Interferon gamma production by natural killer (NK) cells and NK1.1+ T cells upon NKR-P1 cross-linking

Induction of promotive rather than suppressive immune responses from a novel NKT cell repertoire Vα19 NKT cell with α-mannosyl ceramide analogues consisting of the immunosuppressant ISP-I as the sphingosine unit

A 2-substituted 2-aminopropane-1,3-diol or 2-aminoethanol is the minimum structure required for the immunosuppressive activity of ISP-I, an antibiotic isolated from the culture broth of Isaria sinclairil. A series of alpha-mannosyl ceramide (alpha-ManCer) analogues was derived from 2-substituted 2-aminopropane-1,3-diols or 2-aminoethanols in place of sphingosine. The newly synthesized glycosides were evaluated for their effects on immune responses. In contrast to the immunosuppressive activity of the precursors, the alpha-ManCer analogues induced immunopromotive responses from invariant Valpha19-Jalpha26 transgenic mouse lymphocytes more effectively than the original alpha-ManCer. Collectively, it is strongly suggested that the 2-substituted 2-aminopropane-1,3-diols and 2-aminoethanols mimic sphingosine in the alpha-ManCer analogues so that they potentially acquire specific antigenicity toward Valpha19 NKT cell, a novel NKT cell subset.

Dysregulation of signaling pathways in CD45-deficient NK cells leads to differentially regulated cytotoxicity and cytokine production

CD45, a protein tyrosine phosphatase that regulates Src family kinases, is important for regulating T cell and B cell receptor signaling; however, little is known about how CD45 regulates immunoreceptor tyrosine-based activation motif (ITAM)-dependent natural killer (NK) cell receptor signaling and the resulting effector functions. NK cells from CD45-deficient mice are relatively competent for ITAM receptor-induced cell-mediated cytotoxicity, yet completely deficient for cytokine secretion after stimulation with ligands to or antibodies against NK1.1, CD16, Ly49H, Ly49D, and NKG2D. This deficiency in cytokine/chemokine production occurs at the level of mRNA expression. After receptor engagement, extracellular signal-regulated kinase and c-Jun N-terminal kinase activation was markedly perturbed, whereas p38 activation was not substantially affected. The pattern and amounts of basal tyrosine phosphorylation were altered in freshly isolated NK cells and were surprisingly and markedly increased in IL-2-expanded NK cells from CD45-/- mice. These findings indicate that CD45-dependent regulation of ITAM-dependent signaling pathways is essential for NK cell-mediated cytokine production but not cytolytic activity.

How do natural killer cells find self to achieve tolerance?

Natural killer (NK) cells provide innate defense against tumors and infections by virtue of potent capacities to immediately kill cellular targets and produce cytokines. These effector functions may potentially damage normal self-tissues unless they are kept in check by tolerance mechanisms that need clarification. Here, we discuss recent studies indicating that the NK cells acquire functional competence directly through engagement of their MHC-specific receptors by self-MHC. Ironically, these receptors were first identified in terms of recognizing target cell MHC class I molecules and inhibiting NK cells in effector responses. Other studies of NK cell tolerance are also discussed. Although these studies begin to clarify the means by which NK cell tolerance is achieved, much more investigation is needed because NK cell tolerance is relevant to clinical observations in patients with infections and cancer.

Extending missing-self? Functional interactions between lectin-like NKrp1 receptors on NK cells with lectin-like ligands

The functions of natural killer (NK) cells are clearly regulated by major histocompatibility complex (MHC) class I molecules on their cellular targets. In mice, this is due to the action of MHC-specific inhibitory receptors belonging to the Ly49 family oflectin-like molecules. The Ly49 receptors are encoded in the NK gene complex (NKC) that contains clusters of genes for other lectin-like receptors on NK cells and other hematopoietic cells. Interestingly, recent studies have shown that some of these lectin-like receptors, belonging to the Nkrpl family, can recognize other lectin-like molecules, termed Clr, also encoded in the NKC. These genetically linked loci for receptor-ligand pairs suggest a genetic strategy to preserve this interaction and show several other contrasts with Ly49-MHC interactions. In this review, we discuss these issues and summarize recent developments concerning this non-MHC-dependent regulation of NK cell function.

NK Cell Receptors as Tools in Cancer Immunotherapy

Natural killer (NK) cells were identified 30 years ago based on their ability to "spontaneously" kill tumor cells. The basis for NK cell recognition and activation is due to a variety of receptors that bind to specific ligands on tumor cells and normal cells. Some of these receptors have the ability to inhibit NK cell function, and other receptors activate NK cell function. Therapeutic strategies for cancer therapy are being developed based on preventing NK cell inhibition or using NK cell receptors to activate NK cells or T cells. There are intriguing clinical data from studies of bone marrow transplantation that support the idea that preventing NK cell inhibition by human leukocyte antigen (HLA) class I molecules can be a means to promote graft-versus-leukemia (GvL) effects and limit graft-versus-host disease (GvHD) in acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) patients. Experimental findings also support the blockade of NK cell inhibitory receptors as a way to protect against leukemia relapse. It may be possible to use our knowledge of NK cell activating receptors and their ligands to immunize patients with modified tumor cells to promote beneficial NK cell responses and development of host antitumor cytotoxic T lymphocytes (CTLs). Finally, new data support the idea of using modified NK cell receptors as a means to target patients' T cells against their own tumor cells and induce long-term immunity against them. Tumors are essentially tissues that have overcome normal regulation mechanisms, and therefore the ability to distinguish normal cells from abnormal cells is a key part of selectively attacking tumor cells. NK cells have various receptor systems designed to recognize infected and abnormal cells. Understanding NK cell receptors and their recognition mechanisms provides new tools for the development of immunotherapies against cancer.

