The Implication and Significance of Beta 2 Microglobulin: A Conservative Multifunctional Regulator.

OBJECTIVE: This review focuses on the current knowledge on the implication and significance of beta 2 microglobulin (ß2M), a conservative immune molecule in vertebrate. DATA SOURCES: The data used in this review were obtained from PubMed up to October 2015. Terms of ß2M, immune response, and infection were used in the search. STUDY SELECTIONS: Articles related to ß2M were retrieved and reviewed. Articles focusing on the characteristic and function of ß2M were selected. The exclusion criteria of articles were that the studies on ß2M-related molecules. RESULTS: ß2M is critical for the immune surveillance and modulation in vertebrate animals. The dysregulation of ß2M is associated with multiple diseases, including endogenous and infectious diseases. ß2M could directly participate in the development of cancer cells, and the level of ß2M is deemed as a prognostic marker for several malignancies. It also involves in forming major histocompatibility complex (MHC class I or MHC I) or like heterodimers, covering from antigen presentation to immune homeostasis. CONCLUSIONS: Based on the characteristic of ß2M, it or its signaling pathway has been targeted as biomedical or therapeutic tools. Moreover, ß2M is highly conserved among different species, and overall structures are virtually identical, implying the versatility of ß2M on applications.

Invariant natural killer T cells and immunotherapy of cancer.

Invariant CD1d restricted natural killer T (iNKT) cells are regulatory cells that express a canonical TCR-Valpha-chain (Valpha24.Jalpha18 in humans and Valpha14.Jalpha18 in mice) which recognizes glycolipid antigens presented by the monomorphic CD1d molecule. They can secrete a wide variety of both pro-inflammatory and anti-inflammatory cytokines very swiftly upon their activation. Evidence for the significance of iNKT cells in human cancer has been ambiguous. Still, the (pre-)clinical findings reviewed here, provide evidence for a distinct contribution of iNKT cells to natural anti-tumor immune responses in humans. Furthermore, clinical phase I studies that are discussed here have revealed that the infusion of cancer patients with ligand-loaded dendritic cells or cultured iNKT cells is well tolerated. We thus underscore the potential of iNKT cell based immunotherapy in conjunction with established modalities such as surgery and radiotherapy, as adjuvant therapy against carcinomas.

CD1d-restricted glycolipid antigens: presentation principles, recognition logic and functional consequences.

Invariant natural killer T (iNKT) cells are innate lymphocytes whose functions are regulated by self and foreign glycolipid antigens presented by the antigen-presenting molecule CD1d. Activation of iNKT cells in vivo results in rapid release of copious amounts of effector cytokines and chemokines with which they regulate innate and adaptive immune responses to pathogens, certain types of cancers and self-antigens. The nature of CD1d-restricted antigens, the manner in which they are recognised and the unique effector functions of iNKT cells suggest an innate immunoregulatory role for this subset of T cells. Their ability to respond fast and our ability to steer iNKT cell cytokine response to altered lipid antigens make them an important target for vaccine design and immunotherapies against autoimmune diseases. This review summarises our current understanding of CD1d-restricted antigen presentation, the recognition of such antigens by an invariant T-cell receptor on iNKT cells, and the functional consequences of these interactions.

Investigation of the role of CD1d-restricted invariant NKT cells in experimental choroidal neovascularization.

Choroidal neovascularization (CNV) is directly related to visual loss in age-related macular degeneration and other macular disorders. We have investigated the role of CD1d-restricted invariant natural killer T (NKT) cells in laser-induced experimental CNV. Quantitative real-time PCR detected increased expression of NKT cell-related genes (Valpha14 and CXCL16) in whole eyes undergoing CNV, indicating local accumulation of NKT cells. We found a significant reduction of CNV and lower concentrations of vascular endothelial growth factor (VEGF) in ocular fluid in two different NKT cell-deficient mice, CD1d knockout (KO) and Jalpha18 KO mice. We also established in vitro co-cultures of retinal pigment epithelial cells and splenic NKT cells, and confirmed NKT cells could produce VEGF in the dish. Moreover, inoculating alpha-galactosylceramide, the ligand for NKT cells, into the vitreous cavity of C57BL/6 mice promoted CNV. We concluded that NKT cells play an important role in CNV as an inducer of VEGF.

