Soluble antigen therapy induces apoptosis of autoreactive T cells preferentially in the target organ rather than in the peripheral lymphoid organs

Antigen-oriented T cell migration contributes to myelin peptide induced-EAE and immune tolerance

Treatment with soluble myelin peptide can efficiently and specifically induce tolerance to demyelination autoimmune diseases including multiple sclerosis, however the mechanism underlying this therapeutic effect remains to be elucidated. In actively induced mouse model of experimental autoimmune encephalomyelitis (EAE) we analyzed T cell and innate immune cell responses in the central nervous system (CNS) and spleen after intraperitoneal (i.p.) infusion of myelin oligodendrocyte glycoprotein (MOG). We found that i.p. MOG infusion blocked effector T cell recruitment to the CNS and protected mice from EAE and lymphoid organ atrophy. Innate immune CD11b(+) cells preferentially recruited MOG-specific effector T cells, particularly when activated to become competent antigen presenting cells (APCs). During EAE development, mature APCs were enriched in the CNS rather than in the spleen, attracting effector T cells to the CNS. Increased myelin antigen exposure induced CNS-APC maturation, recruiting additional effector T cells to the CNS, causing symptoms of disease. MOG triggered functional maturation of splenic APCs. MOG presenting APCs interacted with MOG-specific T cells in the spleen, aggregating to cluster around CD11b(+) cells, and were trapped in the periphery. This process was MHC II dependent as an MHC II directed antibody blocked CD4(+) T cell cluster formation. These findings highlight the role of myelin peptide-loaded APCs in myelin peptide-induced EAE and immune tolerance.

Programmed Death Ligand-1 on Microglia Regulates Th1 Differentiation via Nitric Oxide in Experimental Autoimmune Encephalomyelitis

Microglia are considered to be potential antigen-presenting cells and have the ability to present antigen under pathological conditions. Nevertheless, whether and how microglia are involved in immune regulation are largely unknown. Here, we investigated the suppressive activity of microglia during experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein, with the goal of understanding their role in regulating the T cell reaction. Using flow cytometric analysis, we found that microglia were characterized by increased cell number and up-regulated programmed death ligand-1 (PD-L1) at the peak phase of EAE. Meanwhile, both the CD4(+) T cells and microglia that infiltrated the central nervous system expressed higher levels of PD1, the receptor for PD-L1, accompanied by a decline of Th1 cells. In an ex vivo co-culture system, microglia from EAE mice inhibited the proliferation of antigen-specific CD4(+) T cells and the differentiation of Th1 cells, and this was significantly inhibited by PD-L1 blockade. Further, microglia suppressed Th1 cells via nitric oxide (NO), the production of which was dependent on PD-L1. Thus, these data suggest a scenario in which microglia are involved in the regulation of EAE by suppressing Th1-cell differentiation via the PD-L1-NO pathway.

Soluble peptide treatment reverses CD8 T-cell-induced disease in a mouse model of spontaneous tissue-selective autoimmunity

Transgenic (Tg) mouse models of autoimmunity have been used to express model antigens that can be recognized by T cells or by autoantibodies. To identify mechanisms of CD8-mediated tissue-specific autoimmune reactions and to identify potential treatments, we generated a double-transgenic (DTg) murine model of autoimmunity by crossing keratin-14 (K14)-soluble chicken ovalbumin (sOVA) mice, which express sOVA predominantly in external ear skin, with OT-I mice whose CD8 T cells express Vα2/Vβ5 regions of the TCR and are specific for SIINFEKL peptide (chicken ovalbumin (OVA) peptide 257-264) in association with class I major histocompatibility complex. The K14-sOVA/OT-I DTg mice develop a destructive process selectively targeting the external ear pinnae in the first 6 days of life. The ear bud area develops an intense inflammatory infiltrate of OT-I cells. Administration of the SIINFEKL peptide intravenously to pregnant F1 (filial 1, first filial generation of animal offspring from cross-mating two parental types) mice and subsequently intraperitoneally to newborn pups resulted in normal external ear development. Treatment with this self-peptide markedly reduced OT-I cell numbers, as well as downregulated the CD8 co-receptor. This model can be useful in studying localized, tissue-specific, immune-mediated skin disease, and provide information about potential therapies for autoimmune diseases in which specific molecular targets are known.

Anamnestic recall of stroke-related deficits: an animal model

BACKGROUND AND PURPOSE

Anamnestic recall of stroke-related deficits is a common clinical observation, especially during periods of systemic infection. The pathophysiology of this transient re-emergence of neurological dysfunction is unknown.

