Differential regulation of Th1 and Th2 functions of NKT cells by CD28 and CD40 costimulatory pathways

Freshly isolated Valpha24+ CD4+ invariant natural killer T cells activated by alpha-galactosylceramide-pulsed B cells promote both IgG and IgE production

CD1d-restricted invariant natural killer T (iNK T) cells activated by their experimental ligand alpha-galactosylceramide (alpha-GC) can produce both T helper 1 (Th1) and Th2 cytokines and display regulatory functions. Recent studies identified CD4(+) and CD4(-) CD8(-) double-negative (DN) iNK T cells as the two major components of the human population and suggest that they display a Th2 and a Th1 profile, respectively. We compared the Th2-promoting activity of freshly isolated human CD4(+) and DN iNK T cells in terms of their capacity to induce Ig production by autologous B cells. Secretion of IgG and IgE but not IgM was enhanced by the CD4(+) T cell subset (including iNK T cells) but not by its DN counterpart. iNK T cells were directly responsible for this pro-Th2 effect, as demonstrated by the requirement for both alpha-GC stimulation and CD1d presentation, as well as by its disappearance upon iNK T cell depletion. Interaction with iNK T cells led to progressive accumulation of isotype-switched and activated B cells. Myeloid dendritic cells (DC) completely block the induction of Ig production in co-culture. This dominant inhibitory effect of myeloid DC was concomitant with a specific loss of interleukin (IL)-4 production by CD4(+) iNK T but not by conventional T cells. These data support the conclusion that, conversely to the interferon (IFN)-gamma-producing DN human iNK T cell population, interleukin (IL)-4-producing CD4(+) iNK T cells can activate and help B cells to produce both IgG and IgE through a CD1d-dependent mechanism, in keeping with a functional Th1/Th2 dichotomy between these subsets.

Nutritional formula improved immune profiles of seniors living in nursing homes

OBJECTIVES

To assess whether an experimental nutritional formula (EXP) supports immune function in seniors living in long-term care facilities.

DESIGN

Prospective, randomized, double-blind, controlled trial conducted September 2002 through January 2003.

SETTING

North central Florida nursing homes.

PARTICIPANTS

Subjects aged 65 and older (n = 157).

INTERVENTION

Subjects received 240 mL/d of EXP or standard liquid nutrition (CON) for 4 weeks before and 6 weeks after an influenza vaccination.

MEASUREMENTS

Influenza vaccine antibody responses, immunophenotyping, lymphocyte activation, cytokines, and clinical measures (fever, number of prescribed antibiotics).

RESULTS

Ninety-two subjects (n = 40, CON; n = 52, EXP) completed the study. Geometric mean antibody titers were similar between groups, yet the percentage of subjects with H1N1 antibody titers greater than 100 postvaccination was higher in the EXP group than in the CON group (43% vs 23%, P=.047). Similar trends were found for the percentage of subjects (intent to treat) with fourfold increases against the B/Hong Kong component (64% vs 46%, P = .09) or with H3N2 antibody titers of 40 or more (97% vs 89%, P=.06). EXP subjects had higher levels of influenza-activated lymphocytes (CD69+ and CD25+). Cytokine production after mitogen activation was lower in EXP than CON subjects (interleukin (IL)-6: 20+/-3 vs 29+/-3 ng/mL, P = .045; IL-10: 310+/-60 vs 603+/-140 pg/mL, P = .06). Fewer EXP subjects were treated for fever (5% vs 16%, P = .02) or prescribed antibiotics (7 vs 11 new antibiotics/100 days of study, P = .06).

CONCLUSION

Seniors consuming the EXP formula demonstrated enhanced immune function, indicated by increased influenza vaccine response and lymphocyte activation, less fever, and fewer newly prescribed antibiotics than those consuming a standard ready-to-drink nutritional supplement.

Human natural killer T cells are heterogeneous in their capacity to reprogram their effector functions

Background

Natural killer T (NKT) cells are a subset of T cells that help potentiate and regulate immune responses. Although human NKT cell subsets with distinct effector functions have been identified, it is unclear whether the effector functions of these subsets are imprinted during development or can be selectively reprogrammed in the periphery.

Results

We found that neonatal NKT cells are predominantly CD4+ and express higher levels of CCR7 and CD62L and lower levels of CD94 and CD161 than adult CD4+ or CD4− NKT cell subsets. Accordingly, neonatal NKT cells were more flexible than adult CD4+ NKT cells in their capacity to acquire Th1- or Th2-like functions upon either cytokine-mediated polarization or ectopic expression of the Th1 or Th2 transcription factors T-bet and GATA-3, respectively. Consistent with their more differentiated phenotype, CD4- NKT cells were predominantly resistant to functional reprogramming and displayed higher cytotoxic function. In contrast to conventional T cells, neither the expression of CXCR3 nor the cytotoxic capacity of neonatal NKT cells could be reprogrammed.

Conclusions and Significance

Together, these results suggest that neonatal CD4+, adult CD4+, and adult CD4− NKT may represent unique states of maturation and that some functions of human NKT cells may be developmentally imprinted, while others are acquired similar to conventional T cell subsets during peripheral maturation and differentiation. Given the potent immuno-regulatory functions of NKT cells, these findings have important implications for the development of novel NKT cell-based therapeutics and vaccines.

IL-21-induced Bepsilon cell apoptosis mediated by natural killer T cells suppresses IgE responses

Epidemiological studies have suggested that the recent increase in the incidence and severity of immunoglobulin (Ig)E-mediated allergic disorders is inversely correlated with Mycobacterium bovis bacillus Calmette Guerin (BCG) vaccination; however, the underlying mechanisms remain uncertain. Here, we demonstrate that natural killer T (NKT) cells in mice and humans play a crucial role in the BCG-induced suppression of IgE responses. BCG-activated murine Vα14 NKT cells, but not conventional CD4 T cells, selectively express high levels of interleukin (IL)-21, which preferentially induces apoptosis in Bɛ cells. Signaling from the IL-21 receptor increases the formation of a complex between Bcl-2 and the proapoptotic molecule Bcl-2–modifying factor, resulting in Bɛ cell apoptosis. Similarly, BCG vaccination induces IL-21 expression by human peripheral blood mononuclear cells (PBMCs) in a partially NKT cell–dependent fashion. BCG-activated PBMCs significantly reduce IgE production by human B cells. These findings provide new insight into the therapeutic effect of BCG in allergic diseases.

Expression of CD1d Molecules by Human Schwann Cells and Potential Interactions with Immunoregulatory Invariant NK T Cells

CD1d-restricted NKT cells expressing invariant TCR alpha-chains (iNKT cells) produce both proinflammatory and anti-inflammatory cytokines rapidly upon activation, and are believed to play an important role in both host defense and immunoregulation. To address the potential implications of iNKT cell responses for infectious or inflammatory diseases of the nervous system, we investigated the expression of CD1d in human peripheral nerve. We found that CD1d was expressed on the surface of Schwann cells in situ and on primary or immortalized Schwann cell lines in culture. Schwann cells activated iNKT cells in a CD1d-dependent manner in the presence of alpha-galactosylceramide. Surprisingly, the cytokine production of iNKT cells stimulated by alpha-galactosylceramide presented by CD1d+ Schwann cells showed a predominance of Th2-associated cytokines such as IL-5 and IL-13 with a marked deficiency of proinflammatory Th1 cytokines such as IFN-gamma or TNF-alpha. Our findings suggest a mechanism by which iNKT cells may restrain inflammatory responses in peripheral nerves, and raise the possibility that the expression of CD1d by Schwann cells could be relevant in the pathogenesis of infectious and inflammatory diseases of the peripheral nervous system.

