic function to limit selection-based survival of GC B cells could become a novel therapy for the treatment of autoimmune disease.

IL-17-producing T cells in lupus nephritis

Significant evidence implicates interleukin-17 (IL-17) in the pathogenesis of systemic lupus erythematosus (SLE), particularly in the development of tissue damage. IL-17 production and IL-17-producing CD4+ and CD3 + CD4-CD8- cells are increased in patients with SLE. IL-17-producing cells are present in the inflamed kidney tissues from patients with lupus nephritis. In lupus-prone mice, IL-17 production appears to be involved in the expression of disease pathology and pharmacologic or genetic manipulation of its production results in suppression of the disease. It becomes obvious that the use of biologics including humanized anti-IL-17 antibodies or decoy IL-17 receptors deserve clinical consideration. Similarly, the development of drugs that suppress the production of IL-17 is in order.

Type I interferon-dependent CD86(high) marginal zone precursor B cells are potent T cell costimulators in mice

OBJECTIVE

To investigate the role of CD86(high) marginal zone (MZ) precursor B cells in type I interferon (IFN)-induced T cell-dependent responses in autoimmune BXD2 mice.

METHODS

Confocal microscopic imaging was used to determine the location of plasmacytoid dendritic cells (DCs), MZ precursor B cells, and CD4 T cells in the spleens of BXD2 and BXD2-Ifnar(-/-) mice. Immunohistochemical staining was used to determine IgG(bright) cells in the spleens of BXD2 and BXD2-Ifnar(-/-) mice. Enzyme-linked immunosorbent assay was used to determine serum levels of IFNα and autoantibodies, and 4-hydroxy-3-nitrophenylacetyl hapten (NP)-chicken γ-globulin (CGG) (NP-CGG)- or NP-Ficoll-induced anti-NP2 antibody titers. Real-time quantitative polymerase chain reaction was used to determine the levels of type I IFN transcripts. T cell proliferation was measured using (3) H-thymidine. The expression of CD86 and CD80 was determined by fluorescence-activated cell sorting analysis.

RESULTS

The deletion of type I IFN receptor abrogated the development of IgG(bright) cells and suppressed a T cell-dependent antibody response. Type I IFN signaling was associated with the expression of CD86, but not CD80, on follicular, MZ, and MZ precursor B cells. However, MZ precursor B cells demonstrated the highest expression of CD86 and the highest capacity for T cell costimulation with intact type I IFN receptor. This effect was blocked by an antibody that neutralizes CD86. In IFN receptor-intact BXD2 mouse spleens, MZ precursor B cells clustered at the T cell-B cell border. CD86 deletion suppressed germinal center formation, autoantibody production, and development of autoimmune diseases in BXD2 mice.

CONCLUSION

Type I IFN can promote autoimmune responses in BXD2 mice through up-regulation of CD86(high) expression on MZ precursor B cells and trafficking of MZ precursor B cells to the T cell-B cell border to provide costimulation of CD4 T cells.

AID dysregulation in lupus-prone MRL/Fas(lpr/lpr) mice increases class switch DNA recombination and promotes interchromosomal c-Myc/IgH loci translocations: modulation by HoxC4

Immunoglobulin gene somatic hypermutation (SHM) and class switch DNA recombination (CSR) play important roles in the generation of autoantibodies in systemic lupus erythematosus. Systemic lupus is characterized by the production of an array of pathogenic high-affinity mutated and class-switched, mainly IgG, antibodies to a variety of self-antigens, including nuclear components, such as dsDNA, histones, and chromatin. We previously found that MRL/Fas(lpr/lpr) mice, which develop a systemic autoimmune syndrome sharing many features with human lupus, display greatly upregulated CSR, particularly to IgG2a, in B cells of the spleen, lymph nodes, and Peyer's patches. In MRL/Fas(lpr/lpr) mice, the significant upregulation of CSR is associated with increased expression of activation-induced cytidine deaminase (AID), which is critical for CSR and SHM. We also found that HoxC4 directly activates the promoter of the AID gene to induce AID expression, CSR and SHM. Here, we show that in both lupus patients and lupus-prone MRL/Fas(lpr/lpr) mice, the expression of HoxC4 and AID is significantly upregulated. To further analyze the role of HoxC4 in lupus, we generated HoxC4(-/-) MRL/Fas(lpr/lpr) mice. In these mice, HoxC4-deficiency resulted in reduced AID expression, impaired CSR, and decreased serum anti-dsDNA IgG, particularly IgG2a, autoantibodies, which were associated with a reduction in IgG deposition in kidney glomeruli. In addition, consistent with our previous findings in MRL/Fas(lpr/lpr) mice that upregulated AID expression is associated with extensive DNA lesions, comprising deletions and insertions in the IgH locus, we found that c-Myc to IgH (c-Myc/IgH) translocations occur frequently in B cells of MRL/Fas(lpr/lpr) mice. The frequency of such translocations was significantly reduced in HoxC4(-/-) MRL/Fas(lpr/lpr) mice. These findings suggest that in lupus B cells, upregulation of HoxC4 plays a major role in dysregulation of AID expression, thereby increasing CSR and autoantibody production and promoting c-Myc/IgH translocations.

