CD1d1 mutant mice are deficient in natural T cells that promptly produce IL-4

Deficiency of invariant NK T cells in Crohn's disease and ulcerative colitis

The aim of this study was to investigate whether immunoregulatory invariant NK T cells are deficient in Crohn's disease or ulcerative colitis. Blood was collected for flow cytometry from 106 Crohn's disease, 91 ulcerative colitis, and 155 control subjects. Invariant NK T cells were assessed by Valpha24 and (alpha-galactosylceramide/CD1d tetramer markers. Intracellular cytokine was measured after in vitro anti-CD3 antibody stimulation. Valpha24+ T cells were quantified in ileocolonic biopsies as mRNA by real-time PCR and by immunofluorescence. Circulating invariant NK T cells were 5.3% of the control levels in Crohn's (P < 0.001) and 7.9% of the control levels in ulcerative colitis (P < 0.001). Interleukin-4 production was impaired in Crohn's disease and ulcerative colitis. Intestinal Valpha24 mRNA expression was 7% in Crohn's disease (P < 0.05) and 9% in ulcerative colitis (P < 0.05). Intestinal Valpha24+ T cells were 23% in Crohn's disease but not reduced in ulcerative colitis. We conclude that invariant NK T cells are deficient in Crohn's disease and in ulcerative colitis.

Toll-like receptor 4 (TLR4)-dependent proinflammatory and immunomodulatory properties of the glycoinositolphospholipid (GIPL) from Trypanosoma cruzi

We have demonstrated recently that the glycoinositolphospholipid (GIPL) molecule from the protozoan Trypanosoma cruzi is a TLR4 agonist with proinflammatory effects. Here, we show that GIPL-induced neutrophil recruitment into the peritoneal cavity is mediated by at least two pathways: one, where IL-1beta acts downstream of TNF-alpha, and a second, which is IL-1beta- and TNFRI-independent. Moreover, NKT cells participate in this proinflammatory cascade, as in GIPL-treated CD1d(-/-) mice, TNF-alpha and MIP-2 levels are reduced significantly. As a consequence of this inflammatory response, spleen and lymph nodes of GIPL-treated mice have an increase in the percentage of T and B cells expressing the CD69 activation marker. Cell-transfer experiments demonstrate that T and B cell activation by GIPL is an indirect effect, which relies on the expression of TLR4 by other cell types. Moreover, although signaling through TNFRI contributes to the activation of B and gammadelta+ T cells, it is not required for increasing CD69 expression on alphabeta+ T lymphocytes. It is interesting that T cells are also functionally affected by GIPL treatment, as spleen cells from GIPL-injected mice show enhanced production of IL-4 following in vitro stimulation by anti-CD3. Together, these results contribute to the understanding of the inflammatory properties of the GIPL molecule, pointing to its potential role as a parasite-derived modulator of the immune response during T. cruzi infection.

A role for natural killer T cells and CD1d molecules in counteracting suppression of hematopoiesis in mice induced by infection with murine cytomegalovirus

OBJECTIVE

Infection of immunocompromised patients with cytomegalovirus (CMV), such as that occurring in patients undergoing hematopoietic stem cell transplantation, is a serious clinical problem. CMV infection has been reported to suppress hematopoiesis. In immunocompetent hosts CMV is controlled initially by the innate immune system, with CD1d molecules and natural killer T (NKT) cells playing a role in the antiviral immune response in several model systems. We hypothesized that CD1d and NKT cells are involved in protection of the hematopoietic modulating effects of CMV, and that adoptive transfer of NKT cells would protect against these infection-induced effects.

METHODS

To address our hypothesis, we used a murine CMV (MCMV) infection model in CD1d(-/-), Jalpha18(-/-), and wild-type (WT) control mice of two different genetic strains each.

RESULTS

Infection with MCMV was associated with significant suppression of absolute numbers and cell cycling status of myeloid progenitor cells (CFU-GM, BFU-E, CFU-GEMM) in the marrow and spleen, especially in CD1d(-/-) (lack both CD1d and NKT cells), and Jalpha18(-/-) (express CD1d but lack NKT cells) mice. Adoptive transfer of NKT cells into WT and Jalpha18(-/-) mice shortly before infection with MCMV counteracted myelosuppression.

CONCLUSIONS

The results implicate NKT cells, and also likely CD1d, in protection of progenitor cells from MCMV-induced suppression and suggest that NKT cells may be of value in an adoptive transfer setting to treat CMV-induced perturbations of hematopoiesis in immunocompromised individuals. However, further studies are required to better understand the full consequences of adoptive transfer in these settings.

Examining the role of CD1d and natural killer T cells in the development of nephritis in a genetically susceptible lupus model

OBJECTIVE

CD1d-reactive invariant natural killer T (iNKT) cells secrete multiple cytokines upon T cell receptor (TCR) engagement and modulate many immune-mediated conditions. The purpose of this study was to examine the role of these cells in the development of autoimmune disease in genetically lupus-prone (NZBxNZW)F1 (BWF1) mice.

METHODS

The CD1d1-null genotype was crossed onto the NZB and NZW backgrounds to establish CD1d1-knockout (CD1d0) BWF1 mice. CD1d0 mice and their wild-type littermates were monitored for the development of nephritis and assessed for cytokine responses to CD1d-restricted glycolipid alpha-galactosylceramide (alphaGalCer), anti-CD3 antibody, and concanavalin A (Con A). Thymus and spleen cells were stained with CD1d tetramers that had been loaded with alphaGalCer or its analog PBS-57 to detect iNKT cells, and the cells were compared between BWF1 mice and class II major histocompatibility complex-matched nonautoimmune strains, including BALB/c, (BALB/cxNZW)F1 (CWF1), and NZW.

RESULTS

CD1d0 BWF1 mice had more severe nephritis than did their wild-type littermates. Although iNKT cells and iNKT cell responses were absent in CD1d0 BWF1 mice, the CD1d0 mice continued to have significant numbers of interferon-gamma-producing NKT-like (CD1d-independent TCRbeta+,NK1.1+ and/or DX5+) cells. CD1d deficiency also influenced cytokine responses by conventional T cells: upon in vitro stimulation of splenocytes with Con A or anti-CD3, type 2 cytokine levels were reduced, whereas type 1 cytokine levels were increased or unchanged in CD1d0 mice as compared with their wild-type littermates. Additionally, numbers of thymic iNKT cells were lower in young wild-type BWF1 mice than in nonautoimmune strains.

CONCLUSION

Germline deletion of CD1d exacerbates lupus in BWF1 mice. This finding, together with reduced thymic iNKT cells in young BWF1 mice as compared with nonautoimmune strains, implies a regulatory role of CD1d and iNKT cells during the development of lupus.

The unique role of natural killer T cells in the response to microorganisms

Natural killer T (NKT) cells combine features of the innate and adaptive immune systems. Recently, it has become evident that these T cells have crucial roles in the response to infectious agents. The antigen receptor expressed by NKT cells directly recognizes unusual glycolipids that are part of the membrane of certain Gram-negative bacteria and spirochetes. Moreover, even in the absence of microbial glycolipid antigens, these T cells respond to innate cytokines produced by dendritic cells that have been activated by microbes. This indirect sensing of infection, by responding to cytokines from activated dendritic cells, allows NKT cells to react to a broad range of infectious agents.