Invariant natural killer T cells in the response to bacteria: the advent of specific antigens

Invariant natural killer T (iNKT) cells are a unique subset of T lymphocytes that have been implicated in diverse immune reactions, ranging from self-tolerance and development of autoimmunity to responses to pathogens and tumors. Although some degree of autoreactivity of iNKT cells has been shown, it remained controversial whether the T-cell antigen receptor expressed by these cells could recognize microbial antigens, hampering the investigation of their physiological role during tolerance and immunity. Several recent publications have now defined natural antigens for the majority of iNKT cells in some Proteobacteria and in Borrelia burgdorferi, demonstrating specificity of these cells for microbes in addition to self-reactivity. The characterization of natural antigens from bacteria, and the iNKT cell response to bacteria containing them, are decisive steps toward the clarification of the natural role of iNKT cells in host defense against pathogens, and will likely spur numerous findings in the near future.

FcgammaRIII engagement provides activating signals to NKT cells in antibody-induced joint inflammation

NKT cells promote antibody-induced arthritis, but the mechanism by which NKT cells are activated in this model remains unclear. It has been proposed that Fcgamma receptor (FcgammaR) contributes to NKT cell activation in antibody-induced arthritis. To address this issue, we explored the functions of FcgammaR on NKT cells in antibody-induced arthritis. RT-PCR and flow cytometric analysis demonstrated that NKT cells constitutively express surface FcgammaRIII but not FcgammaRI, -II, or -IV. FcgammaRIII engagement by aggregated IgG on NKT cells enhanced CD25 and CD69 expression, whereas FcgammaR(-/-) mouse NKT cells did not enhance activation. FcgammaRIII engagement on NKT cells enhanced the production of IL-4, IL-10, IL-13, and IFN-gamma, whereas FcgammaR-deficient NKT cells did not alter the production of these cytokines after aggregated IgG treatment. However, FcgammaR-deficient NKT cells were functionally intact in terms of TCR-induced activation. Moreover, adoptive transfer of FcgammaR-deficient NKT cells could not restore inflammation or TGF-beta production in the joint tissues of CD1d(-/-) mice, whereas adoptive transfer of wild-type NKT cells induced arthritis and reduced TGF-beta production in joint tissues. We conclude that FcgammaRIII engagement by IgG in joint tissues provides activating signals to NKT cells in antibody-induced arthritis.

Invariant V(alpha)19i T cells regulate autoimmune inflammation

T cells expressing an invariant V(alpha)19-J(alpha)33 T cell receptor alpha-chain (V(alpha)19i TCR) are restricted by the nonpolymorphic major histocompatibility complex class Ib molecule MR1. Whether V(alpha)19i T cells are involved in autoimmunity is not understood. Here we demonstrate that T cells expressing the V(alpha)19i TCR transgene inhibited the induction and progression of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Similarly, EAE was exacerbated in MR1-deficient mice, which lack V(alpha)19i T cells. EAE suppression was accompanied by reduced production of inflammatory mediators and increased secretion of interleukin 10. Interleukin 10 production occurred at least in part through interactions between B cells and V(alpha)19i T cells mediated by the ICOS costimulatory molecule. These results suggest an immunoregulatory function for V(alpha)19i T cells.

Engagement of glucocorticoid-induced TNF receptor costimulates NKT cell activation in vitro and in vivo

Glucocorticoid-induced TNF receptor (GITR) is known to provide costimulatory signals to CD4+CD25- and CD4+CD25+ T cells during immune responses in vivo. However, the functional roles of GITR expressed on NKT cells have not been well characterized. In this study, we have explored the functions of GITR as a costimulatory factor on NKT cells. GITR was found to be constitutively expressed on NKT cells and its expression was enhanced by TCR signals. GITR engagement using DTA-1, an agonistic mAb against GITR, in the presence of TCR signals, augmented IL-2 production, the expression of activation markers, cell cycle progression, and the nuclear translocations of NF-kappaB p50 and p65. Furthermore, GITR engagement enhanced the production of IL-4, IL-10, IL-13, and IFN-gamma by NKT cells and the expression level of phosphorylated p65 in NKT cells in the presence of TCR engagement, indicating that GITR provides costimulatory signals to NKT cells. The costimulatory effects of GITR on NKT cells were comparable to those of CD28 in terms of cytokine production. Moreover, the coinjection of DTA-1 and alpha-galactosylceramide into B6 mice induced more IL-4 and IFN-gamma production than the coinjection of control mAbs and alpha-galactosylceramide. In addition, the adoptive transfer of DTA-1-pretreated NKT cells into CD1d(-/-) mice attenuated hypersensitivity pneumonitis more than control IgG pretreated NKT cells in these mice. These findings demonstrate that GITR engagement on NKT cells modulates immune responses in hypersensitivity pneumonitis in vivo. Taken together, our findings suggest that GITR engagement costimulates NKT cells and contributes to the regulation of immune-associated disease processes in vivo.

P2X7 receptors regulate NKT cells in autoimmune hepatitis

Adenine nucleotides induce danger signals in T cells via purinergic receptors, raising the question whether they exert similar effects on innate immunity. Here we show that micromolar concentrations of nicotinamide adenine dinucleotide (NAD) induce a rapid increase of annexin V staining in NKT cells in vitro, a response that requires expression of P2X(7)Rs. Consistent with this result, treatment of mice with NAD causes a temporary decrease of NKT cells in the liver and protects from Con A- and alpha-galactosylceramide-induced hepatitis, both of which require functional NKT cells. Resistance to liver injury is associated with decreased cytokine production by NKT cells in NAD-treated mice. In contrast, when NAD is injected into Con A- or alpha-galactosylceramide-primed mice, liver injury is exacerbated and cytokine production by NKT cells is increased. This effect is caused by P2X(7)R-mediated stimulation of activated NKT cells. In agreement, mice lacking P2X(7)Rs on lymphocytes suffer reduced liver injury, and animals lacking ADP-ribosyltransferase, the enzyme that uses NAD to attach ADP-ribosyl groups to cell surfaces, are also resistant to Con A-induced hepatitis. These results prompt the conclusion that engagement of P2X(7)Rs on NKT cells inhibits naive, while stimulating activated cells, resulting in suppression or stimulation of autoimmune hepatitis.

Role of natural killer cell subsets in cardiac allograft rejection

To achieve donor-specific immune tolerance to allogeneic organ transplants, it is imperative to understand the cell types involved in acute allograft rejection. In wild-type mice, CD4(+) T cells are necessary and sufficient for acute rejection of cardiac allografts. However, when T-cell responses are suboptimal, such as in mice treated with costimulation-targeting agents or in CD28-deficient mice, and perhaps in transplanted patients taking immunosuppressive drugs, the participation of other lymphocytes such as CD8(+) T cells and NK1.1(+) cells becomes apparent. We found that host NK but not NKT cells were required for cardiac rejection. Ly49G2(+) NK cells suppressed rejection, whereas a subset of NK cells lacking inhibitory Ly49 receptors for donor MHC class I molecules was sufficient to promote rejection. Notably, rejection was independent of the activating receptors Ly49D and NKG2D. Finally, our experiments supported a mechanism by which NK cells promote expansion and effector function of alloreactive T cells. Thus, therapies aimed at specific subsets of NK cells may facilitate transplantation tolerance in settings of impaired T-cell function.