The current concept of T (h) 17 cells and their expanding role in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with a multifaceted range of symptoms affecting almost every organ system. The prototypical pathology of SLE involves the production of antinuclear antibodies and the deposition of immune complexes in basement membranes throughout the body where they induce inflammatory responses. The genetic and environmental etiologies of this process are being intensively sought, and recently, T _H 17 cells have been implicated in the pathogenesis of SLE. T _H 17 cells are CD4+ memory T cells that behave as both helper and effector cell populations functioning through their signature IL-17 cytokines. Their differentiation is distinct to either the T _H 1 or T _H 2 cell lineage, but strongly influences development of adaptive responses, including autoimmunity. This paper details the biological functions and regulation of T _H 17 cells, followed by an update of their expanding role in SLE.

IL-17 in systemic lupus erythematosus

IL-17 is a cytokine with powerful proinflammatory activity. Production of IL-17 is abnormally increased in patients with systemic lupus erythematosus (SLE), a multiorgan chronic autoimmune disease. In patients with SLE, CD3⁺CD4⁻CD8⁻ (double negative) T cells are an important source of IL-17. IL-17 produced by double negative and CD4 T cells participates in the pathogenesis of the disease. IL-17-producing T cells are present in the kidneys of patients with lupus nephritis. IL-17 increased production in patients with SLE can amplify the immune response by increasing target organ inflammation and damage and by augmenting the production of antibodies by B cells.

Multiple checkpoints keep follicular helper T cells under control to prevent autoimmunity

Follicular helper T (Tfh) cells select mutated B cells in germinal centres, which can then differentiate into long-lived high affinity memory B cells and plasma cells. Tfh cells are regulated by a unique molecular programme orchestrated by the transcriptional repressor Bcl6. This transcription factor turns down expression of multiple genes, including transcriptional regulators of other T helper lineages and a vast amount of microRNAs. This enables Tfh cells to express a suite of chemokine receptors, stimulatory ligands and cytokines that enable migration into B-cell follicles, and provision of effective help to B cells. Not surprisingly, dysregulation of this powerful helper subset can lead to a range of autoantibody-mediated diseases; indeed, aberrant accumulation of Tfh cells has been linked with systemic lupus erythematosus, Sjogren's disease and autoimmune arthritis. Here we dissect multiple checkpoints that operate throughout Tfh cell development and maturation to maintain immunological tolerance while mounting robust and long-lasting antibody responses.

IL-17 activates the canonical NF-kappaB signaling pathway in autoimmune B cells of BXD2 mice to upregulate the expression of regulators of G-protein signaling 16

We previously identified that autoreactive B cells from BXD2 mice can be targeted by IL-17, leading to upregulation of the expression of regulators of G-protein signaling (Rgs) genes that facilitated the development of spontaneous germinal centers. Little is known about the signaling pathway used by IL-17 to upregulate RGS. In the current study, we found that IL-17 rapidly activates the canonical NF-kappaB signaling pathway and that BXD2 B cells exhibit higher basal and activated phosphorylated p65 levels than B6 or BXD2-Il17ra(-/-) B cells. Inhibition of p65 phosphorylation downregulated RGS16 expression and abrogated the IL-17-induced chemotactic arrest of B cells in response to CXCL12. Knockdown of TNFR-associated factor 6 or NF-kappaB activator 1 in 70Z/3 pre-B cells led to decreased Rgs16 expression, indicating that both of these two genes are involved in IL-17-mediated activation of NF-kappaB signaling in B cells. These findings identify the signaling pathway regulated by IL-17 to contribute to the development of spontaneous germinal centers in autoimmune BXD2 mice.

