Correction of accelerated autoimmune disease by early replacement of the mutated lpr gene with the normal Fas apoptosis gene in the T cells of transgenic MRL-lpr/lpr mice

EAF2 deficiency attenuates autoimmune disease in Fas lpr mice by modulating B cell activation and apoptosis

MRL/lpr mice develop systemic lupus erythematosus-like autoimmunity due to defective FAS-mediated apoptosis. We generated Fas lpr mice deficient in EAF2, a transcription elongation-associated factor known to promote apoptosis in germinal center (GC) B cells and crucial for preventing autoimmunity. Contrary to expectations, EAF2 deficiency significantly reduced lymphadenopathy and splenomegaly, extended lifespan, and alleviated nephritis by decreasing renal immune complex deposition. Additionally, EAF2 deficiency markedly reduced accumulation of activated B cells, GC B cells, plasma cells, and the abnormal B220+CD3+ T cells in Fas lpr mice. Further analysis revealed that Eaf2 -/- Fas lpr B cells showed hyperactivation upon various stimulations, followed by increased death. RNA sequencing of the B220+CD3+ cells revealed a downregulation in survival-promoting genes such as Bcl-2 and Akt and an upregulation of proapoptotic genes. We conclude that the combined deficiency in FAS- and EAF2-mediated apoptotic pathways leads to B cell hyperactivation and subsequent death, thereby ameliorating systemic autoimmunity in this model.

CD95/Fas and metastatic disease: What does not kill you makes you stronger

CD95 (also known as Fas) is the prototype of death receptors; however, evidence suggests that this receptor mainly implements non-apoptotic signaling pathways such as NF-κB, MAPK, and PI3K that are involved in cell migration, differentiation, survival, and cytokine secretion. At least two different forms of CD95 L exist. The multi-aggregated transmembrane ligand (m-CD95 L) is cleaved by metalloproteases to release a homotrimeric soluble ligand (s-CD95 L). Unlike m-CD95 L, the interaction between s-CD95 L and its receptor CD95 fails to trigger apoptosis, but instead promotes calcium-dependent cell migration, which contributes to the accumulation of inflammatory Th17 cells in damaged organs of lupus patients and favors cancer cell invasiveness. Novel inhibitors targeting the pro-inflammatory roles of CD95/CD95 L may provide attractive therapeutic options for patients with chronic inflammatory disorders or cancer. This review discusses the roles of the CD95/CD95 L pair in cell migration and metastasis.

Programmed Cell Death in Immune Defense: Knowledge and Presumptions

Cell-culture studies are our main source of knowledge of the various forms of programmed cell death. Yet genetic perturbations of death-protein function in animal models are almost the only source of our knowledge of the physiological roles of these programs. Shortcomings in the state of knowledge acquired by these two experimental approaches are exemplified in this Perspective by reference to research on the contribution of apoptosis to lymphocyte development, a subject on which there is already much knowledge, and on the role of necroptosis in inflammation, about which information is just beginning to emerge. To address these shortcomings, there is need to find ways to verify the notions obtained through the current experimental approaches by directly monitoring death programs within specific cells in vivo.

Defining Early Life Stress as a Precursor for Autoimmune Disease

Childhood exposure to traumatic events, termed early life stress (ELS), is now widely recognized for causing long-term negative health effects that may not manifest until adulthood. Allostatic load (AL) describes the cumulative "wear-and-tear" effects of chronic stress on the body that may adversely affect human health by accelerating other disease processes. Recent epidemiological studies have reported higher stress levels in industrialized countries and trends of increasing prevalence in autoimmune diseases during recent decades. To elucidate mechanisms of stress-related immune dysregulation, most animal studies up to now have focused on AL and stress-triggered events occurring in adults but have not explored ELS in the context of autoimmune disorders. We have identified a current gap in understanding the impact of ELS on immune system ontogeny and its potential for priming genetically susceptible individuals who are at increased risk for autoimmune diseases later in life, through mechanisms involving neuroendocrine-immune cross talk. In this review, we highlight the intersection between stress and immune function, with a focus on ELS as consequential for increased autoimmune disorder risks later in life.

Localized immune tolerance from FasL-functionalized PLG scaffolds

Intraportal allogeneic islet transplantation has been demonstrated as a potential therapy for type 1 diabetes (T1D). The placement of islets into the liver and chronic immunosuppression to control rejection are two major limitations of islet transplantation. We hypothesize that localized immunomodulation with a novel form of FasL chimeric with streptavidin, SA-FasL, can provide protection and long-term function of islets at an extrahepatic site in the absence of chronic immunosuppression. Allogeneic islets modified with biotin and engineered to transiently display SA-FasL on their surface showed sustained survival following transplantation on microporous scaffolds into the peritoneal fat in combination with a short course (15 days) of rapamycin treatment. The challenges with modifying islets for clinical translation motivated the modification of scaffolds with SA-FasL as an off-the-shelf product. Poly (lactide-co-glycolide) (PLG) was conjugated with biotin and fabricated into particles and subsequently formed into microporous scaffolds to allow for rapid and efficient conjugation with SA-FasL. Biotinylated particles and scaffolds efficiently bound SA-FasL and induced apoptosis in cells expressing Fas receptor (FasR). Scaffolds functionalized with SA-FasL were subsequently seeded with allogeneic islets and transplanted into the peritoneal fat under the short-course of rapamycin treatment. Scaffolds modified with SA-FasL had robust engraftment of the transplanted islets that restored normoglycemia for 200 days. Transplantation without rapamycin or without SA-FasL did not support long-term survival and function. This work demonstrates that scaffolds functionalized with SA-FasL support allogeneic islet engraftment and long-term survival and function in an extrahepatic site in the absence of chronic immunosuppression with significant potential for clinical translation.

Renal tubular epithelial cell-derived BAFF expression mediates kidney damage and correlates with activity of proliferative lupus nephritis in mouse and men

B-cell activating factor of the tumour necrosis factor family (BAFF) is a cytokine, mainly produced by hematopoietic cells (e.g. monocytes/macrophages, dendritic cells), indispensable for B-cell maturation. The BLISS studies have demonstrated that blocking BAFF by the human monoclonal antibody belimumab is a valuable therapeutic approach in patients with clinically and serologically active systemic lupus erythematosus (SLE). However, the defined sources of BAFF, which contributes to SLE, are still unclear. Recent findings show that BAFF expression is not restricted to myeloid cells. Since lupus nephritis is the main cause of morbidity and mortality for SLE patients, the aim of this study was to investigate whether renal tubular epithelial cells (TEC) are an important source of BAFF and thus may contribute to the pathogenesis and progression of SLE. We found BAFF expression both in cultured murine and human TEC. These results could be verified with in situ data from the kidney. Moreover, BAFF expression in the kidneys of lupus-prone MRL- Fas^lpr mice correlated with disease activity, and BAFF expression on TEC in biopsies of patients with diffuse proliferative lupus nephritis showed a correlation with the histopathological activity index. In vitro functional assays revealed an autocrine loop of BAFF with its binding receptors on TEC, resulting in a strong induction of colony stimulating factor-1. Finally, we identified divergent effects of BAFF on TEC depending on the surrounding milieu ('inflammatory versus non-inflammatory'). Taken together, our findings indicate that renal-derived BAFF may play an important role in the pathophysiology of the systemic autoimmune disease SLE.