V alpha 24-invariant NKT cells from patients with allergic asthma express CCR9 at high frequency and induce Th2 bias of CD3+ T cells upon CD226 engagement

We have demonstrated that Valpha24(+)Vbeta11(+) invariant (Valpha24(+)i) NKT cells from patients with allergic asthma express CCR9 at high frequency. CCR9 ligand CCL25 induces chemotaxis of asthmatic Valpha24(+)i NKT cells but not the normal cells. A large number of CCR9-positive Valpha24(+)i NKT cells are found in asthmatic bronchi mucosa, where high levels of Th2 cytokines are detected. Asthmatic Valpha24(+)i NKT cells, themselves Th1 biased, induce CD3(+) T cells into an expression of Th2 cytokines (IL-4 and IL-13) in cell-cell contact manner in vitro. CD226 are overexpressed on asthmatic Valpha24(+)i NKT cells. CCL25/CCR9 ligation causes directly phosphorylation of CD226, indicating that CCL25/CCR9 signals can cross-talk with CD226 signals to activate Valpha24(+)i NKT cells. Prestimulation with immobilized CD226 mAb does not change ability of asthmatic Valpha24(+)i NKT cells to induce Th2-cytokine production, whereas soluble CD226 mAb or short hairpin RNA of CD226 inhibits Valpha24(+)i NKT cells to induce Th2-cytokine production by CD3(+) T cells, indicating that CD226 engagement is necessary for Valpha24(+)i NKT cells to induce Th2 bias of CD3(+) T cells. Our results are providing with direct evidence that aberration of CCR9 expression on asthmatic Valpha24(+)i NKT cells. CCL25 is first time shown promoting the recruitment of CCR9-expressing Valpha24(+)i NKT cells into the lung to promote other T cells to produce Th2 cytokines to establish and develop allergic asthma. Our findings provide evidence that abnormal asthmatic Valpha24(+)i NKT cells induce systemically and locally a Th2 bias in T cells that is at least partially critical for the pathogenesis of allergic asthma.

Immunoregulation of Autoimmunity by Natural Killer T Cells

Natural killer T (NKT) cells are a conserved subpopulation of lymphocytes that recognize glycolipid antigens in a CD1d context. Upon activation through their semi-invariant T cell receptor, these cells rapidly release large amounts of immunomodulating Th1 and Th2 cytokines. NKT cells have therefore been implicated in immune responses controlling various diseases, including infection, cancer, transplantation, and autoimmunity. Stimulation of the immunoregulatory capacity of NKT cells by the prototypical antigen alpha-galactosylceramide results in amelioration of disease in several animal models. This review will focus on the current knowledge of human NKT cells and their role in autoimmune diseases. The features of these cells and their importance in regulation of autoimmunity suggest that NKT cell-based therapies might be an interesting approach for the treatment of autoimmune diseases.

Preferential Th2 polarization by OCH is supported by incompetent NKT cell induction of CD40L and following production of inflammatory cytokines by bystander cells in vivo

The altered glycolipid ligand OCH is a selective inducer of T(h)2 cytokines from NKT cells and a potent therapeutic reagent for T(h)1-mediated autoimmune diseases. Although we have previously shown the intrinsic molecular mechanism of preferential IL-4 production by OCH-stimulated NKT cells, little is known about the extrinsic regulatory network for IFN-gamma production. Here we demonstrate that OCH induces lower production of IFN-gamma, not only by NKT cells but also by NK cells compared with alpha-galactosylceramide. OCH induced lower IL-12 production due to ineffective primary IFN-gamma and CD40 ligand expression by NKT cells, and resulted in lower secondary IFN-gamma induction. Co-injection of a sub-optimal dose of IFN-gamma and stimulatory anti-CD40 mAb compensates for the lower induction of IL-12 by OCH administration. IL-12 converts OCH-induced cytokine expression from IL-4 predominance to IFN-gamma predominance. Furthermore, CpG oligodeoxynucleotide augmented IL-12 production when co-administrated with OCH, resulting in increased IFN-gamma production. Taken together, the lower IL-12 production and subsequent lack of secondary IFN-gamma burst support the effective T(h)2 polarization of T cells by OCH. In addition, highlighted in this study is the characteristic property of OCH that can induce the differential production of IFN-gamma or IL-4 according to the availability of IL-12.

Natural killer T cells are required for the development of a superantigen-driven T helper type 2 immune response in mice

We show, here, that one single injection or weekly injections of staphylococcal enterotoxin B (SEB), starting in 1-day-old newborn mice, induced a powerful immune response with a T helper type 2 (Th2) pattern, as judged by the isotype and cytokine profile, with the production of large amounts of SEB-specific immunoglobulin G1 (IgG1), detectable levels of SEB-specific IgE and increased production of interleukin-4 by spleen cells. These protocols also induced an increase in the levels of total IgE in the serum. Memory of SEB was transferred to secondary recipients by using total spleen cells from primed animals. The secondary humoral response in transferred mice was diminished if spleen cells from SEB-treated mice were previously depleted of CD3+ or Vbeta8+ T cells or NK1.1+ cells. In vivo depletion of NK1.1+ cells in adult mice resulted in a marked reduction in the SEB-specific antibody response in both the primary and secondary immune responses. Additionally, purified NK1.1+ T cells were able to perform SEB-specific helper B-cell actions in vitro and in vivo. These results suggest that NK1.1+ T cells are required for the full development of humoral immunological memory, whilst making neonatal tolerance to SEB unachievable.

LNFPIII/LeX-stimulated macrophages activate natural killer cells via CD40-CD40L interaction

Lacto-N-fucopentaose III (LNFPIII) is a human milk sugar containing the biologically active Lewis X (LeX) trisaccharide. LNFPIII/LeX is also expressed by immunosuppressive helminth parasites, by bacteria, and on a number of tumor/cancer cells. In this report, we first demonstrate that LNFPIII activates macrophages in vitro as indicated by upregulation of Gr-1 expression on F4/80(+) cells. Further, we investigated the effect of LNFPIII-activated macrophages on NK cell activity. We found that LNFPIII-stimulated F4/80(+) cells were able to activate NK cells, inducing upregulation of CD69 expression and gamma interferon (IFN-gamma) production. The experiments show that NK cell activation is macrophage dependent, since NK cells alone did not secrete IFN-gamma in response to LNFPIII. Furthermore, we found that activation of NK cells by glycan-stimulated macrophages required cell-cell contact. As part of the cell-cell contact mechanism, we determined that CD40-CD40L interaction was critical for IFN-gamma secretion by NK cells, as the addition of anti-CD40L antibodies to the coculture blocked IFN-gamma production. We also demonstrated that LNFPIII-stimulated macrophages secrete prostaglandin E(2), interleukin-10 (IL-10), and tumor necrosis factor alpha (TNF-alpha) but a very low level of IL-12. Interestingly, addition of anti-TNF-alpha, anti-IL-10, or anti-IL-12 monoclonal antibodies did not significantly alter NK cell activity. Our data show that these soluble mediators are not critical for LNFPIII-stimulated macrophage activation of NK cells and provide further evidence for the importance of cell-cell contact and CD40-CD40L interactions between macrophages and NK cells.

NKT cell stimulation with glycolipid antigen in vivo: costimulation-dependent expansion, Bim-dependent contraction, and hyporesponsiveness to further antigenic challenge

Activation of NKT cells using the glycolipid alpha-galactosylceramide (alpha-GalCer) has availed many investigations into their immunoregulatory and therapeutic potential. However, it remains unclear how they respond to stimulation in vivo, which costimulatory pathways are important, and what factors (e.g., Ag availability and activation-induced cell death) limit their response. We have explored these questions in the context of an in vivo model of NKT cell dynamics spanning activation, population expansion, and subsequent contraction. Neither the B7/CD28 nor the CD40/CD40L costimulatory pathway was necessary for cytokine production by activated NKT cells, either early (2 h) or late (3 days) after initial stimulation, but both pathways were necessary for normal proliferative expansion of NKT cells in vivo. The proapoptotic Bcl-2 family member Bim was necessary for normal contraction of the NKT cell population between days 3-9 after stimulation, suggesting that the pool size is regulated by apoptotic death, similar to that of conventional T cells. Ag availability was not the limiting factor for NKT cell expansion in vivo, and a second alpha-GalCer injection induced a very blunted response, whereby cytokine production was reduced and further expansion did not occur. This appeared to be a form of anergy that was intrinsic to NKT cells and was not associated with inhibitory NK receptor signaling. Furthermore, NKT cells from mice pre-challenged with alpha-GalCer in vivo showed little cytokine production and reduced proliferation in vitro. In summary, this study significantly enhances our understanding of how NKT cells respond to primary and secondary antigenic challenge in vivo.