Signals that influence T follicular helper cell differentiation and function

Follicular helper T cells have recently emerged as a separate CD4(+) T helper lineage specialised in provision of help to B cells. They develop independently from Th1, Th2 and Th17 cells and are critical for humoral immunity, including the generation of long-lived and high affinity plasma cells and memory cells crucial for long-term protection against infections. A stepwise differentiation programme has emerged in which T cell receptor (TCR) signalling strength, CD28-mediated costimulation, B cell-derived inducible costimulator ligand signals, induction of c-maf and actions of cytokines, including interleukin (IL)-6 and IL-21, lead to upregulation of the transcriptional repressor B cell lymphoma 6 (Bcl-6) that drives T follicular helper (Tfh) cell differentiation. Bcl-6 turns on a repression programme that targets Blimp-1, transcriptional regulators of other helper lineages and microRNAs. Their concerted actions modulate expression of chemokine receptors, surface molecules and cytokines critical for follicular homing and B cell helper functions. Here, we review the nature of Tfh cells providing help to B cells during the two phases of B cell activation that occur in the outer T zone and, for some B cells, in germinal centres (GC). Recent insights into the signalling events that drive terminal differentiation of Tfh cells critical for selecting somatically mutated GC B cells and the consequences of Tfh dysregulation for immunodeficiency and autoimmune pathology are discussed.

T follicular helper cells during immunity and tolerance

Helper T cells are required for the generation of a potent immune response to foreign antigens. Amongst them, T follicular helper (Tfh) cells are specialized in promoting protective, long-lived antibody responses that arise from germinal centers. Within these structures, the specificity of B cell receptors may change, due to the process of random somatic hypermutation aimed at increasing the overall affinity of the antibody response. The danger of emerging self-reactive specificities is offset by a stringent selection mechanism delegated in great part to Tfh cells. Only those B cells receiving survival signals from Tfh cells can exit the germinal centers to join the long-lived pools of memory B cells and bone marrow-homing plasma cells. Thus, a crucial immune tolerance checkpoint to prevent long-term autoantibody production lies in the ability to tolerize Tfh cells and to control positive and negative selection signals delivered by this subset. This review tackles the known mechanisms that ensure Tfh tolerance, many of them shared by other T helper subsets during thymic development and priming, but others unique to Tfh cells. Amongst the latter are checkpoints at the stages of Tfh differentiation, follicular migration, growth, longevity, and quality control of selection signals. Finally, we also discuss the consequences of a breakdown in Tfh tolerance.

Marginal zone precursor B cells as cellular agents for type I IFN-promoted antigen transport in autoimmunity

The pathogenic connection of type I IFN and its role in regulating the migration response of Ag delivery by B cells into lymphoid follicles in an autoimmune condition has not been well-identified. Here, we show that there was a significantly larger population of marginal zone precursor (MZ-P) B cells, defined as being IgM(hi)CD1d(hi)CD21(hi)CD23(hi) in the spleens of autoimmune BXD2 mice compared with B6 mice. MZ-P B cells were highly proliferative compared with marginal zone (MZ) and follicular (FO) B cells. The intrafollicular accumulation of MZ-P B cells in proximity to germinal centers (GCs) in BXD2 mice facilitated rapid Ag delivery to the GC area, whereas Ag-carrying MZ B cells, residing predominantly in the periphery, had a lower ability to carry Ag into the GCs. IFN-alpha, generated by plasmacytoid dendritic cells, induced the expression of CD69 and suppressed the sphingosine-1-phosphate-induced chemotactic response, promoting FO-oriented Ag transport by MZ-P B cells. Knockout of type I IFN receptor in BXD2 (BXD2-Ifnalphar(-/-)) mice substantially diffused the intrafollicular MZ-P B cell conglomeration and shifted their location to the FO-MZ border near the marginal sinus, making Ag delivery to the FO interior less efficient. The development of spontaneous GCs was decreased in BXD2-Ifnalphar(-/-) mice. Together, our results suggest that the MZ-P B cells are major Ag-delivery B cells and that the FO entry of these B cells is highly regulated by type I IFN-producing plasmacytoid dendritic cells in the marginal sinus in the spleens of autoimmune BXD2 mice.