METHODS

Male Lewis rats underwent 3 hours middle cerebral artery occlusion and were treated with lipopolysaccharide or saline at the time of reperfusion. The delayed-type hypersensitivity (DTH) response to myelin basic protein was examined 28 days after middle cerebral artery occlusion. Changes in behavioral outcomes were assessed after DTH testing and repeat administration of lipopolysaccharide or saline at 34 days. At the time of euthanasia (36 days), the immunologic response of splenocytes to myelin basic protein, neuron-specific enolase, and proteolipid protein was determined by enzyme-linked immunospot assay and the number of lymphocytes in the brain determined by immunocytochemistry.

RESULTS

Animals treated with lipopolysaccharide at middle cerebral artery occlusion had a greater DTH response to myelin basic protein than animals treated with saline. Among those animals that had fully recovered on a given behavioral test before DTH testing, those treated with lipopolysaccharide at middle cerebral artery occlusion displayed more neurological deterioration after DTH testing and had more CD8(+) lymphocytes within the ischemic core of the brain. Furthermore, the Th1 immune response to brain antigens in the spleen was more robust among those animals that deteriorated after DTH testing and there were more CD4(+) lymphocytes in the penumbral region of animals with a Th1 response to myelin basic protein.

CONCLUSIONS

Our data suggest that an immune response to the brain contributes to the phenomenon of anamnestic recall of stroke-related deficits after an infection. The contribution of the immune response to this phenomenon deserves further investigation.

Decreased production of TNF-alpha by lymph node cells indicates experimental autoimmune encephalomyelitis remission in Lewis rats

Experimental autoimmune encephalomyelitis (EAE) is mediated by CD4+ Th1 cells that mainly secrete IFN-gamma and TNF-alpha, important cytokines in the pathophysiology of the disease. Spontaneous remission is, in part, attributed to the down regulation of IFN-gamma and TNF-alpha by TGF-beta. In the current paper, we compared weight, histopathology and immunological parameters during the acute and recovery phases of EAE to establish the best biomarker for clinical remission. Female Lewis rats were immunised with myelin basic protein (MBP) emulsified with complete Freund's adjuvant. Animals were evaluated daily for clinical score and weight prior to euthanisation. All immunised animals developed the expected characteristics of EAE during the acute phase, including significant weight loss and high clinical scores. Disease remission was associated with a significant reduction in clinical scores, although immunised rats did not regain their initial weight values. Brain inflammatory infiltrates were higher during the acute phase. During the remission phase, anti-myelin antibody levels increased, whereas TNF-alpha and IFN-gamma production by lymph node cells cultured with MBP or concanavalin A, respectively, decreased. The most significant difference observed between the acute and recovery phases was in the induction of TNF-alpha levels in MBP-stimulated cultures. Therefore, the in vitro production of this cytokine could be used as a biomarker for EAE remission.

Blood-borne soluble protein antigen intensifies T cell activation in autoimmune CNS lesions and exacerbates clinical disease

We explored the effect of i.v. soluble antigen on autoaggressive, myelin basic protein-specific effector T cells within their target organ during acute experimental autoimmune encephalomyelitis (EAE). Intravital two-photon imaging revealed that i.v. autoantigen reached the CNS and was taken up and processed by antigen-presenting cells within 30 min after injection. The exogenous autoantigen dramatically changed the motility and function of autoreactive effector T cells within the EAE lesions: T cells that had been cruising through the tissue slowed down and became tethered to local antigen-presenting cells within 1 h. One hour later, the effector T cells massively produced proinflammatory cytokines and up-regulated membranous activation markers. This strong activation of the T cells boosted CNS inflammation and aggravated clinical disease. Postactivated effector and resting memory T cells specific for a non-CNS antigen (ovalbumin) were recruited to EAE lesions and moved there without contacting antigen-presenting cells. These cells were similarly arrested and activated after i.v. infusion of ovalbumin, and they also exacerbated clinical disease. Our data are relevant for autoantigen-based therapies of autoimmune disorders. Further, the study indicates how brain unrelated antigens (microbial components) leaking into the chronically inflamed CNS through the bloodstream might trigger relapses in multiple sclerosis.