Interdependency of MHC Class II/Self-Peptide and CD1d/Self-Glycolipid Presentation by TNF-Matured Dendritic Cells for Protection from Autoimmunity

Dendritic cells (DC) are key regulators of T cell immunity and tolerance. NKT cells are well-known enhancers of Th differentiation and regulatory T cell function. However, the nature of the DC directing T and NKT cell activation and polarization as well as the role of the respective CD1d Ags presented is still unclear. In this study, we show that peptide-specific CD4(+)IL-10(+) T cell-mediated full experimental autoimmune encephalomyelitis (EAE) protection by TNF-treated semimatured DCs was dependent on NKT cells recognizing an endogenous CD1d ligand. NKT cell activation by TNF-matured DCs induced high serum levels of IL-4 and IL-13 which are absent in NKT cell-deficient mice, whereas LPS plus anti-CD40-treated fully mature DCs induce serum IFN-gamma. In the absence of IL-4Ralpha chain signaling or NKT cells, no complete EAE protection was achieved by TNF-DCs, whereas transfer of NKT cells into Jalpha281(-/-) mice restored it. However, activation of NKT cells alone was not sufficient for EAE protection and early serum Th2 deviation. Simultaneous activation of NKT cells and CD4(+) T cells by the same DC was required for EAE protection. Blocking experiments demonstrated that NKT cells recognize an endogenous glycolipid presented on CD1d on the injected DC. Together, this indicates that concomitant and interdependent presentation of MHC II/self-peptide and CD1d/self-isoglobotrihexosylceramide to T and NKT cells by the same partially or fully matured DC determines protective and nonprotective immune responses in EAE.

Immunoregulatory role of Jalpha281 T cells in aged mice developing lupus-like nephritis

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the emergence of autoreactive T cells. Humans and mice with SLE have reduced numbers of CD1d-restricted invariant natural killer T (iNKT) cells, suggesting a key role for these cells in its immunopathogenesis. This subset uses an invariant TCR constituted by Valpha14 Jalpha281 chains paired with some Vbeta domains. The regulatory role for iNKT cells in non-autoimmune mice was suggested by our previous results showing that aged Jalpha281 knockout (KO) mice produce anti-dsDNA. Here we show that old Jalpha281 KO mice have proteinuria and antibodies against dsDNA and cardiolipin. Histological analysis of Jalpha281 KO mice revealed glomeruli damage and deposition of C3c and IgG, mainly of the IgG3 subclass. In spleens of aged Jalpha281 KO mice there is an increase of activated marginal zone B cells. The evolution of lesions may depend on the age-associated increase of autoantibodies production, preferentially IgG3, mainly secreted by marginal zone B cells. Our results provide the first evidence of a lupus-like syndrome in non-autoimmune mice, supporting an age-related immunoregulatory role of Jalpha281+ cells, probably associated with the activation of marginal zone B cells.

Prevention of type 1 diabetes by invariant NKT cells is independent of peripheral CD1d expression

Invariant NKT (iNKT) cells can prevent diabetes by inhibiting the differentiation of anti-islet T cells. We recently showed that neither iNKT cell protection against diabetes nor iNKT cell inhibition of T cell differentiation in vitro requires cytokines such as IL-4, IL-10, IL-13, and TGF-beta. In contrast, cell-cell contacts were required for iNKT cell inhibition of T cell differentiation in vitro. The present study was designed to determine whether the CD1d molecule is involved in the inhibitory function of iNKT cells. Experiments were performed in vitro and in vivo, using cells lacking CD1d expression. The in vivo experiments used CD1d-deficient mice that were either reconstituted with iNKT cells or expressed a CD1d transgene exclusively in the thymus. Both mouse models had functional iNKT cells in the periphery, even though CD1d was not expressed in peripheral tissues. Surprisingly, both in vitro inhibition of T cell differentiation by iNKT cells and mouse protection against diabetes by iNKT cells were CD1d-independent. These results reveal that iNKT cells can exert critical immunoregulatory effects in the absence of CD1d recognition and that different molecular interactions are involved in iNKT cell functions.

Invariant and noninvariant natural killer T cells exert opposite regulatory functions on the immune response during murine schistosomiasis

CD1d-restricted natural killer T (NKT) cells represent a heterogeneous population of innate memory immune cells expressing both NK and T-cell markers distributed into two major subsets, i.e., invariant NKT (iNKT) cells, which express exclusively an invariant T-cell receptor (TCR) alpha chain (Valpha14Jalpha18 in mice), and non-iNKT cells, which express more diverse TCRs. NKT cells quickly produce Th1- and/or Th2-type cytokines following stimulation with glycolipid antigen (Ag) and, through this property, play potent immunoregulatory roles in autoimmune diseases, cancer, and infection. No study has addressed the role of NKT cells in metazoan parasite infections so far. We show that during murine schistosomiasis, the apparent frequency of both iNKT cells and non-iNKT cells decreased in the spleen as early as 3 weeks postinfection (p.i.) and that both populations expressed a greater amount of the activation marker CD69 at 6 weeks p.i., suggesting an activated phenotype. Two different NKT-cell-deficient mouse models, namely, TCR Jalpha18-/- (exclusively deficient in iNKT cells) and CD1d-/- (deficient in both iNKT and non-iNKT cells) mice, were used to explore the implication of these subsets in infection. We show that whereas both iNKT and non-iNKT cells do not have a major impact on the immune response during the early phase (1 and 4 weeks) of infection, they exert important, although opposite, effects on the immune response during the acute phase of the disease (7 and 12 weeks), after schistosome egg production. Indeed, iNKT cells contribute to Th1 cell differentiation whereas non-iNKT cells might be mostly implicated in Th2 cell differentiation in response to parasite Ag. Our findings suggest, for the first time, that helminths activate both iNKT and non-iNKT cells in vivo, enabling them to differentially influence the Th1/Th2 balance of the immune response.

Sensitivity of NK1.1-negative NKT cells to transgenic BATF defines a role for activator protein-1 in the expansion and maturation of immature NKT cells in the thymus

NKT cells are glycolipid-reactive lymphocytes that express markers and perform functions common to both T lymphocytes and NK cells. Although the genetic events controlling conventional T cell development are well defined, the transcription factors and genetic programs regulating NKT cell development are only beginning to be elucidated. Previously, we described the NKT cell-deficient phenotype of transgenic (Tg) mice constitutively expressing B cell-activating transcription factor (BATF), a basic leucine zipper protein and inhibitor of AP-1. In this study, we show that Tg BATF targets the majority of Valpha14Jalpha281 (Valpha14i(7)) NKT cells, regardless of CD4 expression and Vbeta gene usage. The residual NKT cells in the thymus of BATF-Tg mice are CD44(+), yet are slow to display the NK1.1 marker characteristic of mature cells. As a population, BATF-expressing NKT cells are TCRbeta/CD3epsilon(low), but express normal levels of CD69, suggesting a failure to expand appropriately following selection. Consistent with the sensitivity of NKT cells to BATF-induced changes in AP-1 activity, we detect a full complement of AP-1 basic leucine zipper proteins in wild-type NKT cells isolated from the thymus, spleen, and liver, and show that AP-1 DNA-binding activity and cytokine gene transcription are induced in NKT cells within a few hours of glycolipid Ag exposure. This study is the first to characterize AP-1 activity in NKT cells and implicates the integrity of this transcription factor complex in developmental events essential to the establishment of this unique T cell subset in the thymus.

Dendritic Cell Function Can Be Modulated through Cooperative Actions of TLR Ligands and Invariant NKT Cells

The quality of signals received by dendritic cells (DC) in response to pathogens influences the nature of the adaptive response. We show that pathogen-derived signals to DC mediated via TLRs can be modulated by activated invariant NKT (iNKT) cells. DC maturation induced in vivo with any one of a variety of TLR ligands was greatly improved through simultaneous administration of the iNKT cell ligand alpha-galactosylceramide. DC isolated from animals treated simultaneously with TLR and iNKT cell ligands were potent stimulators of naive T cells in vitro compared with DC from animals treated with the ligands individually. Injection of protein Ags with both stimuli resulted in significantly improved T cell and Ab responses to coadministered protein Ags over TLR stimulation alone. Ag-specific CD8(+) T cell responses induced in the presence of the TLR4 ligand monophosphoryl lipid A and alpha-galactosylceramide showed faster proliferation kinetics, and increased effector function, than those induced with either ligand alone. Human DC exposed to TLR ligands and activated iNKT cells in vitro had enhanced expression of maturation markers, suggesting that a cooperative action of TLR ligands and iNKT cells on DC function is a generalizable phenomenon across species. These studies highlight the potential for manipulating the interactions between TLR ligands and iNKT cell activation in the design of effective vaccine adjuvants.