CD1d ligation on human monocytes directly signals rapid NF-kappaB activation and production of bioactive IL-12

Natural killer T cells (NKT cells) expressing a semi-invariant CD1d-reactive T cell receptor (invariant NKT, iNKT) can be rapidly activated by monocytes or immature dendritic cells (iDCs) bearing a CD1d-presented glycolipid antigen and can in turn stimulate these myeloid cells to mature and produce IL-12. Previous studies have shown that iNKT-produced IFNgamma and CD40 ligand contribute to this dendritic cell maturation. This study demonstrates that CD1d ligation alone, in the absence of iNKT, could rapidly (within 24 h) stimulate production of bioactive IL-12p70 by CD1d+ human peripheral blood monocytes as well as iDCs. IFNgamma alone had no effect, but it markedly enhanced CD1d-stimulated IL-12 production. Monocyte differentiation, as assessed by CD40 and CD1a up-regulation, was also accelerated by CD1d stimulation, consistent with this representing a physiological response. CD1d ligation on the human monocytic cell line THP-1 similarly specifically stimulated IL-12 production. Biochemical studies showed that IL-12 release correlated with rapid phosphorylation of IkappaB, a critical step in NF-kappaB activation. Selective NF-kappaB inhibition blocked this CD1d-stimulated IL-12 production. Finally, CD1d ligation could also enhance IL-12 production in the presence of suboptimal LPS or CD40 stimulation. These findings demonstrate an innate immune signaling function for CD1d and provide a mechanism for the rapid activation of monocytes and iDCs by CD1d-reactive T cells.

The diverse functions of CD1d-restricted NKT cells and their potential for immunotherapy

CD1d-restricted NKT cells have been identified as an important component of the immune system that have the capacity both to augment beneficial host immunity and to prevent harmful autoimmunity. These cells have the ability to produce a wide variety of cytokines, including both proinflammatory and antiinflammatory cytokines that can have multiple different effects on the outcome of immune reactions. The discovery that these T cells are activated by specific recognition of glycolipids in the glycosylceramide family has led to new approaches to manipulate the pleiotropic functions of these cells. Here, we review the multiple activities that have been attributed to NKT cells in a variety of different disease models, and the current state of our understanding of the mechanisms that control the functional outcome of NKT cell activation.

Hepatic natural killer and natural killer T cells markedly decreased in two cases of drug-induced fulminant hepatic failure rescued by living donor liver transplantation

The human liver contains significant numbers of innate immune cells, such as natural killer (NK) cells and natural killer T (NKT) cells, which express both T-cell receptors and NK-cell receptors simultaneously. It has been suggested that the innate immune system plays a crucial role in the liver. In this report, the distribution of NK and NKT cells in the liver and peripheral blood of two patients with drug-induced fulminant hepatic failure (FHF) who had undergone living donor liver transplantation was examined. In both the liver and peripheral blood, the proportions of NK and NKT cells markedly decreased compared with those in healthy donors. It was also revealed that, unlike murine NKT cells, human CD56(+) T cells and CD57(+) T cells did not constitutively express CD28, which is one of the important costimulatory molecules on T cells. Additionally, the residual CD56(+) T cells and CD57(+) T cells in the patients expressed more CD28 than in controls. This result suggests that NKT cells might be more activated in FHF. Although the accumulation of further cases is required, it is suggested that both NK and NKT cells might be involved in hepatic injury in FHF.

Distinct Roles of Dendritic Cells and B Cells in Va14Ja18 Natural T Cell Activation In Vivo

Va14Ja18 natural T (iNKT) cells are innate, immunoregulatory lymphocytes that recognize CD1d-restricted lipid Ags such as alpha-galactosylceramide (alpha GalCer). The immunoregulatory functions of iNKT cells are dependent upon either IFN-gamma or IL-4 production by these cells. We hypothesized that alpha GalCer presentation by different CD1d-positive cell types elicits distinct iNKT cell functions. In this study we report that dendritic cells (DC) play a critical role in alpha GalCer-mediated activation of iNKT cells and subsequent transactivation of NK cells. Remarkably, B lymphocytes suppress DC-mediated iNKT and NK cell activation. Nevertheless, alpha GalCer presentation by B cells elicits low IL-4 responses from iNKT cells. This finding is particularly interesting because we demonstrate that NOD DC are defective in eliciting iNKT cell function, but their B cells preferentially activate this T cell subset to secrete low levels of IL-4. Thus, the differential immune outcome based on the type of APC that displays glycolipid Ags in vivo has implications for the design of therapies that harness the immunoregulatory functions of iNKT cells.

Both CD1d antigen presentation and interleukin-12 are required to activate natural killer T cells during Trypanosoma cruzi infection

Mechanisms of natural killer T (NKT)-cell activation remain unclear. Here, we report that during Trypanosoma cruzi infection, interleukin-12 (IL-12) deficiency or anti-CD1d antibody treatment prevents normal activation. The required IL-12 arises independently of MyD88. The data support a model of normal NKT-cell activation that requires IL-12 and TCR stimulation.

Immune properties of recombinant vaccinia virus encoding CD154 (CD40L) are determined by expression of virally encoded CD40L and the presence of CD40L protein in viral particles

Expression of costimulatory molecules by recombinant poxviruses is a promising strategy for enhancing therapeutic vaccines. CD40-CD40L interactions are critical for conditioning dendritic cells (DC) and priming T- and B-cell immunity. We constructed a vaccinia virus expressing murine CD40L (rV-CD40L) and studied its immunomodulatory properties in vitro. Direct DC infection with control vaccinia or psoralen/UV-inactivated rV-CD40L stimulated high levels of interleukin 12 (IL-12) release. However, replication-competent rV-CD40L did not stimulate IL-12 under similar conditions. We observed a high level of CD40L protein on purified viral particles and demonstrated that induction of IL-12 by nonreplicating rV-CD40L was blocked by anti-CD40 antibodies suggesting that functional CD40L on viral particles contributed to alterations in IL-12 synthesis. Since cross-presentation of tumor-associated antigens by DC is augmented by viral infection of tumor cells, we infected MC38 murine colon carcinoma cells with rV-CD40L. Infected cells stimulated IL-12 secretion by DC and proliferation of B cells and DX5(+) (NK/NKT) cells through direct CD40-CD40L interaction. A subpopulation of NKT cells expressing CD40 (NK1.1(+), CD3(lo)) appeared to be a major effector population responding to MC38/rV-CD40L. These results highlight the complex immune regulatory effects of rV-CD40L defined by the cumulative effects of CD40L expression, presence of CD40L protein in viral particles, and the replication potential of the virus.

IFN-gamma-mediated negative feedback regulation of NKT-cell function by CD94/NKG2

Activation of invariant natural killer T (iNKT) cells with CD1d-restricted T-cell receptor (TCR) ligands is a powerful means to modulate various immune responses. However, the iNKT-cell response is of limited duration and iNKT cells appear refractory to secondary stimulation. Here we show that the CD94/NKG2A inhibitory receptor plays a critical role in down-regulating iNKT-cell responses. Both TCR and NK-cell receptors expressed by iNKT cells were rapidly down-modulated by priming with alpha-galactosylceramide (alpha-GalCer) or its analog OCH [(2S,3S,4R)-1-O-(alpha-D-galactopyranosyl)-N-tetracosanoyl-2-amino-1,3,4-nonanetriol)]. TCR and CD28 were re-expressed more rapidly than the inhibitory NK-cell receptors CD94/NKG2A and Ly49, temporally rendering the primed iNKT cells hyperreactive to ligand restimulation. Of interest, alpha-GalCer was inferior to OCH in priming iNKT cells for subsequent restimulation because alpha-GalCer-induced interferon gamma (IFN-gamma) up-regulated Qa-1b expression and Qa-1b in turn inhibited iNKT-cell activity via its interaction with the inhibitory CD94/NKG2A receptor. Blockade of the CD94/NKG2-Qa-1b interaction markedly augmented recall and primary responses of iNKT cells. This is the first report to show the critical role for NK-cell receptors in controlling iNKT-cell responses and provides a novel strategy to augment the therapeutic effect of iNKT cells by priming with OCH or blocking of the CD94/NKG2A inhibitory pathway in clinical applications.

alpha-Galactosylceramide therapy for autoimmune diseases: prospects and obstacles

Autoimmune responses are normally kept in check by immune-tolerance mechanisms, which include regulatory T cells. In recent years, research has focused on the role of a subset of natural killer T (NKT) cells - invariant NKT (iNKT) cells, which are a population of glycolipid-reactive regulatory T cells - in controlling autoimmune responses. Because iNKT cells strongly react with a marine-sponge-derived glycolipid, alpha-galactosylceramide (alpha-GalCer), it has been possible to specifically target and track these cells. As I discuss here, although preclinical studies have shown considerable promise for the development of treatment with alpha-GalCer as a therapeutic modality for autoimmune diseases, several obstacles need to be overcome before moving alpha-GalCer therapy from the bench to the bedside.

