Helen Braley-Mullen

The type III histone deacetylase Sirt1 is essential for maintenance of T cell tolerance in mice.

Although many self-reactive T cells are eliminated by negative selection in the thymus, some of these cells escape into the periphery, where they must be controlled by additional mechanisms. However, the molecular mechanisms underlying peripheral T cell tolerance and its maintenance remain largely undefined. In this study, we report that sirtuin 1 (Sirt1), a type III histone deacetylase, negatively regulates T cell activation and plays a major role in clonal T cell anergy in mice. In vivo, we found that loss of Sirt1 function resulted in abnormally increased T cell activation and a breakdown of CD4+ T cell tolerance. Conversely, upregulation of Sirt1 expression led to T cell anergy, in which the activity of the transcription factor AP-1 was substantially diminished.Furthermore, Sirt1 interacted with and deacetylated c-Jun, yielding an inactive AP-1 factor. In addition, Sirt1-deficient mice were unable to maintain T cell tolerance and developed severe experimental allergic encephalomyelitis as well as spontaneous autoimmunity. These findings provide insight into the molecular mechanisms of T cell activation and anergy, and we suggest that activators of Sirt1 may be useful as therapeutic agents for the treatment and/or prevention of autoimmune diseases.

Early Requirement for B Cells for Development of Spontaneous Autoimmune Thyroiditis in NOD.H-2h4 Mice

B cells are known to play an important role in the pathogenesis of several autoimmune diseases. NOD.H-2h4 mice develop spontaneous autoimmune thyroiditis (SAT) and anti-mouse thyroglobulin (MTg) autoantibodies, the levels of which correlate closely with the severity of thyroid lesions. NOD.H-2h4 mice genetically deficient in B cells (NOD.Kμnull) or rendered B cell-deficient by treatment from birth with anti-IgM develop minimal SAT. B cells were required some time in the first 4–6 wk after birth, because NOD.Kμnull or NOD.H-2h4 mice did not develop SAT when they were reconstituted with B cells as adults. The requirement for B cells was apparently not solely to produce anti-MTg autoantibodies, because passive transfer of anti-MTg Ab did not enable B cell-deficient mice to develop SAT, and mice given B cells as adults produced autoantibodies but did not develop SAT. B cell-deficient mice developed SAT if their T cells developed from bone marrow precursors in the presence of B cells. Because B cells are required early in life and their function cannot be replaced by anti-MTg autoantibodies, B cells may be required for the activation or selection of autoreactive T cells. These autoreactive T cells are apparently unable to respond to Ag if B cells are absent in the first 4–6 wk after birth.

B cell–deficient NOD.H-2h4 mice have CD4+CD25+ T regulatory cells that inhibit the development of spontaneous autoimmune thyroiditis

Wild-type (WT) NOD.H-2h4 mice develop spontaneous autoimmune thyroiditis (SAT) when given 0.05% NaI in their drinking water, whereas B cell–deficient NOD.H-2h4 mice are SAT resistant. To test the hypothesis that resistance of B cell–deficient mice to SAT was due to the activity of regulatory CD4+CD25+ T (T reg) cells activated if autoantigen was initially presented on non–B cells, CD25+ T reg cells were transiently depleted in vivo using anti-CD25. B cell–deficient NOD.H-2h4 mice given three weekly injections of anti-CD25 developed SAT 8 wk after NaI water. Thyroid lesions were similar to those in WT mice except there were no B cells in thyroid infiltrates. WT and B cell–deficient mice had similar numbers of CD4+CD25+Foxp3+ cells. Mice with transgenic nitrophenyl-specific B cells unable to secrete immunoglobulin were also resistant to SAT, and transient depletion of T reg cells resulted in severe SAT with both T and B cells in thyroid infiltrates. T reg cells that inhibit SAT were eliminated by day 3 thymectomy, indicating they belong to the subset of naturally occurring T reg cells. However, T reg cell depletion did not increase SAT severity in WT mice, suggesting that T reg cells may be nonfunctional when effector T cells are activated; i.e., by autoantigen-presenting B cells.

Immunopotentiating effects of the adjuvants SGP and Quil A: I. Antibody responses to T-dependent and T-independent antigens

