Endogenous collagen peptide activation of CD1d-restricted NKT cells ameliorates tissue-specific inflammation in mice.

NKT cells in the mouse recognize antigen in the context of the MHC class I-like molecule CD1d and play an important role in peripheral tolerance and protection against autoimmune and other diseases. NKT cells are usually activated by CD1d-presented lipid antigens. However, peptide recognition in the context of CD1 has also been documented, although no self-peptide ligands have been reported to date. Here, we have identified an endogenous peptide that is presented by CD1d to activate mouse NKT cells. This peptide, the immunodominant epitope from mouse collagen type II (mCII707-721), was not associated with either MHC class I or II. Activation of CD1d-restricted mCII707-721-specific NKT cells was induced via TCR signaling and classical costimulation. In addition, mCII707-721-specific NKT cells induced T cell death through Fas/FasL, in an IL-17A-independent fashion. Moreover, mCII707-721-specific NKT cells suppressed a range of in vivo inflammatory conditions, including delayed-type hypersensitivity, antigen-induced airway inflammation, collagen-induced arthritis, and EAE, which were all ameliorated by mCII707-721 vaccination. The findings presented here offer new insight into the intrinsic roles of NKT cells in health and disease. Given the results, endogenous collagen peptide activators of NKT cells may offer promise as novel therapeutics in tissue-specific autoimmune and inflammatory diseases.

CD1d-dependent NKT cells play a protective role in acute and chronic arthritis models by ameliorating antigen-specific Th1 responses.

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-gamma production accompanied these findings rather than changes in IL-17alpha. 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.

CD1-dependent regulation of chronic central nervous system inflammation in experimental autoimmune encephalomyelitis.

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 CD+/+ and CD1-/- mice but an amplified cytokine response in CD1-/- mice as measured by both the Th1 cytokine IFN-gamma and the Th2 cytokine IL-4. Investigation of cytokine production at the site of inflammation showed a CNS influx of TGF-beta1-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-beta1 production and through limiting autoreactive T cell activation, but not necessarily via effects on the Th1/Th2 balance.

IFN-beta gene deletion leads to augmented and chronic demyelinating experimental autoimmune encephalomyelitis.

Since the basic mechanisms behind the beneficial effects of IFN-beta in multiple sclerosis (MS) patients are still obscure, here we have investigated the effects of IFN-beta gene disruption on the commonly used animal model for MS, experimental autoimmune encephalomyelitis (EAE). We show that IFN-beta 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-gamma in response to recall Ag. Consequently, we addressed the effect of IFN-beta 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-beta 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-beta 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-alpha production in IFN-beta KO mice; this was virtually absent in wt littermates. This coincided with an increase in effector functions of T cells in IFN-beta KO mice, as measured by IFN-gamma and IL-4 production. We suggest that lack of endogenous IFN-beta in CNS leads to augmented microglia activation, resulting in a sustained inflammation, cytokine production, and tissue damage with consequent chronic neurological deficits.