Induction of natural killer cell responses by ectromelia virus controls infection

Natural killer (NK) cells play a pivotal role in the innate immune response to viral infections, particularly murine cytomegalovirus (MCMV) and human herpesviruses. In poxvirus infections, the role of NK cells is less clear. We examined disease progression in C57BL/6 mice after the removal of NK cells by both antibody depletion and genetic means. We found that NK cells were crucial for survival and the early control of virus replication in spleen and to a lesser extent in liver in C57BL/6 mice. Studies of various knockout mice suggested that gammadelta T cells and NKT cells are not important in the C57BL/6 mousepox model and CD4+ and CD8+ T cells do not exhibit antiviral activity at 6 days postinfection, when the absence of NK cells has a profound effect on virus titers in spleen and liver. NK cell cytotoxicity and/or gamma interferon (IFN-gamma) secretion likely mediated the antiviral effect needed to control virus infectivity in target organs. Studies of the effects of ectromelia virus (ECTV) infection on NK cells demonstrated that NK cells proliferate within target tissues (spleen and liver) and become activated following a low-dose footpad infection, although the mechanism of activation appears distinct from the ligand-dependent activation observed with MCMV. NK cell IFN-gamma secretion was detected by intracellular cytokine staining transiently at 32 to 72 h postinfection in the lymph node, suggesting a role in establishing a Th1 response. These results confirm a crucial role for NK cells in controlling an ECTV infection.

IL-10, regulatory T cells, and Kupffer cells mediate tolerance in concanavalin A-induced liver injury in mice

The liver appears to play an important role in immunological tolerance, for example, during allo-transplantation. We investigated tolerance mechanisms in the model of concanavalin A (ConA)-induced immune-mediated liver injury in mice. We found that a single injection of a sublethal ConA dose to C57BL/6 mice induced tolerance toward ConA-induced liver damage within 8 days. This tolerogenic state was characterized by suppression of the typical Th1 response in this model and increased IL-10 production. Tolerance induction was fully reversible in IL-10 -/- mice and after blockade of IL-10 responses by anti-IL10R antibody. Co-cultures of CD4+CD25+ regulatory T cells (T(reg)s) and CD4+CD25- responder cells revealed T(reg) from ConA-tolerant mice being more effective in suppressing polyclonal T cell responses than T(reg) from control mice. Moreover, T(reg) from tolerant but not from control mice were able to augment in vitro IL-10 expression. Depletion by anti-CD25 monoclonal antibody (MAb) indicated a functional role of T(reg)s in ConA tolerance in vivo. Cell depletion studies revealed T(reg)S and Kupffer cells (KC) to be crucial for IL-10 expression in ConA tolerance. Studies with CD1d -/- mice lacking natural killer T (NKT) cells disclosed these cells as irrelevant for the tolerogenic effect. Finally, cellular immune therapy with CD4+CD25+ cells prevented ConA-induced liver injury, with higher protection by Treg from ConA-tolerized mice.

CONCLUSION

The immunosuppressive cytokine IL-10 is crucial for tolerance induction in ConA hepatitis and is mainly expressed by CD4+CD25+ T(reg) and KC. Moreover, T(reg)s exhibit therapeutic potential against immune-mediated liver injury.

Reciprocal regulation between natural killer cells and autoreactive T cells

The initiation and the progression of autoimmune diseases stem from complex interactions that involve cells of both the innate and the adaptive immune system. As we discuss here, natural killer (NK) cells, which are components of the innate immune system, can inhibit or promote the activation of autoreactive T cells during the initiation of autoimmunity. After they have been activated, autoreactive T cells contribute to the homeostatic contraction of NK-cell populations. The dynamic interaction between NK cells and autoreactive T cells might indicate the transition from the innate immune triggering of autoimmunity to the progressive phase of the disease. Understanding the mechanisms and signals that control the reciprocal regulation of NK cells and autoreactive T cells could have important implications for treatment in the clinic.

Cellular mechanisms of fatal early-onset autoimmunity in mice with the T cell-specific targeting of transforming growth factor-beta receptor

Transforming growth factor-beta (TGF-beta) has been implicated in the control of differentiation and proliferation of multiple cell types. However, a role for TGF-beta in the control of immune homeostasis is not fully understood because of its pleiotropic action. Here we report that complete ablation of the TGF-beta signaling in T cells engendered aggressive early-onset, multiorgan, autoimmune-associated lesions with 100% mortality. Peripheral CD4+ and CD8+ T cells with TGF-beta-receptor II (TGF-betaRII) deficiency activated cytolytic and T helper 1 (Th1) differentiation program in a cell-intrinsic T cell receptor (TCR)-specific fashion. Furthermore, TGF-betaRII deficiency blocked the development of canonical CD1d-restricted NKT cells. Instead, it facilitated generation of a highly pathogenic T cell subset exhibiting multiple hallmarks of NK cells and sharply elevated amounts of FasL, perforin, granzymes, and interferon-gamma. Thus, TGF-beta signaling in peripheral T cells is crucial in restraining TCR activation-dependent Th1, cytotoxic, and NK cell-like differentiation program which, when left unchecked, leads to rapidly progressing fatal autoimmunity.

Pivotal advance: alpha-galactosylceramide induces protection against lipopolysaccharide-induced shock

alpha-galactosylceramide, a natural killer T cell ligand, and its synthetic homolog, KRN7000, consistently influence IFN-gamma and TNF-alpha release, both mediators of LPS-induced shock. To modify the course of endotoxin shock, we injected KRN7000 at different time points of experimental systemic Shwartzman reaction. Mice treated with KRN7000 survived when it was injected within 2 h before and after LPS challenge. Mice survival was associated with low levels of T helper 1 (Th1) cytokines, such as IFN-gamma and TNF-alpha. By contrast, protection from endotoxin shock was associated with an increase of T helper 2 (Th2) cytokines, like IL-4 and IL-10. A role of Th2 cytokines in counteracting LPS-induced shock was supported by experiments in which the protection against Shwartzman reaction by KRN7000 was abrogated by in vivo coadministration of anti-Th2 cytokines antibodies. In addition, cytofluorimetric analysis showed that surviving animals have higher percentages of NKT-IL-10-positive cells and lower percentages of NKT-IFN-gamma and macrophages/TNF-alpha-stained cells than nonprotected mice. Taken together, our data demonstrate that KRN7000 treatment given at times near LPS challenge is protective for endotoxin shock inhibiting IFN-gamma and TNF-alpha release. Moreover, KRN7000-mediated protection occurs through an increased production of IL-4 and IL-10, which are mainly secreted by NKT cells. Since IFN-gamma release by NKT requires a longer TCR stimulation than that required for Th2 cytokines production, we demonstrate that timing of KRN7000 in vivo exposure affect the pattern of cytokines expression protecting animals by endotoxin shock.

IL-4-Secreting NKT Cells Prevent Hypersensitivity Pneumonitis by Suppressing IFN-γ-Producing Neutrophils

Hypersensitivity pneumonitis (HP) is mediated by Th1 immune response. NKT cells regulate immune responses by modulating the Th1/Th2 balance. Therefore, we postulated that NKT cells play a critical role in the development of the HP by modulating the Th1/Th2 response. To address this issue, we explored the functional roles of NKT cells in Saccharopolyspora rectivirgula (SR)-induced HP. In CD1d(-/-) mice, the HP was worse in terms of histological changes, hydroxyproline levels, the CD4:CD8 ratio in bronchoalveolar lavage fluid, and SR-specific immune responses than in control mice. CD1d(-/-) mice showed elevated IFN-gamma production in the lung during the HP, and this was produced mainly by Gr-1+ neutrophils. The blockade of IFN-gamma in CD1d(-/-) mice attenuated the HP, whereas the injection of rIFN-gamma aggravated it. Moreover, the depletion of Gr-1+ neutrophils reduced CD8+ T cell numbers in bronchoalveolar lavage fluid during the HP. The adoptive transfer of IL-4(-/-) mouse NKT cells did not attenuate the HP, whereas wild-type or IFN-gamma(-/-) mouse NKT cells suppressed the HP. In conclusion, NKT cells producing IL-4 play a protective role in SR-induced HP by suppressing IFN-gamma-producing neutrophils, which induce the activation and proliferation of CD8+ T cells in the lung.