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.

Murine CD160, Ig-Like Receptor on NK Cells and NKT Cells, Recognizes Classical and Nonclassical MHC Class I and Regulates NK Cell Activation

Human and mouse NK cells use different families of receptors to recognize MHC class I (MHC I) on target cells. Although human NK cells express both Ig-like receptors and lectin-like receptors specific for MHC I, all the MHC I-specific receptors identified on mouse NK cells to date are lectin-like receptors, and no Ig-like receptors recognizing MHC I have been identified on mouse NK cells. In this study we report the first MHC I-specific Ig-like receptor on mouse NK cells, namely, murine CD160 (mCD160). The expression of mCD160 is restricted to a subset of NK cells, NK1.1+ T cells, and activated CD8+ T cells. The mCD160-Ig fusion protein binds to rat cell lines transfected with classical and nonclassical mouse MHC I, including CD1d. Furthermore, the level of mCD160 on NK1.1+ T cells is modulated by MHC I of the host. Overexpression of mCD160 in the mouse NK cell line KY-2 inhibits IFN-gamma production induced by phorbol ester plus ionomycin, whereas it enhances IFN-gamma production induced by NK1.1 cross-linking or incubation with dendritic cells. Cross-linking of mCD160 also inhibits anti-NK1.1-mediated stimulation of KY-2 cells. Anti-mCD160 mAb alone has no effect. Thus, mCD160, the first MHC I-specific Ig-like receptor on mouse NK cells, regulates NK cell activation both positively and negatively, depending on the stimulus.

Profiles of NK, NKT cell activation and cytokine production following vaccination against hepatitis B

Human natural killer (NK) cells (CD56+ CD3-) represent crucial components of the innate immune system especially against viral infections and because their activation can modulate the outcome of the adaptive immune response. NKT cells (CD56+CD3+), a lymphocyte T population characterized by expression of surface markers of NK cells, are known to be abundant in the liver and their activation could be associated with hepatic injury. Using three-color flow cytometry to measure surface receptors and intracellular cytokines, we have explored early activation signals and cytokine production in NK and NKT cells within a group of hepatitis B vaccinated and non-vaccinated individuals. A specific increase of the CD56bright cell population, the activation receptor CD69 and IFN-gamma, was observed in NK cells following incubation with recombinant HBsAg in responders to vaccination. Comparable results were observed in NKT cells showing an increment of CD69, CD25, IL-2 and IFN-gamma expression in responder subjects. These parameters were statistically diminished in non-responder individuals (p<0.05) in both groups of cells. These results demonstrate a diminished activation of these cells in non-responders to the vaccine, suggesting that NK and NKT cells play an important role in the immune response following hepatitis B vaccination.

NK cell recognition

The integrated processing of signals transduced by activating and inhibitory cell surface receptors regulates NK cell effector functions. Here, I review the structure, function, and ligand specificity of the receptors responsible for NK cell recognition.

Toward an understanding of NKT cell biology: progress and paradoxes

Natural killer T (NKT) cells constitute a conserved T cell sublineage with unique properties, including reactivity for a synthetic glycolipid presented by CD1d, expression of an invariant T cell antigen receptor (TCR) alpha chain, and unusual requirements for thymic selection. They rapidly produce many cytokines after stimulation and thus influence diverse immune responses and pathogenic processes. Because of intensive research effort, we have learned much about factors promoting the development and survival of NKT cells, regulation of their cytokine production, and the means by which they influence dendritic cells and other cell types. Despite this progress, knowledge of the natural antigen(s) they recognize and their physiologic role remain incomplete. The activation of NKT cells paradoxically can lead either to suppression or stimulation of immune responses, and we cannot predict which will occur. Despite this uncertainty, many investigators are hopeful that immune therapies can be developed based on NKT cell stimulation.

Suppression of hepatocellular carcinoma by transplantation of ex-vivo immune-modulated NKT lymphocytes

