Generation Of Pathogenic Autoantibodies Research Articles

Selective HDAC6 inhibition decreases early stage of lupus nephritis by down-regulating both innate and adaptive immune responses.

We have demonstrated previously that histone deacetylase (HDAC6) expression is increased in animal models of systemic lupus erythematosus (SLE) and that inhibition of HDAC6 decreased disease. In our current studies, we tested if an orally active selective HDAC6 inhibitor would decrease disease pathogenesis in a lupus mouse model with established early disease. Additionally, we sought to delineate the cellular and molecular mechanism(s) of action of a selective HDAC6 inhibitor in SLE. We treated 20-week-old (early-disease) New Zealand Black (NZB)/White F1 female mice with two different doses of the selective HDAC6 inhibitor (ACY-738) for 5 weeks. As the mice aged, we determined autoantibody production and cytokine levels by enzyme-linked immunosorbent assay (ELISA) and renal function by measuring proteinuria. At the termination of the study, we performed a comprehensive analysis on B cells, T cells and innate immune cells using flow cytometry and examined renal tissue for immune-mediated pathogenesis using immunohistochemistry and immunofluorescence. Our results showed a reduced germinal centre B cell response, decreased T follicular helper cells and diminished interferon (IFN)-γ production from T helper cells in splenic tissue. Additionally, we found the IFN-α-producing ability of plasmacytoid dendritic cells was decreased along with immunoglobulin isotype switching and the generation of pathogenic autoantibodies. Renal tissue showed decreased immunoglobulin deposition and reduced inflammation as judged by glomerular and interstitial inflammation. Taken together, these studies show selective HDAC6 inhibition decreased several parameters of disease pathogenesis in lupus-prone mice. The decrease was due in part to inhibition of B cell development and response.

Accelerated Systemic Autoimmunity in the Absence of Somatic Hypermutation in 564Igi: A Mouse Model of Systemic Lupus with Knocked-In Heavy and Light Chain Genes.

564Igi mice have knocked-in immunoglobulin (Ig) heavy (H) and light (L) chain genes that encode an autoantibody recognizing RNA. Previously, we showed that these mice produce pathogenic IgG autoantibodies when activation-induced deaminase (AID) is expressed in pre-B and immature B cells but not when it is expressed only in mature B cells. AID has two functions; it is necessary for somatic hypermutation (SHM) and class switch recombination (CSR). To determine the role of each of these functions in the generation of pathogenic autoantibodies, we generated 564Igi mice that carry a mutant AID-encoding gene, Aicda (AicdaG23S), which is capable of promoting CSR but not SHM. We found that 564Igi AicdaG23S mice secreted class-switched antibodies (Abs) at levels approximately equal to 564Igi mice. However, compared to 564Igi mice, 564Igi AicdaG23S mice had increased pathogenic IgG Abs and severe systemic lupus erythematosus-like disease, including, glomerulonephritis, and early death. We suggest that in 564Igi mice SHM by AID changes Ig receptors away from self reactivity, thereby mitigating the production of autoantibody, providing a novel mechanism of tolerance.

Selective HDAC6 inhibitor decreases lupus in mice

Abstract Histone deacetylase 6 (HDAC6) is a Class IIb HDACs enzyme primarily residing in the cytoplasm. HDAC6 alters gene transcription by removing acetyl groups from lysine residues on transcription factors. We, and others, have previously demonstrated that HDAC6 expression is increased in systemic lupus erythematosus (SLE) patients and animal models of lupus and that inhibition of HDAC6 decreased disease. In our current studies, we tested if an orally active selective HDAC6 inhibitor would decrease disease pathogenesis in a lupus mouse model with established early disease. Importantly, we sought to delineate the cellular and molecular mechanism(s) of action for the HDAC6 inhibitor. We treated 20-week-old early-diseased NZB/W F1 (lupus) female mice with two different doses of the selective HDAC6 inhibitor (ACY-738) for five weeks. At the termination of the study, our results showed a reduced germinal center B cell response, decreased T follicular helper cells and diminished IFN-g production from T helper cells in splenic tissue. Additionally, we found the IFNa-producing ability of plasmacytoid dendritic cells was decreased along with immunoglobulin isotype switching and the generation of pathogenic autoantibodies. Renal tissue showed decreased immunoglobulin deposition and reduced inflammation as judged by glomerular and interstitial inflammation. Taking together, these studies show selective HDAC inhibition decreased several parameters of disease pathogenesis in lupus prone mice. The decrease was in part due to inhibition of autoreactive B cell differentiation. Studies are currently underway to define further the mechanism of how HDAC6 inhibits auto-reactive B cell differentiation.