Rapid development of a gamma interferon-secreting glycolipid/CD1d-specific Valpha14+ NK1.1- T-cell subset after bacterial infection

The phenotypic and functional changes of glycolipid presented by CD1d(glycolipid/CD1d) specific Valpha14+ T cells in the liver of mice at early stages of bacterial infection were investigated. After Listeria monocytogenes infection or interleukin-12 (IL-12) treatment, alpha-galactosylceramide/CD1d tetramer-reactive (alpha-GalCer/CD1d+) T cells coexpressing natural killer (NK) 1.1 marker became undetectable and, concomitantly, cells lacking NK1.1 emerged in both euthymic and thymectomized animals. Depletion of the NK1.1+ subpopulation prevented the emergence of alpha-GalCer/CD1d+ NK1.1- T cells. Before infection, NK1.1+, rather than NK1.1-, alpha-GalCer/CD1d+ T cells coexpressing CD4 were responsible for IL-4 production, whereas gamma interferon (IFN-gamma) was produced by cells regardless of NK1.1 or CD4 expression. After infection, IL-4-secreting cells became undetectable among alpha-GalCer/CD1d+ T cells, but considerable numbers of IFN-gamma-secreting cells were found among NK1.1-, but not NK1.1+, cells lacking CD4. Thus, NK1.1 surface expression and functional activities of Valpha14+ T cells underwent dramatic changes at early stages of listeriosis, and these alterations progressed in a thymus-independent manner. In mutant mice lacking all alpha-GalCer/CD1d+ T cells listeriosis was ameliorated, suggesting that the subtle contribution of the NK1.1- T-cell subset to antibacterial protection is covered by more profound detrimental effects of the NK1.1+ T-cell subset.

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.

NKT cells play a limited role in the neutrophilic inflammatory responses and host defense to pulmonary infection with Pseudomonas aeruginosa

CD1d-restricted NKT cells are reported to play a critical role in the host defense to pulmonary infection with Pseudomonas aeruginosa. However, the contribution of a major subset expressing a Valpha14-Jalpha18 gene segment remains unclear. In the present study, we re-evaluated the role of NKT cells in the neutrophilic inflammatory responses and host defense to this infection using mice genetically lacking Jalpha18 or CD1d (Jalpha18KO or CD1dKO mice). These mice cleared the bacteria in lungs at a comparable level to wild-type (WT) mice. There was no significant difference in the local neutrophilic responses, as shown by neutrophil counts and synthesis of MIP-2 and TNF-alpha, in either KO mice from those in WT mice. Administration of alpha-galactosylceramide, a specific activator of Valpha14+ NKT cells, failed to promote the bacterial clearance and neutrophilic responses, although the same treatment increased the synthesis of IFN-gamma, suggesting the involvement of this cytokine downstream of NKT cells. In agreement against this notion, these responses were not further enhanced by administration of recombinant IFN-gamma in the infected Jalpha18KO mice. Our data indicate that NKT cells play a limited role in the development of neutrophilic inflammatory responses and host defense to pulmonary infection with P. aeruginosa.

Impaired selection of invariant natural killer T cells in diverse mouse models of glycosphingolipid lysosomal storage diseases

Glycolipid ligands for invariant natural killer T cells (iNKT cells) are loaded onto CD1d molecules in the late endosome/lysosome. Accumulation of glycosphingolipids (GSLs) in lysosomal storage diseases could potentially influence endogenous and exogenous lipid loading and/or presentation and, thus, affect iNKT cell selection or function. The percentages and frequency of iNKT cells were reduced in multiple mouse models of lysosomal GSL storage disease, irrespective of the specific genetic defect or lipid species stored. Reduced numbers of iNKT cells resulted in the absence of cytokine production in response to alpha-galactosylceramide (alpha-GalCer) and reduced iNKT cell-mediated lysis of wild-type targets loaded with alpha-GalCer. The reduction in iNKT cells did not result from defective expression of CD1d or a lack of antigen-presenting cells. Although H-2 restricted CD4(+) T cell responses were generally unaffected, processing of a lysosome-dependent analogue of alpha-GalCer was impaired in all the strains of mice tested. These data suggest that GSL storage may result in alterations in thymic selection of iNKT cells caused by impaired presentation of selecting ligands.

Natural killer T cell-mediated antitumor immune responses and their clinical applications

A unique lymphocyte population, CD1d-restricted NKT cells, has been revealed to be a key player in both the innate and acquired immune responses, including antitumor effects. Recent studies revealed that at least two subsets of CD1d-restricted NKT cells exist: type I, having invariant Valpha14 receptor; and type II, having heterogeneous non-Valpha14 receptor. The specific glycolipid ligand, alpha-GalCer, effectively stimulates mouse and human type I NKT cells. The activation of type I NKT cells substantially influences function of other various cell types, particularly DC, NK cells, CD4 Th1 cells, and CD8 cytotoxic T cells, all contributing to the antitumor immune responses. Recent studies also indicated that, unlike type I NKT cells, type II NKT cells have a potential to repress antitumor immune responses. In this review, we summarize the characteristics of the antitumor immune responses mediated by both mouse and human CD1d-restricted NKT cells and discuss their potential in clinical applications against cancer.

Granulocyte-macrophage colony-stimulating factor regulates effector differentiation of invariant natural killer T cells during thymic ontogeny

Invariant natural killer T (iNKT) cell-derived cytokines have important functions in inflammation, host defense, and immunoregulation. Yet, when and how iNKT cells undergo effector differentiation, which endows them with the capacity to rapidly secrete cytokines upon activation, remains unknown. We discovered that granulocyte-macrophage colony-stimulating factor (Csf-2)-deficient mice developed iNKT cells that failed to respond to the model antigen alpha-galactosylceramide because of an intrinsic defect in the fusion of secretory vesicles with the plasma membrane. Exogenous Csf-2 corrected the functional defect only when supplied during the development of thymic, but not mature, splenic Csf-2-deficient iNKT cells. Thus, we ascribe a unique function to Csf-2, which regulates iNKT cell effector differentiation during development by a mechanism that renders them competent for cytokine secretion.

Participatory role of natural killer and natural killer T cells in atherosclerosis: lessons learned from in vivo mouse studies

Atherosclerosis is a multifactor, highly complex disease with numerous aetiologies that work synergistically to promote lesion development. One of the emerging components that drive the development of both early- and late-stage atherosclerotic lesions is the participation of both the innate and acquired immune systems. In both humans and animal models of atherosclerosis, the most prominent cells that infiltrate evolving lesions are macrophages and T lymphocytes. The functional loss of either of these cell types reduces the extent of atherosclerosis in mice that were rendered susceptible to the disease by deficiency of either apolipoprotein E or the LDL (low density lipoprotein) receptor. In addition to these major immune cell participants, a number of less prominent leukocyte populations that can modulate the atherogenic process are also involved. This review will focus on the participatory role of two "less prominent" immune components, namely natural killer (NK) cells and natural killer T (NKT) cells. Although this review will highlight the fact that both NK and NKT cells are not sufficient for causing the disease, the roles played by both these cells types are becoming increasingly important in understanding the complexity of this disease process.

Injury-induced suppression of effector T cell immunity requires CD1d-positive APCs and CD1d-restricted NKT cells

Overwhelming infection remains the leading cause of death from serious burn injury despite recent advances in the care of burn patients and a better understanding of immune and inflammatory consequences of injury. In this study, we report a critical requirement for CD1d-restricted NKT cells and CD1d expression by APCs in the immune dysfunction that occurs early after burn injury. Using a well-established murine scald injury model with BALB/c and BALB/c CD1d knockout mice, we investigated whether peripheral T cell immunity was affected by the presence or absence of CD1d-restricted NKT cells in the early stages after injury. Using Ag-specific delayed-type hypersensitivity, T cell proliferation, and cytokine production as indices of immune responsiveness, we observed that both CD1d expression by APCs and CD1d-restricted NKT cells are required for immune suppression after injury. Via adoptive transfer of splenocytes from injured mice to uninjured recipients, we found injury-induced suppression of immunity to be Ag specific, long lasting, and critically dependent on cell surface expression of CD1d by APCs. Together, our results suggest that the defects in T cell responsiveness that occur subsequent to severe burn injury are not merely the result of global or passive suppression, but instead represent an active form of CD1d/NKT cell-dependent immunologic tolerance.