Co-inhibitory roles for glucocorticoid-induced TNF receptor in CD1d-dependent natural killer T cells.

Invariant natural killer T (iNKT) cells are a special subset of alphabeta T cells with invariant TCR, which recognize alpha-galactosylceramide (alpha-GalCer) presented by CD1d. In addition to signals through the invariant TCR upon stimulation with alpha-GalCer, costimulatory signals, such as signals through CD28 and OX40, are indispensable for full activation of iNKT cells. In this study, we investigated the functions of a well-known costimulatory molecule, glucocorticoid-induced TNF receptor (GITR), on Ag-induced iNKT cell activation. Unexpectedly, engagement of GITR by agonistic mAb DTA-1 suppressed proliferation and cytokine production of iNKT cells upon alpha-GalCer stimulation. In addition, GITR signals in iNKT cells during only the Ag-priming phase was sufficient to inhibit the iNKT cell activation. Consistent with these results, the GITR-deficient iNKT cells showed enhanced proliferation and increased cytokine production upon alpha-GalCer stimulation both in vitro and in vivo. Furthermore, the in vivo administration of alpha-GalCer suppressed tumor metastasis more efficiently in GITR-deficient mice than in wild-type mice. Collectively, GITR plays a co-inhibitory role in Ag-induced iNKT cell activation.

Cutting edge: a naturally occurring mutation in CD1e impairs lipid antigen presentation.

The human CD1a-d proteins are plasma membrane molecules involved in the presentation of lipid Ags to T cells. In contrast, CD1e is an intracellular protein present in a soluble form in late endosomes or lysosomes and is essential for the processing of complex glycolipid Ags such as hexamannosylated phosphatidyl-myo-inositol, PIM(6). CD1e is formed by the association of beta(2)-microglobulin with an alpha-chain encoded by a polymorphic gene. We report here that one variant of CD1e with a proline at position 194, encoded by allele 4, does not assist PIM(6) presentation to CD1b-restricted specific T cells. The immunological incompetence of this CD1e variant is mainly due to inefficient assembly and poor transport of this molecule to late endosomal compartments. Although the allele 4 of CD1E is not frequent in the population, our findings suggest that homozygous individuals might display an altered immune response to complex glycolipid Ags.

A novel immunoregulatory axis of NKT cell subsets regulating tumor immunity.

There are many mechanisms that regulate and dampen the immune response to cancers, including several types of regulatory T cells. Besides the T reg cell, we have identified another immunoregulatory circuit initiated by NKT cells that produce IL-13 in response to tumor growth and this IL-13 then induces myeloid cells to make TGF-beta that inhibits cytotoxic T cell-mediated tumor immunosurveillance in several mouse tumor models. This finding created a paradox in the role of NKT cells in tumor immunity, in that they can also contribute to protection. We resolve this paradox by the finding that the suppressive NKT cell is a type II NKT cell that lacks the canonical invariant T cell receptor, whereas the protective cell is a type I NKT cell that expresses the invariant receptor. Further, we see that these two subsets of NKT cells counter-regulate each other, defining a new immunoregulatory axis. The balance along this axis may determine the outcome of tumor immunosurveillance as well as influence the efficacy of anti-cancer vaccines and immunotherapy.

A glycosylphosphatidylinositol-based treatment alleviates trypanosomiasis-associated immunopathology.