Targeted therapeutics in SLE: emerging strategies to modulate the interferon pathway.

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by impaired immune tolerance, resulting in the generation of pathogenic autoantibodies and immune complexes. Although autoreactive B lymphocytes have been the first targets for biologic therapies in SLE, the importance of the innate immune system, and in particular, pathways involved in interferon (IFN) signaling, has emerged. There are now data supporting a central role for a plasmacytoid dendritic cell-derived type I IFN pathway in SLE, with a number of biologic therapeutics and small-molecule inhibitors undergoing clinical trials. Monoclonal antibodies targeting IFN-α have completed phase II clinical trials, and an antibody against the type I IFN receptor is entering a phase III trial. However, other IFNs, such as IFN gamma, and the more recently discovered type III IFNs, are also emerging as targets in SLE; and blockade of upstream components of the IFN signaling pathway may enable inhibition of more than one IFN subtype. In this review, we discuss the current understanding of IFNs in SLE, focusing on emerging therapies.

Epigenetics of Peripheral B-Cell Differentiation and the Antibody Response.

Epigenetic modifications, such as histone post-translational modifications, DNA methylation, and alteration of gene expression by non-coding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), are heritable changes that are independent from the genomic DNA sequence. These regulate gene activities and, therefore, cellular functions. Epigenetic modifications act in concert with transcription factors and play critical roles in B cell development and differentiation, thereby modulating antibody responses to foreign- and self-antigens. Upon antigen encounter by mature B cells in the periphery, alterations of these lymphocytes epigenetic landscape are induced by the same stimuli that drive the antibody response. Such alterations instruct B cells to undergo immunoglobulin (Ig) class switch DNA recombination (CSR) and somatic hypermutation (SHM), as well as differentiation to memory B cells or long-lived plasma cells for the immune memory. Inducible histone modifications, together with DNA methylation and miRNAs modulate the transcriptome, particularly the expression of activation-induced cytidine deaminase, which is essential for CSR and SHM, and factors central to plasma cell differentiation, such as B lymphocyte-induced maturation protein-1. These inducible B cell-intrinsic epigenetic marks guide the maturation of antibody responses. Combinatorial histone modifications also function as histone codes to target CSR and, possibly, SHM machinery to the Ig loci by recruiting specific adaptors that can stabilize CSR/SHM factors. In addition, lncRNAs, such as recently reported lncRNA-CSR and an lncRNA generated through transcription of the S region that form G-quadruplex structures, are also important for CSR targeting. Epigenetic dysregulation in B cells, including the aberrant expression of non-coding RNAs and alterations of histone modifications and DNA methylation, can result in aberrant antibody responses to foreign antigens, such as those on microbial pathogens, and generation of pathogenic autoantibodies, IgE in allergic reactions, as well as B cell neoplasia. Epigenetic marks would be attractive targets for new therapeutics for autoimmune and allergic diseases, and B cell malignancies.

Regulatory T Cells Are Not Required for Prevention of RBC-Specific Autoantibody Generation