Autoimmunity-Basics and link with periodontal disease

Autoimmune reactions reflect an imbalance between effector and regulatory immune responses, typically develop through stages of initiation and propagation, and often show phases of resolution (indicated by clinical remissions) and exacerbations (indicated by symptomatic flares). The fundamental underlying mechanism of autoimmunity is defective elimination and/or control of self-reactive lymphocytes. Periodontal diseases are characterized by inflammatory conditions that directly affect teeth-supporting structures, which are the major cause of tooth loss. Several studies have demonstrated the involvement of autoimmune responses in periodontal disease. Evidence of involvement of immunopathology has been reported in periodontal disease. Bacteria in the dental plaque induce antibody formation. Autoreactive T-cells, natural killer cells, ANCA, heat shock proteins, autoantibodies, and genetic factors are reported to have an important role in the autoimmune component of periodontal disease. The present review describes the involvement of autoimmune responses in periodontal diseases and also the mechanisms underlying these responses.

The effects of vitamin A derivative etretinate on the skin of MRL mice

MRL/Mp-lpr/lpr (MRL/lpr) mice are characterized by the disorder of apoptosis due to defects in Fas antigens and autoimmune symptoms including spontaneous lupus erythematosus (LE)-like skin lesions. MRL/Mp- +/+ (MRL/n) mice do not carry the defect of lpr mutation nor do they exhibit skin disorders during the first six months of life. Retinoids are known to inhibit the proliferation of skin fibroblasts, collagen synthesis, modulate immune responses, and apoptosis by Fas ligand upregulation in skin fibroblasts. We examined changes in dermal thickness and appearance of skin disorders in five months old MRL/lpr mice by oral treatment with etretinate, a retinoic acid derivative. Etretinate treated MRL/lpr mice did not have skin lesions or dermatopathological characteristics including an increase in cells infiltrating the dermis. The mean dermal thickness of MRL/lpr and MRL/n mice treated with etretinate decreased significantly and apoptotic cells density in the dermis of MRL/lpr mice with etretinate was significantly higher compared with the control group (P, 0.05) although MRL/lpr mice have a defect within the Fas antigen. We assumed that etretinate reduced dermal thickness, and suppressed the appearance of skin lesions by inducting apoptosis and perhaps regulation of cytokine expression.

Lymphatic mapping of mice with systemic lymphoproliferative disorder: usefulness as an inter-lymph node metastasis model of cancer

Preclinical models of lymph node (LN) metastasis are fundamental to the study and design of new techniques for the diagnosis and treatment of LN metastasis. However, the identification of LNs and lymphatic vessels (LVs) in mice is challenging with conventional imaging modalities, since the LN diameter in normal mice is 1-2 mm. Here, we describe MXH10/Mo-lpr/lpr (MXH10/Mo/lpr) inbred mice, which develop systemic swelling of LNs up to 10 mm in diameter, allowing investigation of the topography of LNs and LVs. Using a gross anatomy dissection approach, we identified 22 different LNs situated in the head and neck, limbs, thoracic and abdominal regions. Furthermore, four peripheral inter-LN vessels were found: from the subiliac LN (SiLN) to the proper axillary LN (PALN); from the parotid LN to the caudal deep cervical LN; and from the popliteal LN to both the sciatic LN and the SiLN. Metastasis to the PALN via LVs was induced by inoculating FM3A/Luc mouse mammary carcinoma cells into the SiLN. Our results demonstrate that the MXH10/Mo/lpr mouse strain is an excellent model in which to investigate lymphatic drainage and inter-LN metastasis of cancer. This paper unveils the anatomy of murine lymphatics to give new insights into the investigation of inter-LN metastasis of cancer, especially the mechanisms involved in the trafficking of cancer cells through inter-LN vessels. The results provide data that may prove very useful in the quest to develop better lymph drainage-based drug delivery systems.

Lupus nephritis: role of antinucleosome autoantibodies

The discovery of autoantigen clustering in blebs at the surface of apoptotic cells boosted research on the role of apoptosis in systemic lupus erythematosus (SLE) and led to the discovery of autoantigen modification during apoptosis. Normally, apoptotic cells are cleared efficiently and swiftly. However, it became clear that in SLE insufficient removal of apoptotic material leads to the release of these modified autoantigens. This creates the danger that these modified autoantigens are recognized by the immune system. Indeed, dendritic cells, the professional antigen-presenting cells, phagocytose these modified autoantigens, which leads to maturation and induction of a proinflammatory state of these dendritic cells. As a consequence, they present these modified autoantigens to T cells in an immunogenic way, which become activated and stimulate autoreactive B cells to secrete autoantibodies. In this review the currently available evidence for the sequential steps in the pathogenesis of SLE is discussed. Furthermore, the mechanisms responsible for the nephritogenicity of antinucleosome antibodies are reviewed. This will reveal that nucleosomes are not only a major driving force in the formation of antinuclear antibodies, but also play a pivotal role in the development of tissue lesions by mediating binding of autoantibodies to basement membranes as exemplified for the kidney.

Upregulation of Fas and downregulation of CD94/NKG2A inhibitory receptors on circulating natural killer cells in patients with new-onset psoriasis

BACKGROUND

Psoriasis has been considered as a T-helper 1 cell-mediated autoimmune disease driven by collaboration with multiple components of innate and acquired immune cells. Natural killer (NK) cells have been shown to bridge innate and acquired immunity, and thus could potentially contribute to the pathophysiology of psoriasis.

OBJECTIVES

To investigate the phenotypic changes of circulating NK cells in patients with new-onset psoriasis.

METHODS

Fifteen patients with plaque psoriasis (eight women and seven men) who visited our clinic after their first episode of psoriasis and did not have a history of previous systemic therapy or phototherapy participated in this study. Peripheral blood mononuclear cells were isolated and stained with a panel of antibodies against cell surface receptors expressed on T and/or NK cells and analysed by flow cytometry.

RESULTS

As compared with normal healthy volunteers, patients with new-onset psoriasis showed no significant changes in numbers of peripheral NK, NK-T or T cells. NK activating receptors 2B4, CD48, NKG2D, CD16 and CD56 were found to be unchanged in new-onset psoriasis. However, the expression of Fas (activation-induced death receptor) was upregulated, whereas the expression of the NK inhibitory receptors CD94 and NKG2A was dramatically reduced on NK cells of new-onset psoriasis. These changes occurred at the level of mean fluorescent intensity, but minimally affected percentages of cells expressing Fas, CD94 and NKG2A.

CONCLUSIONS

Our findings demonstrate that changes in the expression of Fas and CD94/NKG2A receptors on NK cells may occur during new-onset psoriasis, and are likely to contribute to the pathogenesis of psoriasis.

Expression of CD95 on mature leukocytes of MRL/lpr mice after transplantation of genetically modified bone marrow stem cells

Bone marrow transplantation (BMT) is commonly used for the treatment of severe haematological and immunological diseases. For instance, the autoimmune lymphoproliferative syndrome (ALPS) caused by a complete expression defect of CD95 (Fas, APO-1) can be cured by allogeneic BMT. However, since this therapy may not generate satisfactory results when only partially compatible donors are available, we were interested in the development of a potential alternative treatment by using lentiviral gene transfer of a normal copy of CD95 cDNA in hematopoietic stem cells. Here, we show that this approach applied to MRL/lpr mice results in the expression of functional CD95 receptors on the surface of lymphocytes, monocytes, and granulocytes. This suggests that correction of CD95 deficiency can be achieved by gene therapy.