Natural killer T cells and haemopoiesis

Invariant natural killer T (iNKT) cells are a small but powerful subset of regulatory T cells involved in the modulation of a variety of normal and pathological immune responses. In contrast to conventional or other types of regulatory T cells, they are activated by glycolipid and phospholipid ligands that are presented to them by the non-polymorphic, major histocompatibility complex class I-like molecule CD1d. The in-depth understanding of their function has resulted in successful, iNKT cell-centred experimental therapeutic interventions including prevention of graft-versus-host disease and anti-leukaemia effects. Extending these successes into the clinical arena will require better understanding of their contribution to the pathogenesis of human, including haematological, diseases.

CD4+CD25+ regulatory T cells and CD1-restricted NKT cells do not mediate facial motoneuron survival after axotomy

CD4+ T cells rescue facial motoneurons (FMN) from axotomy-induced cell death. The objective of this study is to determine if the CD4+ T regulatory subsets, CD4+CD25+ T or CD1d-restricted NKT cells are critical for FMN survival after facial nerve axotomy. Surviving FMN within facial motor nuclei from axotomized and control sides 4 weeks after axotomy were counted to determine percent FMN survival. Data generated by applying this paradigm to recombination activating gene-2-deficient mice reconstituted with CD4+ T cells depleted of CD4+CD25+ T cells and to CD1-/- mice, deficient in CD1d-restricted NKT cells, suggest that neither regulatory CD4+ T subset is critical for FMN survival.

CD4+CD25+ Tregs and NKT cells: regulators regulating regulators

CD4+CD25+ regulatory T cells (Tregs) and natural killer T (NKT) cells are two populations of T lymphocytes that can independently regulate adaptive and innate immune responses. Although most studies have investigated the regulatory properties of these T-cell subsets independently of each other, recent reports have provided evidence for cross-talk between Tregs and NKT cells, and, consequently, the immunoregulatory networks are seen in a new perspective. Activated NKT cells seem to modulate quantitatively and qualitatively Treg function through IL-2-dependent mechanisms, whereas Tregs can suppress the proliferation, cytokine release and cytotoxic activity of NKT cells by cell-contact-dependent mechanisms. Importantly, Tregs and NKT cells share crucial signaling pathways that could be responsible for their concerted responses. The advances in our understanding of the interactions between distinct subsets of regulatory T cells in autoimmunity might unveil new methods for harnessing these cells with immunotherapeutic properties.

The neuronal chemokine CX3CL1/fractalkine selectively recruits NK cells that modify experimental autoimmune encephalomyelitis within the central nervous system

Leukocyte trafficking to the central nervous system (CNS), regulated in part by chemokines, determines severity of the demyelinating diseases multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). To examine chemokine receptor CX3CR1 in EAE, we studied CX3CR1(GFP/GFP) mice, in which CX3CR1 targeting by insertion of Green Fluorescent Protein (GFP) allowed tracking of CX3CR1+ cells in CX3CR1(+/GFP) animals and cells destined to express CX3CR1 in CX3CR1(GFP/GFP) knockouts. NK cells were markedly reduced in the inflamed CNS of CX3CR1-deficient mice with EAE, whereas recruitment of T cells, NKT cells and monocyte/macrophages to the CNS during EAE did not require CX3CR1. Impaired recruitment of NK cells in CX3CR1(GFP/GFP) mice was associated with increased EAE-related mortality, nonremitting spastic paraplegia and hemorrhagic inflammatory lesions. The absence of CD1d did not affect the severity of EAE in CX3CR1(GFP/GFP) mice, arguing against a role for NKT cells. Accumulation of NK cells in livers of wild-type (WT) and CX3CR1(GFP/GFP) mice with cytomegalovirus hepatitis was equivalent, indicating that CX3CL1 mediated chemoattraction of NK cells was relatively specific for the CNS. These results are the first to define a chemokine that governs NK cell migration to the CNS, and the findings suggest novel therapeutic manipulation of CX3CR1+ NK cells.

Autoreactive T Cells Mediate NK Cell Degeneration in Autoimmune Disease

Emerging evidence indicates that NK cells play an important and complex role in autoimmune disease. Humans with autoimmune diseases often have reduced NK cell numbers and compromised NK cell functions. Mechanisms underlying this NK cell degeneration and its biological significance are not known. In this study we show that, in an experimental model of human autoimmune myasthenia gravis induced by a self-Ag, the acetylcholine receptor, NK cells undergo proliferation during the initiation of autoimmunity, followed by significant degeneration associated with the establishment of the autoreactive T cell response. We show that NK cell degeneration was mediated by IL-21 derived from autoreactive CD4(+) T cells, and that acetylcholine receptor-immunized IL-21R-deficient mice, with competent NK cells, developed exacerbated autoimmunity. Thus, NK cell degeneration may serve as a means evolved by the immune system to control excessive autoimmunity.

DOCK2 Is Required in T Cell Precursors for Development of Vα14 NK T Cells

Mouse CD1d-restricted Valpha14 NKT cells are a unique subset of lymphocytes, which play important roles in immune regulation, tumor surveillance and host defense against pathogens. DOCK2, a mammalian homolog of Caenorhabditis elegans CED-5 and Drosophila melanogaster myoblast city, is critical for lymphocyte migration and regulates T cell responsiveness through immunological synapse formation, yet its role in Valpha14 NKT cells remains unknown. We found that DOCK2 deficiency causes marked reduction of Valpha14 NKT cells in the thymus, liver, and spleen. When alpha-galactosylceramide (alpha-GalCer), a ligand for Valpha14 NKT cells, was administrated, cytokine production was scarcely detected in DOCK2-deficient mice, suggesting that DOCK2 deficiency primarily affects generation of Valpha14 NKT cells. Supporting this idea, staining with CD1d/alpha-GalCer tetramers revealed that CD44- NK1.1- Valpha14 NKT cell precursors are severely reduced in the thymuses of DOCK2-deficient mice. In addition, studies using bone marrow chimeras indicated that development of Valpha14 NKT cells requires DOCK2 expression in T cell precursors, but not in APCs. These results indicate that DOCK2 is required for positive selection of Valpha14 NKT cells in a cell-autonomous manner, thereby suggesting that avidity-based selection also governs development of this unique subset of lymphocytes in the thymus.

Gut motor function: immunological control in enteric infection and inflammation

Alteration in gastrointestinal (GI) motility occurs in a variety of clinical settings which include acute enteritis, inflammatory bowel disease, intestinal pseudo-obstruction and irritable bowel syndrome (IBS). Most disorders affecting the GI tract arise as a result of noxious stimulation from the lumen via either microbes or chemicals. However, it is not clear how injurious processes initiated in the mucosa alter function in the deeper motor apparatus of the gut wall. Activation of immune cells may lead to changes in motor-sensory function in the gut resulting in the development of an efficient defence force which assists in the eviction of the noxious agent from the intestinal lumen. This review addresses the interface between immune and motor system in the context of host resistance based on the studies in murine model of enteric nematode parasite infection. These studies clearly demonstrate that the infection-induced T helper 2 type immune response is critical in producing the alterations of infection-induced intestinal muscle function in this infection and that this immune-mediated alteration in muscle function is associated with host defence mechanisms. In addition, by manipulating the host immune response, it is possible to modulate the accompanying muscle function, and this may have clinical relevance. These observations not only provide valuable information on the immunological control of gut motor function and its role in host defence in enteric infection, but also provide a basis for understanding pathophysiology of gastrointestinal motility disorders such as in IBS.