The GPI-anchored trypanosome variant surface glycoprotein (VSG) triggers macrophages to produce TNF, involved in trypanosomiasis-associated inflammation and the clinical manifestation of sleeping sickness. Aiming at inhibiting immunopathology during experimental Trypanosoma brucei infections, a VSG-derived GPI-based treatment approach was developed. To achieve this, mice were exposed to the GPI before an infectious trypanosome challenge. This GPI-based strategy resulted in a significant prolonged survival and a substantial protection against infection-associated weight loss, liver damage, acidosis, and anemia; the latter was shown to be Ab-independent and correlated with reduced macrophage-mediated RBC clearance. In addition, GPI-based treatment resulted in reduced circulating serum levels of the inflammatory cytokines TNF and IL-6, abrogation of infection-induced LPS hypersensitivity, and an increase in circulating IL-10. At the level of trypanosomiasis-associated macrophage activation, the GPI-based treatment resulted in an impaired secretion of TNF by VSG and LPS pulsed macrophages, a reduced expression of the inflammatory cytokine genes TNF, IL-6, and IL-12, and an increased expression of the anti-inflammatory cytokine gene IL-10. In addition, this change in cytokine pattern upon GPI-based treatment was associated with the expression of alternatively activated macrophage markers. Finally, the GPI-based treatment also reduced the infection-associated pathology in Trypanosoma congolense and Trypanosoma evansi model systems as well as in tsetse fly challenge experiments, indicating potential field applicability for this intervention strategy.

Treatment of PC12 cells with nerve growth factor induces proteasomal degradation of T-cadherin that requires tyrosine phosphorylation of its cadherin domain.

T-cadherin (T-Cad), a unique member of the cadherin family of proteins, plays an important role in cell adhesion and cell signaling. Recently, we demonstrated that T-Cad is transcriptionally repressed by DNA methyltransferase 3b during nerve growth factor (NGF)-induced neuronal differentiation of PC12 cells. Here, we show that T-Cad expression is also regulated at the post-translational level by the proteasomal pathway in these cells, which is facilitated upon NGF treatment. Pulse-chase experiments demonstrated that NGF treatment significantly reduced the half-life of T-Cad. Degradation of T-Cad was blocked upon treatment of PC12 cells with the proteasomal inhibitor ZLLL or lactacystin. Ectopic expression of Cdh1 (CDC20 homolog 1), one of the substrate recognition components of anaphase promoting complex (E3 ligase), stimulated T-Cad degradation. Deletion of CD1, one of the five extracellular cadherin domains (CD), promoted degradation of T-Cad, especially in the presence of NGF. On the contrary, deletion of CD2 stabilized this protein maximally. Ubiquitination of different deletion mutants indicates that T-Cad harbors multiple ubiquitination signals. Furthermore, genistein, a protein-tyrosine kinase inhibitor, impeded T-Cad degradation in PC12 cells, implicating requirement of tyrosine phosphorylation in this process. Mutation at tyrosine 327 (Y327F) markedly increased the half-life of T-Cad, suggesting that phosphorylation of this tyrosine residue located within CD2 is critical for this process. These results show that T-cadherin is subject to dual regulation during NGF-induced differentiation of PC12 cells, namely transcriptional repression mediated by Dnmt3b and post-translational degradation through the proteasomal pathway. These data, together with the inhibitory role of T-Cad in neurite outgrowth of PC12 cells upon NGF treatment, underscore the significance of its stringent regulation during this differentiation process.

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.

Antigen presentation by CD1 molecules and the generation of lipid-specific T cell immunity.

It is now well demonstrated that the repertoire of T cells includes not only cells that recognize specific MHC-presented peptide antigens, but also cells that recognize specific self and foreign lipid antigens. This T cell recognition of lipid antigens is mediated by a family of conserved MHC class I-like cell surface glycoproteins known as CD1 molecules. These are specialized antigen-presenting molecules that directly bind a wide variety of lipids and present them for T cell recognition at the surface of antigen-presenting cells. Distinct populations of T cells exist that recognize CD1-presented lipids of microbial, environmental or self origin, and these T cells participate in immune responses associated with infectious, neoplastic, autoimmune and allergic diseases. Here we review the current knowledge of the biology of the CD1 system, including the structure, biosynthesis and trafficking of CD1 molecules, the structures of defined lipid antigens and the types of functional responses mediated by T cells specific for CD1-presented lipids.

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.

Low levels of circulating invariant natural killer T cells predict poor clinical outcome in patients with head and neck squamous cell carcinoma.