A novel multimeric form of FasL modulates the ability of diabetogenic T cells to mediate type 1 diabetes in an adoptive transfer model

Activation induced cell death (AICD) via Fas/FasL is the primary homeostatic molecular mechanism employed by the immune system to control activated T-cell responses and promote tolerance to self-antigens. We herein investigated the ability of a novel multimeric form of FasL chimeric with streptavidin (SA-FasL) having potent apoptotic activity to induce apoptosis in diabetogenic T cells and modulate insulin-dependent type 1 diabetes (IDDM) in an adoptive transfer model. Diabetogenic splenocytes from NOD/Lt females were co-cultured in vitro with SA-FasL, SA control protein, or alone without protein, and adoptively transferred into NOD/Lt-Rag1(null) recipients for diabetes development. All animals receiving control (Alone: n=16 or SA: n=17) cells developed diabetes on average by 6 weeks, whereas animals receiving SA-FasL-treated (n=25) cells exhibited significantly delayed progression (p<.001) and decreased incidence (70%). This effect was associated with an increase in CD4(+)CD25(+) T cells and correlated with FoxP3 expression in pancreatic lymph nodes. Extracorporeal treatment of peripheral blood lymphocytes using SA-FasL during disease onset represents a novel approach that may alter the ability of pathogenic T cells to mediate diabetes and have therapeutic utility in clinical management of IDDM.

Do antivirals have any utility in the treatment of arthritis?

Viruses have been linked to arthritides by several pathways. Apart from the ability of different viral pathogens to cause arthritic symptoms directly, only some circumstantial evidence for the involvement of (retro)viruses in the pathogenesis of rheumatoid arthritis has been presented in recent years. Therefore, the question of whether antiviral agents can be used to treat arthritis has become of interest. However, the mechanisms by which exogenous retroviral infection as well as activation of endogenous retroviral sequences may potentially lead to the induction of rheumatoid arthritis is just beginning to emerge. Moreover, the hypothesis that persistent viral infection may account for some hitherto unclassified, chronic arthritides, still needs to be confirmed. Therefore, the use of antiviral agents in the treatment of arthritides has been limited to viral complications of anti-arthritic therapy and to some experimental approaches. In this review, we will focus on current concepts of viral involvement in arthritis and point to future directions in the use of antiviral agents for arthritis.

The keratan sulfate disaccharide Gal(6S03) beta1,4-GlcNAc(6S03) modulates interleukin 12 production by macrophages in murine Thy-1 type autoimmune disease

It has been reported that disaccharides of the glycosaminoglycans (GAGs), heparin, or heparan sulfate suppress the production of cytokines. Therefore, we examined the effects of GAGs (keratan sulfate, hyaluronan, chondroitin, chondroitin sulfate, and heparin sulfate) disaccharides on production of interleukin (IL)-12, a pivotal cytokine in the Th-1 type immune system. Among the GAG disaccharides, only a keratan sulfate disaccharide, Gal(6-SO(3))-GlcNAc(6-SO(3)) (L4), suppressed IL-12 production in macrophages stimulated with lipopolysaccharides and interferon-gamma. Neither keratan sulfate chains nor keratan sulfate tetrasaccharides elicited any change in the IL-12 production. N-Acetyl-lactosamine, Gal-GlcNAc (LacNAc), also did not change IL-12 production. These results indicated that a certain size, i.e. disaccharide and sulfate, are essential to suppress IL-12 production. L4 was then applied to MRL-lpr/lpr mice, a Th-1 type autoimmune disease model. The treatment of MRL-lpr/lpr mice with L4 1) decreased in serum IL-12, 2) induced apoptosis in T cells in lymph nodes thereby suppressing lymphoaccumulation, and 3) suppressed hypergammaglobulinemia and glomerulonephritis. We showed previously that IL-12 suppresses cell death of T cells, thereby enhancing the lymphoaccumulation in MRL-lpr/lpr mice. Moreover, it has been reported that IL-12 deficiency in MRL-lpr/lpr mice diminishes lymphoaccumulation and delays glomerulonephritis. The treatment with L4 suppressed phosphoprotein kinase C and phosphoinositide 3-kinase expression in macrophages, suggesting that L4 suppresses IL-12 production by inhibiting phosphoprotein kinase C and phosphoinositide 3-kinase pathways.

Induction of tolerance using Fas ligand: a double-edged immunomodulator

Apoptosis mediated by Fas ligand (FasL) interaction with Fas receptor plays a pivotal regulatory role in immune homeostasis, immune privilege, and self-tolerance. FasL, therefore, has been extensively exploited as an immunomodulatory agent to induce tolerance to both autoimmune and foreign antigens with conflicting results. Difficulties associated with the use of FasL as a tolerogenic factor may arise from (1) its complex posttranslational regulation, (2) the opposing functions of different forms of FasL, (3) different modes of expression, systemic versus localized and transient versus continuous, (4) the level and duration of expression, (5) the sensitivity of target tissues to Fas/FasL-mediated apoptosis and the efficiency of antigen presentation in these tissues, and (6) the types and levels of cytokines, chemokines, and metalloproteinases in the extracellular milieu of the target tissues. Thus, the effective use of FasL as an immunomodulator to achieve durable antigen-specific immune tolerance requires careful consideration of all of these parameters and the design of treatment regimens that maximize tolerogenic efficacy, while minimizing the non-tolerogenic and toxic functions of this molecule. This review summarizes the current status of FasL as a tolerogenic agent, problems associated with its use as an immunomodulator, and new strategies to improve its therapeutic potential.

The potential pathogenetic link between peripheral immune activation and the central innate immune response in neuropsychiatric systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology. Neuropsychiatric disturbances unexplained by drugs or by other untoward manifestations of disease are present in up to one-half of SLE patients and have profound economic and social impact. In patients with neuropsychiatric SLE, structural lesions have been identified in the hippocampus and proinflammatory cytokines have been detected in the cerebrospinal fluid. Similarly, murine models of lupus, such as MRL-lpr/lpr mice display behavioral disturbances which map to the hippocampus and exhibit overexpression of proinflammatory cytokine genes in hippocampal homogenates. Neuropsychiatric SLE typically occurs in the presence of serologically and clinically active lupus. In animal models of SLE, such as MRL-lpr/lpr, NZB, BXSB, and [NZB x NZW]F(1), uncontrolled autoreactivity in the periphery is accompanied by behavioral disturbances that are chronic and progressive. These observations suggest the hypothesis that central nervous system disease in SLE is driven by cross-talk between the peripheral immune system and the brain's innate immune system, which results in the inexorable activation of astrocytes, microglia, and/or neurons within the hippocampus. This leads to overproduction of brain cytokines, which induce the synthesis of pro-oxidant molecules, such as eicosanoids and reactive oxygen species, with resultant tissue injury. The cascade becomes self-perpetuating and eventuates in neuronal death, which is followed by impaired cognition. A better understanding of the molecular events that operate in the pathogenesis of neuropsychiatric SLE may provide the basis for a more rational therapeutic approach to this incompletely understood disease.