NKT cells are a regulatory subset of T lymphocytes with immune modulatory effects and an important role in anti-tumor immunity. The feasibility of "ex-vivo education" of NKT cells has recently been demonstrated. To evaluate the anti-tumor effect of ex-vivo immune-modulated NKT lymphocytes in a murine model of hepatocellular carcinoma. Athymic Balb/C mice were sublethally irradiated and transplanted with human Hep3B HCC. NKT cells prepared from immunocompetent Balb/C mice were pulsed ex vivo with HCC-derived antigens (Group A), Hep3B cells (group B) or BSA (group C), and adoptively transferred into HCC harboring mice (1 x 0(6) NKT cells per mouse). Group D mice did not undergo NKT cell transplantation. Group E mice were transplanted with 1 x 10(6) NKT cells from HBV-immunized donors. Mice were followed for tumor size and weight. To determine the mechanism of the anti-tumor effect, intrasplenic lymphocyte populations were analyzed by FACS for NKT, CD4+ and CD8+ lymphocyte subpopulations; STAT 1, 4 and 6 expression in splenocytes was assessed by Western blot, and serum cytokine levels were measured by ELISA. Adoptive transfer of NKT cells pulsed with HCC-derived antigens (group A) and NKT cells from immunized donors (group E) resulted in complete disappearance of tumors within 4 weeks and attenuated weight loss (6.5% and 7% in groups A and E, respectively). In contrast, mice in groups B, C, and D developed large, necrotic tumors and severe weight loss (21%, 17% and 23% weight loss in groups B, C, and D, respectively). NKT/CD4 and CD8/CD4 ratios were significantly increased in groups A and E (12.3 and 17.6 in groups A and D, respectively, compared to 6.4, 4.8 and 5.6 in groups B, C and D, respectively, for the NKT/CD4 ratio; 41 and 19.8 in groups A and E, respectively, compared to 6.5, 11.8 and 3.2 in groups B, C, and D, respectively, for the CD8/CD4 ratio). Expression of the transcription factor STAT4 was evident in group A, but not in groups B-D. Serum IFNgamma, IL12 and IL4 levels were increased in groups A and E. Adoptive transfer of NKT lymphocytes exposed ex vivo by HCC-derived antigens loaded on dendritic cells and NKT cells from immunized donors led to suppression of HCC in mice. NKT-mediated anti-tumor activity was associated increased NKT and CD8+ T lymphocyte numbers, increased expression of STAT4, a marker for IL-12 activity and elevated serum levels of the proinflammatory cytokines IFNgamma and IL12, and of IL4. Ex-vivo modulation of NKT lymphocytes holds promise as a novel mode of immune therapy for HCC.

Functional requirements for signaling through the stimulatory and inhibitory mouse NKR-P1 (CD161) NK cell receptors

The NK cell receptor protein 1 (NKR-P1) (CD161) molecules represent a family of type II transmembrane C-type lectin-like receptors expressed predominantly by NK cells. Despite sharing a common NK1.1 epitope, the mouse NKR-P1B and NKR-P1C receptors possess opposing functions in NK cell signaling. Engagement of NKR-P1C stimulates cytotoxicity of target cells, Ca2+ flux, phosphatidylinositol turnover, kinase activity, and cytokine production. In contrast, NKR-P1B engagement inhibits NK cell cytotoxicity. Nonetheless, it remains unclear how different signaling outcomes are mediated at the molecular level. Here, we demonstrate that both NKR-P1B and NKR-P1C associate with the tyrosine kinase, p56(lck). The interaction is mediated through the di-cysteine CxCP motif in the cytoplasmic domains of NKR-P1B/C. Disrupting this motif leads to abrogation of both stimulatory and inhibitory NKR-P1 signals. In addition, mutation of the consensus ITIM (LxYxxL) in NKR-P1B abolishes both its Src homology 2-containing protein tyrosine phosphatase-1 recruitment and inhibitory function. Strikingly, engagement of NKR-P1C on NK cells obtained from Lck-deficient mice failed to induce NK cytotoxicity. These results reveal a role for Lck in the initiation of NKR-P1 signals, and demonstrate a requirement for the ITIM in NKR-P1-mediated inhibition.

Adoptive transfer of NK 1.1+ lymphocytes in immune-mediated colitis: a pro-inflammatory or a tolerizing subgroup of cells?

T lymphocytes expressing NK1.1 marker (NKT) have been suggested to play crucial roles in immune modulation.

AIM

To determine the role of NK1.1+ cells in induction and maintenance of pro-inflammatory and/or tolerizing responses.

METHODS

Colitis was induced in C57/B6 donor mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Donor mice received five oral doses of colonic proteins extracted from TNBS-colitis colonic wall. Depletion of NK1.1+ lymphocytes was performed before lymphocyte harvesting. Splenocytes were harvested and separated into T-cell subpopulations, and transplanted into recipient mice before intracolonic instillation of TNBS. Standard clinical, macroscopic, and microscopic scores, and intracellular staining, flow cytometry, and cytotoxicity assays were performed.

RESULTS

The adoptive transfer of CD4+ and NK1.1+ cells harvested from tolerized mice markedly ameliorated the colitis in recipient mice. In contrast, the adoptive transfer of CD8+ and double negative lymphocytes failed to transfer the tolerance. Recipients of splenocytes from tolerized mice exhibited an increase in CD4+ IL4+/CD4+ IFNgamma+ ratio. In contrast, recipients of splenocytes from NK1.1-depleted-tolerized mice exhibited severe colitis with a significant decrease of the CD4+ IL4+/CD4+ IFNgamma+ ratio. However adoptive transfer of splenocytes from non-tolerized NKT-depleted mice led to an alleviation of colitis with a relative increase of the CD4+ IL4+/CD4+ IFNgamma+ ratio.

CONCLUSIONS

NK1.1+ lymphocytes play a critical role in immune regulation. They may be accountable for an alteration of the inflammatory response and the CD4+ IL4+/CD4+ IFNgamma ratio immune-mediated colitis and in peripheral tolerance induction.

