Synthetic glycolipid OCH prevents insulitis and diabetes in NOD mice
Introduction
Non-obese diabetic (NOD) mice develop spontaneous autoimmune (type I) diabetes (T1D) very similar to the human disease. In female mice, insulitis usually begins at 3 to 5 weeks of age, eventually leading to β-cell destruction and overt diabetes by 4 to 6 months of age. Autoimmune destruction of β-cells is preceded by infiltration of pancreatic islets by macrophages, B cells and T cells. The capacity to transfer disease by islet specific T cells purified from diabetic NOD mice or T cell clones demonstrates the key role of T cells in the pathogenesis of diabetes. Th1 type CD4 cells, which preferentially secrete IFN-γ and TNF-α and CD8 T cells, have been implicated in the development of diabetes in NOD mice [1], [2]. In parallel with these effector T cells, regulatory cells including CD4+CD25+ T cells have been suggested to inhibit the development of diabetes. Although the mechanisms of suppressive effect of these regulatory T cells are not fully understood, it is believed that an imbalance between autoreactive effector T cells and regulatory T cells may trigger the development of destructive insulitis and T1D [3]. Previous studies indicate that the β-cell-destructive immune response in NOD mice is biased toward Th1 and treatment with Th2 cytokines such as IL-4 or IL-10 have been shown to prevent the onset of spontaneous diabetes [4], [5], [6], [7], [8].
Natural killer T (NKT) cells are a unique subset of T cells that coexpress receptors of the NK lineage and α/β T cell receptor (TCR) [9], [10], [11]. NKT cells express an invariant TCRα chain (encoded by a Vα14-Jα281 rearrangement in mice and a homologous Vα24-Jα15 rearrangement in humans). Unlike conventional T cells that recognize peptides in association with MHC, NKT cells recognize glycolipid antigens such as α-galactosylceramide (α-GC) bound by the non-polymorphic MHC class I-like protein CD1d [12]. One striking feature of NKT cells is their capacity to secrete large amounts of cytokines including IL-4 and IFN-γ in response to TCR ligation. Although the precise function of NKT cells remains to be elucidated, evidence indicates that NKT cells play critical roles in the regulation of autoimmune responses [13], [14], [15]. Abnormalities in the number and function of NKT cells have been observed in patients with autoimmune diseases as well as in a variety of mouse strains that are genetically predisposed for development of autoimmune diseases. The putative involvement of NKT cells in the control of islet β-cell reactive T cells in NOD mice was suggested by prevention of diabetes following infusion of NKT cell-enriched thymocyte preparations [16] and by over-expression of NKT cells in Vα14-Jα281 transgenic NOD mice [17]. Moreover, several recent studies have investigated the effect of treating NOD mice with α-GC [18], [19], [20], [21]. When started at around 3 or 4 weeks of age, repeated injections at least once a week delayed the onset and reduced the incidence of diabetes by inducing Th2 bias of autoreactive T cells. We have recently developed a synthetic glycolipid ligand, OCH, which stimulates NKT cells to selectively produce IL-4. OCH is a synthetic glycolipid, sphingosine truncation analogue of α-GC [22]. Administration of OCH inhibited experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis (CIA) by inducing Th2 bias of autoreactive T cells [22], [23]. These findings led us to examine the effect of OCH on the development of diabetes in NOD mice.
In the present study, we show that OCH can inhibit the development of insulitis and diabetes in NOD mice by inducing a Th2 bias of autoreactive T cells. These results imply that targeting NKT cells with OCH could be an attractive means for intervention in T1D.
Section snippets
Mice
C57BL/6(B6) mice were purchased from CLEA Laboratory Animal Corp. (Tokyo, Japan). NOD/Shi mice were obtained from CLEA Japan (Tokyo, Japan). The animals were kept under specific pathogen-free conditions. We followed the guidelines for the use and care of laboratory animals of National Institute of Neuroscience, NCNP.
In vitro responses of NKT cells to α-GC or OCH
Splenocytes of naïve B6 mice were cultured with α-GC or OCH in RPM I1640 medium supplemented with 5 × 10−5 M 2-ME, 2 mM l-glutamine, 100 U/mg/ml penicillin/streptomycin, and 1% syngenic
OCH induces selective production of Th2 cytokines in NOD mice
NOD mice have been reported to exhibit the defect in the number and the function of NKT cells [26]. We first examined whether OCH stimulates proliferation and selective IL-4 production in NOD mice. Spleen cells from NOD mice proliferated in response to in vitro stimulation with OCH and produced significant amounts of IL-4 and IL-10, although OCH was less active in inducing cell proliferation and the cytokine production compared with α-GC (Fig. 1A). In contrast, IFN-γ was barely detectable in
Discussion
In this study, we found that OCH treatment prevented spontaneous autoimmune diabetes in NOD mice, a model of human type I diabetes, by inducing Th2 bias. OCH treatment strongly inhibited insulitis in NOD mice. The proportion of IL-10 producing cells among infiltrated leukocytes was increased in OCH-treated mice. Although the correlation between a defect in NKT cells and the susceptibility of diabetes in NOD mice is still debated [13], [14], [15], the putative involvement of NKT cells in the
Acknowledgements
This work was supported by the Pharmaceuticals and Medical Devices Agency (PMDA), Grant-in-Aid for Scientific Research (B) 14370169 from Japan Society for the Promotion of Science, Uehara Memorial Foundation, Kato Memorial Bioscience Foundation and Kanae Foundation for Life & Socio-Medical Science.
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2016, Journal of AutoimmunityCitation Excerpt :Restoration of iNKT cell numbers by transgenic overexpression of the Vα24Jα18 TCR [190] or adoptive transfer of iNKT cells from healthy mice [192] protected NOD mice from developing diabetes. This protection was mediated in part by IL-4 production by iNKT cells [190,193] and was associated with migration of tolerogenic CD1c+ mDC to the pancreatic lymph nodes [194]. Th2-biased iNKT cell numbers are also low in patients with multiple sclerosis (MS) and they increase in patients during remission [195,196].