Increased expression of activation-induced cytidine deaminase is associated with anti-CCP and rheumatoid factor in rheumatoid arthritis

Rheumatoid arthritis (RA) is associated with higher levels of autoantibodies and IL-17. Here, we investigated if ectopic lymphoid follicles and peripheral blood mononuclear cells (PBMCs) from RA patients exhibit increased activation-induced cytidine deaminase (AID), and if increased AID is correlated with serum levels of autoantibodies and IL-17. The results of immunohistochemical staining showed that organized AID(+) germinal centres were observed in six of the 12 RA synovial samples, and AID(+) cells were found almost exclusively in the B-cell areas of these follicles. Aggregated but not organized lymphoid follicles were found in only one OA synovial sample without AID(+) cells. Significantly higher levels of AID mRNA (Aicda) detected by RT-PCR were found in the PBMCs from RA patients than PBMCs from normal controls (P < 0.01). In the PBMCs from RA patients, AID was expressed predominately by the CD10(+)IgM(+)CD20(+) B-cell population and the percentage of these cells that expressed AID was significantly higher than in normal controls (P < 0.01). AID expression in the PBMCs correlated significantly and positively with the serum levels of rheumatoid factor (RF) (P </= 0.0001) and anti-cyclic citrullinated peptide (CCP) (P = 0.0005). Serum levels of IFN-gamma (P = 0.0005) and IL-17 (P = 0.007), but not IL-4, also exhibited positive correlation with the expression of AID. These results suggest that the higher levels of AID expression in B cells of RA patients correlate with, and may be associated with the higher levels of T helper cell cytokines IFN-gamma and IL-17, leading to the development of anti-CCP and RF.

Interleukin-17 and systemic lupus erythematosus: current concepts

The emerging role of interleukin (IL)-17 as a hallmark proinflammatory cytokine of the adaptive immune system, produced primarily by a new T helper cell subset termed 'Th17', has received considerable attention. Differentiation of Th17 cells is driven by the simultaneous presence of transforming growth factor-beta and certain inflammatory cytokines (e.g. IL-6, IL-21), and recent studies have shown that inflammation instigated by IL-17-producing cells is central to the development and pathogenesis of several human autoimmune diseases and animal models of autoimmunity. In this review, we focus on the information regarding IL-17 and systemic lupus erythematosus (SLE), a chronic autoimmune disease. The work that has explored the development and behaviour of IL-17-producing cells in SLE is discussed, and different mechanisms by which IL-17 could potentially augment inflammation and autoantibody production in the context of SLE are proposed.

Lupus-prone MRL/faslpr/lpr mice display increased AID expression and extensive DNA lesions, comprising deletions and insertions, in the immunoglobulin locus: concurrent upregulation of somatic hypermutation and class switch DNA recombination

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of an array of pathogenic autoantibodies, including high-affinity anti-dsDNA IgG antibodies. These autoantibodies are mutated and class-switched, mainly to IgG, indicating that immunoglobulin (Ig) gene somatic hypermutation (SHM) and class switch DNA recombination (CSR) are important in their generation. Lupus-prone MRL/fas(lpr/lpr) mice develop a systemic autoimmune syndrome that shares many features with human SLE. We found that Ig genes were heavily mutated in MRL/fas(lpr/lpr) mice and contained long stretches of DNA deletions and insertions. The spectrum of mutations in MRL/fas(lpr/lpr) B cells was significantly altered, including increased dG/dC transitions, increased targeting of the RGYW/WRCY mutational hotspot and the WGCW AID-targeting hotspot. We also showed that MRL/fas(lpr/lpr) greatly upregulated CSR, particularly to IgG2a and IgA in B cells of the spleen, lymph nodes and Peyer's patches. In MRL/fas(lpr/lpr) mice, the significant upregulation of SHM and CSR was associated with increased expression of activation-induced cytidine deaminase (AID), which mediates DNA lesion, the first step in SHM and CSR, and translesion DNA synthesis (TLS) polymerase (pol) theta, pol eta and pol zeta, which are involved in DNA synthesis/repair process associated with SHM and, possibly, CSR. Thus, in lupus-prone MRL/fas(lpr/lpr) mice, SHM and CSR are upregulated, as a result of enhanced AID expression and, therefore, DNA lesions, and dysregulated DNA repair factors, including TLS polymerases, which are involved in the repair process of AID-mediated DNA lesions.