Differential effects of IL-21 during initiation and progression of autoimmunity against neuroantigen

The cytokine IL-21 is closely related to IL-2 and IL-15, a cytokine family that uses the common gamma-chain for signaling. IL-21 is expressed by activated CD4(+) T cells. We examined the role of IL-21 in the autoimmune disease experimental autoimmune encephalomyelitis (EAE), an animal model for human multiple sclerosis. IL-21 administration before induction of EAE with a neuroantigen, myelin oligodendrocyte glycoprotein peptide 35-55, and adjuvant enhanced the inflammatory influx into the CNS, as well as the severity of EAE. Autoreactive T cells purified from IL-21-treated mice transferred more severe EAE than did the control encephalitogenic T cells. No such effects were observed when IL-21 was administered after EAE progressed. Additional studies demonstrated that IL-21 given before the induction of EAE boosted NK cell function, including secretion of IFN-gamma. Depletion of NK cells abrogated the effect of IL-21. Therefore, IL-21, by affecting NK cells, has differential effects during the initiation and progression of autoimmune responses against neuroantigens.

Response of lung NK1.1-positive natural killer cells to experimental sepsis in mice

Natural killer cells (NKC) participate in the initiation of the immune response and coordination between innate and adaptive immune mechanisms. Their role in systemic inflammation induced by trauma or infection (sepsis) is still controversial. In the present study, lung NKC and their response to experimental sepsis were investigated. Mice were subjected to cecal ligation and puncture (CLP) to induce sepsis and acute lung injury (ALI). Animals were sacrificed 1, 4, and 7 days postoperatively, and lung histopathology, pulmonary vascular permeability, and inflammatory cells accumulation were assessed. On day 4, parameters of ALI were most prominent, and lung NK1.1+CD3- cells were isolated and studied by flow cytometry. Although CLP did not change the absolute number of lung NKC (2.47 +/- 0.52 x 10(5)/lung compared with 2.97 +/- 0.27 x 10(5)/lung in the sham group), the peak of the CLP-induced ALI was associated with severe dysfunction of lung NKC. Cell cytotoxicity decreased to 25.1 +/- 2.4% (P = 0.002), and percentage of perforin-positive NKC to 2.7 +/- 0.5% (P = 0.03). Cytokine profile of lung NK1.1+CD3- cells was prominently changed. The percentage of IFN-gamma-positive cells decreased to 19.7 +/- 5.7% (P = 0.047), but TNF-alpha-positive cells grew to 26.7 +/- 3.3% (P = 0.02). In summary, severe CLP-induced dysfunction of lung NK1.1+CD-3 cells was demonstrated. This may influence the outcome of the animals during sepsis and acute lung damage.

The natural killer complex regulates severe malarial pathogenesis and influences acquired immune responses to Plasmodium berghei ANKA

The natural killer complex (NKC) is a genetic region of highly linked genes encoding several receptors involved in the control of NK cell function. The NKC is highly polymorphic, and allelic variability of various NKC loci has been demonstrated in inbred mice. Making use of BALB.B6-Cmv1r congenic mice, in which the NKC from disease-susceptible C57BL/6 mice has been introduced into the disease-resistant BALB/c background, we show here that during murine malaria infection, the NKC regulates a range of pathophysiological syndromes such as cerebral malaria, pulmonary edema, and severe anemia, which contribute to morbidity and mortality in human malaria. Parasitemia levels were not affected by the NKC genotype, indicating that control of malarial fatalities by the NKC cells does not operate through effects on parasite growth rate. Parasite-specific antibody responses and the proinflammatory gene transcription profile, as well as the TH1/TH2 balance, also appeared to be influenced by NKC genotype, providing evidence that this region, known to control innate immune responses via NK and/or NK T-cell activation, can also significantly regulate acquired immunity to infection. To date, NKC-encoded innate system receptors have been shown mainly to regulate viral infections. Our data provide evidence for critical NKC involvement in the broad immunological responses to a protozoan parasite.

alpha-Galactosylceramide therapy for autoimmune diseases: prospects and obstacles

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

Induction and regulation of IFNs during viral infections

Interferons (IFN)s are involved in numerous immune interactions during viral infections and contribute to both induction and regulation of innate and adaptive antiviral mechanisms. IFNs play a pivotal rule in the outcome of a viral infection, as demonstrated by the impaired resistance against different viruses in mice deficient for the receptors IFNAR-2 and IFNGR. During viral infections, IFNs are involved in numerous immune interactions as inducers, regulators, and effectors of both innate and adaptive antiviral mechanisms. IFN-alpha/beta is produced rapidly when viral factors, such as envelope glycoproteins, CpG DNA, or dsRNA, interact with cellular pattern-recognition receptors (PRRs), such as mannose receptors, toll-like receptors (TLRs), and cytosolic receptors. These host-virus interactions signal downstream to activate transcription factors needed to achieve expression from IFN-alpha/beta genes. These include IFN regulatory factor-3 (IRF-3), IRF-5, IRF-7, c-Jun/ATF-2, and NF-kappaB. In contrast, IFN-gamma is induced by receptor-mediated stimulation or in response to early produced cytokines, including interleukin-2 (IL-12), IL-18, and IFN-alpha/beta, or by stimulation through T cell receptors (TCRs) or natural killer (NK) cell receptors. IFNs signal through transmembrane receptors, activating mainly Jak-Stat pathways but also other signal transduction pathways. Cytokine and TCR-induced IFN-gamma expression uses distinct signal transduction pathways involving such transcription factors as NFAT, Stats and NF-kappaB. This results in induction and activation of numerous intrinsic antiviral factors, such as RNA-activated protein kinase (PKR), the 2-5A system, Mx proteins, and several apoptotic pathways. In addition, IFNs modulate distinct aspects of both innate and adaptive immunity. Thus, IFN-alpha/beta and IFN-gamma affect activities of macrophages, NK cells, dendritic cells (DC), and T cells by enhancing antigen presentation, cell trafficking, and cell differentiation and expression profiles, ultimately resulting in enhanced antiviral effector functions. This review focuses on the latest findings regarding induction and regulation of IFNs, primarily during the early phase of an antiviral immune response. Both cellular and molecular aspects are discussed from the perspective of host-virus interactions.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.

