Differential roles of Fas ligand in spontaneous and actively induced autoimmune encephalomyelitis.

To determine the roles of Fas/Fas ligand (FasL) in autoimmunity, we studied spontaneous and actively induced autoimmune encephalomyelitis in 541 myelin basic protein-specific T cell receptor transgenic mice. We found that spontaneous autoimmune encephalomyelitis, which was initiated by unidentified microbial factors, was dramatically exacerbated in mice carrying Fas or FasL gene mutation. The exacerbation of autoimmune encephalomyelitis was reflected primarily by an increase in disease incidence and a decrease in spontaneous disease recovery. By contrast, actively induced encephalomyelitis, which was initiated by pertussis toxin, was significantly inhibited by Fas or FasL gene mutation. These results suggest that environmental factors that trigger autoimmune disease may determine not only whether disease will occur but also whether an immune molecule such as FasL will promote or inhibit the autoimmune process.

Experimental autoimmune encephalomyelitis in NF-kappa B-deficient mice:roles of NF-kappa B in the activation and differentiation of autoreactive T cells.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the CNS, which has long been used as an animal model for human multiple sclerosis. Development of autoimmune disease requires coordinated expression of a number of genes that are involved in the activation and effector functions of inflammatory cells. These include genes that encode costimulatory molecules, cytokines, chemokines, and adhesion molecules. Activation of these genes is regulated at the transcriptional level by several families of transcription factors. One of these is the NF-kappa B family, which is present in a variety of cell types and becomes highly activated at sites of inflammation. To test the roles of NF-kappa B in the development of autoimmune diseases, we studied EAE in mice deficient in one of the NF-kappa B isoforms, i.e., NF-kappa B1 (p50). We found that NF-kappa B1-deficient mice were significantly resistant to EAE induced by myelin oligodendrocyte glycoprotein. The resistance was primarily evidenced by a decrease in disease incidence, clinical score, and the degree of CNS inflammation. Furthermore, we established that the resistance to EAE in NF-kappa B1-deficient mice was associated with a deficiency of myelin oligodendrocyte glycoprotein-specific T cells to differentiate into either Th1- or Th2-type effector cells in vivo. These results strongly suggest that NF-kappa B1 plays crucial roles in the activation and differentiation of autoreactive T cells in vivo and that blocking NF-kappa B function can be an effective means to prevent autoimmune encephalomyelitis.

IL-6-deficient mice are resistant to experimental autoimmune encephalomyelitis: roles of IL-6 in the activation and differentiation of autoreactive T cells.

Although autoreactive T cells recognizing self myelin Ags are present in most individuals, autoimmune disease of the central nervous system is a relatively rare medical condition. Development of autoimmune disease may require not only the presence of autoreactive T cells but also that autoreactive T cells become activated. Activation of T cells may require a minimum of two signals: an Ag-specific signal delivered by MHC-peptide complex and a second signal delivered by costimulatory molecules or cytokines. Although in vitro studies have suggested that cytokines, especially proinflammatory cytokines such as IL-1, IL-6, and TNF are involved in T cell activation, their precise roles in vivo are not clear. To determine the roles of proinflammatory cytokines in T cell activation in vivo and in the development of autoimmune disease, we have studied experimental autoimmune encephalomyelitis (EAE) in mice deficient in IL-6. We found that IL-6-deficient mice were completely resistant to EAE induced by myelin oligodendrocyte glycoprotein (MOG), whereas IL-6-competent control mice developed EAE characterized by focal inflammation and demyelination in the central nervous system and deficiency in neurologic functions. Furthermore, we established that the resistance to EAE in IL-6-deficient mice was associated with a deficiency of MOG-specific T cells to differentiate into either Th1 or Th2 type effector cells in vivo. These results strongly suggest that IL-6 plays a crucial role in the activation and differentiation of autoreactive T cells in vivo and that blocking IL-6 function can be an effective means to prevent EAE.

Experimental autoimmune encephalomyelitis in intercellular adhesion molecule-1-deficient mice.

Intercellular adhesion molecule (ICAM)-1, or CD54, is a member of the immunoglobulin superfamily that binds to lymphocyte function-associated antigen-1 and macrophage-1 antigen. ICAM-1:LFA-1/Mac-1 interaction may be involved in both activation and extravasation of leukocytes. To determine the roles of ICAM-1 in the development of autoimmune disease, we studied experimental autoimmune encephalomyelitis (EAE) in mice deficient in ICAM-1. We found that T cell proliferation and TH1-type cytokine production in response to myelin antigen were significantly reduced in ICAM-1-deficient mice, whereas TH2-type cytokine IL-10 was increased. Unexpectedly, EAE induced by either myelin oligodendrocyte glycoprotein or myelin basic protein was significantly enhanced in mice deficient in ICAM-1. The enhancement was evidenced primarily by the increase in disease severity, mortality, and the degree of central nervous system inflammation. The cellular composition of the inflammatory infiltrates in the central nervous system is similar in control and ICAM-1-deficient mice. These results suggest that (1) ICAM-1 is involved in the activation of autoreactive TH-1, but not TH2 cells, and (2) ICAM-1 plays an important role in down-regulating autoimmune inflammation in the central nervous system.