Treating autoimmune demyelination by augmenting lymphocyte apoptosis in the central nervous system

The elimination of autoreactive T cells from the central nervous system (CNS) by apoptosis plays an important role in switching off autoimmune attack. B-cell apoptosis in the CNS probably also has a key role in downregulating autoimmunity. Augmenting lymphocyte apoptosis in the CNS is a potential strategy for treating autoimmune CNS diseases such as multiple sclerosis. These strategies involve modulation of the physiological pro-apoptotic and anti-apoptotic pathways that control lymphocyte fate in the CNS. In the case of T cells, apoptosis can be augmented by enhancing activation-induced T-cell apoptosis through the CD95 (Fas) pathway and by inhibiting costimulation-induced anti-apoptotic pathways mediated through BCL-2 and BCL-X L.

Antigen therapy of experimental autoimmune encephalomyelitis selectively induces apoptosis of pathogenic T cells

Administration of high-dose myelin antigen induces massive T cell apoptosis in experimental autoimmune encephalomyelitis (EAE) but the nature of the target cells remains elusive. Here we have used a cell line established in eGFP-transgenic Lewis rats to distinguish between pathogenic and bystander T cells in adoptive transfer EAE. Intravenous application of gpMBP strongly reduced the amount of encephalitogenic cells in spinal cord and spleen while the number of the other T cells remained constant. This could be attributed to their differential sensitivity to apoptosis. Thus, antigen therapy selectively targets pathogenic T cells and should therefore limit potential adverse effects.

Systemic immunomodulation of autoimmune disease using MHC-derived recombinant TCR ligands

Human autoimmune disease involves local activation of antigen-specific CD4(+) T cells that produce inflammatory Th1 cytokines leading to the further recruitment and activation of lymphocytes and monocytes, resulting ultimately in the destruction of target tissue. Antigen presenting cells (APCs) initiate activation of CD4(+) T cells in a multistep process that minimally involves co-ligation of the TCR and CD4 by the MHC class II/peptide complex and costimulation through additional T cell surface molecules such as CD28. Disruption of this highly orchestrated series of events can result in the direct modulation of CD4(+) T cell behavior. The interaction between MHC and TCR holds unique promise as a focal point for therapeutic intervention in the pathology of CD4(+) T cell-mediated diseases, and MHC class II-derived Recombinant TCR Ligands ("RTLs") have emerged as a new class of therapeutics with potent clinical efficacy in a diverse set of animal models for multiple sclerosis. Here I review the systemic effect that RTL therapy has on the intact immune system and present an overview of a molecular mechanism by which RTL therapy could induce these systemic changes.

Cerebrospinal fluid CD4+ T cells from a multiple sclerosis patient cross-recognize Epstein-Barr virus and myelin basic protein

Epstein-Barr virus-specific CD4+ T cells could be involved in the pathogenesis of multiple sclerosis, provided they can gain entry to the intrathecal compartment. The authors have previously demonstrated that cerebrospinal fluid T cells from multiple sclerosis patients recognize autologous Epstein-Barr virus-transformed B cells. They now report that CD4+ T cells specific for the Epstein-Barr virus DNA polymerase peptide EBV 627-641 were present in the cerebrospinal fluid from one of two multiple sclerosis patients, and that a high proportion of these CD4+ T cells cross-recognized an immunodominant myelin basic protein peptide, MBP 85-99. In the observed patient, the proportion of EBV 627-641-specific CD4+ T cells seemed to exceed 1/10,000 in cerebrospinal fluid, compared to approximately 1/100,000 in blood. These findings prove that Epstein-Barr-virus specific CD4+ T cells can gain access to the intrathecal compartment, and suggest that Epstein-Barr virus-specific CD4+ T cells could target myelin basic protein in the central nervous system.

Fas ligand-mediated apoptosis in degenerative disorders of the brain

While defective apoptosis predisposes to neoplasia, inappropriate apoptosis in the brain leads to permanent neurological deficits. Disregulated apoptosis has been implicated in several neurodegenerative disorders including Alzheimer's, Parkinson's, and Huntington's diseases. Recent reports have suggested that the key apoptosis regulator Fas ligand (FasL) may participate in both neuronal and immune cell apoptosis in Alzheimer's disease. FasL has also been implicated as a negative regulator for the inflammatory component of the demyelinating brain disorder multiple sclerosis (MS). Here we discuss how FasL-mediated apoptosis may balance immune cell access to the brain with Alzheimer's disease and MS representing extremes of too little and too much immune access, respectively.