Interleukin-13-regulated M2 macrophages in combination with myeloid suppressor cells block immune surveillance against metastasis

CD1-deficient mice reject established, disseminated 4T1 metastatic mammary cancer and survive indefinitely if their primary mammary tumors are surgically removed. This highly effective immune surveillance is due to three interacting mechanisms: (a) the generation of inducible nitric oxide synthase (iNOS)-producing M1 macrophages that are tumoricidal for 4T1 tumor cells; (b) a rapid decrease in myeloid-derived Gr1(+)CD11b(+) suppressor cells that are elevated and down-regulate the CD3zeta chain when primary tumor is present and that suppress T cells by producing arginase; and (c) production of activated lymphocytes. Macrophages from wild-type BALB/c mice are polarized by interleukin-13 (IL-13) towards a tumor-promoting M2 phenotype, thereby inhibiting the generation of tumoricidal M1 macrophages. In contrast, CD1(-/-) mice, which are deficient for IL-13 because they lack IL-13-producting NKT cells, generate M1 macrophages that are cytotoxic for 4T1 via the production of nitric oxide. Although tumoricidal macrophages are a necessary component of immune surveillance in CD1(-/-) mice, they alone are not sufficient for tumor resistance because IL-4Ralpha(-/-) mice have M1 macrophages and retain high levels of myeloid suppressor cells after surgery; in addition, they are susceptible to 4T1 metastatic disease. These results show that effective immune surveillance against established metastatic disease is negatively regulated by IL-13 and requires the induction of tumoricidal M1 macrophages and lymphocytes combined with a reduction in tumor-induced myeloid suppressor cells.

Activation of Invariant NKT Cells by the Helminth Parasite Schistosoma mansoni

Mouse CD1d-restricted NKT cells, including invariant (i)NKT cells, are innate cells activated by glycolipid Ags and play important roles in the initiation and regulation of immune responses. Through their ability to promptly produce large amounts of Th1 and/or Th2 cytokines upon TCR engagement, iNKT cells exert crucial functions in the immune/inflammatory system during bacterial, protozoan, fungal, and viral infections. However, their roles during metazoan parasite infection, which are generally associated with strong Th2 responses, still remain elusive. In this study, we show that during the course of murine schistosomiasis, iNKT cells exhibit an activated phenotype and that following schistosome egg encounter in the liver, hepatic iNKT cells produce both IFN-gamma and IL-4 in vivo. We also report that schistosome egg-sensitized dendritic cells (DCs) activate, in a CD1d-dependent manner, iNKT cells to secrete IFN-gamma and IL-4 in vitro. Interestingly, transfer of egg-sensitized DCs promotes a strong Th2 response in recipient wild-type mice, but not in mice that lack iNKT cells. Engagement of TLRs in DCs is not necessary for iNKT cell stimulation in response to egg-sensitized DCs, suggesting an alternative pathway of activation. Finally, we propose that self, rather than parasite-derived, CD1d-restricted ligands are implicated in iNKT cell stimulation. Taken together, our data show for the first time that helminths can activate iNKT cells to produce immunoregulatory cytokines in vivo, enabling them to influence the adaptive immune response.

Natural killer T (NKT) cells attenuate bleomycin-induced pulmonary fibrosis by producing interferon-gamma

Pulmonary fibrosis is a progressive illness characterized by interstitial fibrosis. Although the precise mechanism for pulmonary fibrosis is not completely understood, an immune response involving interferon (IFN)-gamma appears to play a role. Therefore, we examined the functional roles of natural killer T (NKT) cells, which produce IFN-gamma and interleukin-4 on activation, in bleomycin-induced pulmonary fibrosis. In NKT cell-deficient mice, pulmonary fibrosis was worse in terms of histology, hydroxyproline levels, and mortality than in control mice. The transforming growth factor (TGF)-beta1 levels were higher in the lung after injecting bleomycin, and blockade of TGF-beta1 by neutralizing monoclonal antibody attenuated the pulmonary fibrosis in CD1d-/- mice. In contrast, the production of IFN-gamma was reduced in lungs from CD1d-/- mice. Moreover, the adoptive transfer of NKT cells into CD1d-/- mice increased IFN-gamma and reduced TGF-beta1 production, attenuating pulmonary fibrosis. An in vitro assay demonstrated that IFN-gamma was involved in suppressing TGF-beta1 production in cells collected from bronchoalveolar lavage. The adoptive transfer of NKT cells from IFN-gamma-/- mice did not reverse pulmonary fibrosis or TGF-beta1 production in lungs of CD1d-/- mice whereas NKT cells from B6 control mice attenuated fibrosis and reduced TGF-beta1 production. In conclusion, IFN-gamma-producing NKT cells play a novel anti-fibrotic role in pulmonary fibrosis by regulating TGF-beta1 production.

A Cell-Type Specific CD1d Expression Program Modulates Invariant NKT Cell Development and Function

Invariant NK T (iNKT) cells are a distinct subset of T cells that rapidly produce an array of immunoregulatory cytokines upon activation. Cytokines produced by iNKT cells subsequently transactivate other leukocytes and elicit their respective effector functions. In this way, iNKT cells play a central role in coordinating the development of immune responses in a variety of settings. However, the mechanisms governing the quality of the iNKT cell response elicited remain poorly defined. To address whether changes in the CD1d expression pattern could regulate iNKT cell function, we generated a transgenic (Tg) mouse model in which thymocytes and peripheral T cells express high levels of CD1d (Lck-CD1d Tg+ mice). The expression of CD1d by T cells was sufficient to rescue development of iNKT cells in mice deficient of endogenous CD1d. However, the relative proportions of iNKT cell subsets in Lck-CD1d Tg+ mice were distinctly different from those in wild-type mice, suggesting an altered developmental program. Additionally, iNKT cells were hyporesponsive to antigenic stimulation in vivo. Interestingly, Lck-CD1d Tg+ mice develop liver pathology in the absence of any exogenous manipulation. The results of these studies suggest that changes to the CD1d expression program modulate iNKT cell development and function.

Differential antitumor immunity mediated by NKT cell subsets in vivo

We showed previously that NKT cell–deficient TCR Jα18^−/− mice are more susceptible to methylcholanthrene (MCA)-induced sarcomas, and that normal tumor surveillance can be restored by adoptive transfer of WT liver-derived NKT cells. Liver-derived NKT cells were used in these studies because of their relative abundance in this organ, and it was assumed that they were representative of NKT cells from other sites. We compared NKT cells from liver, thymus, and spleen for their ability to mediate rejection of the sarcoma cell line (MCA-1) in vivo, and found that this was a specialized function of liver-derived NKT cells. Furthermore, when CD4⁺ and CD4⁻ liver-derived NKT cells were administered separately, MCA-1 rejection was mediated primarily by the CD4⁻ fraction. Very similar results were achieved using the B16F10 melanoma metastasis model, which requires NKT cell stimulation with α-galactosylceramide. The impaired ability of thymus-derived NKT cells was due, in part, to their production of IL-4, because tumor immunity was clearly enhanced after transfer of IL-4–deficient thymus-derived NKT cells. This is the first study to demonstrate the existence of functionally distinct NKT cell subsets in vivo and may shed light on the long-appreciated paradox that NKT cells function as immunosuppressive cells in some disease models, whereas they promote cell-mediated immunity in others.

Inhibition of antitumor immunity by invariant natural killer T cells in a T-cell lymphoma modelin vivo

We have investigated the role of the host's CD1d-dependent innate antitumor immune response in a murine T-cell lymphoma model in vivo. We found that C57BL/6 wildtype (WT) mice inoculated with RMA/S cells transfected with murine CD1d1 died at the same rate as mice inoculated with vector-transfected cells. In contrast, natural killer T (NKT) cell-deficient CD1d or Jalpha18 knockout mice inoculated with CD1d-transfected RMA/S cells survived significantly longer than mice inoculated with vector-transfected RMA/S cells, implicating the involvement of invariant NKT (iNKT) cells in inhibiting antitumor activity in vivo. In contrast to the mutant mice, which produced more of the proinflammatory cytokines IFN-gamma and GM-CSF, WT mice produced significantly elevated amounts of IL-13. Antitumor activity in the knockout mice was not due to the development of CD1d-specific cytotoxic T lymphocytes or circulating antibodies. However, iNKT cell numbers were elevated in tumor-bearing mice. Thus, iNKT cells may be playing a negative role in the host's antitumor immune response against T-cell lymphomas in a CD1d-dependent manner.

