Since the basic mechanisms behind the beneficial effects of IFN-β in multiple sclerosis (MS) patients are still obscure, here we have investigated the effects of IFN-β gene disruption on the commonly used animal model for MS, experimental autoimmune encephalomyelitis (EAE). We show that IFN-β knockout (KO) mice are more susceptible to EAE than their wild-type (wt) littermates; they develop more severe and chronic neurological symptoms with more extensive CNS inflammation and demyelination. However, there was no discrepancy observed between wt and KO mice regarding the capacity of T cells to proliferate or produce IFN-γ in response to recall Ag. Consequently, we addressed the effect of IFN-β on encephalitogenic T cell development and the disease initiation phase by passive transfer of autoreactive T cells from KO or wt littermates to both groups of mice. Interestingly, IFN-β KO mice acquired a higher incidence and augmented EAE regardless of the source of T cells. This shows that the anti-inflammatory effect of endogenous IFN-β is predominantly exerted on the effector phase of the disease. Histopathological investigations of CNS in the effector phase revealed an extensive microglia activation and TNF-α production in IFN-β KO mice; this was virtually absent in wt littermates. This coincided with an increase in effector functions of T cells in IFN-β KO mice, as measured by IFN-γ and IL-4 production. We suggest that lack of endogenous IFN-β in CNS leads to augmented microglia activation, resulting in a sustained inflammation, cytokine production, and tissue damage with consequent chronic neurological deficits.

IntroductionThe immune system responds to invading pathogens by recognizing their antigenic structures, while remaining unresponsive to self antigens. This simplified model, however, is challenged by the understanding that autoreactivity is a common feature of healthy organisms and a part of peripheral tolerance mechanisms. To generate animal models for autoimmune diseases, susceptible species are often immunized with self antigens. However, not all immunogenic self antigens have the capacity to provoke a pathogenic autoimmune response, and some of them confer protection (1). A widely accepted animal model for human rheumatoid arthritis is collageninduced arthritis (CIA) in mice. CIA is induced by immunizing susceptible mouse strains with cartilage-derived triple helical type II collagen (CII). In mice expressing the MHC class II molecule H-2A q , the disease-mediating epitope is an immunodominant glycopeptide derived from position 260-270 of rat CII (2). In comparison with heterologous CII, mouse CII, although capable of inducing arthritis, provokes a much weaker immune response to the immunodominant epitope and induces a lower incidence of arthritis (3). However, mouse CII immunization induces a recall proliferative response toward multiple epitopes in addition to the MHC class II-restricted CII 260-270 peptide (4). The major epitopes share a common motif, with the strongest located at position 707-721 (mCII [707][708][709][710][711][712][713][714][715][716][717][718][719][720][721] ). By investigating the immune response to this epitope, surprisingly, we found that this peptide was not MHC I/II restricted, but was binding and presented by CD1d, a cluster of

The existence of T cells restricted for the MHC I-like molecule CD1 is well established, but the function of these cells is still obscure; one implication is that CD1-dependent T cells regulate autoimmunity. In this study, we investigate their role in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, using CD1-deficient mice on a C57BL/6 background. We show that CD1−/− mice develop a clinically more severe and chronic EAE compared with CD1+/+ C57BL/6 mice, which was histopathologically confirmed with increased demyelination and CNS infiltration in CD1−/− mice. Autoantigen rechallenge in vitro revealed similar T cell proliferation in CD1+/+ and CD1−/− mice but an amplified cytokine response in CD1−/− mice as measured by both the Th1 cytokine IFN-γ and the Th2 cytokine IL-4. Investigation of cytokine production at the site of inflammation showed a CNS influx of TGF-β1-producing cells early in the disease in CD1+/+ mice, which was absent in the CD1−/− mice. Passive transfer of EAE using an autoreactive T cell line induced equivalent disease in both groups, which suggested additional requirements for activation of the CD1-dependent regulatory pathway(s). When immunized with CFA before T cell transfer, the CD1−/− mice again developed an augmented EAE compared with CD1+/+ mice. We suggest that CD1 exerts its function during CFA-mediated activation, regulating development of EAE both through enhancing TGF-β1 production and through limiting autoreactive T cell activation, but not necessarily via effects on the Th1/Th2 balance.

A protective and anti-inflammatory role for CD1d-dependent NKT cells (NKTs) has been reported in experimental and human autoimmune diseases. However, their role in arthritis has been unclear, with conflicting reports of CD1d-dependent NKTs acting both as regulatory and disease-promoting cells in arthritis. These differing modes of action might be due to genetic differences of inbred mice and incomplete backcrossing of gene-modified mice. We therefore put special emphasis on controlling the genetic backgrounds of the mice used. Additionally, we used two different murine arthritis models, Ag-induced arthritis (AIA) and collagen-induced arthritis (CIA), to evaluate acute and chronic arthritis in CD1d knockout mice and mice depleted of NK1.1+ cells. CD1d-deficient mice developed more severe AIA compared with wild-type littermates, with a higher degree of inflammation and proteoglycan depletion. Chronic arthritis in CIA was also worse in the absence of CD1d-dependent NKTs. Elevated levels of Ag-specific IFN-γ production accompanied these findings rather than changes in IL-17α. Depletion of NK1.1+ cells supported these findings in AIA and CIA. This report provides support for CD1d-dependent NKTs being suppressor cells in acute and chronic arthritis, likely via inhibition of arthritogenic Th1 cells. These results make CD1d-dependent NKTs an attractive target for therapeutic intervention.