Acceleration of experimental autoimmune encephalomyelitis in interleukin-10-deficient mice: roles of interleukin-10 in disease progression and recovery.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the central nervous system (CNS) which is often used as an animal model for human multiple sclerosis (MS). The disease is mediated by autoreactive lymphocytes recognizing myelin self-antigens. The autoreactive lymphocytes elicit autoimmune inflammation in the CNS and lead to demyelination and loss of neurological functions. Although autoimmune encephalomyelitis can lead to irreversible nervous tissue injury and demise of animals, EAE is often characterized by spontaneous disease recovery or remission. It is not known how EAE progression is regulated, nor is it clear how autoimmune inflammation in the CNS can resolve while the myelin-specific lymphocytes and myelin self-antigens remain in the animals. Cytokines, especially TH2-type cytokines, have long been suggested to play a role in regulating EAE. However, experiments using recombinant cytokines or neutralizing antibodies to cytokines have generated conflicting results. To determine the roles of interleukin (IL)-4 and IL-10 in experimental autoimmune encephalomyelitis, we have studied mice deficient in IL-4 or IL-10. We found that IL-10- but not IL-4-deficient mice had accelerated EAE following immunization with myelin oligodendrocyte glycoprotein (MOG). Importantly, spontaneous recovery from EAE occurred in normal and IL-4-deficient mice, but not in mice deficient in IL-10. Furthermore, we established that the acceleration of EAE in IL-10-deficient mice was associated with a decrease in IL-4 and an increase in IFN-gamma production in response to MOG antigen. These results strongly suggest that IL-10 plays a crucial role in the progression and recovery of autoimmune encephalomyelitis.

CTLA-4 is required for the induction of high dose oral tolerance.

Mucosal and systemic administrations of high dose antigens induce long-lasting peripheral T cell tolerance. We and others have shown that high dose peripheral T cell tolerance is mediated by anergy or deletion and is preceded by T cell activation. Co-stimulatory molecules B7-1 (CD80)/B7-2 (CD86) and their counter-receptors CD28/CTLA-4 play pivotal roles in T cell activation and immune regulation. In the present study, we examined the roles of the B7 co-stimulation pathway in the generation of high dose peripheral T cell tolerance. We found that blocking B7:CD28/CTLA-4 interaction at the time of tolerance induction partially prevented T cell tolerance, whereas selective blockade of B7:CTLA-4 interaction completely abrogated peripheral T cell tolerance induced by either oral or i.p. antigens. These results suggest that CTLA-4-mediated feedback regulation plays a crucial role in the induction of high dose peripheral T cell tolerance.

Amelioration of collagen-induced arthritis by CD95 (Apo-1/Fas)-ligand gene transfer.

Both rheumatoid arthritis and animal models of autoimmune arthritis are characterized by hyperactivation of synovial cells and hyperplasia of the synovial membrane. The activated synovial cells produce inflammatory cytokines and degradative enzymes that lead to destruction of cartilage and bones. Effective treatment of arthritis may require elimination of most or all activated synovial cells. The death factor Fas/Apo-1 and its ligand (FasL) play pivotal roles in maintaining self-tolerance and immune privilege. Fas is expressed constitutively in most tissues, and is dramatically upregulated at the site of inflammation. In both rheumatoid arthritis and animal models of autoimmune arthritis, high levels of Fas are expressed on activated synovial cells and infiltrating leukocytes in the inflamed joints. Unlike Fas, however, the levels of FasL expressed in the arthritic joints are extremely low, and most activated synovial cells survive despite high levels of Fas expression. To upregulate FasL expression in the arthritic joints, we have generated a recombinant replication-defective adenovirus carrying FasL gene; injection of the FasL virus into inflamed joints conferred high levels of FasL expression, induced apoptosis of synovial cells, and ameliorated collagen-induced arthritis in DBA/1 mice. The Fas-ligand virus also inhibited production of interferon-gamma by collagen-specific T cells. Coadministration of Fas-immunoglobulin fusion protein with the Fas-ligand virus prevented these effects, demonstrating the specificity of the Fas-ligand virus. Thus, FasL gene transfer at the site of inflammation effectively ameliorates autoimmune disease.

CD40L blockade prevents autoimmune encephalomyelitis and hampers TH1 but not TH2 pathway of T cell differentiation.

Although it is well established that CD40 and its ligand (CD40L) play pivotal roles in the development of humoral immunity, their roles in cell-mediated immunity and cell-mediated autoimmune diseases are not well defined. We report here that CD40:CD40L interaction is crucial for the development of experimental autoimmune encephalomyelitis (EAE), a prototype TH1-cell mediated autoimmune disease. Specific blockade of CD40L at the time of immunization markedly suppressed the incidence, mortality, day of onset, and clinical scores of EAE in (PLJ x SJL) F1 mice. Importantly, the disease suppression was not associated with anergy or deletion of autoreactive T cells but was accompanied by a drastic alteration of their cytokine profiles. The production of interferon (IFN)-gamma was markedly suppressed while that of interleukin (IL)-4 enhanced. These results suggest that CD40:CD40L interaction plays important roles in the differentiation of autoreactive TH1 versus TH2 cells in vivo, and that CD40L blockade is effective in preventing autoimmune encephalomyelitis.

B7 blockade prevents activation-induced cell death of thymocytes.

Although both B7 and its counter-receptor CD28 are expressed in the thymus, the role of B7 in thymic selection is not clear. We investigated the role of B7 in intrathymic deletion of antigen-specific T cells using a TCR transgenic model specific for antigen ovalbumin (OVA) and H-2Ad. Intraperitoneal injection of OVA induced apoptosis of thymocytes and drastic reduction of thymocyte numbers. This was significantly inhibited by co-injection of CTLA-4-Ig which blocks B7 co-stimulation. Deletion of T cells in the thymus following i.p. injection of OVA was associated with T cell pre-activation as demonstrated by T cell proliferation and cytokine production. Injection of CTLA-4-Ig blocked all these activation events and rescued thymocytes from activation-induced cell death. These results demonstrate that B7 is required for the activation-induced cell death of MHC class II-restricted thymocytes in vivo.