Introduction: Loss of humoral tolerance to red blood cell (RBC) antigens may lead to the generation of pathogenic autoantibodies and result in autoimmune hemolytic anemia (AIHA), a severe and potentially fatal disease. Failure of tolerance to RBC antigens occurs with considerable frequency (1-3 cases/1,000 adults) and prevalence of AIHA is as high as 30% in persons with compromised B and/or T cell tolerance mechanisms. However, RBC-specific tolerance mechanisms are poorly understood. To elucidate the immune tolerances to RBC autoantigens, we utilized HOD mice. The HOD mouse expresses an RBC-specific transgene consisting of hen egg lysozyme (HEL), ovalbumin (OVA), and Duffy. Using the HOD model, we previously demonstrated B cell tolerance to RBC-specific HOD antigen is incomplete; however, T cell tolerance is stringent. HOD mice have similar detectable frequencies of HOD-specific CD4+ T cells compared to B6 mice. Although present, autoreactive HOD-specific CD4+ T cells are non-functional. Circumventing T cell tolerance by adoptive transfer, HOD mice make high titer anti-HOD autoantibodies in vivo. Thus, despite the presence of autoreactive B cells, no HOD-reactive antibodies are detectable unless CD4+ T cells are given, indicating T cell tolerance is a stopgap to autoimmunity. Methods: Leukocytes from C57BL/6 (B6) and HOD mice were harvested and OVA-specific CD4+ T cell responses were assessed by tetramer-pulldown assays with pooled tetramers I-Ab-OVA 329-337/326-334. Isolated cells were stained for surface and intracellular markers and analyzed via flow cytometry. For in vivo analysis, mice were treated with 300ug anti-CD25 (clone PC-61) depleting antibody or isotype control; a subset of antibody-treated mice was immunized with OVA/CFA. Antibodies bound to HOD RBCs were determined by direct antibody test. Anti-HOD antibodies were quantified by indirect immunofluorescence using HOD RBCs as targets. Results: Tetramer pull-down assays revealed similar numbers of OVA-reactive CD4+ T cells from HOD and B6 mice (mean 56 and 40, respectively, p = 0.3). However, cell surface and intracellular marker staining demonstrated that HOD mice had higher numbers of OVA-tetramer reactive CD4+ T cells that express regulatory markers CD25 and FoxP3, and exhaustion marker PD1 as compared to control B6 mice. Inhibitory CTLA4 expression was not detectable on OVA-reactive CD4+ T cells from HOD or B6 mice. To test whether regulatory T cells were required for RBC-specific immune tolerance, HOD and B6 mice were treated with CD25 depleting antibody or isotype control antibody. Anti-CD25 antibody treated mice had a significant reduction of CD25+ cells 4 days post treatment (p < 0.001, 2 independent experiments). Similarly, there was a significant reduction in FoxP3+CD25+CD4+ T cells (Tregs) in anti-CD25 treated mice (p < 0.001), compared to isotype. Mice received weekly injections of anti-CD25 or isotype antibody to maintain depletion for one month. A subset of mice received an OVA/CFA immunization. Sustained CD25+ depletion did not result in anti-HOD autoantibody generation. Further, there was no change in the endogenous frequency of OVA-reactive CD4+ T cells between HOD and B6 mice, regardless of antibody treatment. Similarly, HOD mice treated with depletion (or isotype) antibody and immunized with OVA/CFA did not make detectable anti-HOD autoantibodies. Consistent with lack of detectable autoantibodies, no expansion of OVA-tetramer reactive CD4+ T cells was observed in HOD mice. In contrast, B6 mice (treated with anti-CD25 or isotype antibody) had a detectable expansion of OVA-specific CD4+ T cells as a result of immunization. Conclusions: The data demonstrate a phenotypic difference between the OVA-reactive CD4+ T cells from HOD and B6 mice, with an increase in number of Tregs detectable in HOD mice. Administration of anti-CD25 antibody significantly reduced the number of overall CD25+ cells and Tregs. Prolonged depletion of these cellular subsets did not elicit autoantibodies in HOD mice. Further, immunization of CD25 depleted mice with a strong immune stimulus (OVA/CFA, known to expand OVA-reactive T cells in B6 mice), did not induce anti-HOD autoantibodies nor did it expand OVA-specific autoreactive CD4+ T cells in HOD mice. Together, these data demonstrate that CD25+ cells are not required for the maintenance of RBC-specific T cell tolerance and suggest a role for other regulatory mechanisms. Disclosures No relevant conflicts of interest to declare.