BALB/c mice genetically susceptible to proteoglycan-induced arthritis and spondylitis show colony-dependent differences in disease penetrance

Introduction

The major histocompatibility complex (H-2d) and non-major histocompatibility complex genetic backgrounds make the BALB/c strain highly susceptible to inflammatory arthritis and spondylitis. Although different BALB/c colonies develop proteoglycan-induced arthritis and proteoglycan-induced spondylitis in response to immunization with human cartilage proteoglycan, they show significant differences in disease penetrance despite being maintained by the same vendor at either the same or a different location.

Methods

BALB/c female mice (24 to 26 weeks old after 4 weeks of acclimatization) were immunized with a suboptimal dose of cartilage proteoglycan to explore even minute differences among 11 subcolonies purchased from five different vendors. In vitro-measured T-cell responses, and serum cytokines and (auto)antibodies were correlated with arthritis (and spondylitis) phenotypic scores. cDNA microarrays were also performed using spleen cells of naïve and immunized BALB/cJ and BALB/cByJ mice (both colonies from The Jackson Laboratory, Bar Harbor, ME, USA), which represent the two major BALB/c sublines.

Results

The 11 BALB/c colonies could be separated into high (n = 3), average (n = 6), and low (n = 2) responder groups based upon their arthritis scores. While the clinical phenotypes showed significant differences, only a few immune parameters correlated with clinical or histopathological abnormalities, and seemingly none of them affected differences found in altered clinical phenotypes (onset time, severity or incidence of arthritis, or severity and progression of spondylitis). Affymetrix assay (Affymetrix, Santa Clara, CA, USA) explored 77 differentially expressed genes (at a significant level, P < 0.05) between The Jackson Laboratory's BALB/cJ (original) and BALB/cByJ (transferred from the National Institutes of Health, Bethesda, MD, USA). Fourteen of the 77 differentially expressed genes had unknown function; 24 of 77 genes showed over twofold differences, and only 8 genes were induced by immunization, some in both colonies.

Conclusions

Using different subcolonies of the BALB/c strain, we can detect significant differences in arthritis phenotypes, single-nucleotide polymorphisms (SNPs), and a large number of differentially expressed genes, even in non-immunized animals. A number of the known genes (and SNPs) are associated with immune responses and/or arthritis in this genetically arthritis-prone murine strain, and a number of genes of as-yet-unknown function may affect or modify clinical phenotypes of arthritis and/or spondylitis.

Toll-like receptors in autoimmunity

Both genetic predispositions and environmental factors contribute to the development of autoimmunity. Toll-like receptors (TLR) are a family of pattern recognition receptors (PRRs), and their stimulus by pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) is an important prerequisite for the induction of various autoimmune diseases. However, activation of specific TLRs can not only induce but also inhibit autoimmune diseases in certain mouse models. The contribution of individual TLRs to the induction of autoimmunity or tolerance involves hematopoietic as well as nonhematopoietic cells expressing combinations of different TLRs. The intercellular and intracellular orchestration of signals from different TLRs, other PRRs, and membrane-standing receptors dictates activating or inhibitory responses. Here, we summarize TLR-dependent tolerance mechanisms in B cells and intestinal epithelial cells and TLR-mediated activation mechanisms leading to the induction of Th17 T cell differentiation in different autoimmune diseases and in inflammatory bowel diseases. Understanding the opposing mechanisms of TLRs for the induction and suppression of autoimmune processes in specific diseases will help to develop novel therapies to treat autoimmunity.