Fas-Fas ligand interactions are essential for the binding to and killing of activated macrophages by gamma delta T cells

Gammadelta T cells have a direct role in resolving the host immune response to infection by eliminating populations of activated macrophages. Macrophage reactivity resides within the Vgamma1/Vdelta6.3 subset of gammadelta T cells, which have the ability to kill activated macrophages following infection with Listeria monocytogenes (Lm). However, it is not known how gammadelta T cell macrophage cytocidal activity is regulated, or what effector mechanisms gammadelta T cells use to kill activated macrophages. Using a macrophage-T cell coculture system in which peritoneal macrophages from naive or Lm-infected TCRdelta-/- mice were incubated with splenocytes from wild-type and Fas ligand (FasL)-deficient mice (gld), the ability of Vgamma1 T cells to bind macrophages was shown to be dependent upon Fas-FasL interactions. Combinations of anti-TCR and FasL Abs completely abolished binding to and killing of activated macrophages by Vgamma1 T cells. In addition, confocal microscopy showed that Fas and the TCR colocalized on Vgamma1 T cells at points of contact with macrophages. Collectively, these studies identify an accessory or coreceptor-like function for Fas-FasL that is essential for the interaction of Vgamma1 T cells with activated macrophages and their elimination during the resolution stage of pathogen-induced immune responses.

T cell-specific ablation of Fas leads to Fas ligand-mediated lymphocyte depletion and inflammatory pulmonary fibrosis

To study the role of Fas–Fas ligand (FasL) interaction-mediated apoptosis in lymphocyte homeostasis, we generated a mutant fas allele allowing conditional inactivation of the fas gene through Cre-mediated recombination. Experiments in which Fas was ablated in T cells, B cells, T and B cells, or in a more generalized manner demonstrated that the development of lymphoproliferative disease as seen in Fas-deficient mice requires Fas ablation in lymphoid and nonlymphoid tissues. Selective inactivation of Fas in T cells led to a severe lymphopenia over time, accompanied by up-regulation of FasL on activated T cells and apoptosis of peripheral lymphocytes. In addition, the mutant animals developed a fatal wasting syndrome caused by massive leukocyte infiltration in the lungs together with increased inflammatory cytokine production and pulmonary fibrosis. Inhibition of Fas–FasL interaction in vivo completely prevented the loss of lymphocytes and initial lymphocyte infiltration in the lungs. Thus, FasL-mediated interaction of activated, Fas-deficient T cells with Fas-expressing cells in their environment leads to break down of lymphocyte homeostasis and development of a lung disease strikingly resembling idiopathic pulmonary fibrosis in humans, a common and severe disease for which the mutant mice may serve as a first animal model.

Akt is an endogenous inhibitor toward tumor necrosis factor-related apoptosis inducing ligand-mediated apoptosis in rheumatoid synovial cells

Akt is known to be activated in the rheumatoid synovial tissues. We examined here functional role of Akt during tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-mediated apoptosis in rheumatoid synovial cells. Rheumatoid synovial cells in vitro were rapidly committed to apoptosis in response to TRAIL in mitochondria-dependent manner whereas Akt and extracellular signal-regulated kinase (ERK) were also phosphorylated. TRAIL-mediated apoptosis in synovial cells was significantly increased through inactivation of Akt by LY294002, however, that process was not so changed by adding ERK inhibitor, PD98059. Platelet-derived growth factor (PDGF) clearly phosphorylated both Akt and ERK in synovial cells, and PDGF pretreatment markedly suppressed TRAIL-mediated synovial cell apoptosis. The use of not PD98059 but LY294002 abrogated PDGF-mediated inhibitory effect toward TRAIL-induced apoptosis in synovial cells. The above protective effect of Akt was confirmed by the use of short interfering RNA (siRNA)-directed inhibition of Akt. Our data suggest that Akt is an endogenous inhibitor during TRAIL-mediated synovial cell apoptotic pathway, which may explain that synovial cells in situ of the rheumatoid synovial tissues are resistant toward apoptotic cell death in spite of death receptor expression.

Up-regulation of FLIP in cisplatin-selected HeLa cells causes cross-resistance to CD95/Fas death signalling

Cisplatin-selected cervix carcinoma HeLa cell lines induced less apoptosis, and weaker activation by cisplatin or Fas-activating antibody, of mitochondrial-associated caspase-9 and death receptor-mediated caspase-8 than did parental cells. Furthermore, less DISC (death-inducing signalling complex) was formed in cisplatin-selected cell lines than in parental cells. Ac-IETD-CHO (acetyl-Ile-Glu-Thr-Asp-aldehyde), which has a certain preference for inhibiting caspase-8, or Fas-antagonistic antibody, significantly inhibited cisplatin-induced apoptosis in both parental and cisplatin-selected HeLa cell lines. These results imply that cell-surface death signalling is inducible by cisplatin; that reduction of this pathway is associated with drug resistance, and that cisplatin-selected cells acquire cross-resistance to cell-surface death signalling. Sequential up-regulation of FLIP (FLICE-like inhibitory protein), but not Bcl-2, Bcl-x(L) or inhibitors of apoptosis protein (IAPs), was observed in resistant cells but not in parental cells. The inhibition of FLIP by FLIP antisense oligonucleotides promotes cisplatin and Fas-antibody-induced apoptosis. However, the modulation of apoptosis by FLIP antisense oligonucleotides in resistant cells is greater than that in parental cells. The presented data reveal that the up-regulation of FLIP may contribute to the suppression of apoptosis and thereby change cells that are resistant to cisplatin and Fas-mediated death signals. The results also show that cancer cells that have undergone long-term chemotherapy and become chemoresistant may change the FLIP level, becoming cross-resistant to death factors such as Fas.

Triggers for anti-chromatin autoantibody production in SLE

The formation of autoantibodies against chromatin is the main feature of systemic lupus erythematosis (SLE), an autoimmune disease, which is T-cell dependent and autoantigen-driven. Historically, antibodies against dsDNA, one of the components of chromatin, are considered as a hallmark of SLE. However, dsDNA is poorly immunogenic. Nucleosome-specific T helper cells have been identified. These T cells propagate not only nucleosome-specific antibodies, but also anti-dsDNA antibodies. Nucleosomes are formed during apoptosis by cleavage of chromatin, and evidence of disturbed apoptosis has been found especially in certain murine models of lupus. In addition to an increased rate of apoptosis, autoimmunity against chromatin might also result from an impaired phagocytosis of apoptotic material, for which strong evidence has been provided by studies in certain knock-out mice (C1q, SAP, Dnase I). The induction of an immune response to nucleosomes could be enhanced by modifications of histones or DNA during apoptosis, altered presentation by antigen presenting cells or a viral infection. The release of nucleosomes and the formation of anti-chromatin autoantibodies result in formation of complexes, which bind to the glomerular basement membrane via heparan sulfate. This deposition incites glomerulonephritis, the most serious manifestation of SLE.

Cell membrane modification for rapid display of proteins as a novel means of immunomodulation: FasL-decorated cells prevent islet graft rejection

Long-term display of exogenous proteins on the cell surface may have important research and therapeutic implications. We report a novel method for the cell-surface display of proteins that involves generation of a chimeric protein with core streptavidin, biotinylation of cells, and "decoration" with the protein. A chimeric protein with the extracellular portions of FasL (SA-FasL) was efficiently displayed on the cell surface within 2 hr without detectable cellular toxicity. Biotin and SA-FasL persisted on the cell surface for weeks in vitro and in vivo. Immunomodulation with SA-FasL-decorated splenocytes effectively blocked alloreactive responses in naive and presensitized rodents and prevented the rejection of allogeneic pancreatic islets. This approach may serve as an alternative to gene transfer-based expression with broad research and therapeutic applications.