ICOS costimulates invariant NKT cell activation

It has been reported that costimulatory molecules, CD80/86-CD28 and CD154-CD40, critically contribute to activation of CD1d-restricted invariant NKT (iNKT) cells. Here we have demonstrated that ICOS, a new member of the CD28 family, plays a substantial role in iNKT cell activation. iNKT cells constitutively expressed ICOS as well as CD28 independently, and ICOS expression was further up-regulated 2-3 days after alpha-galactosylceramide (alpha-GalCer) treatment. Blockade of ICOS-mediated costimulation by administration of anti-ICOS ligand (B7RP-1) mAb or by ICOS gene knockout substantially inhibited alpha-GalCer-induced IFN-gamma and IL-4 production, cytotoxic activity, and anti-metastatic effect. Moreover, blockade of both B7RP-1-ICOS and CD80/86-CD28 interactions mostly abolished the alpha-GalCer-induced immune responses. These findings indicate that iNKT cell activation is regulated by CD28 and IOCS independently.

Regulation of antitumour immunity by CD1d-restricted NKT cells

An understanding of the complex interactions occurring between tumours and the immune system is a prerequisite for the rational design of effective cancer immunotherapies. To date, attention has focused mainly on the role the adaptive immune system plays in controlling tumourigenesis, with conventional T cells, which recognize peptide antigens presented by classical MHC molecules, coming under close scrutiny. Accumulating reports now suggest that an additional T-cell subset, known as CD1d-restricted natural killer T (NKT) cells, also plays a pivotal role in modulating antitumour responses. Found in both humans and mice, CD1d-restricted NKT cells are a highly specialized cell type that, in contrast to conventional T cells, recognize lipid/glycolipid antigens presented by the non-classical MHC molecule CD1d. Several features of NKT cells, including their ability to rapidly produce large quantities of cytokines upon primary stimulation, make them ideal targets for developing anticancer immunotherapies. This intriguing cell type is the focus of this review.

Immunoregulatory T cells in tumor immunity

One mechanism of cancer immune evasion is the suppression of anti-tumor immunity by immunoregulatory T cells. Recent studies of these cells, especially CD4(+)CD25(+) T cells and NKT cells, have revealed molecular and cellular mechanisms of immunosuppression. Mouse studies have shown that either removing immunoregulatory T cells or blocking an immunoregulatory pathway induced by such cells unmasks natural tumor immunosurveillance and improves responses to cancer vaccines. Studies of the corresponding T-cell populations in human cancer patients support a similar role for immunoregulatory T cells in immunosuppression, implying that blocking immunoregulatory T-cell activity might improve the efficacy of tumor vaccines or the immunotherapy of cancer.

Essential role of LFA-1 in activating Th2-like responses by alpha-galactosylceramide-activated NKT cells

NKT cells produce large amounts of cytokines associated with both the Th1 (IFN-gamma) and Th2 (IL-4) responses following stimulation of their invariant Valpha14 Ag receptor. The role of adhesion molecules in the activation of NKT cells by the Valpha14 ligand alpha-galactosylceramide (alpha-GalCer) remains unclear. To address this issue, LFA-1-/- (CD11a-/-) mice were used to investigate IL-4 and IFN-gamma production by NKT cells following alpha-GalCer stimulation. Intriguingly, LFA-1-/- mice showed increased IL-4, IL-5, and IL-13 production and polarized Th2-type responses in response to alpha-GalCer in vitro and in vivo. Furthermore, the Th2-specific transcription factor GATA-3 was up-regulated in alpha-GalCer-activated NKT cells from LFA-1-/- mice. These results provide the first genetic evidence that the adhesion receptor LFA-1 has a crucial role in Th2-polarizing functions of NKT cells.

CD40-CD154 interactions between macrophages and natural killer cells during sepsis are critical for macrophage activation and are not interferon gamma dependent

Natural killer (NK) cell interactions with macrophages have been shown to be important during bacterial sepsis in activating macrophages to improve bacterial clearance. The mechanism for this increased activation, however, is unclear. This study determines the relative roles of interferon (IFN)-gamma and CD40/CD154 direct cell interactions on macrophage and NK cell activation in an experimental model of sepsis. Splenic NK cells and peritoneal macrophages were isolated and cultured alone or in coculture, with and without LPS. CD69 expression on NK cells, phagocytosis ability of macrophages, and cell cytokine production was assessed at 24 and 48 h. Coculture of NK cells and macrophages significantly increased activation levels of both cell types, and through experiments culturing NK cells with supernatants from stimulated macrophages and macrophages with supernatants from stimulated NK cells, this activation was determined to be cell-contact-dependent. Similar experiments were conducted using NK cells from IFN-gamma deficient (-/-) mice, as well as anti-IFN-gamma neutralizing antibody. These experiments determined that IFN-gamma is not required for NK or macrophage activation, although it did augment activation levels. Experiments were again repeated using peritoneal macrophages from CD40-/- mice or splenic NK cells from CD154-/- mice. CD40/CD154 interactions were important in the ingestion of bacteria by macrophages, but did not affect NK cell activation at 24 h. There was, however, a protective effect of CD40/CD154 interactions on NK cell activation-induced cell death that occurred at 48 h. CD40/CD154 interactions between macrophages and NK cells are therefore important in macrophage phagocytosis, and are not dependent on IFN-gamma.

The variations during the circadian cycle of liver CD1d-unrestricted NK1.1+TCR gamma/delta+ cells lead to successful ageing. Role of metallothionein/IL-6/gp130/PARP-1 interplay in very old mice

NKT cells derive from the thymus and home to the liver. Liver NKT cells can be divided in two groups: 'classical' and 'non-classical'. The first is CD1d-restricted, the second is CD1d-unrestricted. NKT cells (classical and non-classical) co-express T-cell receptor (TCR) and NK-cell marker (NK1.1), display cytotoxicity and produce IFN-gamma under IL-12 stimulation affecting, thereby, Th1 response and innate immunity. NK1.1(+)TCR alpha/beta(+) cells belong to both groups. NK1.1(+)TCR gamma/delta(+) cells belong to the second group. Anyway, both NKT cell subtypes, via IFN-gamma production, protect against viruses and bacteria from early in life. Immune variations as well as zinc rhythmicity during the circadian cycle confer the immune plasticity, which is essential for successful ageing. Liver NK1.1(+)TCR gamma/delta(+) cells, rather than TCR alpha/beta(+), from young and very old mice display 'in vitro' (under IL-12 stimulation) nocturnal peaks in cytotoxicity and IFN-gamma production. The acrophase of liver NK1.1(+)TCR gamma/delta(+) cells is present in young and very old mice, not in old. The interplay among zinc-bound metallothionein (MT)/IL-6/gp130/poly(ADP-ribose) polymerase-1 (PARP-1) may be involved in conferring plasticity to liver NK1.1(+)TCR gamma/delta(+) cells. IL-6, via sub-unit receptor gp130, induces MTmRNA. At night, gene expressions of MT, IL-6, gp130 are lower in very old mice than old and young MT-I transgenic mice (MT-I*). In very old mice, this phenomenon allows limited sequester of intracellular zinc from MT leading to good free zinc ion bioavailability for immune efficiency and zinc-dependent PARP-1 activity. Indeed (1) in vitro, high IL-6 provokes strong accumulation of MT, impaired cytotoxicity and low zinc ion bioavailability in liver NK1.1(+)TCR gamma/delta(+) cells exclusively from old and MT-I* mice. (2) The ratio total/endogen PARP-1 activity is higher in very old than in old and MT-I* mice, suggesting a higher capacity of PARP-1 in base excision DNA-repair in very old age thanks to low zinc-bound MT. Cytotoxicity and IFN-gamma production from liver NK1.1(+)TCR gamma/delta(+) cells are thus preserved leading to successful ageing. In conclusion, MT/IL-6/gp130/PARP-1 interplay may confer plasticity to liver CD1d-unrestricted NK1.1(+)TCR gamma/delta(+) cells, where MT, IL-6, gp130 are the main upstream protagonists, and PARP-1 is the main downstream protagonist in immunosenescence.