Liposome-encapsulated CpG oligodeoxynucleotides as a potent adjuvant for inducing type 1 innate immunity

Unmethylated cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG-ODNs) exhibit potent immunostimulating activity by binding with Toll-like receptor 9 (TLR9) expressed on antigen-presenting cells. Here, we show that CpG-ODN encapsulated in cationic liposomes (CpG-liposomes) improves its incorporation into CD11c(+) dendritic cells (DCs) and induces enhanced serum interleukin (IL)-12 levels compared with unmodified CpG-ODN. CpG-liposome potently activated natural killer (NK) cells (84.3%) and NKT cells (48.3%) to produce interferon-gamma (IFN-gamma), whereas the same dose of unmodified CpG-ODN induced only low numbers of IFN-gamma-producing NK cells (12.7%) and NKT cells (1.6%) to produce IFN-gamma. In contrast with the NKT cell agonist alpha-galactosylceramide, which induces both IFN-gamma and IL-4 production by NKT cells, CpG-liposome only induced IFN-gamma production by NKT cells. Such potent adjuvant activities of CpG-liposome were absent in TLR9-deficient mice, indicating that CpG-liposome was as effective as CpG-ODN in stimulating type 1 innate immunity through TLR9. In addition to TLR9, at least two other factors, IL-12 production by DCs and direct contact between DCs and NK or NKT cells, were essential for inducing type 1 innate immunity by CpG-liposome. Furthermore, ligation of TLR9 by CpG-liposome coencapsulated with ovalbumin (OVA) caused the induction of OVA-specific CTLs, which exhibited potent cytotoxicity against OVA-expressing tumor cells. These results indicate that CpG-liposome alone or combined with tumor antigen protein provides a promising approach for the prevention or therapy of tumors.

Single dose of OCH improves mucosal T helper type 1/T helper type 2 cytokine balance and prevents experimental colitis in the presence of valpha14 natural killer T cells in mice

BACKGROUND AND AIMS

Valpha14 natural killer T (NKT) cells seem to play important roles in the development of various autoimmune diseases. However, the pathophysiologic role of NKT cells in inflammatory bowel disease remains unclear. To clarify the mechanism by which the activation of NKT cells mediates protection against intestinal inflammation, we investigated the antiinflammatory role of specifically activated Valpha14 NKT cells by glycolipids in a mouse experimental model of colitis induced by dextran sulfate sodium (DSS).

METHODS

Colitis was induced in C57BL/6 mice by the oral administration of 1.5% DSS for 9 days. A single dose of OCH or alpha-galactosylceramide, a ligand for NKT cells, was administered on day 3 after the induction of colitis. Body weights and colonic mucosal injury were assessed in each glycolipid-treated group. Interferon-gamma and interleukin-4 levels in the supernatants from colonic lamina propria lymphocytes (LPLs) were measured by enzyme-linked immunosorbent assay.

RESULTS

The administration of a single dose of OCH attenuated colonic inflammation, as defined by body weights and histologic injury. The protective effects of OCH could not be observed in Valpha14 NKT cell-deficient mice. In vivo treatment with OCH had improved the interferon-gamma/interleukin-4 ratio from colonic LPLs on day 9 after DSS treatment.

CONCLUSION

The present data indicated that the activation of Valpha14 NKT cells by OCH plays a pivotal role in mediating intestinal inflammation via altered mucosal T-helper type 1/type 2 responses. Therapeutic strategies that are designed to activate specifically Valpha14 NKT cells may prove to be beneficial in treating intestinal inflammation.

Critical proinflammatory and anti-inflammatory functions of different subsets of CD1d-restricted natural killer T cells during Trypanosoma cruzi infection

Trypanosoma cruzi infects 15 to 20 million people in Latin America and causes Chagas disease, a chronic inflammatory disease with fatal cardiac and gastrointestinal sequelae. How the immune response causes Chagas disease is not clear, but during the persistent infection both proinflammatory and anti-inflammatory responses are critical. Natural killer T (NKT) cells have been shown to regulate immune responses during infections and autoimmune diseases. We report here that during acute T. cruzi infection NKT-cell subsets provide distinct functions. CD1d(-/-) mice, which lack both invariant NKT (iNKT) cells and variant NKT (vNKT) cells, develop a mild phenotype displaying an increase in spleen and liver mononuclear cells, anti-T. cruzi antibody response, and muscle inflammation. In contrast, Jalpha18(-/-) mice, which lack iNKT cells but have vNKT cells, develop a robust phenotype involving prominent spleen, liver, and skeletal muscle inflammatory infiltrates comprised of NK, dendritic, B and T cells. The inflammatory cells display activation markers; produce more gamma interferon, tumor necrosis factor alpha, and nitric oxide; and show a diminished antibody response. Strikingly, most Jalpha18(-/-) mice die. Thus, in response to the same infection, vNKT cells appear to augment a robust proinflammatory response, whereas the iNKT cells dampen this response, possibly by regulating vNKT cells.