Correlation of renal tubular epithelial cell-derived interleukin-18 up-regulation with disease activity in MRL-Faslpr mice with autoimmune lupus nephritis

OBJECTIVE

MRL-Fas(lpr) mice spontaneously develop an autoimmune disease that mimics systemic lupus erythematosus in humans. Infiltrating T cells expressing interferon-gamma (IFNgamma) are responsible for the autoimmune kidney destruction in MRL-Fas(lpr) mice, and interleukin-18 (IL-18) released by mononuclear phagocytes stimulates T cells to produce the IFNgamma. Since MRL-Fas(lpr) T cells are characterized by an overexpression of the IL-18 receptor accessory chain, we sought to determine the impact of IL-18 on the progression of lupus nephritis in MRL-Fas(lpr) mice.

METHODS

IL-18 expression in sera and kidney tissues from MRL-Fas(lpr) mice was determined by enzyme-linked immunosorbent assay (ELISA), reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and Western blotting. IL-18 production by primary cultured tubular epithelial cells (TECs) from MRL-Fas(lpr) and BALB/c mice were examined by RT-PCR, ELISA, and Western blotting. The interactions of TEC-derived IL-18 and MRL-Fas(lpr) T cells were studied in coculture assays. IL-18-related effects on TEC viability and adhesion molecule expression were determined by fluorescence-activated cell sorting and cell proliferation assays.

RESULTS

Up-regulation of mature IL-18 was restricted to nephritic MRL-Fas(lpr) kidneys and increased in parallel with the severity of lupus nephritis. IL-18 expression was not confined to infiltrating monocytes but was primarily detected in TECs. Similarly, interleukin-1beta-converting enzyme expression, which is required for the processing of precursor IL-18, was localized in TECs. De novo synthesis of IL-18 by MRL-Fas(lpr) TECs was confirmed by RT-PCR and Western blotting. Functional assays revealed that activated TECs induced IFNgamma production in MRL-Fas(lpr) T cells through IL-18. IL-18, in turn, increased apoptotic TEC death and up-regulation of intercellular adhesion molecule 1 and vascular cell adhesion molecule 1.

CONCLUSION

Taken together, our findings suggest that IL-18-producing TECs may directly be involved in the pathogenesis of lupus nephritis.

Suppression of antibody production by TNF-related apoptosis-inducing ligand (TRAIL)

TNF-related apoptosis-inducing ligand (TRAIL), a type II membrane protein belonging to the TNF family, induces apoptotic cell death in various types of tumor cells. However, little is known about its pathological and physiological functions in the immune system. In this study, we showed that administration of neutralizing anti-TRAIL mAb markedly increased serum auto-Ab levels, particularly of IgG1 subclass, in autoimmune-prone C3H/HeJ gld/gld mice without affecting lymphocytosis and lymphocytes populations. In an experimental system where TNP-specific Ab production was induced by immunization with TNP-modified syngeneic B lymphoma cells, expression of TRAIL on these cells significantly reduced TNP-specific Ab production, especially of IgG1 subclass, without affecting T cell priming. These results suggest a new role for TRAIL in the suppression of Ab production.

Systemic lupus erythematosus and B-cell hematologic neoplasm

The association of systemic lupus erythematosus (SLE) and B-cell malignancy is widely reported in the literature. Here we report nine cases of concurrent of SLE or discoid lupus erythematosus (DLE) and lymphoma or plasma cell disorder. A MEDLINE search was done using the keywords, 'SLE' and 'lymphoma' and the characteristics of all identified cases were summarized and analyzed, along with data from our own cases. Numerous variants of B-cell malignancies were encountered in these patients. B-cell malignancy occurs after the diagnosis and treatment of SLE in most reported cases, although it may precede SLE, or occur synchronously with it. The age at onset of the B-cell neoplasm in SLE patients is similar to that in the general population. Mortality in patients with both diseases is associated with progressive B-cell neoplasm, sepsis secondary to either disease, or both. B-cell malignancy and SLE seem to run independent clinical courses rather than being affected by each other. The use of immunosuppressive drugs is common in patients with SLE diagnosed prior to B-cell lymphoma, arguing that the effect of immunosuppression on the pathogenesis of lymphoma can not be excluded. Three areas worthy of study regarding the probable mechanisms for the occurrence of SLE and B-cell malignancies are discussed. A tumor suppressor gene PTEN may link the two disorders via a defective apoptosis pathway to eliminate hyperactive B and T cells in SLE. The accumulation of clonally expanded hyperactive B-cells that recognize self-antigens in the lymph nodes of SLE may predispose these B-cells to DNA breaks, facilitating tumorigenesis. Lastly, EBV infection, found to have a high prevalence in SLE patients, may serve as a common etiological factor in both disorders.

Immunopathogenesis of lupus and lupus nephritis: recent insights

Systemic lupus erythematosus is a multisystemic autoimmune disease. The immunopathogenesis is characterized by the loss of tolerance to self. While many abnormalities in the immune system have been detected, genetic factors play a central role in the pathogenesis. The event proximate to target organ involvement appears to be autoantigen-driven, T cell-mediated, B cell activation. High levels of autoantibodies are produced. However, not all autoantibodies are pathogenic to the kidney (i.e. 'nephritogenic'). These nephritogenic autoantibodies appear to share specific physiochemical features that correlate well with patterns of renal injury. While DNA was initially regarded as the inciting autoantigen, this view does not appear to be supported by the prevailing evidence. Nucleosomes, which are structures comprising histones and DNA, have emerged as the more likely candidate autoantigen. Autoantibodies directed against nucleosomes that cross-react with nucleosomal epitopes have been identified. Furthermore, evidence suggests that immunoglobulin-nucleosomal complexes may be important in target organ immune deposition. In-vivo generation of nucleosomes requires apoptosis; in fact, there are several examples of aberrant apoptotic processes that present with autoimmunity. Aberrant apoptosis may also be critical in lupus immunopathogenesis. Indeed, studies on Fas/FasL and Bcl-2 in animal models and in humans have underscored the importance of apoptosis as an etiological factor in lupus. Cytokines, hormonal, infectious and environmental factors have also been found to be important in the pathogenesis of systemic lupus erythematosus. Overall, much progress has been made in elucidating the etiological agents and pathogenic mechanisms by which lupus develops. However, there is still some way to go before arriving at a unifying hypothesis. The reward for a better understanding of lupus immunopathogenesis will be the development of more specific targets for treatment, and the introduction of better and safer treatment modalities.

Acid sphingomyelinase activation requires caspase-8 but not p53 nor reactive oxygen species during Fas-induced apoptosis in human glioma cells

During apoptosis of human glioma cells induced by anti-Fas antibody, ceramide formation with activation of acid, but not neutral sphingomyelinase (SMase), was observed. A potent inhibitor of acid SMase, SR33557, effectively inhibited ceramide formation and apoptosis. Fas-induced apoptosis and ceramide formation proceeded regardless of p53 status. The agents, which modify intracellular levels of reactive oxygen species (ROS) and reduced glutathione (GSH), failed to modulate Fas-induced acid SMase activation and apoptosis. Moreover, expression of functional p53 protein using a temperature-sensitive human p53val(138) induced ceramide generation by activation of neutral SMase but not acid SMase through ROS formation. Peptide inhibitors for caspases-8 (z-IETD-fmk) and -3 (z-DEVD-fmk) suppressed Fas-induced apoptosis. However, activation of acid SMase was inhibited only by z-IETD-fmk. Thus, ceramide generated by acid SMase may take a part in Fas-induced apoptosis of human glioma cells and acid SMase activation may be dependent on caspase-8 activation, but not on p53 nor ROS.