AID dysregulation in lupus-prone MRL/Faslpr/lpr mice promotes interchromosomal c-Myc/IgH loci translocations, increased class switch DNA recombination and production of anti-dsDNA IgG autoantibodies: modulation by HoxC4 (148.25)

Abstract Activation-induced cytidine deaminase (AID) initiates immunoglobulin (Ig) gene somatic hypermutation (SHM) and class switch DNA recombination (CSR), which are critical in the generation of pathogenic autoantibodies. In these studies, we addressed the regulation of AID by HoxC4 in lupus. We found that SLE patients and lupus-prone MRL/Faslpr/lpr mice displayed increased expression of HoxC4, which directly activates the promoter of the AID gene, and increased expression of AID. Dysregulation of these proteins was associated with increased CSR in B cells of MRL/Faslpr/lpr mice. In the HoxC4-/- MRL/Faslpr/lpr mice we generated, HoxC4-deficiency resulted in reduced AID expression, impaired CSR and decreased serum anti-dsDNA IgG, particularly IgG2a production, in association with a reduction in IgG deposition in kidney glomeruli. Consistent with our previous findings that upregulated AID expression is associated with extensive DNA lesions, we found a high frequency of c-Myc to IgH translocations in MRL/Faslpr/lpr mice. The frequency of c-Myc to IgH translocations was significantly reduced in autoimmune MRL/Faslpr/lpr mice deficient in HoxC4. Our findings showed that HoxC4 is upregulated in lupus B cells, and this plays a major role in dysregulating AID expression, increasing CSR and autoantibody production, and promoting c-Myc to IgH translocations.

Inhibition of Activation‐Induced Cytidine Deaminase (AID) Preserved Spontaneous Germinal Centers but Suppressed Autoimmune Disease in BXD2 Mice

Increased expression of AID in B cells as a result of extensive spontaneous germinal centers (GCs) has been found to be associated with the development of arthrogenic and nephrogenic autoantibodies in autoimmune BXD2 mice. To determine if inhibition of AID can prevent the generation of pathogenic autoantibodiese, a transgenic (Tg) BXD2 mouse strain expressing a dominant negative (DN) form of AID cloned downstream of the chicken albumin promoter was generated by direct injection of BXD2 single cell embryos. This AID‐DN gene contains the H56R/E58Q mutation in the AID catalytic domain and the S38A mutation at the phosphorylation site that is essential for interaction of AID with replication protein A. At 6–8‐month of age, there was a significant decrease in the IgG isotype of autoantibodies and autoantibody producing B cells against histone, DNA, and BiP in BXD2 AID‐DN Tg+ mice compared to wild‐type (WT) BXD2 mice. At this age, BXD2 AID‐DN Tg+ mice were protected from development of arthritis. There was also decreased IgG2b and IgG2c containing C1q‐circulating immune complexes and decreased IgG deposition in glomeruli in BXD2 AID‐DN Tg+ mice, compared to WT BXD2 mice. The generation of spontaneous GCs in the spleens of BXD2 AID‐DN Tg+ mice, however, remained comparable to that found in the spleens of WT BXD2 mice. Our results suggest that over‐expression and high activity of AID is a down‐stream product of spontaneous autoreactive GCs that plays an essential role in the generation of pathogenic autoantibodies and development of autoimmune disease in BXD2 mice. This work is supported by Arthritis Foundation, VA Merit Review, American College of Rheumatology, and Daiichi‐Sankyo Co., Ltd.

The Structure of Human Lupus Anti-DNA Antibodies

B-cell hyperactivity and production of pathogenic autoantibodies are the main immunological events in the pathogenesis of the human autoimmune disease systemic lupus erythematosus. One approach to studying the pathogenesis of this disease and to understanding how the autoantibody response is initiated and sustained has been to analyze the variable genes expressed by antibodies that have the hallmarks of the disease-causing subset of pathogenic autoantibodies. Such studies have provided important clues. Quantitation of this repertoire revealed the presence of a specific expansion of IgG clonotypes that impart reactivity with disease-related autoantigens. The sequences of the genes encoding autoantibodies derived from these patients and expressing nephritogenic idiotopes (present in immune complexes and renal eluates of subjects with active disease) show features of molecular diversification with a high rate of replacement/silent mutations and clustering of the mutations in the hypervariable regions. These characteristics imply that a pure polyclonal B-cell activation process cannot be the only mechanism responsible for autoantibody production. More likely, an antigen drive plays a role in generation of pathogenic autoantibodies. Based on additional studies of their light chain variable region genes, we have offered a novel genetically based model whereby B cells secreting pathogenic lupus autoantibodies are blocked in their capacity to turn off their autoreactivity and to acquire a new specificity, a mechanism called receptor editing. Studies of the molecular events involved in this mechanism and of the clonal fates of B cellsin vivowill be important for future research.