Quantitative and Qualitative Differences in Proatherogenic NKT Cells in Apolipoprotein E–Deficient Mice

Background— Atherosclerosis is a disease marked by lipid accumulation and inflammation. Recently, atherosclerosis has gained recognition as an autoimmune-type syndrome characterized by increased activation of the innate and acquired immune systems. Natural killer T (NKT) cells have characteristics of both conventional T cells and NK cells and recognize glycolipid antigens presented in association with CD1d molecules on antigen-presenting cells. The capacity of NKT cells to respond to lipid antigens and modulate innate and acquired immunity suggests that they may play a role in atherogenesis.

Methods and Results— We examined the role of NKT cells in atherogenesis and how the atherosclerotic environment affects the NKT cell population itself. The data show that CD1d-deficiency in male apolipoprotein E–deficient (apoE 0 ) mice results in reduction in atherosclerosis, and treatment of apoE 0 mice with α-galactosylceramide, a potent and specific NKT cell activator, results in a 2-fold increase in atherosclerosis. Interestingly, we demonstrate that α-galactosylceramide–induced interferon-γ responses and numbers of NKT cells in apoE 0 mice show age-dependent qualitative and quantitative differences as compared with age-matched wild-type mice.

Conclusions— Collectively, these findings reveal that hyperlipidemia and atherosclerosis have significant effects on NKT cell responses and that these cells are proatherogenic.

CD40 signaling induces reciprocal outcomes in Leishmania-infected macrophages; roles of host genotype and cytokine milieu

We investigated the influence of CD40-CD40 ligand-mediated signaling on induction of microbicidal activity against Leishmania major in macrophages from resistant (B6) and susceptible (BALB) mouse strains. CD40 engagement induced leishmanicidal activity in resistant macrophages, but increased parasite replication in susceptible macrophages. CD40 engagement induced comparable TNF-alpha production in macrophages from both strains. However, increased IL-10 production was restricted to susceptible macrophages. Increased parasite replication in susceptible macrophages was prevented by a neutralizing anti-IL-10 antibody. In the presence of IFN-gamma, CD40 engagement induced Leishmania killing by macrophages from both strains. Therefore, the outcome of CD40 signaling on effector responses against L. major depends on host genotype and the cytokine milieu, and a source of IFN-gamma is required for a protective response.

Frequency of Valpha24+CD161+ natural killer T cells and invariant TCRAV24-AJ18 transcripts in atopic and non-atopic individuals

Th2 cells play a central role in type I allergies. However, the source of interleukin-4 which may lead to a Th1/Th2 imbalance is unknown. Valpha24+CD161+ Natural killer T (NKT) cells secrete high amounts of interleukin-4 and/or interferon-gamma and are assumed to participate in the initiation of Th1/Th2 immune responses. Their contribution to the development of Th2-dependent type I allergies is controversial. Our objective in this paper was to determine whether Valpha24+CD161+ NKT cells differ in atopic and non-atopic adults. Venous blood was obtained from thirteen atopic and sixteen healthy adult probands. Valpha24+CD161+ NKT cells were determined in CD4+, CD8(bright/dim) and CD4-CD8- lymphocytes by flow cytometry. At the molecular level, the amounts of T cell receptor (TCR) AV24-AJ18 transcripts were quantified with respect to TCRAV24 chain transcripts alone or to all TCR alpha chain transcripts. To detect potential inserted nucleotides in the N-region, a novel real-time PCR-based technology was applied. Both CD4+ and CD4-CD8- NKT cells were present at higher frequencies than CD8+ NKT cells in all probands. CD8(dim) NKT cell levels were lower in healthy individuals, although not statistically significantly different to the patients. Amounts of AV24-AJ18 transcripts in relation to total TCR alpha-chains and to TCRAV24 alone were equal in both proband groups. N-region diversity was detected in four clones from four different individuals, but altered the amino acid sequence in only one clone of an atopic donor. Analysis of Valpha24+CD161+ NKT cell frequencies at both the cellular and molecular levels failed to reveal significant differences in peripheral blood of atopic and non-atopic probands. If NKT cells contribute to development of type I allergies they must do so at earlier times or in other locations.

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

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

The dynamic life of natural killer cells

Natural killer (NK) cells play important roles in immunological processes, including early defense against viral infections. This review provides an overview of the dynamic in vivo life of NK cells from their development in the bone marrow to their mature peripheral responses and their ultimate demise, with particular emphasis on mouse NK cells and viral infections.