Requirement of Fas expression in B cells for tolerance induction

Fas is a death receptor that belongs to the tumor necrosis factor receptor family and is expressed in various cell types, in particular, in lymphoid cells. A loss-of-function mutation in the Fas gene (lpr mutation) causes lymphadenopathy and splenomegaly, and accelerates autoimmune diseases in some strains of mice such as MRL. In this report, Fas cDNA driven by murine lck distal promoter was used to establish transgenic MRL-lpr mouse lines. The transgenic mice expressed functional Fas in mature T cells and B cells. The lymphadenopathy and splenomegaly caused by accumulation of abnormal T cells in the lpr mice were rescued in the transgenic mice. The number of B cells in the periphery as well as the serum IgG level were significantly reduced, and the autoimmune symptoms and mortality were ameliorated. These results indicate that both mature B cells and T cells must undergo Fas-mediated apoptosis to prevent the development of autoimmune diseases.

Inhibition of NF-kappaB in T cells blocks lymphoproliferation and partially rescues autoimmune disease in gld/gld mice

The Fas ligand (FasL)/Fas pathway is crucial for the maintenance of homeostasis of the peripheral immune system. Its importance is illustrated by the spontaneous mouse mutants gld andlpr which lack functional FasL and Fas receptor, respectively. These animals develop lymphadenopathy, splenomegaly, increased serum Ig and autoantibodies, leading to an autoimmune syndromeand premature death. The Rel/NF-kappaB family of transcription factors plays an important role in peripheral lymphocyte proliferation and survival. In this report, we studied the consequences of T cell-specific inhibition of NF-kappaB on the development of the gld phenotype. Transgenic gld/gld mice expressing a non-degradable form of IkappaBalpha under the control of T cell-specific regulatory elements show dramatically reduced lymphadenopathy, splenomegaly, and an almost complete elimination of Thy-1(+)B220(+)CD4(-)CD8(-) abnormal T cells, correlating with reduced proliferative responses and increased apoptosis of peripheral T cells upon TCR triggering. Interestingly, the B cell abnormalities that are characteristic of gld/gld mice, such as the production of autoantibodies, high levels of serum Ig, and the development of glomerulonephritis, are partially corrected. These results suggest that the T cell-specific inhibition of NF-kappaB opens apoptotic pathways distinct from FasL/Fas which, along with a diminished proliferative response, blocks splenomegaly and lymphadenopathy and partially rescues autoimmune disease in gld/gld mice.

CD95 antigen mutations in hematopoietic malignancies

The CD95 receptor, also known as Fas/Apo-1, is a member of the Tumor Necrosis Factor receptor (TNF-R) family of death receptors. Apoptosis mediated by CD95 plays a central role in maintaining homeostasis of the immune system. Dysregulation of the CD95 apoptotic pathway has been proposed as a mechanism of oncogenesis by providing a survival advantage to potentially malignant cells. This extended lifespan could allow the accumulation of further mutations leading to malignant transformation. Several mechanisms of resistance to CD95 mediated apoptosis have been identified, including reduced surface expression of the receptor, overexpression of anti-apoptotic molecules, and loss of function mutations. This review will focus on the potential role of the CD95-CD95 ligand system in the pathogenesis of hematological malignancies, with particular emphasis on recent work from our laboratory examining the expression of CD95 in B cell lymphomas. We demonstrate that CD95 mutations occur at low frequency in NHL tumors, however, surface expression of the CD95 protein varies with the subtype of lymphoma. Loss of surface CD95 is more likely to occur in lymphomas of aggressive histology, and is unrelated to the detection of CD95 mutations.

Limited endothelial E- and P-selectin expression in MRL/lpr lupus-prone mice

OBJECTIVE

Inflammation in MRL/lpr mice may involve dysfunctional leucocyte-endothelial cell (EC) interactions. Previously, we have shown that intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) increase with age in a tumour necrosis factor alpha (TNF alpha)- and interleukin-1 (IL-1)-dependent manner. The object of this study was to determine the expression of E- and P-selectin.

METHODS

Selectin expression was quantified in MRL/lpr mice and BALB/c controls by intravenous injection of differentially radio-labelled antibodies.

RESULTS

E-selectin, but not P-selectin, was up-regulated in the kidneys of older mice. Neither was up-regulated elsewhere. There was no defect in selectin inducibility, as a further inflammatory stimulus (intraperitoneal lipopolysaccharide) resulted in up-regulation. Serum from older MRL/lpr did not induce selectin expression by EC in vitro.

CONCLUSION

The increase in E-selectin in the kidney may contribute to the development of glomerulonephritis. However, the lack of systemic E- and P-selectin expression may represent a protective mechanism which limits the interaction between leucocytes and the endothelium in the chronic inflammatory context.

Cell cycle phase-specific survival of CD95 ligand-challenged Jurkat cells: upregulation of heat-shock response

An important means of regulating T-cell function occurs via physical deletion (cytolysis) of unnecessary/unwanted T cells. Among cytolytic pathways, CD95 (Fas)-based killing plays a prominent role. Although activation of T cells results in rapid upregulation of surface CD95 expression, sensitivity to CD95-based killing lags behind. To assess determinants of resistance to CD95-based killing, we used Jurkat cells as a model. Analysis of the 10% survivors of a LD(90) dose of CD95 ligand (CD95L) at 24 h demonstrated them to arise preferentially from the S + G2/M phases of the cell cycle and to remain clustered in S + G2/M without undergoing cell division. Protein immunoblot, immunocytochemistry, and RT-PCR analyses demonstrated that hsp72 was markedly upregulated in CD95L survivors within hours of CD95L challenge, indicative of a heat-shock response. Indeed, exposure of Jurkat cells to bona fide heat shock did markedly upregulate hsp72 and, upon subsequent CD95L challenge, did greatly enhance cell survival with persistent clustering to S + G2/M. These findings collectively suggest that in response to a CD95L insult, development of a heat-shock response above some critical threshold level can protect against lethality. This raises the possibility that exaggerated and/or protracted heat-shock responses under in vivo conditions may favor the survival of T cells (including autoaggressive T cells) that otherwise would be destined to die via a CD95-based pathway.

Cerebellar dysfunction is associated with overexpression of proinflammatory cytokine genes in lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology accompanied by central nervous system involvement in up to 60% of patients. The current study chronicles the expression of cerebellar dysfunction in SLE using MRL-lpr/lpr mice as the experimental model. These mice spontaneously develop an illness that has immunological and clinical features of human lupus. We found that MRL-lpr/lpr mice manifest severe and progressive behavioral disturbances indicative of cerebellar dysfunction beginning at 11 weeks of age. Although the lpr gene is known to induce autoimmune features, immunologically normal mice rendered congenic for lpr failed to exhibit disturbances in cerebellar function. Because lupus is a cytokine-driven disease and overexpression of certain proinflammatory cytokines has been associated with neurodegeneration, the relationship between cerebellar dysfunction and cytokine gene expression was examined. Relative to immunologically normal CBA/J mice, the cerebellum of young (11-15 weeks of age) MRL-lpr/lpr mice contained high levels of interleukin (IL)-6 and interferon-gamma (IFNgamma) mRNA, which became even more pronounced in old (22-30 weeks of age) autoimmune mice. mRNA levels for the cytokines IL-1beta and IL-10 were elevated in the cerebellum of old, but not young, MRL-lpr/lpr mice relative to CBA/J. In contrast, the levels of cerebellar transcripts for IL-3 and tumor necrosis factor-alpha were comparable in autoimmune and normal mice, indicating that enhanced gene expression of IL-6, IFNgamma, IL-1beta, and IL-10 was selective. These results suggest a potential role for certain proinflammatory cytokines in the pathogenesis of cerebellar disturbances in SLE.