Immunotherapeutic approaches in multiple sclerosis

The progress in understanding the mechanisms of T cell activation, inactivation and modulation has been translated into different immunotherapeutic strategies aiming at treating multiple sclerosis (MS). Key attack points for selective immunointervention in MS include modulation of antigen recognition, costimulation blockade, induction of regulatory cells, deviation to non-pathogenic or protective responses, neutralization of proinflammatory cytokines and administration of anti-inflammatory cytokines. In addition, several attempts have been made using less specific forms of immunointervention. The two resounding successes in the immunotherapy of MS, IFN-failed and glatiramer acetate, contrast with the many attempts, equally based on sound reasoning and promising animal data. Nevertheless, antigen-based immunointervention will continue to be tested clinically, and we will certainly witness the application of more articulate strategies able to selectively target cytokine production by Th1 or Th2 cells or to modify the Th1/Th2 balance. Perhaps, an effective manipulation of pathogenic and protective cells in MS may eventually rely on a combination of antigen- and cytokine-based approaches to selectively target autoreactive T cells and divert them from autoaggression. Most importantly, new avenues are opening, such as the use of chemokine receptor antagonists, and others look very promising, as targeting dendritic cells to favour their capacity to induce regulatory T cells.

Fas ligand-mediated apoptosis in degenerative disorders of the brain

While defective apoptosis predisposes to neoplasia, inappropriate apoptosis in the brain leads to permanent neurological deficits. Disregulated apoptosis has been implicated in several neurodegenerative disorders including Alzheimer's, Parkinson's, and Huntington's diseases. Recent reports have suggested that the key apoptosis regulator Fas ligand (FasL) may participate in both neuronal and immune cell apoptosis in Alzheimer's disease. FasL has also been implicated as a negative regulator for the inflammatory component of the demyelinating brain disorder multiple sclerosis (MS). Here, we discuss how FasL-mediated apoptosis may balance immune cell access to the brain with Alzheimer's disease and MS representing extremes of too little and too much immune access, respectively.

Cerebrospinal fluid T cells from multiple sclerosis patients recognize autologous Epstein-Barr virus-transformed B cells

The association between multiple sclerosis and Epstein-Barr virus infection could involve Epstein-Barr virus-specific T cells, provided that these T cells get access to the intrathecal compartment. We report that CD4+ T cells from the cerebrospinal fluid of six out of six multiple sclerosis patients, and four out of six patients with other neurological diseases, recognized autologous B cells transformed with Epstein-Barr virus. The cerebrospinal fluid T-cell responses were predominantly HLA-DR restricted. These T cells did not recognize B cells activated through stimulation of CD40 or the inducible autoantigen alphaB crystalline. These findings support that the immunological response to Epstein-Barr virus could contribute to the pathogenesis of multiple sclerosis.

Characterizing a soluble survival signal for activated lymphocytes from CD14+ cells

T-cell activation requires at least two signals: antigen and a costimulatory signal. As antigen-presenting cells play an important role in this area, the role of CD14+ cells in T-cell activation, proliferation and activation-induced cell death (AICD) was investigated. Using phytohaemagglutinin (PHA) activation, it was found that CD14+ cell depletion resulted in significantly greater AICD, decreased lymphocyte growth and up-regulated interleukin-2 (IL-2) secretion. However, T-cell activation was delayed according to the expression of CD69 and CD25. Dynabeads conjugated with anti-CD14 monoclonal antibody (mAb) bound CD14+ cells and induced secretion of IL-1beta, tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta) and IL-6, but not IL-2, IL-12 or IL-15. Supernatants were collected from Dynabeads-activated CD14+ cell cultures and designated as 'CD14 cocktails'. Addition of CD14 cocktails to CD14+ cell-depleted mononuclear cell cultures reversed the increased AICD, decreased lymphocyte growth and increased IL-2 secretion. Depletion of IL-1beta and TNF-alpha in the CD14 cocktails by panning followed by blocking with the corresponding mAbs had no effect on the active AICD protection. TGF-beta was determined not to be the active factor owing to the presence of >1.0 ng of TGF-beta in the media for culturing both CD14+ and CD14- peripheral blood mononuclear cells (PBMC). The CD14 cocktails did not contain IL-12 and IL-15. Depletion of IL-6 with panning followed by blocking residual IL-6 with anti-IL-6 mAb significantly reduced the protective effect of the CD14 cocktails. Human recombinant IL-6 also partially reversed the effects of CD14+ cell depletion on AICD, lymphocyte growth and IL-2 secretion. The data suggest that IL-6 is one of the active factors in the survival signal from CD14+ cells.