CD1: antigen presentation and T cell function

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

IL-21 induces the functional maturation of murine NK cells

IL-21 is a recently identified cytokine that stimulates mouse NK cell effector functions in vitro. In this study we demonstrate that IL-21 achieves its stimulatory effect by inducing the development of mature NK cells into a large granular lymphocyte phenotype with heightened effector function. IL-21 treatment results in increased cell size and granularity and a corresponding decrease in cell viability and proliferative potential. These cells up-regulate the expression of the inhibitory CD94-NKG2A receptor complex and the activation markers CD154 and killer cell, lectin-like-receptor G1. Surprisingly, IL-21 treatment also results in down-regulation of the pan-NK marker, NK1.1. Coinciding with these cellular changes IL-21 enhances cytolytic capacity across a spectrum of target sensitivities and induces IL-10 and IFN-gamma production. In vivo treatment with IL-21 results in a very similar activation and phenotypic maturation of NK cells as well as a potent increase in NK cell-mediated anti-tumor immunity that is perforin dependent. These developmental changes suggested that IL-21 functions to induce the terminal differentiation of mouse NK cells, resulting in heightened NK cell-mediated cytotoxicity and immune surveillance.

The role of intrahepatic CD8+ T cell trapping and NK1.1+ cells in liver-mediated immune regulation

The liver was previously suggested as a site of lymphocyte clearance. Liver-associated lymphocytes that express NK1.1 marker (NKT LAL) play a role in immune modulation.

AIM

To determine the role of the liver and of NKT LAL in determining the CD4+/CD8+ balance during tolerance induction.

METHODS

Colitis was induced in C57 mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Immune tolerance was induced via five oral feedings of colitis-extracted proteins (CEP) from TNBS-colitis colonic wall, starting on the day of colitis induction (group A). Control mice were fed with BSA (group B). To determine the role of NKT cells in immune modulation, NK1.1 depletion was performed in nonfed (group C) and fed (group D) mice. To further evaluate the role of NKT cells in this model, mice in group E were tolerized following NKT depletion. To determine the effect of NKT depletion in a tolerized environment, tolerized mice in group F were NKT depleted following tolerance induction. Peripheral and intrahepatic NK1.1+ and CD4+/CD8+ T cells were determined in all groups. Colitis was assessed by standard clinical and histologic scores. Serum cytokines levels were measured by ELISA.

RESULTS

Oral tolerance induction led to a marked alleviation of colitis as manifested by a significant improvement of the clinical, macroscopic, and microscopic scores of colitis (group A vs. group B). NK1.1+ depletion without tolerance induction had a favorable effect on colitis (C). Depletion of NKT LAL prevented the ability to induce tolerance (group D). However, induction of tolerance following NK1.1+ depletion, and NK1.1+ depletion following tolerance induction led to a marked improvement of colitis (groups E and F). Tolerance induction led to a significant increase in NKT LAL numbers. The peripheral CD4+/CD8+ ratio increased up to 3-fold in tolerized vs. non-tolerized mice. A similar increase was observed in NKT-depleted healthy mice in groups C, E, and F (P < 0.005). In contrast, NK1.1+ depletion in the presence of antigen in the bowel led to a reverse effect with a significant decrease in the peripheral CD4+/CD8+ ratio. An opposite effect was observed in the intrahepatic CD4+/CD8+. The peripheral/intrahepatic CD4+/CD8+ ratio increased significantly in tolerized and in healthy mice (A, D, E, F, P < 0.005). In contrast, NK1.1+ depleted fed mice in group C manifested a marked decrease in the peripheral/intrahepatic CD4+/CD8+ ratio. Induction of tolerance led to a marked increase in the IL-10/interferon gamma (IFNgamma) and IL-4/IFNgamma ratios.

CONCLUSIONS

In the experimental colitis model, the liver is an important site for CD8+ accumulation during tolerance induction in a process that is independent of NK1.1+ cells. NK1.1+ cells play a dual role in the pro/anti-inflammatory balance. In the presence of antigen, these lymphocytes may be accountable for keeping an anti-inflammatory lymphocyte balance. However, in the absence of antigen, they may induce a pro-inflammatory shift.

Regulation of immunity and pathogenesis in infectious diseases by CD1d-restricted NKT cells

CD1d-restricted NKT cells are emerging as an unusual lymphoid lineage with important immunoregulatory properties. To date, much of our understanding of the biology of the CD1/NKT system comes from studies that utilise non-natural glycolipid ligands. Recent evidence suggests that NKT cells play an important role in the response to pathogens, manifesting a range of functions including cytotoxicity, help for antibody formation and regulation of Th1/Th2 differentiation. Infectious disease models provide appropriate physiological and pathophysiological systems to explore the biological roles of this lineage in immunity and disease. Novel insights are emerging from infection models, particularly with respect to the nature of ligands recognised by the T cell receptor of NKT cells, and to the role of diverse non-T cell receptor NK activation and inhibitory receptors in regulation of the lineage. Such insights have the potential to add considerably to our understanding of the CD1/NKT cell system and to the immunology and pathogenesis of infectious diseases.