Relevance of sexual dimorphism to regulatory T cells: estradiol promotes IFN-gamma production by invariant natural killer T cells

Mechanisms accounting for gender dimorphism during immune responses are still poorly understood. Since invariant natural killer T (iNKT) cells exert important regulatory functions through their capacity to produce both T helper 1 (Th1) and Th2 cytokines, we addressed the question of whether these activities could be modulated by sexual hormones. We found that in vivo challenge with the specific ligand of iNKT cells, alpha-galactosylceramide (alpha-GalCer), induced significantly higher concentrations of interferon gamma (IFN-gamma) in the serum of female than in that of male mice, while interleukin 4 (IL-4) production was not modified. In support of a crucial role of ovarian hormones in this phenomenon, a significant decrease of serum IFN-gamma concentrations occurred in ovariectomized females, in response to treatment with alpha-GalCer, while orchidectomy affected neither IFN-gamma nor IL-4 serum concentrations in males. The implication of estrogens in this selective enhancement of IFN-gamma production by iNKT cells was demonstrated by (1) the increased alpha-GalCer-induced IFN-gamma synthesis by iNKT cells upon both in vitro and in vivo exposure to estradiol and (2) the abolition of the sex-linked difference in alpha-GalCer-induced IFN-gamma release in estrogen receptor alpha-deficient mice. These results provide the first evidence that estrogens influence iNKT cells leading to this gender dimorphism in their cytokine production profile.

The immunoregulatory role of CD1d-restricted natural killer T cells in disease

Natural killer T (NKT) cells constitute a T cell subpopulation that shares several characteristics with NK cells. NKT cells are characterized by a narrow T cell antigen receptor (TCR) repertoire, recognize glycolipid antigen in the context of the monomorphic CD1d antigen-presenting molecule, and have the unique capacity to rapidly produce large amounts of both T helper (Th) 1 and Th2 cytokines. Important roles of NKT cells have now been demonstrated in the regulation of autoimmune, allergic, antimicrobial, and antitumor immune responses. Here, we review the immunoregulatory role of NKT cells in disease and discuss NKT cell based immunotherapeutic strategies.

CD1: antigen presentation and T cell function

This review summarizes the major features of CD1 genes and proteins, the patterns of intracellular trafficking of CD1 molecules, and how they sample different intracellular compartments for self- and foreign lipids. We describe how lipid antigens bind to CD1 molecules with their alkyl chains buried in hydrophobic pockets and expose their polar lipid headgroup whose fine structure is recognized by the TCR of CD1-restricted T cells. CD1-restricted T cells carry out effector, helper, and adjuvant-like functions and interact with other cell types including macrophages, dendritic cells, NK cells, T cells, and B cells, thereby contributing to both innate and adaptive immune responses. Insights gained from mice and humans now delineate the extensive range of diseases in which CD1-restricted T cells play important roles and reveal differences in the role of CD1a, CD1b, and CD1c in contrast to CD1d. Invariant TCR alpha chains, self-lipid reactivity, and rapid effector responses empower a subset of CD1d-restricted T cells (NKT cells) to have unique effector functions without counterpart among MHC-restricted T cells. This review describes the function of CD1-restricted T cells in antimicrobial responses, antitumor immunity, and in regulating the balance between tolerance and autoimmunity.

Immune response in mouse experimental cholangitis associated with colitis induced by dextran sulfate sodium

BACKGROUND AND AIM

Primary sclerosing cholangitis is frequently complicated by inflammatory bowel disease. Although many colitis models have been reported, little information has been obtained about complicated cholangitis. The aim of the present study was to determine whether hepatobiliary disorders occur in mice experimental colitis, and to clarify the underlying mechanisms.

METHODS

The CD-1 mice were fed standard chow with or without dextran sulfate sodium in the drinking water, followed by histological examination of the liver and colon. Mononuclear cells were isolated from these organs, and cytokine production was assessed. The CD4/CD8 ratio and the population of natural killer T (NKT) cells were analyzed by flow cytometry.

RESULTS

Inflammatory cell infiltration and focal necrosis in the liver were found in 33% of treated mice. In treated mice, the CD4/CD8 ratio increased in the liver, whereas no such change was found in the colon. Also an increase of interferon-gamma and a decrease of interleukin-4 production were observed. The NKT cell population showed transient changes in the liver and colon.

CONCLUSIONS

Hepatobiliary disorders were complicated with experimental colitis in CD-1 mice. Immunological findings indicate a T-helper-1-dominant underlying mechanism, and NKT cells may play a pathogenic role in this model. This model may help to elucidate the relationship between hepatic and colonic inflammations.

Oral Tolerance to Nickel Requires CD4+ Invariant NKT Cells for the Infectious Spread of Tolerance and the Induction of Specific Regulatory T Cells

Previously, oral administration of nickel to C57BL/6 wild-type (WT) mice was shown to render both their splenic T cells and APCs (i.e., T cell-depleted spleen cells) capable of transferring nickel tolerance to naive syngeneic recipients. Moreover, sequential adoptive transfer experiments revealed that on transfer of tolerogenic APCs and immunization, the naive T cells of the recipients differentiated into regulatory T (Treg) cells. Here, we demonstrate that after oral nickel treatment Jalpha18(-/-) mice, which lack invariant NKT (iNKT) cells, were not tolerized and failed to generate Treg cells. However, transfer of APCs from those Jalpha18(-/-) mice did tolerize WT recipients. Hence, during oral nickel administration, tolerogenic APCs are generated that require iNKT cell help for the induction of Treg cells. To obtain this help, the tolerogenic APCs must address the iNKT cells in a CD1-restricted manner. When Jalpha18(-/-) mice were used as recipients of cells from orally tolerized WT donors, the WT Treg cells transferred the tolerance, whereas WT APCs failed to do so, although they proved tolerogenic on transfer to WT recipients. However, Jalpha18(-/-) recipients did become susceptible to the tolerogenicity of transferred WT APCs when they were reconstituted with IL-4- and IL-10-producing CD4(+) iNKT cells. We conclude that CD4(+) iNKT cells are required for the induction of oral nickel tolerance and, in particular, for the infectious spread of tolerance from APCs to T cells. Once induced, these Treg cells, however, can act independently of iNKT cells.