Transfection of tubule cells with Fas ligand causes leukocyte apoptosis

BACKGROUND

Since the Fas/Fas Ligand (FasL) interaction is recognized as a major pathway of apoptosis in immune cells, we hypothesized that selective expression of FasL by tubular cells (TC) may promote the resolution of interstitial inflammation by inducing apoptosis of infiltrating immune cells. In this study, the effect of FasL transfection of rat TC on apoptosis of leukocytes was examined.

METHODS

Rat tubule cells (NRK52E) were transfected with plasmids constructed using human and rat FasL (hFasL and rFasL). The propensity of activated, transfected TC to undergo apoptosis was examined. Similarly, the effects of FasL transfection on apoptosis of Jurkat cells and activated leukocytes were assessed directly following co-culture for 12 hours and in a cell insert system intended to assess the effects of soluble FasL. Fas and FasL expression was assessed by flow cytometry and apoptosis was examined using Annexin V staining and the TUNEL method.

RESULTS

Expression of FasL in TC was increased after FasL transfection. Transfected TC showed no detectable increase in apoptosis following lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-alpha) activation. Jurkat cell apoptosis was increased ninefold and eightfold after co-culture with TC transfected with hFasL and rFasL, respectively (67.0 +/- 12.1% and 60.1 +/- 8.8% vs. 6.7 +/- 1.8% with un-transfected TC, P < 0.01). Similarly, apoptosis of activated leukocytes was increased fourfold by co-culture (26.8 +/- 4.9% vs. 6.7 +/- 2.0% with untransfected TC, P < 0.01). Leukocyte apoptosis also was increased in an insert culture system (18.2 +/- 4.4% vs. 5.8 +/- 2.3% with un- transfected TC, P < 0.01). No increase of TC apoptosis was detected in any of the co-culture experiments.

CONCLUSION

Enhanced expression of FasL by TC is capable of inducing apoptosis of activated leukocytes, without evidence for increased susceptibility to apoptosis of the transfected cells themselves. This suggests a potential role for this approach in the limitation and resolution of renal tubulointerstitial inflammation.

Apoptosis of inflammatory cells in immune control of the nervous system: role of glia

The elimination of inflammatory cells within the central nervous system (CNS) by apoptosis plays an important role in protecting the CNS from immune-mediated damage. T cells, B cells, macrophages, and microglia all undergo apoptosis in the CNS. The apoptotic elimination of CNS-reactive T cells is particularly important, as these cells can recruit and activate other inflammatory cells. T-cell apoptosis contributes to the resolution of CNS inflammation and clinical recovery from attacks of experimental autoimmune encephalomyelitis (EAE), an animal model of the demyelinating disease multiple sclerosis (MS). T-cell apoptosis in the CNS in EAE occurs in both an antigen-specific and an antigen-nonspecific manner. In antigen-specific T-cell apoptosis, it is proposed that T cells that recognize their antigen in the CNS, such as CNS-reactive T cells, are deleted by the process of activation-induced apoptosis after activation of the T-cell receptor. This may result from the ligation of T-cell death receptors (such as CD95 (Fas) or tumor necrosis factor (TNF) receptor 1) by CD95 ligand (CD95L) or TNF expressed by the same T cell or possibly by microglia, astrocytes or neurons. Inadequate costimulation of the T cell by antigen-presenting glial cells may render T cells susceptible to activation-induced apoptosis. T cells expressing CD95 may also die in an antigen-nonspecific manner after interacting with glial cells expressing CD95L. Other mechanisms for antigen-nonspecific T-cell apoptosis include the endogenous release of glucocorticosteroids, deprivation of interleukin-2, and the release of nitric oxide by macrophages or glia. Apoptosis of autoreactive T cells in the CNS is likely to be important in preventing the development of autoimmune CNS diseases such as MS.

Selective immunointervention in autoimmune diseases: lessons from multiple sclerosis

Activation of peripheral T cells by foreign and self antigens is under stringent control by different mechanisms, both thymic and peripheral. Control of T cell reactivity is accomplished by three major types of mechanisms: 1) deletion, the physical elimination of T cells specific for a given antigen, 2) anergy, the functional incapacity of T cells to respond to antigen, 3) suppression, the inhibition of T cell function by a regulatory (suppressor) cell. Their failure may lead to autoimmune diseases. The progress in understanding T cell activation, inactivation and modulation is being translated into strategies able to induce selective immunosuppression to treat different pathological situations, notably autoimmune diseases, allergies, and allograft rejection. The medical need for selective immunosuppression is very high, as the available immunosuppressive drugs are substantially inadequate because of limited efficacy, modest selectivity, and considerable toxicity. Key attack points for selective immunointervention have been identified: modulation of antigen recognition, co-stimulation blockade, induction of regulatory cells, deviation to non-pathogenic or protective responses, neutralization of proinflammatory cytokines, induction or administration of anti-inflammatory cytokines, and modulation of leukocyte trafficking. All these forms of immunointervention have been successfully used to prevent and sometimes treat experimental autoimmune diseases. Based on these results, expectations have been raised for exploiting the same strategies to inhibit the activation of human autoreactive T cells. In this overview, we will examine recent advances towards immunointervention in multiple sclerosis (MS) as a paradigm for successes and failures of current immunotherapeutic approaches in human autoimmune diseases.