Protein nitration in placenta - functional significance

Crucial roles of the placenta are disrupted in early and mid-trimester pregnancy loss, preeclampsia, eclampsia and intrauterine growth restriction. The pathophysiology of these disorders includes a relative hypoxia of the placenta, ischemia/reperfusion injury, an inflammatory response and oxidative stress. Reactive oxygen species including nitric oxide (NO), carbon monoxide and superoxide have been shown to participate in trophoblast invasion, regulation of placental vascular reactivity and other events. Superoxide, which regulates expression of redox sensitive genes, has been implicated in up-regulation of transcription factors, antioxidant production, angiogenesis, proliferation and matrix remodeling. When superoxide and nitric oxide are present in abundance, their interaction yields peroxynitrite a potent pro-oxidant, but also alters levels of nitric oxide, which in turn affect physiological functions. The peroxynitrite anion is extremely unstable thus evidence of its formation in vivo has been indirect via the occurrence of nitrated moieties including nitrated lipids and nitrotyrosine residues in proteins. Formation of 3-nitrotyrosine (protein nitration) is a "molecular fingerprint" of peroxynitrite formation. Protein nitration has been widely reported in a number of pathological states associated with inflammation but is reported to occur in normal physiology and is thought of as a prevalent, functionally relevant post-translational modification of proteins. Nitration of proteins can give either no effect, a gain or a loss of function. Nitration of a range of placental proteins is found in normal pregnancy but increased in pathologic pregnancies. Evidence is presented for nitration of placental signal transduction enzymes and transporters. The targets and extent of nitration of enzymes, receptors, transporters and structural proteins may markedly influence placental cellular function in both physiologic and pathologic settings.

PDIA3, HSPA5 and vimentin, proteins identified by 2-DE in the valvular tissue, are the target antigens of peripheral and heart infiltrating T cells from chronic rheumatic heart disease patients

Rheumatic fever (RF) is a post-infectious autoimmune disease due to sequel of group A streptococcus (GAS) pharyngitis. Rheumatic heart disease (RHD), the major manifestation of RF, is characterized by inflammation of heart valves and myocardium. Molecular mimicry between GAS antigens and host proteins has been shown at B and T cell level. However the identification of the autoantigens recognized by B and T cells within the inflammatory microenvironment of heart tissue in patients with RHD is still incompletely elucidated. In the present study, we used two-dimensional gel electrophoresis (2-DE) and mass spectrometry to identify valvular tissue proteins target of T cells from chronic RHD patients. We could identify three proteins recognized by heart infiltrating and peripheral T cells as protein disulfide isomerase ER-60 precursor (PDIA3), 78kD glucose-regulated protein precursor (HSPA5) and vimentin, with coverage of 45%, 43 and 34%, respectively. These proteins were recognized in a proliferation assay by peripheral and heart infiltrating T cells from RHD patients suggesting that they may be involved in the autoimmune reactions that leads to valve damage. We also observed that several other proteins isolated by 2-DE but not identified by mass spectrometry were also recognized by T cells. The identified cardiac proteins are likely relevant antigens involved in T cell-mediated autoimmune responses in RF/RHD that may contribute to the development of RHD.

Interleukin 17-producing T helper cells and interleukin 17 orchestrate autoreactive germinal center development in autoimmune BXD2 mice

Interleukin 17 (IL-17) is a cytokine associated with inflammation, autoimmunity and defense against some bacteria. Here we show that IL-17 can promote autoimmune disease through a mechanism distinct from its proinflammatory effects. As compared with wild-type mice, autoimmune BXD2 mice express more IL-17 and show spontaneous development of germinal centers (GCs) before they increase production of pathogenic autoantibodies. We show that blocking IL-17 signaling disrupts CD4+ T cell and B cell interactions required for the formation of GCs and that mice lacking the IL-17 receptor have reduced GC B cell development and humoral responses. Production of IL-17 correlates with upregulated expression of the genes Rgs13 and Rgs16, which encode regulators of G-protein signaling, and results in suppression of the B cell chemotactic response to the chemokine CXCL12. These findings suggest a mechanism by which IL-17 drives autoimmune responses by promoting the formation of spontaneous GCs.