NKT cells are not critical for HSV‐1 disease resolution

NKT cells are a minor subset of T cells that have important roles in controlling immune responses in disease states including cancer, autoimmunity and pathogenic infections. In contrast to conventional T cells, NKT cells express an invariant TCR and respond to glycolipids presented by CD1d. In this study, we sought to investigate the role of NKT cells in regulating the response to infection with HSV-1, and the mechanism involved, in well-established mouse models. Previous studies of HSV-1 disease in mice have shown clear roles for CD4+ and CD8+ T cells. The role of NKT cells in the resolution of HSV-1 (KOS strain) infection was investigated through flank zosteriform or footpad infection in wild-type versus CD1d-deficient mice, by measurement of viral plaque-forming units at different sites after infection, lesion severity and HSV-1-specific T-cell responses. In contrast to a previous study using a more virulent strain of HSV-1 (SC16 strain), no differences were observed in disease magnitude or resolution, and furthermore, the T-cell response to HSV-1 (KOS strain) was unaltered in the absence of NKT cells. In conclusion, this study shows that NKT cells do not play a general role in controlling the resolution or severity of HSV-1 infection. Instead, the resolution or severity of the infection may depend on the HSV-1 strain under investigation.

Glycolipid antigen induces long-term natural killer T cell anergy in mice

Natural killer T (NKT) cells recognize glycolipid antigens presented by the MHC class I-related glycoprotein CD1d. The in vivo dynamics of the NKT cell population in response to glycolipid activation remain poorly understood. Here, we show that a single administration of the synthetic glycolipid alpha-galactosylceramide (alpha-GalCer) induces long-term NKT cell unresponsiveness in mice. NKT cells failed to proliferate and produce IFN-gamma upon alpha-GalCer restimulation but retained the capacity to produce IL-4. Consequently, we found that activation of anergic NKT cells with alpha-GalCer exacerbated, rather than prevented, B16 metastasis formation, but that these cells retained their capacity to protect mice against experimental autoimmune encephalomyelitis. NKT cell anergy was induced in a thymus-independent manner and maintained in an NKT cell-autonomous manner. The anergic state could be broken by IL-2 and by stimuli that bypass proximal TCR signaling events. Collectively, the kinetics of initial NKT cell activation, expansion, and induction of anergy in response to alpha-GalCer administration resemble the responses of conventional T cells to strong stimuli such as superantigens. Our findings have important implications for the development of NKT cell-based vaccines and immunotherapies.

The analysis of systemic tolerance elicited by antigen inoculation into the vitreous cavity: vitreous cavity-associated immune deviation

The immune privilege that exists in the eye is maintained by various mechanisms. One of the best studied is a form of systemic tolerance termed anterior chamber-associated immune deviation (ACAID). We have investigated the mechanisms by which ocular inflammation associated with the vitreous cavity (VC) is reduced, by injecting either ovalbumin (OVA) or allogeneic splenocytes into the VCs of mice, and assessed the effect of this on delayed type hypersensitivity (DTH) responses. After antigen inoculation into the VC, antigen-specific DTH responses were significantly impaired and we named this phenomenon 'vitreous cavity-associated immune deviation' (VCAID). VCAID could also be induced by inoculating antigen-pulsed macrophages into the VC. However, VCAID did not develop either in mice with inflamed eyes, whether as a result of experimental autoimmune uveitis or coadministration of interleukin (IL)-6 in the VC, or in knockout mice deficient for natural killer T (NKT) cells. Finally, we found that so-called 'hyalocytes' are the only cells present in the VCs of normal mice, uniformly distributed on the retinal surface. Interestingly, they express F4/80, suggesting that hyalocytes are candidate antigen-presenting cells (APCs) responsible for mediating VCAID. As for the anterior chamber model, systemic tolerance can be induced in the VC in non-inflamed eyes and in the presence of invariant NKT cells.

Cooperation of Invariant NKT Cells and CD4+CD25+ T Regulatory Cells in the Prevention of Autoimmune Myasthenia

CD1d-restricted NKT cells and CD4+CD25+ regulatory T (Treg) cells are thymus-derived subsets of regulatory T cells that have an important role in the maintenance of self-tolerance. Whether NKT cells and Treg cells cooperate functionally in the regulation of autoimmunity is not known. We have explored this possibility in experimental autoimmune myasthenia gravis (EAMG), an animal model of human myasthenia gravis, induced by immunization of C57BL/6 mice with the autoantigen acetylcholine receptor. We have demonstrated that activation of NKT cells by a synthetic glycolipid agonist of NKT cells, alpha-galactosylceramide (alpha-GalCer), inhibits the development of EAMG. alpha-GalCer administration in EAMG mice increased the size of the Treg cell compartment, and augmented the expression of foxp3 and the potency of CD4+CD25+ cells to inhibit proliferation of autoreactive T cells. Furthermore, alpha-GalCer promoted NKT cells to transcribe the IL-2 gene and produce IL-2 protein. Depletion of CD25+ cells or neutralization of IL-2 reduced the therapeutic effect of alpha-GalCer in this model. Thus, alpha-GalCer-activated NKT cells can induce expansion of CD4+CD25+ Treg cells, which in turn mediate the therapeutic effects of alpha-GalCer in EAMG. Induced cooperation of NKT cells and Treg cells may serve as a superior strategy to treat autoimmune disease.

The influence of CD1d in postselection NKT cell maturation and homeostasis

After being positively selected on CD1d-expressing thymocytes, NKT cells undergo a series of developmental changes that can take place inside or outside the thymus. We asked whether CD1d continues to play a role in late-stage NKT cell development and, in particular, during the functionally significant acquisition of NK1.1 that is indicative of NKT cell maturity. We report that CD1d is indeed crucial for this step, because immature NK1.1(-) NKT cells fail to fully mature when transferred to a CD1d-deficient environment. Surprisingly, however, the lack of CD1d did not greatly affect the long-term survival of NKT cells, and they continued to express CD69 and slowly proliferate. This directly contradicts the currently held view that these phenomena are caused by autoreactivity directed against CD1d/TCR-restricted self-Ags. Our findings demonstrate an ongoing role for TCR-mediated signaling throughout NKT cell development, but the characteristic semiactivated basal state of NKT cells is controlled by CD1d-independent factors or is intrinsic to the cells themselves.

Early cytokine production is associated with protection from murine cerebral malaria

Cerebral malaria (CM) is an infrequent but serious complication of Plasmodium falciparum infection in humans. Animal and human studies suggest that the pathogenesis of CM is immune mediated, but the precise mechanisms leading to cerebral pathology are unclear. In mice, infection with Plasmodium berghei ANKA results in CM on day 6 postinoculation (p.i.), while infection with the closely related strain P. berghei K173 does not result in CM. Infection with P. berghei K173 was associated with increased plasma gamma interferon (IFN-gamma) at 24 h p.i. and with increased splenic and hepatic mRNAs for a range of cytokines (IFN-gamma, interleukin-10 [IL-10], and IL-12) as well as the immunoregulatory enzyme indoleamine 2,3-dioxygenase. In contrast, P. berghei ANKA infection was associated with an absence of cytokine production at 24 h p.i. but a surge of IFN-gamma production at 3 to 4 days p.i. When mice were coinfected with both ANKA and K173, they produced an early cytokine response, including a burst of IFN-gamma at 24 h p.i., in a manner similar to animals infected with P. berghei K173 alone. These coinfected mice failed to develop CM. In addition, in a low-dose P. berghei K173 infection model, protection from CM was associated with early production of IFN-gamma. Early IFN-gamma production was present in NK-cell-depleted, gammadelta-cell-depleted, and Jalpha281(-/-) (NKT-cell-deficient) mice but absent from beta2-microglobulin mice that had been infected with P. berghei K173. Taken together, the results suggest that the absence of a regulatory pathway involving IFN-gamma and CD8(+) T cells in P. berghei ANKA infection allows the development of cerebral immunopathology.