Aminoguanidine reduces apoptosis of circulating V Beta 8.2 T lymphocytes in Lewis rats with actively induced experimental autoimmune encephalomyelitis. Association with persistent inflammation of the central nervous system and lack of recovery

Aminoguanidine therapy delayed the onset of actively induced EAE in Lewis rats, but recovery was impaired in most animals. In the central nervous system this was correlated with persistent inflammation and production of proinflammatory cytokines. In the periphery of aminoguanidine-treated animals, T lymphocytes showed increased proliferation against myelin basic protein, and the percentage of Vbeta 8.2(+) T lymphocytes undergoing early apoptosis was markedly decreased, although it was unchanged in Vbeta 8.2(+) T cells isolated from the spinal cord. These results suggest that the prolonged survival of circulating encephalitogenic cells achieved by aminoguanidine would favor a longer lasting entry of these cells into the nervous system resulting in persistent inflammation and lack of recovery.

Systemic administration of agonist peptide blocks the progression of spontaneous CD8-mediated autoimmune diabetes in transgenic mice without bystander damage

Insulin-dependent diabetes is an autoimmune disease targeting pancreatic beta-islet cells. Recent data suggest that autoreactive CD8+ T cells are involved in both the early events leading to insulitis and the late destructive phase resulting in diabetes. Although therapeutic injection of protein and synthetic peptides corresponding to CD4+ T cell epitopes has been shown to prevent or block autoimmune disease in several models, down-regulation of an ongoing CD8+ T cell-mediated autoimmune response using this approach has not yet been reported. Using CL4-TCR single transgenic mice, in which most CD8+ T cells express a TCR specific for the influenza virus hemagglutinin HA512-520 peptide:Kd complex, we first show that i.v. injection of soluble HA512-520 peptide induces transient activation followed by apoptosis of Tc1-like CD8+ T cells. We next tested a similar tolerance induction strategy in (CL4-TCR x Ins-HA)F1 double transgenic mice that also express HA in the beta-islet cells and, as a result, spontaneously develop a juvenile onset and lethal diabetes. Soluble HA512-520 peptide treatment, at a time when pathogenic CD8+ T cells have already infiltrated the pancreas, very significantly prolongs survival of the double transgenic pups. In addition, we found that Ag administration eliminates CD8+ T cell infiltrates from the pancreas without histological evidence of bystander damage. Our data indicate that agonist peptide can down-regulate an autoimmune reaction mediated by CD8+ T cells in vivo and block disease progression. Thus, in addition to autoreactive CD4+ T cells, CD8+ T cells may constitute targets for Ag-specific therapy in autoimmune diseases.

Expression of TRAIL receptors in human autoreactive and foreign antigen-specific T cells

Deletion of T cells due to apoptosis induction is a regulatory mechanism in the human immune system that may be impaired in autoimmune diseases such as multiple sclerosis (MS). Involvement of the apoptosis-mediating CD95/CD95 ligand system in MS has been demonstrated. Here, we report that (auto)antigen-specific human T cells are not killed in vitro by soluble TNF-related apoptosis-inducing ligand (TRAIL) although expressing death-inducing receptors, TRAIL receptor 1 (TRAIL-R1) and TRAIL-R2. Apoptosis was assessed by caspase activation and DNA fragmentation, receptor expression was detected by RT - PCR and flow cytometry. The (auto)antigen-specific T cells were also resistant to specific TRAIL-R1/TRAIL-R2-directed induction of apoptosis, indicating that coexpression of the truncated TRAIL-R3 and TRAIL-R4 in these T cells is not responsible for the observed resistance. Upon stimulation, levels of death-inducing TRAIL receptors decreased whereas TRAIL was up-regulated on the cell surface. In contrast to CD95, the role of TRAIL receptors in MS might not involve regulation of T cell vulnerability.