Using proteomics to identify targets of antiendothelial cell antibodies

Antiendothelial cell antibodies represent a heterogeneous group of antibodies directed against a variety of antigen determinants of endothelial cells. Antibodies reacting with endothelial structures have been detected in sera from patients with autoimmune vasculitis, both primary and secondary to systemic connective tissue diseases. It may interfere with several functions and, therefore, may be a pathophysiological relevance. The analysis of the antigens recognized by antiendothelial cell antibodies showed that the antibodies are directed against a heterogeneous family of both constitutive and nonconstitutive surface endothelial proteins. Proteomics is a field of science that evaluates a large number of proteins expressed from a given cell line or organism. The technology of proteomics has been used as a method for discovering the target protein specific to a particular disease by searching for the expression or modification of the protein. Recently, progress has been made in defining the target antigens of these antibodies and proteomic technologies is one of them. This review will focus on the proteomic technologies in searching autoantigens/autoantibodies associated with disease of the endothelium.

α-Actinin Immunization Elicits Anti-Chromatin Autoimmunity in Nonautoimmune Mice

Anti-dsDNA Abs are characteristic of lupus and can be found deposited in the kidneys of lupus mice. Previously, we have shown that pathogenic anti-dsDNA Abs as well as Ig eluted from the kidneys of nephritic lupus mice cross-react with alpha-actinin. Moreover, cross-reactivity with alpha-actinin characterizes nephritogenic anti-dsDNA Abs in humans with lupus as well. To determine whether Abs generated against alpha-actinin in vivo cross-react with nuclear Ags, we s.c. immunized 10-wk-old female BALB/c mice (and several other nonautoimmune mice strains) with alpha-actinin in adjuvant. Immunized but not control mice displayed high titers of anti-nuclear Abs and IgG anti-chromatin autoantibodies, hypergammaglobulinemia, renal Ig deposition, and proteinuria. The specificity of the anti-chromatin response was determined by Western blotting of purified chromatin with serum from alpha-actinin immunized mice. By proteomic analysis, a 25-kDa doublet band was conclusively identified as high mobility group box (HMGB) proteins 1 and 3, and a 70-kDa band was identified as heat shock protein 70 (hsp70), both of which are known antigenic targets in murine lupus. Binding to purified HMGB1 and hsp70 by immunized mice sera was confirmed by ELISA and Western blot. Immunized mice sera binding to both 25- and 70-kDa bands were significantly inhibited by alpha-actinin and chromatin. Importantly, a panel of nephritogenic mAbs had significantly higher affinity for alpha-actinin, chromatin, HMGB, and hsp70 as compared with nonpathogenic Abs, suggesting a common motif in these Ags that is targeted by pathogenic autoantibodies.

Overexpression of activation-induced cytidine deaminase in B cells is associated with production of highly pathogenic autoantibodies

Defective receptor editing or defective B cell checkpoints have been associated with increased frequency of multireactive autoantibodies in autoimmune disease. However, Ig somatic hypermutation and/or class switch recombination may be mechanisms enabling the development of pathogenic multireactive autoantibodies. In this study, we report that, in the BXD2 mouse model of autoimmune disease, elevated expression of activation-induced cytidine deaminase (AID) in recirculating follicular CD86(+) subsets of B cells and increased germinal center B cell activity are associated with the production of pathogenic multireactive autoantibodies. CD4 T cells from BXD2 mice that expressed increased levels of CD28 and an increased proliferative response to anti-CD3 and anti-CD28 stimulation are required for this process. Inhibition of the CD28-CD86 interaction in BXD2 mice with AdCTLA4-Ig resulted in normalization of AID in the B cells and suppression of IgG autoantibodies. This treatment also prevented the development of germinal center autoantibody-producing B cells, suggesting that an optimal microenvironment enabling AID function is important for the formation of pathogenic autoantibodies. Taken together, our data indicate that AID expression in B cells is a promising therapeutic target for the treatment of autoimmune diseases and that suppression of this gene may be a molecular target of CTLA4-Ig therapy.

Use of proteomics in analysis of autoimmune diseases

Autoimmune diseases are common by diseases characterized by disorders of immune responses and autoimmune impairment involving multiple tissues, organs and systems. The autoantigens (Ags)/autoantibodies (Abs) are not only hallmarks but also involved in pathogenesis of autoimmune diseases. In recent years, proteomics technologies have been used and demonstrated effective in searching new Ags/Abs as well as disease biomarkers in autoimmune diseases.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.