The present study was undertaken to compare the effects of two adjuvants, SGP (a starch-acrylamide polymer) and Quil A (purified saponin), with that of aluminum hydroxide (Al(OH)3) on murine primary antibody responses to T-independent (TI) and T-dependent (TD) antigens. All three adjuvants augmented the responses to the TD antigens, dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH), and sheep erythrocytes (SRBC). SGP was the most potent adjuvant and increased the primary IgG response to DNP-KLH as much as 90-fold. Quil A and Al(OH)3 had comparable effects on the primary response to DNP-KLH, but Quil A was less effective than Al(OH)3 for augmenting the primary response to SRBC. Quil A and SGP both augmented the primary IgM and IgG responses to trinitrophenyl-lipopolysaccharide (TNP-LPS), TNP-Brucella (TI-1 antigens), and TNP-Ficoll (TI-2 antigens). Al(OH)3, like most commonly used adjuvants, had little or no effect on responses to TI antigens. The kinetics of the response to TNP-Ficoll was altered by SGP, since peak responses were maintained for at least 7 days, while the response to TNP-Ficoll alone peaked on Day 4 and had declined considerably by Day 7. Both SGP and Quil A could augment responses to both optimal and suboptimal doses of antigen. The adjuvant activity of SGP was diminished, but still effective, when smaller amounts of SGP were used with the immunizing antigen, and all three adjuvants were able to augment primary responses when given in separate injections from the antigen. These results demonstrate that SGP is a very effective adjuvant, and show that both Quil A and SGP have a unique ability to increase antibody responses to TI antigens, suggesting that their effects may be mediated at least partially through B cells.

Dual Roles for IFN-γ, But Not for IL-4, in Spontaneous Autoimmune Thyroiditis in NOD.H-2h4 Mice

Spontaneous autoimmune thyroiditis (SAT) is an organ-specific autoimmune disease characterized by chronic inflammation of the thyroid by T and B lymphocytes. To investigate the roles of Th1 and Th2 cytokines in the pathogenesis of SAT, IFN-γ−/− and IL-4−/− NOD.H-2h4 mice were generated. IL-4−/− mice developed lymphocytic SAT (L-SAT) comparable to that of wild-type (WT) mice. They produced little anti-mouse thyroglobulin (MTg) IgG1, but had levels of anti-MTg IgG2b comparable to WT mice. Compared with WT mice, IFN-γ−/− mice produced significantly less anti-MTg IgG1 and IgG2b. Absence of IFN-γ resulted in abnormal proliferation of thyroid epithelial cells with minimal lymphocyte infiltration. Thyroids of IFN-γ−/− mice had markedly reduced B lymphocyte chemoattractant expression, B cell and plasma cell infiltration, and decreased MHC class II expression on thyrocytes compared with WT mice. Adoptive transfer of WT splenocytes to IFN-γ−/− mice restored the capacity to develop typical L-SAT, enhanced anti-MTg IgG1 and IgG2b production, up-regulated MHC class II expression on thyrocytes and decreased thyrocyte proliferation. These results suggest that IFN-γ plays a dual role in the development of SAT. IFN-γ is required for development of L-SAT, and it also functions to inhibit thyroid epithelial cell proliferation.

Decreasing TNF-α results in less fibrosis and earlier resolution of granulomatous experimental autoimmune thyroiditis

Granulomatous experimetal autoimmune thyroiditis (G‐EAT) is induced in DBA/1 mice by adoptive transfer of mouse thyroglobulin (MTg)‐primed spleen cells. TNF‐α is an important proinflammatory cytokine and apoptotic molecule involved in many autoimmune diseases. To study its role in G‐EAT, anti‐TNF‐α mAb was given to recipient mice. Disease severity was comparable between mice with or without anti‐TNF‐α treatment at days 19–21, the time of maximal severity of G‐EAT, suggesting TNF‐α is not essential for development of thyroid inflammation. However, thyroid lesions resolved at day 48 in anti‐TNF‐α‐treated mice, while thyroids of rat Ig‐treated controls had fibrosis. These results suggested that reducing TNF‐α contributed to resolution of inflammation and inhibited fibrosis. Gene and protein expression of inflammatory molecules was examined by RT‐PCR and immunostaining, and apoptosis was detected using TUNEL staining and an apoptosis kit. Thyroids of anti‐TNF‐α‐treated controls had reduced proinflammatory and profibrotic molecules, e.g., IFN‐γ, IL‐1β, IL‐17, inducible NOS and MCP‐1, at day 19 compared with thyroids of rat Ig‐treated mice. There were more apoptotic thyrocytes in rat Ig‐treated controls than in anti‐TNF‐α‐treated mice. The site of expression of the anti‐apoptotic molecule FLIP also differed between rat Ig‐treated and anti‐TNF‐α‐treated mice. FLIP was predominantly expressed by inflammatory cells of rat Ig‐treated mice and by thyrocytes of anti‐TNF‐α‐treated mice. These results suggest that anti‐TNF‐α may regulate expression of proinflammatory cytokines and apoptosis in thyroids, resulting in less inflammation, earlier resolution, and reduced fibrosis.