B cell apoptosis in the central nervous system in experimental autoimmune encephalomyelitis: roles of B cell CD95, CD95L and Bcl-2 expression

The role and fate of B cells in the central nervous system (CNS) in experimental autoimmune encephalomyelitis (EAE) are unknown. Using enzyme-linked immunospot assays we now show that B cells reactive to myelin basic protein (MBP) accumulate in the CNS of Lewis rats with acute EAE induced by immunization with MBP and adjuvants. We also report that B cells are eliminated from the CNS by apoptosis during spontaneous recovery from this disease. Apoptotic B cells were identified by flow cytometry of inflammatory cells extracted from the spinal cord and by histological sections of the spinal cord using light and electron microscopic immunocytochemistry. B cell apoptosis occurred preferentially in the CNS rather than in the peripheral lymphoid organs and was maximal just prior to the onset of spontaneous clinical recovery. Three colour flow cytometry indicated that B cells expressing CD95 (Fas) or CD95 ligand (CD95L) were highly vulnerable to apoptosis, whereas B cells expressing Bcl-2 were relatively protected from apoptosis. We propose that B cells are eliminated from the CNS by the interaction of CD95L and CD95 on the same B cell and that this contributes to the spontaneous resolution of CNS inflammation and clinical recovery in acute EAE.

Partial synergy of bisindolylmaleimide with apoptotic stimulus in antigen-specific T cells--implications for multiple sclerosis

In multiple sclerosis (MS), induction of T cell apoptosis constitutes a promising therapeutic strategy. Recently, bisindolylmaleimide has been shown to be an effective treatment of experimental autoimmune encephalomyelitis, presumably due to enhancement of CD95-mediated T cell apoptosis. Therefore, we studied the effects of bisindolylmaleimide on human (auto)antigen-specific T cells. We observed a synergistic effect of bisindolylmaleimide with apoptotic stimulus assessed via caspase activity and annexin V-binding, but no potentiation of DNA fragmentation or cell death. Thus, bisindolylmaleimide might be useful for modulating T cell apoptosis, yet more potent substances have to be generated re-establishing immunological control over auto-reactive T cells.

The effect of apoptosis inhibitors on experimental autoimmune encephalomyelitis: apoptosis as a regulatory factor

The effect of apoptosis inhibitors on experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis, was investigated by intraperitoneal or intracisternal administration of apoptosis inhibitors Ac-YVAD-cmk and zVAD-fmk. After onset of the disease, these agents had no suppressive effect on EAE and resulted in impaired recovery or earlier relapse. Histological examination revealed that administration of zVAD-fmk suppressed the apoptotic death of inflammatory cells in the central nervous system (CNS) of mice with EAE. The results indicated that the apoptotic elimination of infiltrated cells in the CNS might be one of the recovery mechanisms in EAE.

Suppressor cells in demyelinating disease: a new paradigm for the new millennium

This brief review highlights investigations conducted over the past three decades concerning the role of suppressor T cells in the regulation of experimental autoimmune encephalomyelitis (EAE). In addition, more recent studies are summarized which suggest that apoptosis of autoreactive T cells is also involved in the regulation of EAE. The possibility that natural killer (NK) cells mediate apoptosis is also considered.

Fas system up-regulation in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a T-cell-mediated disorder characterized by infiltration of the central nervous system (CNS) by mononuclear cells and macrophages, and serves as a model for multiple sclerosis. In acute monophasic and relapsing remitting forms of EAE, the CNS inflammatory infiltrates are cleared within a few days and, simultaneously, animals recover from their clinical disability. The mechanisms for rapid disappearance of the inflammatory cells are not fully understood. Fas and Fas-ligand (Fas-L) molecules are thought to play an important role in the deletion of autoimmune reactive T cells through apoptosis. However, recent observations in transgenic lpr and gld mice show that mutations inactivating Fas and Fas-L respectively ameliorate signs of EAE despite persistence of immune cell infiltrates into the CNS. In the current study, the expression of Fas and Fas-L was investigated by immunochemistry and in situ hybridization during the course of EAE in DA rats that were actively immunized with syngenic spinal cord homogenate. CNS apoptotic cells were simultaneously examined using terminal transferase dUTP nick end-labeling techniques. During the acute phase of the disease, a significant proportion of CNS CD4+ cells (80%) and macrophages (50%) expressed Fas and Fas-L (80 and 60%, respectively). Simultaneously, about 20% of CD4+ cells and 30% of macrophages were found to be apoptotic. Some astrocytes and neurons also expressed Fas and Fas-L, although they did not appear to be apoptotic. These results further support a role for Fas-mediated lymphocyte and macrophage apoptosis in this model of CNS autoimmune disease but they also suggest a more complex role for Fas/Fas-L interactions in CNS autoimmunity, including resident cells.