PURPOSE: Evading antitumor immune responses is an important aspect of the pathogenesis of head and neck squamous cell carcinoma (HNSCC). Invariant CD1d-restricted natural killer T (iNKT) cells play an allegedly pivotal role in such responses via transactivation of immune effector cells. It has been reported that iNKT cells are reduced in peripheral blood of cancer patients compared with healthy controls. Here, we investigated whether the extent of this deficiency affected disease outcome in HNSCC patients. PATIENTS AND METHODS: In a prospective study, circulating iNKT cell numbers were evaluated in 47 patients before radiotherapy. Patients were stratified in three groups based on iNKT cell levels, and clinical data were obtained during a median follow-up period of 31 months. RESULTS: A small, compared with an intermediate or large, circulating iNKT cell fraction was significantly associated with decreased 3-year overall survival rate (39% v 75% and 92%, respectively), disease-specific survival rate (43% v 87% and 92%, respectively), and locoregional control rate (31% v 74% and 92%, respectively) in HNSCC patients. Cox regression revealed that the iNKT cell level, as well as clinical T stage, was an independent prognostic parameter even after correction for the confounding effect of age. CONCLUSION: A severe circulating iNKT cell deficiency was related to poor clinical outcome in HNSCC patients, suggesting their critical contribution to antitumor immune responses. Furthermore, screening for iNKT cell levels may be useful for determining which patients can benefit from immunotherapeutic adjuvant therapies aimed at reconstitution of the circulating iNKT cell pool.

Adenosine A2A receptor activation reduces hepatic ischemia reperfusion injury by inhibiting CD1d-dependent NKT cell activation.

Ischemia reperfusion injury results from tissue damage during ischemia and ongoing inflammation and injury during reperfusion. Liver reperfusion injury is reduced by lymphocyte depletion or activation of adenosine A2A receptors (A2ARs) with the selective agonist 4-{3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]- prop-2-ynyl}-cyclohexanecarboxylic acid methyl ester (ATL146e). We show that NKT cells are stimulated to produce interferon (IFN)-gamma by 2 h after the initiation of reperfusion, and the use of antibodies to deplete NK1.1-positive cells (NK and NKT) or to block CD1d-mediated glycolipid presentation to NKT cells replicates, but is not additive to, the protection afforded by ATL146e, as assessed by serum alanine aminotransferase elevation, histological necrosis, neutrophil accumulation, and serum IFN-gamma elevation. Reduced reperfusion injury observed in RAG-1 knockout (KO) mice is restored to the wild-type (WT) level by adoptive transfer of NKT cells purified from WT or A2AR KO mice but not IFN-gamma KO mice. Additionally, animals with transferred A2AR-/- NKT cells are not protected from hepatic reperfusion injury by ATL146e. In vitro, ATL146e potently inhibits both anti-CD3 and alpha-galactosylceramide-triggered production of IFN-gamma by NKT cells. These findings suggest that hepatic reperfusion injury is initiated by the CD1d-dependent activation of NKT cells, and the activation of these cells is inhibited by A2AR activation.

CD1d ligands: the good, the bad, and the ugly.

The MHC class I-like CD1d glycoprotein is a member of the CD1 family of Ag-presenting molecules and is responsible for the selection of NKT cells. A number of ligands that can be presented by CD1d to NKT or other CD1d-restricted T cells have been identified. These include glycolipids from a marine sponge, bacterial glycolipids, normal endogenous glycolipids, tumor-derived phospholipids and glycolipids, and nonlipidic molecules. The presentation of many of these molecules can have immunopotentiating effects, such as serving as an adjuvant against malaria or resulting in a more rapid clearance of certain virus infections. They can also be protective in autoimmune diseases or cancer or can be deleterious. This review will highlight these ligands in a discussion of their potential use against (and role in the pathogenesis of) these diseases.

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 regulation of cytokine production by CD1d-restricted NKT cells in response to superantigen staphylococcal enterotoxin B exposure.