Antibodies to Thyroid Peroxidase Arise Spontaneously with Age in NOD.H-2h4 Mice and Appear after Thyroglobulin Antibodies

Hashimotos thyroiditis, a common autoimmune disease, is associated with autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO). TPO, unlike abundant and easily purified Tg, is rarely investigated as an autoantigen in animals. We asked whether antibodies (Abs) develop to both TPO and Tg in thyroiditis that is induced (C57BL/6 and DBA/1 mice) or arises spontaneously (NOD.H-2h4 mice). Screening for TPOAbs was performed by flow cytometry using mouse TPO-expressing eukaryotic cells. Sera were also tested for binding to purified mouse Tg and human TPO. The antibody data were compared with the extent of thyroiditis. Immunization with mouse TPO adenovirus broke self-tolerance to this protein in C57BL/6 mice, but thyroiditis was minimal and TgAbs were absent. In DBA/1 mice with extensive granulomatous thyroiditis induced by Tg immunization, TPOAbs were virtually absent despite high levels of TgAbs. In contrast, antibodies to mouse TPO, with minimal cross-reactivity with human TPO, arose spontaneously in older (7-12 months) NOD.H-2h4 mice. Unexpectedly, TgAbs preceded TPOAbs, a time course paralleled in relatives of probands with juvenile Hashimotos thyroiditis. These findings demonstrate a novel aspect of murine and human thyroid autoimmunity, namely breaking B cell self-tolerance occurs first for Tg and subsequently for TPO.

B cell depletion inhibits spontaneous autoimmune thyroiditis in NOD.H-2h4 mice.

B cells are important for the development of most autoimmune diseases. B cell depletion immunotherapy has emerged as an effective treatment for several human autoimmune diseases, although it is unclear whether B cells are necessary for disease induction, autoantibody production, or disease progression. To address the role of B cells in a murine model of spontaneous autoimmune thyroiditis (SAT), B cells were depleted from adult NOD.H-2h4 mice using anti-mouse CD20 mAb. Anti-CD20 depleted most B cells in peripheral blood and cervical lymph nodes and 50–80% of splenic B cells. Flow cytometry analysis showed that marginal zone B cells in the spleen were relatively resistant to depletion by anti-CD20, whereas most follicular and transitional (T2) B cells were depleted after anti-CD20 treatment. When anti-CD20 was administered before development of SAT, development of SAT and anti-mouse thyroglobulin autoantibody responses were reduced. Anti-CD20 also reduced SAT severity and inhibited further increases in anti-mouse thyroglobulin autoantibodies when administered to mice that already had autoantibodies and thyroid inflammation. The results suggest that B cells are necessary for initiation as well as progression or maintenance of SAT in NOD.H-2h4 mice.

Comparison of sensitivity of Th1, Th2, and Th17 cells to Fas-mediated apoptosis

Following activation through the TCR, CD4+ T cells can differentiate into three major subsets: Th1, Th2, and Th17 cells. IL‐17‐secreting Th17 cells play an important role in the pathogenesis of several autoimmune diseases and in immune responses to pathogens, but little is known about the regulation of apoptosis in Th17 cells. In this study, the sensitivity of in vitro‐polarized Th1, Th2, and Th17 cells to Fas‐mediated apoptosis was compared directly by different methods. The order of sensitivity of T cell subsets to Fas‐mediated apoptosis is: Th1 > Th17 > Th2. The greater sensitivity of Th17 cells to Fas‐mediated apoptosis compared with Th2 cells correlated with their higher expression of FasL and comparable expression of the antiapoptotic molecule FLIP. The decreased sensitivity of Th17 compared with Th1 cells correlated with the higher expression of FLIP by Th17 cells. Transgenic overexpression of FLIP in T cells protected all three subsets from Fas‐mediated apoptosis. These findings provide new knowledge for understanding how survival of different subsets of T cells is regulated.

Inhibition of TGFβ1 by Anti-TGFβ1 Antibody or Lisinopril Reduces Thyroid Fibrosis in Granulomatous Experimental Autoimmune Thyroiditis

In this study, a murine model of granulomatous experimental autoimmune thyroiditis (G-EAT) was used to determine the role of TGFβ1 in fibrosis initiated by an autoimmune inflammatory response. The fibrotic process was evaluated by staining thyroid tissue for collagen, α-smooth muscle actin, TGFβ1, and angiotensin-converting enzyme (ACE), and measuring serum thyroxine in mice given anti-TGFβ1 or the ACE inhibitor lisinopril. The role of particular inflammatory cells in fibrosis was tested by depletion experiments, and the cytokine profile in thyroids was examined by RT-PCR. Neutralization of TGFβ1 by anti-TGFβ1 or lisinopril resulted in less collagen deposition and less accumulation of myofibroblasts, and levels of active TGFβ1 and ACE were reduced in thyroids of treated mice compared with those of untreated controls. Other profibrotic molecules, such as platelet-derived growth factor, monocyte chemotactic protein-1, and IL-13, were also reduced in thyroids of anti-TGFβ1- and lisinopril-treated mice compared with those of controls. Confocal microscopy showed that CD4+ T cells and macrophages expressed TGFβ1. Fibrosis was reduced by injection of anti-CD4 mAb on day 12, when G-EAT was very severe (4–5+). Together, these results suggest a critical role for TGFβ1 in fibrosis initiated by autoimmune-induced inflammation. Autoreactive CD4+ T cells may contribute to thyroid fibrosis through production of TGFβ1. This G-EAT model provides a new model to study how fibrosis associated with autoimmune damage can be inhibited.