Association of NKT cells and granulocytes with liver injury after reperfusion of the portal vein

Reperfusion of the liver was conducted by clamping the portal vein for 30 min in mice, followed by unclamping. Unique variation in the number of lymphocytes was induced and liver injury occurred thereafter. The major expander cells in the liver were estimated to be natural killer T cells (i.e., NKT cells), whereas conventional T cells and NK cells increased only slightly or somewhat decreased in number and proportion at that time. Reflecting the expansion of NKT cells in the liver, a Th0-type of cytokine profile was detected in sera, and cytotoxic activity was enhanced in liver lymphocytes. In NKT cell-deficient mice including CD1d (-/-) mice and athymic nude mice, the magnitude of liver injury decreased up to 50% of that of control mice. It was also suspected that accumulating granulocytes which produce superoxides might be associated with liver injury after reperfusion. This might be due to stress-associated production of catecholamines. It is known that granulocytes bear surface adrenergic receptors and that they are activated by sympathetic nerve stimulation after stress. The present results therefore suggest that liver injury after reperfusion may be mainly caused by the activation of NKT cells and granulocytes, possibly by their cytotoxicity and superoxide production, respectively.

α-Galactosylceramide-induced iNKT cells suppress experimental allergic asthma in sensitized mice: Role of IFN-γ

Allergic asthma is a multifaceted syndrome consisting of eosinophil-rich airway inflammation, bronchospasm, and airway hyper-responsiveness (AHR). Using a mouse model of allergic asthma, we previously reported that invariant NKT (iNKT) cells increase the severity of this disease. Herein, we demonstrate that a single i.v. injection of alpha-galactosylceramide (alpha-GalCer), 1 h before the first airway allergen challenge of OVA-sensitized mice, abrogates elicitation of AHR, airway eosinophilia, IL-4 and IL-5 production in bronchoalveolar lavage fluid, and specific anti-OVA IgE antibodies. Further, alpha-GalCer administered intranasally also strongly inhibited the major symptoms of asthma in sensitized and challenged mice. Alpha-GalCer treatment induces iNKT cell accumulation in the lungs, and shifts their cytokine profile from pro-asthmatic IL-4 to a protective IFN-gamma production. The role of IFN-gamma from iNKT cells in protection was shown by adoptive transfer of sorted iNKT cells from OVA-sensitized and alpha-GalCer-treated mice which protected immunized recipients from manifesting asthma by an IFN-gamma-dependent pathway. Our findings demonstrate for the first time that alpha-GalCer administered locally inhibits asthma symptoms, even in predisposed asthmatic mice, through an iNKT cell- and IFN-gamma-dependent pathway.

NKT cells are critical for the initiation of an inflammatory bowel response against Toxoplasma gondii

We demonstrated in this study the critical role of NKT cells in the lethal ileitis induced in C57BL/6 mice after infection with Toxoplasma gondii. This intestinal inflammation is caused by overproduction of IFN-gamma in the lamina propria. The implication of NKT cells was confirmed by the observation that NKT cell-deficient mice (Jalpha281(-/-)) are more resistant than C57BL/6 mice to the development of lethal ileitis. Jalpha281(-/-) mice failed to overexpress IFN-gamma in the intestine early after infection. This detrimental effect of NKT cells is blocked by treatment with alpha-galactosylceramide, which prevents death in C57BL/6, but not in Jalpha281(-/-), mice. This protective effect is characterized by a shift in cytokine production by NKT cells toward a Th2 profile and correlates with an increased number of mesenteric Foxp3 lymphocytes. Using chimeric mice in which only NKT cells are deficient in the IL-10 gene and mice treated with anti-CD25 mAb, we identified regulatory T cells as the source of the IL-10 required for manifestation of the protective effect of alpha-galactosylceramide treatment. Our results highlight the participation of NKT cells in the parasite clearance by shifting the cytokine profile toward a Th1 pattern and simultaneously to immunopathological manifestation when this Th1 immune response remains uncontrolled.

Synthetic alpha-mannosyl ceramide as a potent stimulant for an NKT cell repertoire bearing the invariant Valpha19-Jalpha26 TCR alpha chain

A NKT cell repertoire is characterized by the expression of the Valpha19-Jalpha26 invariant TCR alpha chain (Valpha19 NKT cell). This repertoire, as well as a well-established Valpha14-Jalpha281 invariant TCR alpha(+) NKT cell subset (Valpha14 NKT cell), has been suggested to have important roles in the regulation of the immune system and, thus, is a major therapeutic target. Here, we attempted to find specific antigens for Valpha19 NKT cells. Valpha19 as well as Valpha14 NKT cells exhibited reactivity to alpha-galactosyl ceramide (alpha-GalCer). Thus, a series of monoglycosyl ceramides with an axially oriented glycosidic linkage between the sugar and ceramide moiety were synthesized and their antigenicity to Valpha19 NKT cells was determined by measuring their immune responses in culture with glycolipids. Comprehensive examinations revealed substantial antigenic activity for Valpha19 NKT cells by alpha-mannosyl ceramide.

NK cells promote islet allograft tolerance via a perforin-dependent mechanism

Although major histocompatibility complex (MHC) class II-restricted CD4 T cells are well appreciated for their contribution to peripheral tolerance to tissue allografts, little is known regarding MHC class I-dependent reactivity in this process. Here we show a crucial role for host MHC class I-dependent NK cell reactivity for allograft tolerance in mice induced through either costimulation blockade using CD154-specific antibody therapy or by targeting LFA-1 (also known as CD11a). Tolerance induction absolutely required host expression of MHC class I, but was independent of CD8 T cell-dependent immunity. Rather, tolerance required innate immunity involving NK1.1(+) cells, but was independent of CD1d-restricted NKT cells. Therefore, NK cells seem to be generally required for induction of tolerance to islet allografts. Additional studies indicate that CD154-specific antibody-induced allograft tolerance is perforin dependent. Notably, NK cells that are perforin competent are sufficient to restore allograft tolerance in perforin-deficient recipients. Together, these results show an obligatory role for NK cells, through perforin, for induction of tolerance to islet allografts.

Exacerbated susceptibility to infection-stimulated immunopathology in CD1d-deficient mice

Mice lacking functional CD1d genes were used to study mechanisms of resistance to the protozoan parasite Toxoplasma gondii. Wild-type (WT) BALB/c mice, CD1d-deficient BALB/c mice, and WT C57BL/6 mice all survived an acute oral infection with a low dose of mildly virulent strain ME49 T. gondii cysts. In contrast, most CD1d-deficient C57BL/6 mice died within 2 wk of infection. Despite having parasite burdens that were only slightly higher than WT mice, CD1d-deficient C57BL/6 mice displayed greater weight loss and intestinal pathology. In C57BL/6 mice, CD4(+) cells can cause intestinal pathology during T. gondii infection. Compared with WT mice, infected CD1d-deficient C57BL/6 mice had higher frequencies and numbers of activated (CD44(high)) CD4(+) cells in mesenteric lymph nodes. Depletion of CD4(+) cells from CD1d-deficient mice reduced weight loss and prolonged survival, demonstrating a functional role for CD4(+) cells in their increased susceptibility to T. gondii infection. CD1d-deficient mice are deficient in Valpha14(+) T cells, a major population of NKT cells. Involvement of these cells in resistance to T. gondii was investigated using gene-targeted Jalpha18-deficient C57BL/6 mice, which are deficient in Valpha14(+) T cells. These mice did not succumb to acute infection, but experienced greater weight loss and more deaths than B6 mice during chronic infection, indicating that Valpha14(+) cells contribute to resistance to T. gondii. The data identify CD4(+) cells as a significant component of the marked susceptibility to T. gondii infection observed in CD1d-deficient C57BL/6 mice, and establish T. gondii as a valuable tool for deciphering CD1d-dependent protective mechanisms.