NKT cells are a heterogeneous population characterized by the ability to rapidly produce cytokines, such as interleukin 2 (IL-2), IL-4, and gamma interferon (IFN-gamma) in response to infections by viruses, bacteria, and parasites. The bacterial superantigen staphylococcal enterotoxin B (SEB) interacts with T cells bearing the Vbeta3, -7, or -8 T-cell receptors, inducing their expansion and cytokine secretion, leading to death in some cases due to cytokine poisoning. The majority of NKT cells bear the Vbeta7 or -8 T-cell receptor, suggesting that they may play a role in regulating this response. Using mice lacking NKT cells (CD1d(-/-) and Jalpha18(-/-) mice), we set out to identify the role of these cells in T-cell expansion, cytokine secretion, and toxicity induced by exposure to SEB. We find that Vbeta8(+) CD4(+) T-cell populations similarly expand in wild-type (WT) and NKT cell-null mice and that NKT cells did not regulate the secretion of IL-2. By contrast, these cells positively regulated the secretion of IL-4 and IFN-gamma production and negatively regulated the secretion of tumor necrosis factor alpha (TNF-alpha). However, this negative regulation of TNF-alpha secretion by NKT cells provides only a minor protective effect on SEB-mediated shock in WT mice compared to mice lacking NKT cells. These data suggest that NKT cells may regulate the nature of the cytokine response to exposure to the superantigen SEB and may act as regulatory T cells during exposure to this superantigen.

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.

Human invariant NKT cells are required for effective in vitro alloresponses.

NKT cells are a small subset of regulatory T cells conserved in humans and mice. In humans they express the Valpha24Jalpha18 invariant chain (hence invariant NKT (iNKT) cells) and are restricted by the glycolipid-presenting molecule CD1d. In mice, iNKT cells may enhance or inhibit anti-infectious and antitumor T cell responses but suppress autoimmune and alloreactive responses. We postulated that iNKT cells might also modulate human alloreactive responses. Using MLR assays we demonstrate that in the presence of the CD1d-presented glycolipid alpha-galactosylceramide (alphaGC) alloreactivity is enhanced (37 +/- 12%; p < 0.001) in an iNKT cell-dependent manner. iNKT cells are activated early during the course of the MLR, presumably by natural ligands. In MLR performed without exogenous ligands, depletion of iNKT cells significantly diminished the alloresponse in terms of proliferation (58.8 +/- 24%; p < 0.001) and IFN-gamma secretion (43.2 +/- 15.2%; p < 0.001). Importantly, adding back fresh iNKT cells restored the reactivity of iNKT cell-depleted MLR to near baseline levels. CD1d-blocking mAbs equally reduced the reactivity of the iNKT cell-replete and -depleted MLR compared with IgG control, indicating that the effect of iNKT cells in the in vitro alloresponse is CD1d-dependent. These findings suggest that human iNKT cells, although not essential for its development, can enhance the alloreactive response.

CD1d-restricted NKT cells contribute to the age-associated decline of T cell immunity.

NKT cells are known to regulate effector T cell immunity during tolerance, autoimmunity, and antitumor immunity. Whether age-related changes in NKT cell number or function occur remains unclear. Here, we investigated whether young vs aged (3 vs 22 mo old) mice had different numbers of CD1d-restricted NKT cells and whether activation of NKT cells by CD1d in vivo contributed to age-related suppression of T cell immunity. Flow cytometric analyses of spleen and LN cells revealed a 2- to 3-fold increase in the number of CD1d tetramer-positive NKT cells in aged mice. To determine whether NKT cells from aged mice differentially regulated T cell immunity, we first examined whether depletion of NK/NKT cells affected the proliferative capacity of splenic T cells. Compared with those from young mice, intact T cell preparations from aged mice had impaired proliferative responses whereas NK/NKT-depleted preparations did not. To examine the specific contribution of NKT cells to age-related T cell dysfunction, Ag-specific delayed-type hypersensitivity and T cell proliferation were examined in young vs aged mice given anti-CD1d mAb systemically. Compared with young mice, aged mice given control IgG exhibited impaired Ag-specific delayed-type hypersensitivity and T cell proliferation, which could be significantly prevented by systemic anti-CD1d mAb treatment. The age-related impairments in T cell immunity correlated with an increase in the production of the immunosuppressive cytokine IL-10 by splenocytes that was likewise prevented by anti-CD1d mAb treatment. Together, our results suggest that CD1d activation of NKT cells contributes to suppression of effector T cell immunity in aged mice.