Type 1 diabetes (T1D) in non-obese diabetic (NOD) mice may be favored by immune dysregulation leading to the hyporesponsiveness of regulatory T cells and activation of effector T-helper type 1 (Th1) cells. The immunoregulatory activity of natural killer T (NKT) cells is well documented, and both interleukin (IL)-4 and IL-10 secreted by NKT cells have important roles in mediating this activity. NKT cells are less frequent and display deficient IL-4 responses in both NOD mice and individuals at risk for T1D (ref. 8), and this deficiency may lead to T1D (refs. 1,6-9). Thus, given that NKT cells respond to the alpha-galactosylceramide (alpha-GalCer) glycolipid in a CD1d-restricted manner by secretion of Th2 cytokines, we reasoned that activation of NKT cells by alpha-GalCer might prevent the onset and/or recurrence of T1D. Here we show that alpha-GalCer treatment, even when initiated after the onset of insulitis, protects female NOD mice from T1D and prolongs the survival of pancreatic islets transplanted into newly diabetic NOD mice. In addition, when administered after the onset of insulitis, alpha-GalCer and IL-7 displayed synergistic effects, possibly via the ability of IL-7 to render NKT cells fully responsive to alpha-GalCer. Protection from T1D by alpha-GalCer was associated with the suppression of both T- and B-cell autoimmunity to islet beta cells and with a polarized Th2-like response in spleen and pancreas of these mice. These findings raise the possibility that alpha-GalCer treatment might be used therapeutically to prevent the onset and recurrence of human T1D.

An immunoregulatory role has recently been attributed to the discrete subset of major histocompatibility complex class I-restricted NK1+ mature heat-stable antigen- (HSA-) thymocytes expressing an unusual Vbeta8-biased T cell receptor repertoire. NK1+ T cells are the main interleukin (IL)-4 producers upon priming. We have studied the size and the function of this subset in the nonobese diabetic (NOD) mouse, a model of spontaneous T cell-mediated autoimmune insulin-dependent diabetes. This study was complicated by the absence in this strain of the NK1.1 allele, the only one for which an antibody is available. To circumvent this difficulty, the cells, hereafter designated the NK1+-like T subset, were characterized by the use of monoclonal antibodies which showed the Vbeta8 bias in the CD44+ Ly-49+ MEL-14- 3G11- thymocyte subset of non-autoimmune strains and of its absence in class I-deficient (beta2-microglobulin-/-) mice. A clear deficit in the number of NK1+-like cells was evidenced at 3 weeks of age in NOD mice. It was still present at 8 weeks of age in the double-negative CD4-CD8- population. The functional anomaly was even more striking: NOD mouse NK1+-like thymocytes virtually lacked the ability to produce IL-4 at 3 weeks and still showed a very reduced capacity at 8 weeks. NK1+ T cell deficiency was also suggested in the periphery by the reduction of Ly-49A+ cells in the spleen of 3- and 8-week-old NOD mice and the absence of short-term production of IL-4 in vitro by NOD mouse spleen cells 90 min after the administration of anti-CD3 antibody, a response attributed to NK1+ T cells. Taken together, these data demonstrate a very early defect in NK1+-like T cells which could be involved in the genesis of autoimmunity in NOD mice through a deficiency in Th2 cell function.

IL-33 has recently been identified as a cytokine endowed with pro-Th2 functions, raising the question of its effect on invariant natural killer T cell (iNKT), which are potent IL-4 producers. Here, we report a two-fold increase of iNKT-cell counts in spleen and liver after a 7-day treatment of mice with IL-33, which results from a direct effect, given that purified iNKT cells express the T1/ST2 receptor constitutively and respond to IL-33 by in vitro expansion and functional activation. Conversely to the expected pro-Th2 effect, IL-33 induced a preferential increase in IFN-c rather than IL-4 production upon TCR engagement that depended on endogenous IL-12. Moreover, in combination with the pro-inflammatory cytokine IL-12, IL-33 enhanced IFN-c production by both iNKT and NK cells. Taken together these data support the conclusion that IL-33 can contribute as a co-stimulatory factor to innate cellular immune responses.Key words: Cytokines . Inflammation . Natural killer cells . Natural killer T cells .Th1/Th2 cells Introduction IL-33 (or IL-1F11) has recently been identified as a ligand of the orphan T1/ST2 receptor, a member of the IL-1 receptor (IL-1R) family [1] that was initially described as a nuclear factor, nuclear factor from high endothelial venules, abundantly expressed by endothelial cells in lymphoid tissues [2,3]. IL-33 induces its biological effects through a heterodimeric complex comprising the T1/ST2 receptor [1] and the IL-1R accessory protein (IL-1RAcP), another member of IL-1R family [4,5]. T1/ST2 engagement triggers a signalling pathway that requires MyD88 and NF-kB [1,4,6]. It has long been known that T1/ST2 is expressed primarily in mast and Th2 cells and is associated with important Th2 effector functions [7][8][9]. Accordingly, IL-33 has been found to promote Th2 cytokine production by mast cells and polarized T cells in vitro, and to induce pulmonary and mucosal Th2 inflammation when administered in vivo [1].iNKT cells constitute a distinctive subpopulation of mature ab-T cells bearing an invariant TCR a-chain together with NK-cell receptors [10,11]. They recognize glycosphingolipid Ags presented by CD1d, a non-classical class I-like Ag-presenting molecule, and respond rapidly to TCR stimulation with a-galactosylceramide (a-GC) by generating a number of cytokines, 1046particularly 11]. In most disease models in which iNKT cells have been implicated their beneficial or detrimental effects have been ascribed to either Th1 or Th2 cytokines [10,11]. It has also been established that the balance between these two profiles depends essentially on the microenvironment, which favours IL-4 or IFN-g production [12][13][14][15][16][17].Given its previously established pro-Th2 functions, IL-33 seemed a plausible candidate for the regulation of iNKT-cell activities, prompting us to investigate whether it could directly interact with this regulatory cell subset to drive IL-4 production. Starting from the observation that the incidence of iNKT cells was increased in spleen and liver of mice injected with ...