CD56+Cells Induce Steroid Resistance in B Cells Exposed to IL-15

Interleukin-2 can induce steroid resistance in T cells. IL-15 shares biological activities with IL-2, as both cytokines use IL-2Rgamma for signal transduction. We therefore sought to determine whether IL-15 contributes to induction of PBMC corticosteroid resistance. Surprisingly, we found that incubation of unfractionated PBMC with IL-15 for 48 h resulted in the inhibition of glucocorticoid receptor (GCR) nuclear translocation in response to dexamethasone (DEX) treatment in CD19-positive B cells significantly greater than CD19-negative non-B cells (p < 0.01). However, pure B cells incubated with IL-15 responded normally with nuclear translocation of GCR in response to steroids, but failed to translocate GCR when they were grown in the presence of CD19(-) cells. Coculture of B cells with CD3(+) (T cells), CD14(+) (monocytes), or CD56(+) (NK and NKT cells) in the presence of IL-15 revealed that only CD56(+) cells contributed to the steroid insensitivity of B cells. IL-15 stimulation significantly increased production of IL-4 by CD56(+) cells (p < 0.02). Treatment of purified B cells with combination IL-15/IL-4 resulted in abrogation of glucocorticoid receptor nuclear translocation and the inability of DEX to suppress cytokine production by B cells. In the presence of IL-4-neutralizing Ab, when B cells were cocultured with CD56(+) cells and IL-15, the B cells were found to be steroid sensitive, i.e., DEX induced GCR nuclear translocation. This study demonstrates that B cells develop steroid resistance in the presence of CD56(+) cells after IL-15 stimulation. Furthermore, IL-15 and IL-4 have the capacity to induce B cell insensitivity to steroids.

Control of NKT cell differentiation by tissue-specific microenvironments

CD1d-restricted Valpha14 NKT cells play an important role in both Th1- and Th2-type immune responses. To determine whether NKT cells develop two functionally distinct subsets that provoke different types of responses, we examined the phenotypes and cellular functions of NK1.1(+) and DX5(+) T cells. We found that both NK1.1(+) and DX5(+) T cells are CD1d-restricted Valpha14 T cells with identical Ag specificities, phenotypes, tissue locations, and functions. Similar to the NK1.1 marker, the DX5 marker (CD49b) is expressed on mature NKT cells in both NK1.1 allele-positive and allele-negative strains. However, when NK1.1(+) and DX5(+) NKT cells isolated from different tissues were compared, we found that thymic and splenic NKT cells differed not only in their cytokine profiles, but also in their phenotype and requirements for costimulatory signals. Thymic NKT cells displayed the phenotype of activated T cells and could be fully activated by TCR ligation. In contrast, splenic NKT cells displayed the phenotype of memory T cells and required a costimulatory signal for activation. Furthermore, the function and phenotype of thymic and splenic NKT cells were modulated by APCs from various tissues that expressed different levels of costimulatory molecules. Modulation of NKT cell function and differentiation may be mediated by synergic effects of costimulatory molecules on the surface of APCs. The results of the present study suggest that the costimulatory signals of tissue-specific APCs are key factors for NKT cell differentiation, and these signals cannot be replaced by anti-CD28 or anti-CD40 ligand Abs.

NKT cells enhance CD4+ and CD8+ T cell responses to soluble antigen in vivo through direct interaction with dendritic cells

Modification in the function of dendritic cells (DC), such as that achieved by microbial stimuli or T cell help, plays a critical role in determining the quality and size of adaptive responses to Ag. NKT cells bearing an invariant TCR (iNKT cells) restricted by nonpolymorphic CD1d molecules may constitute a readily available source of help for DC. We therefore examined T cell responses to i.v. injection of soluble Ag in the presence or the absence of iNKT cell stimulation with the CD1d-binding glycolipid alpha-galactosylceramide (alpha-GalCer). Considerably enhanced CD4(+) and CD8(+) T cell responses were observed when alpha-GalCer was administered at the same time as or close to OVA injection. This enhancement was dependent on the involvement of iNKT cells and CD1d molecules and required CD40 signaling. Studies in IFN-gammaR(-/-) mice indicated that IFN-gamma was not required for the adjuvant effect of alpha-GalCer. Consistent with this result, enhanced T cell responses were observed using OCH, an analog of alpha-GalCer with a truncated sphingosine chain and a reduced capacity to induce IFN-gamma. Splenic DC from alpha-GalCer-treated animals expressed high levels of costimulatory molecules, suggesting maturation in response to iNKT cell activation. Furthermore, studies with cultured DC indicated that potentiation of T cell responses required presentation of specific peptide and alpha-GalCer by the same DC, implying conditioning of DC by iNKT cells. The iNKT-enhanced T cell responses resisted challenge with OVA-expressing tumors, whereas responses induced in the absence of iNKT stimulation did not. Thus, iNKT cells exert a significant influence on the efficacy of immune responses to soluble Ag by modulating DC function.

Immunological Foundations to the Quest for New Vaccine Adjuvants

Developing efficient adjuvants for human vaccines that elicit broad and sustained immune responses at systemic or mucosal levels remains a formidable challenge for the vaccine industry. Conventional approaches in the past have been largely empirical and--at best--partially successful. Importantly, recent advances in our understanding of the immune system, most particularly with respect to early proinflammatory signals, are leading to the identification of new biological targets for vaccine adjuvants. This review covers both the current status of adjuvant testing in humans, the residual needs for vaccines in development, and the emerging immunological foundations for adjuvant design. A better understanding of the biology of toll-like receptors, non-conventional T cell subpopulations, T and B cell memory, regulatory T cells, and mucosal immunity has profound implications for a modern approach to adjuvant screening and development. The future lies in the high throughput screening of synthetic chemical entities targeting well-characterized biological molecules. Used alone or in combination, such synthetic adjuvants will allow stimulation or modulation in a safe and efficient manner of strong effector, regulatory and memory immune mechanisms.

Phenotypic and functional characterization of long-term cultured rhesus macaque spleen-derived NKT cells

Natural killer T cells are immunoregulatory cells, which have important roles in tolerance and autoimmunity, as demonstrated primarily in mice and humans. In this study, we define the phenotype and function of Valpha24(+) T cells derived from the spleens of rhesus macaques, a species increasingly used in models of immune tolerance. Valpha24(+) cells were isolated and expanded with monocyte-derived immature dendritic cells in the presence of alpha-galactosylceramide, IL-2, and IL-15. Rhesus NKT cells were stained with mAbs against both Valpha24 and the invariant complementarity-determining region 3 epitope of the human Valpha24/JalphaQ TCR. The cells were CD4, CD8 double negative and expressed CD56. Rhesus NKT cells also exhibited moderate to high expression of CD95, CD45RO, CD11a, and beta(7) integrin, but did not express CD45 RA, CD62L, CCR7, CD28, and other activation, costimulatory molecules (CD69 and CD40L). By intracellular staining, >90% of unstimulated rhesus NKT cells expressed IL-10, but not IFN-gamma. However, the latter was strongly expressed after stimulation. Rhesus NKT secreted large amounts of TGF-beta, IL-13, and IL-6, and modest levels of IFN-gamma, whereas IL-10 secretion was negligible and no detectable IL-4 was observed either intracellularly or in culture supernatants. Functionally, the NKT cells and their supernatants suppressed T cell proliferation in allogeneic MLR. We conclude that long-term cultured rhesus macaque spleen-derived Valpha24(+) T cells are semi-invariant double-negative cells with effector memory phenotype. These cells are semianergic, polarized to a uniquely Th3 > T regulatory-1 regulatory cell phenotype, and have regulatory/suppressive function in vitro.

Alpha-galactosylceramide (KRN7000) suppression of chemical- and oncogene-dependent carcinogenesis

Recent studies have revealed significant efficacy of the marine sponge glycolipid, alpha-galactosylceramide (alpha-GalCer), in treatment of experimental metastatic cancers, infections, and autoimmune diseases. However, the capacity of alpha-GalCer to prevent tumor development had never, to our knowledge, been evaluated in mouse models of chemical- and oncogene-dependent carcinogenesis. In this study, we demonstrate that long-term administration of soluble alpha-GalCer, spanning the time of tumor initiation, inhibits primary tumor formation in three different models: methylcholanthrene-induced sarcomas, mammary carcinomas in Her-2/neu transgenic mice, and spontaneous sarcomas in p53-/- mice. Weekly treatment of mice with alpha-GalCer maintained lymphoid tissue natural killer cell and T cell activation and elevated serum IFN-gamma and IL-4 concentrations. Consistent with the antimetastatic activity of alpha-GalCer, prevention of methylcholanthrene-induced sarcoma was IFN-gammaand tumor necrosis factor-related apoptosis-inducing ligand dependent, but not perforin-dependent. Taken together, our results demonstrate that NK1.1+alphabetaTCR+ cell-based immune therapy can inhibit primary tumorigenesis.