Lessons from BXSB and related mouse models

The BXSB murine strain spontaneously develops an autoimmune syndrome with features of systemic lupus erythematosus (SLE) that affects males much earlier than females, due to the presence of an as yet unidentified mutant gene located on its Y chromosome, designated Yaa (Y-linked autoimmune acceleration). The Yaa gene by itself is unable to induce significant autoimmune responses in mice without an apparent SLE background, while it can induce and accelerate the development of an SLE in combination with autosomal susceptibility alleles present in lupus-prone mice. Although the genes encoded within or closely linked to the MHC locus play an important role in the development or protection of SLE, the MHC effect can be completely masked by the presence of the Yaa gene in mice highly predisposed to SLE. The role of the Yaa gene for the acceleration of SLE is apparently two-fold; it enhances overall autoimmune responses against autoantigens to which mice respond relatively weakly, and promotes Th 1 responses against autoantigens to which mice respond relatively well, leading to the production of more pathogenic autoantibodies, i.e., FcgammaR-fixing IgG2a and cryoglobulin IgG3 autoantibodies. Yaa+ - Yaa- double bone marrow chimera experiments revealed that the Yaa defect is expressed in B cells, but not in T cells, and that T cells from non-autoimmune mice are capable of providing help for autoimmune responses by collaborating Yaa+ B cells. We speculate that the Yaa defect may decrease the threshold for antigen receptor-dependent stimulation, leading to the triggering and excessive stimulation of autoreactive T and B cells.

Apoptosis: implications for inflammatory bowel disease

Cells of the intestinal mucosa live in a harsh environment and therefore rely heavily on the highly regulated process of cell death, apoptosis, to maintain tissue integrity. Imbalance in the intracellular events that modulate apoptosis may contribute to the pathogenesis of inflammatory bowel disease.

Strong and selective glomerular localization of CD134 ligand and TNF receptor-1 in proliferative lupus nephritis

CD134 (OX40) is a member of the tumor necrosis factor (TNF) receptor (TNFR) family that can be expressed on activated T lymphocytes. Interaction between CD134 and its ligand (CD134L) is involved in costimulation of T and B lymphocyte activation, and in T cell adhesion to endothelium. To examine the possible role of this interaction in the pathogenesis of systemic lupus erythematosus (SLE), expression of CD134 and CD134L on peripheral blood leukocytes was studied, and no significant differences between SLE patients and control individuals were found. Immunohistology on renal biopsies from patients with lupus nephritis or other renal disorders, using a recombinant human CD134-containing chimeric molecule to detect CD134L, demonstrated the abundant presence of CD134L in all cases of proliferative lupus nephritis in a granular distribution predominantly along the epithelial side of the glomerular capillary wall. Confocal laser scanning microscopy indicated colocalization with subepithelial immune deposits. In none of the other renal disorders examined, including nonproliferative forms of lupus nephritis, was glomerular staining for CD134L detected in a similar pattern. Endothelial CD134L expression was frequently observed in different types of vasculitis. CD134 was detected on perivascular infiltrating leukocytes and on part of the tubular epithelium, but not on glomerular resident cells. Immunohistology for several other TNF(R) family members revealed in proliferative lupus nephritis a similar distribution for TNFR1 as was observed for CD134L. In contrast, glomerular expression of TNFR2 was similar in all cases examined. The glomerular presence of CD134L and TNFR1 in proliferative lupus nephritis in association with subepithelial immune deposits may be of pathogenetic significance and have diagnostic value.

Two different types of sialoadenitis in the NOD- and MRL/lpr mouse models for Sjögren's syndrome: a differential role for dendritic cells in the initiation of sialoadenitis?

Sjögren's syndrome is an autoimmune disease that primarily affects the salivary and lacrimal glands. In these glands, focal lymphocytic infiltrates develop. Little is known about the initiation of this autoimmune disease. Antigen-presenting cells (APC) such as dendritic cells (DC) can play a role in the initiation of autoimmunity. To date, no data on the presence of DC in Sjögren's syndrome are available. Several mouse strains, the nonobese diabetic (NOD) and the MRL/Ipr mouse, can be used as models for Sjögren's syndrome. We compared the development of sialoadenitis in the submandibular glands (SMG) of NOD and MRL/Ipr mice with particular focus on the presence of APC. DC, macrophages, T cells, and B cells in the SMG were studied by means of immunohistochemistry, after which positively stained cells were quantified. NOD-severe combined immunodeficiency (SCID) mice were used to study the presence of APC in the SMG in the absence of lymphocytes. Before lymphocytic infiltration, increased numbers of DC were detected in the SMG of NOD mice compared with those numbers in control mice and MRL/Ipr mice, which suggests that DC play a role in the initiation of sialoadenitis in NOD mice. In the SMG of NOD mice, lymphocytic infiltrates organized in time. In MRL/Ipr mice, however, lymphocytic infiltrates were already organized at the time of appearance. This organization was lost over time. In conclusion, two types of sialoadenitis are described in two mouse models for Sjögren's syndrome. Differences exist with regard to early events that may lead to the development of sialoadenitis and to the composition and organization of inflammatory infiltrates. It is possible that different types of sialoadenitis also exist in humans and that the pathogenetic process in both the early and late phases of the autoimmune reaction differs among patients.

Differential regulation and function of Fas expression on glial cells

Fas/Apo-1 is a member of the TNF receptor superfamily that signals apoptotic cell death in susceptible target cells. Fas or Fas ligand (FasL)-deficient mice are relatively resistant to the induction of experimental allergic encephalomyelitis, implying the involvement of Fas/FasL in this disease process. We have examined the regulation and function of Fas expression in glial cells (astrocytes and microglia). Fas is constitutively expressed by primary murine microglia at a low level and significantly up-regulated by TNF-alpha or IFN-gamma stimulation. Primary astrocytes express high constitutive levels of Fas, which are not further affected by cytokine treatment. In microglia, Fas expression is regulated at the level of mRNA expression; TNF-alpha and IFN-gamma induced Fas mRNA by approximately 20-fold. STAT-1alpha and NF-kappaB activation are involved in IFN-gamma- or TNF-alpha-mediated Fas up-regulation in microglia, respectively. The cytokine TGF-beta inhibits basal expression of Fas as well as cytokine-mediated Fas expression by microglia. Upon incubation of microglial cells with FasL-expressing cells, approximately 20% of cells underwent Fas-mediated cell death, which increased to approximately 60% when cells were pretreated with either TNF-alpha or IFN-gamma. TGF-beta treatment inhibited Fas-mediated cell death of TNF-alpha- or IFN-gamma-stimulated microglial cells. In contrast, astrocytes are resistant to Fas-mediated cell death, however, ligation of Fas induces expression of the chemokines macrophage inflammatory protein-1beta (MIP-1beta), MIP-1alpha, and MIP-2. These data demonstrate that Fas transmits different signals in the two glial cell populations: a cytotoxic signal in microglia and an inflammatory signal in the astrocyte.