Strain Variation in Autoimmunity: Attempted Tolerization of DA Rats Results in the Induction of Experimental Autoimmune Encephalomyelitis

This paper reports that DA rats develop experimental autoimmune encephalomyelitis (EAE) when immunized with encephalitogenic myelin basic protein (MBP) peptide (MBP63–81) in IFA. In contrast, most rodent strains are tolerized by this procedure. Doses as low as 5 μg peptide + IFA induced EAE in DA rats. Lewis (LEW) rats did not develop EAE, even after immunization with 100 μg encephalitogenic peptide (MBP68–86) + IFA, but were rendered tolerant to EAE. DA rat T cells proliferated to peptide, and proliferation was inhibited by CTLA4Ig, and by anti-B7.1 and anti-B7.2 mAbs. This indicates that the ease of induction of EAE in this strain does not reflect a decreased requirement for T cell costimulation through the B7/CD28 costimulatory pathway. The inhibitory effect of CTLA4Ig was abrogated in the presence of anti-TGF-β-neutralizing Ab. An encephalitogenic DA T cell line expressed mRNA for the Th1 cytokines IFN-γ and TNF-α, as well as IL-10, and secreted these cytokines. In contrast, a T cell line from peptide + IFA-immunized LEW rats (which did not develop EAE) failed to secrete these cytokines. Although this line did not express TNF-α or IL-10 mRNA, IFN-γ mRNA was detected, suggesting posttranscriptional regulation of IFN-γ expression. Attempts to induce unresponsiveness in DA rats with encephalitogenic peptide-coupled splenocytes were also unsuccessful.

Mature T lymphocyte apoptosis--immune regulation in a dynamic and unpredictable antigenic environment

Apoptosis of mature T lymphocytes preserves peripheral homeostasis and tolerance by countering the profound changes in the number and types of T cells stimulated by diverse antigens. T cell apoptosis occurs in at least two major forms: antigen-driven and lymphokine withdrawal. These forms of death are controlled in response to local levels of IL-2 and antigen in a feedback mechanism termed propriocidal regulation. Active antigen-driven death is mediated by the expression of death cytokines such as FasL and TNF. These death cytokines engage specific receptors that assemble caspase-activating protein complexes. These signaling complexes tightly regulate cell death but are vulnerable to inherited defects. Passive lymphokine withdrawal death may result from the cytoplasmic activation of caspases that is regulated by mitochondria and the Bcl-2 protein. The human disease, Autoimmune Lymphoproliferative Syndrome (ALPS) is due to dominant-interfering mutations in the Fas/APO-1/CD95 receptor and other components of the death pathway. The study of ALPS patients reveals the necessity of apoptosis for preventing autoimmunity and allows the genetic investigation of apoptosis in humans. Immunological, cellular, and molecular evidence indicates that throughout the life of a T cell, apoptosis may be evoked in excessive, harmful, or useless clonotypes to preserve a healthy and balanced immune system.

Activation-induced apoptosis of autoreactive and alloreactive T lymphocytes in the target organ as a major mechanism of tolerance

Normal individuals have mature T lymphocytes that are capable of reacting to self-antigens and can be activated by cross-reacting environmental antigens. The mechanism that maintains immune tolerance and prevents these activated autoreactive T cells from causing autoimmune disease is unclear. We have previously hypothesized that activation-induced apoptosis of previously activated autoreactive T cells in the target organ is a major mechanism for maintaining tolerance. Here I review the current evidence to support this hypothesis. It is proposed that when activated autoreactive T cells enter the target organ, they are reactivated mainly by non-professional antigen-presenting cells (APC) and deleted by activation-induced apoptosis through the Fas (CD95) pathway before producing significant target organ damage. This apoptosis occurs because the reactivated T cells do not receive sufficient costimulation from the non-professional APC to up-regulate their expression of Bcl-2-related anti-apoptotic proteins, which inhibit the CD95 pro-apoptotic pathway. This is in contrast to the situation in peripheral lymphoid organs, where reactivation of T cells by professional APC results in sufficient costimulation-induced up-regulation of Bcl-2-related proteins to inhibit the CD95 pathway and allow T cell proliferation and survival as memory T cells. Activation-induced apoptosis of alloreactive T cells in allografts can similarly account for spontaneous allograft acceptance, as occurs after MHC-mismatched liver transplantation.