Mouse V alpha 14i natural killer T cells are resistant to cytokine polarization in vivo

Under different circumstances, natural killer T (NKT) cells can cause a T helper (Th) 1 or a Th2 polarization of immune responses. We show here, however, that mouse NKT cells with an invariant V alpha 14 rearrangement (V alpha 14i NKT cells) rapidly produce both IL-4 and IFN-gamma, and this pattern could not be altered by methods that polarize naive CD4+ T cells. Surprisingly, although cytokine protein was detected only after activation, resting V alpha 14i NKT cells contained IL-4 and IFN-gamma mRNAs. Despite this finding, in vivo priming of mice with the glycolipid antigen recognized by V alpha 14i NKT cells resulted in a more Th2-oriented response upon antigen re-exposure. The V alpha 14i NKT cells from primed mice retain the ability to produce IL-4 and IFN-gamma, but they are less effective at activating NK cells to produce IFN-gamma. Our data therefore indicate that V alpha 14i NKT cells have a relatively inflexible immediate cytokine response, but that changes in their ability to induce IFN-gamma secretion by NK cells may determine the extent to which they promote Th1 responses.

Innate immune responses support adaptive immunity: NKT cells induce B cell activation

Invariant NKT cells are a peculiar subset of T lymphocytes whose features, highly conserved both in the mouse and the human system, strongly recall those of other "innate lymphocytes". Following recognition of CD1d-presented glycosphingolipid antigens invariant NKT promptly release high amount of diverse cytokines concurring to the activation of the actors of both innate and acquired immune responses. For this reason, in recent years NKT cells have been the object of intensive study, aimed to understand their role in diverse patho-physiological conditions and to exploit the possibility to take advantage of their "adjuvant-like" activity in the formulation of new vaccines. As antibodies are an essential part of many immune responses, we focused our attention on invariant NKT-B cell interactions analyzing their influences on B cell activation and effector functions. The results of this study demonstrate that human invariant NKT cells can provide direct help for B cell proliferation and antibody production through CD1d-restricted mechanisms. Remarkably, help to B lymphocytes by invariant NKT cells is delivered also in the absence of exogenous antigen, suggesting the existence of an endogenous ligand presented by CD1d on B cells.

CD1d-restricted help to B cells by human invariant natural killer T lymphocytes

Invariant natural killer T (NKT) cells are a highly conserved subset of T lymphocytes expressing a semi-invariant T cell receptor (TCR), which is restricted to CD1d and specific for the glycosphingolipid antigen alpha-galactosylceramide. Their ability to secrete a variety of cytokines, which in turn modulate the activation of cells of both innate and acquired immune responses, suggests that invariant NKT cells exert a regulatory role mainly via indirect mechanisms. A relevant question is whether invariant NKT cells can directly help B cells. We document here that human invariant NKT cells are as efficient as conventional CD4+ Th0 lymphocytes in promoting proliferation of autologous memory and naive B lymphocytes in vitro, and in inducing immunoglobulin production. Help to B cells by invariant NKT cells is CD1d-dependent and delivered also in the absence of alpha-galactosylceramide, suggesting that NKT cells recognize an endogenous ligand presented by CD1d on B cells. The two major subsets of invariant NKT cells, CD4+ and double negative (CD4-CD8-), express comparable levels of CD40 ligand and cytokines, but differ in helper functions. Indeed, both subsets induce similar levels of B cell proliferation, whereas CD4+ NKT cells induce higher levels of immunoglobulin production. These results suggest a direct role for invariant NKT cells in regulating B lymphocyte proliferation and effector functions.

Janus-like role of regulatory iNKT cells in autoimmune disease and tumour immunity

Invariant CD1D-restricted natural killer T (iNKT) cells function during innate and adaptive immunity and regulate numerous immune responses, such as autoimmune disease, tumour surveillance, infectious disease and abortions. However, the molecular basis of their functions and the nature of disease-associated defects of iNKT cells are unclear and have been the subject of recent controversy. Here, we review recent findings that underscore the potential importance of interactions between iNKT cells and dendritic cells (DCs) that indicate that iNKT cells regulate DC activity to shape both pro-inflammatory and tolerogenic immune responses. The ability to modulate iNKT-cell activity in vivo using the ligand alpha-galactosylceramide and to treat patients with autoimmune disease or cancer is evaluated also.

Activation of NKT cells protects mice from tuberculosis

The T-cell immune response to Mycobacterium tuberculosis is critical in preventing clinical disease. While it is generally accepted that both major histocompatibility complex class I (MHC-I)-restricted CD8(+) and MHC-II-restricted CD4(+) T cells are important for the immune response to M. tuberculosis, the role of non-MHC-restricted T cells is still not clearly delineated. We have previously reported that CD1d(-/-) mice do not differ from CD1d(+/+) mice in their survival following infection with M. tuberculosis. We now show that, although CD1d-restricted NKT cells are not required for optimum immunity to M. tuberculosis, specific activation of NKT cells by the CD1d ligand alpha-galactosylceramide protects susceptible mice from tuberculosis. Treatment with alpha-galactosylceramide reduced the bacterial burden in the lungs, diminished tissue injury, and prolonged survival of mice following inoculation with virulent M. tuberculosis. The capacity of activated NKT cells to stimulate innate immunity and modulate the adaptive immune response to promote a potent antimicrobial immune response suggests that alpha-galactosylceramide administration could have a role in new strategies for the therapy of infectious diseases.

NKT cells: potential targets for autoimmune disease therapy?

NKT cells represent a unique T cell lineage that recognize glycolipid antigens in the context of the non-classical MHC class I molecule CD1d. NKT cells are potent producers of immunoregulatory cytokines, and have been implicated in several different autoimmune diseases in mice and humans, including Type 1 diabetes, experimental autoimmune encephalomyelitis--a mouse model for multiple sclerosis, systemic lupus erythematosus, and scleroderma. This review will cover the evidence for an involvement for NKT cells in these autoimmune diseases, and discuss the potential for therapeutic manipulation of these cells as a means of preventing autoimmune disease in the clinic.

Activating immunity in the liver. II. IFN-beta attenuates NK cell-dependent liver injury triggered by liver NKT cell activation

Dendritic cell (DC)-dependent activation of liver NKT cells triggered by a single i.v. injection of a low dose (10-100 ng/mouse) of alpha-galactosyl ceramide (alphaGalCer) into mice induces liver injury. This response is particularly evident in HBs-tg B6 mice that express a transgene-encoded hepatitis B surface Ag in the liver. Liver injury following alphaGalCer injection is suppressed in mice depleted of NK cells, indicating that NK cells play a role in NK T cell-initiated liver injury. In vitro, liver NKT cells provide a CD80/86-dependent signal to alphaGalCer-pulsed liver DC to release IL-12 p70 that stimulates the IFN-gamma response of NKT and NK cells. Adoptive transfer of NKT cell-activated liver DC into the liver of nontreated, normal (immunocompetent), or immunodeficient (RAG(-/-) or HBs-tg/RAG(-/-)) hosts via the portal vein elicited IFN-gamma responses of liver NK cells in situ. IFN-beta down-regulates the pathogenic IL-12/IFN-gamma cytokine cascade triggered by NKT cell/DC/NK cell interactions in the liver. Pretreating liver DC in vitro with IFN-beta suppressed their IL-12 (but not IL-10) release in response to CD40 ligation or specific (alphaGalCer-dependent) interaction with liver NKT cells and down-regulated the IFN-gamma response of the specifically activated liver NKT cells. In vivo, IFN-beta attenuated the NKT cell-triggered induction of liver immunopathology. This study identifies interacting subsets of the hepatic innate immune system (and cytokines that up- and down-regulate these interactions) activated early in immune-mediated liver pathology.