Involvement of CD28/CTLA4-B7 costimulatory pathway in the development of lymphadenopathy and splenomegaly in MRL/lpr mice

MRL/lpr mouse is an established animal model which develops autoimmune diseases including glomerulonephritis, sialoadenitis, hepatitis and inflammatory lung disease. Additionally, it has been reported that lpr strains uniquely accumulate CD3+ CD4- CD8- B220+ (double negative, DN) T cells in lymphoid organs leading to lymphadenopathy and splenomegaly. To investigate the role of CD28/CTLA4-B7 pathway in the development of lymphadenopathy and splenomegaly, MRL/lpr mice were treated with soluble form of CTLA4 molecules, CTLA4IgG, which efficiently blocks this pathway. It was demonstrated that (i) the development of DN T cells was independent of the CD28/CTLA4-B7 pathway, (ii) the CD28/CTLA4-B7 pathway was required for the development of lymphadenopathy and splenomegaly, (iii) the CD28/CTLA4-B7 pathway was important for the accumulation of various cell populations in the lymph node and spleen, (iv) composition of the accumulating cell populations was not altered by CTLA4IgG treatment, and (v) activation of conventional T cells and IL-4 production from conventional T cells were the CD28/CTLA4-B7 pathway dependent. Thus, we concluded that the CD28/CTLA4-B7 pathway was required for the development of full-blown lymphadenopathy and splenomegaly in MRL/lpr mice.

Environmentally induced autoimmune diseases: potential mechanisms

Environmental and other xenobiotic agents can cause autoimmunity. Examples include drug-induced lupus, toxic oil syndrome, and contaminated l-tryptophan ingestion. Numerous mechanisms, based on (italic)in vitro(/italic) evidence and animal models, have been proposed to explain how xenobiotics induce or accelerate autoimmunity. The majority of these can be divided into three general categories. The first is those inhibiting the processes involved in establishing tolerance by deletion. Inhibiting deletion can result in the release of newly generated autoreactive cells into the periphery. The second mechanism is the modification of gene expression in the cells participating in the immune response, permitting lymphocytes to respond to signals normally insufficient to initiate a response or allowing the antigen-presenting cells to abnormally stimulate a response. Abnormal gene expression can thus disrupt tolerance maintained by suppression or anergy, permitting activation of autoreactive cells. The third is the modification of self-molecules such that they are recognized by the immune system as foreign. Examples illustrating these concepts are presented, and related mechanisms that have the potential to similarly affect the immune system are noted. Some mechanisms appear to be common to a variety of agents, and different mechanisms appear to produce similar diseases. However, evidence that any of these mechanisms are actually responsible for xenobiotic-induced human autoimmune disease is still largely lacking, and the potential for numerous and as yet unidentified mechanisms also exists.

Polyamine-fas interactions: inhibition of polyamine biosynthesis in MRL-lpr/lpr mice is associated with the up-regulation of fas mRNA in thymocytes

MRL-lpr/lpr is a strain of mice that develops spontaneous signs of the autoimmune disease, systemic lupus erythematosus (SLE or lupus). The lpr (lymphoproliferation) defect has been identified as an insertion of an early transposon (ETn) derived sequence into the fas apoptosis gene. We studied the in vivo effects of difluoromethylornithine (DFMO), an irreversible inhibitor of the polyamine biosynthetic enzyme, ornithine decarboxylase (ODC), on the expression of fas in MRL-lpr/lpr mice as well as in congenic MRL- + / + and autoimmune NZB/W strains. Using Northern blot hybridization and reverse transcription polymerase chain reaction (RT-PCR), we found that DFMO treatment resulted in an increase in the expression of fas mRNA in the thymus of MRL-lpr/lpr mice. Using RT-PCR, we further found that the increased expression of fas was associated with the suppression of chimeric ETn/fas mRNA. With fractionated CD4 + and CD8 + T cells, we found a cell-specific effect of DFMO on chimeric ETn/fas expression in CD8 + cells. ETn/fas expression was detected in CD8+ T cells from untreated mice, but it was eliminated after DFMO treatment. HPLC analysis of polyamines showed depletion of putrescine and partial reduction of spermidine (35%) in DFMO-treated mice compared to controls. These results indicate that DFMO-mediated polyamine depletion is linked to the regulation of fas and chimeric ETn/fas in MRL-lpr/lpr mice. Elevated levels of polyamines in this strain, as found in earlier studies, may be associated with the progression of the autoimmune disease by altering the expression of fas gene or by facilitating the expression of chimeric ETn/fas. Our data also provide new mechanistic insights into the beneficial effects of DFMO on these mice.

Severe impairment of B cell function in lpr/lpr mice expressing transgenic Fas selectively on B cells

Transgenic lpr/lpr mice expressing functional Fas selectively on B cells were produced in an attempt to elucidate the role of Fas on B cells in the regulation of autoantibody production. The homozygous lpr/lpr mice carrying the transgene did not produce anti-double-stranded DNA antibodies throughout their lives, whereas the development of abnormal lpr T cells (double negative, B220(+)) was not suppressed. Further analyses, however, revealed that the expression of the transgenic Fas on B cells of lpr/lpr homozygous mice resulted in severe impairment of the B cell function. The defect was characterized by a decrease in the number of mature peripheral B cells, a reduction in the serum Ig level and the total failure of B cells to mount antibody responses to stimulations of T-dependent as well as T-independent antigens. Such a defect was prominent only when the transgene was expressed on the lpr/lpr homozygous background. On the contrary, B cells of the transgenic lpr/lpr mice were shown to be capable of producing Ig when stimulated with anti-CD40 in the presence of IL-4 and IL-5. Furthermore, lpr/lpr T cells showed enhanced non-specific cytolytic activity. These observations suggested that the observed B cell defect was probably attributable to the destruction of activated B cells expressing transgenic Fas by aggressive lpr/lpr T cells.

Effects of immunosuppression on the development of cochlear disease in the MRL-Fas(lpr) mouse

OBJECTIVES

The MRL-Fas(lpr) mouse, an animal that spontaneously develops multisystemic autoimmune disease, has been proposed as model of immune-mediated inner ear disease. Previous studies revealed that this mouse manifested elevated auditory brainstem response thresholds, hydropic degeneration of strial cells, and antibody deposition within strial capillaries. As the etiology of the observed strial disease may be immune, genetic, or uremic, a study was designed to attempt to delineate between these possible etiologic factors.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Dexamethasone, which is known to suppress autoantibody production and glomerulonephritis in these animals, was administered systemically on a daily basis to experimental animals, beginning at 6 weeks of age. Control animals received no treatment. Animals were allowed to age, with control animals predictably manifesting systemic disease at 20 weeks of age, at which point all animals were sacrificed.

RESULTS

Animals receiving dexamethasone treatment manifested a significant reduction in serum immunoglobulin levels, lymphoid hyperplasia, and a significant improvement in the level of renal function. However, morphologic analysis revealed a persistence of strial disease despite the elimination of strial antibody deposition.

CONCLUSION

The results of this experiment support the hypothesis that genetic mechanisms may be responsible for the observed strial disease. Further studies are under way to confirm these findings.