Missing self-recognition of Ocil/Clr-b by inhibitory NKR-P1 natural killer cell receptors

The NKR-P1 family of C-type lectin-like receptors are expressed on natural killer (NK) cells and NKT cells. We report the cloning and characterization of a cognate ligand for the inhibitory mouse NK receptors (NKR)-P1B and NKR-P1D (CD161b/d). The NKR-P1B/D ligand is osteoclast inhibitory lectin (Ocil), also known as Clr-b, a member of a previously cloned group of C-type lectin-related (Clr) proteins linked to the NKR-P1 receptors in the mouse NK gene complex (NKC). Expression of Ocil/Clr-b on mouse tumor cell lines inhibits NK cell-mediated killing. Inhibition is blocked with a new mAb (4A6) specific for Ocil/Clr-b. By using 4A6 mAb, we demonstrate that Ocil/Clr-b is displayed at high levels on nearly all hematopoietic cells, with the exception of erythrocytes, in a pattern that is similar to that of class I MHC molecules. Remarkably, Ocil/Clr-b is frequently down-regulated on mouse tumor cell lines, indicating a role for this receptor-ligand system in a new form of "missing self-recognition" of tumor cells.

Attenuated innate mechanisms of interferon-gamma production in rats susceptible to postviral airway dysfunction

After Sendai virus (SeV)-induced bronchiolitis as weanlings, BN, but not F344, rats develop a postbronchiolitis asthma-like phenotype, which can be prevented by supplemental interferon (IFN)-gamma treatment. We have shown that splenocytes from BN weanlings, compared with those from F344 weanlings, have a markedly reduced capacity for IFN-gamma production. We hypothesized that SeV-induced IFN-gamma production occurs via innate mechanisms that are attenuated in BN weanlings. Therefore, we investigated potential mechanisms of SeV-induced IFN-gamma production in BN and F344 weanlings. SeV-stimulated splenocytes secreted the IFN-gamma-inducing cytokines, interleukin (IL)-12 and IL-18. BN splenocytes produced significantly less IL-12 (P = 0.001) and IL-18 (P < 0.001) than did F344 splenocytes. Depletion studies demonstrated that natural killer cells were the primary source of SeV-induced IFN-gamma production. Anti-IL-12 antibody, IL-12 p40 homodimer, and IL-18 binding protein each inhibited SeV-induced IFN-gamma production by 82-94%, and the combination of IL-12 p40 homodimer and IL-18 binding protein abolished SeV-induced IFN-gamma production, demonstrating synergism between IL-12 and IL-18. Therefore, SeV-induced IFN-gamma production occurred via innate IL-12-, IL-18-, and natural killer cell-dependent mechanisms, which were attenuated in BN weanlings. Attenuation of innate IFN-gamma-producing responses to SeV in BN weanlings may be a critical factor in their susceptibility to postbronchiolitis chronic airway dysfunction.

Adoptive transfer of ex vivo immune-programmed NKT lymphocytes alleviates immune-mediated colitis

T lymphocyte-expressing natural killer (NK) cell markers (NKT cells) play a role in immune regulation. Our aim was to evaluate the in vivo effect of adoptive transfer of immune-programmed NKT cells. Colitis was induced in C57/B6 mice by 2,4,6-trinitrobenzenesulfonic acid. NKT, CD4, CD8 lymphocytes, and dendritic cells (DC) were prepared from spleens of naive mice, animals with colitis, and animals with colitis that were orally tolerized. Subsets of splenocytes, NKT, CD4, and CD8 and NKT+CD4, NKT+CD8, and NKT+DC lymphocytes were prepared. Assessment of the T helper cell type 1 (Th1)/Th2 cytokine secretion paradigm in vitro was performed before and following exposure to the antigen. Adoptive transfer of ex vivo immune-programmed lymphocytes from each group was performed into recipient mice, followed by colitis induction. Ex vivo exposure of NKT cells harvested from mice with colitis-to-colitis proteins [colitis-extracted proteins (CEP)] led to a Th2 cytokine shift. The interleukin (IL)-4/interferon-gamma (IFN-gamma) ratio increased for NKT harvested from colitis-harboring mice following exposure to CEP. Adoptive transfer of NKT lymphocytes harvested from colitis-harboring mice, which were ex vivo-educated, significantly alleviated experimental colitis in vivo. Intrahepatic NKT lymphocytes increased significantly in mice transplanted with NKT lymphocytes harvested from colitis-harboring donor mice, which were ex vivo-exposed to CEP, similar to mice transplanted with NKT lymphocytes harvested from tolerized donors. Exposure of NKT cells to the disease-target antigen induced a significant increase in the IL-4/IFN-gamma cytokine ratio. Adoptive transfer of a relatively small number of immune-programmed NKT cells induced a systemic Th1 to Th2-immune shift and alleviated immune-mediated colitis.

The response of natural killer T cells to glycolipid antigens is characterized by surface receptor down-modulation and expansion

CD1d-restricted natural killer T (NKT) cells are a subset of regulatory T cells that react with glycolipid antigens. Although preclinical studies have effectively targeted NKT cells for immunotherapy, little is known regarding the early in vivo response of these cells to antigenic stimulation. We have analyzed the early response of NKT cells to glycolipid antigens and bacterial infection by using specific reagents for tracking these cells. Our results demonstrate dramatic in vivo expansion and surface phenotype alterations after NKT cell activation with alpha-galactosylceramide. In addition, we show significant NK1.1 down-modulation on NKT cells in the setting of oral Salmonella infection. Our results indicate that in vivo activation of NKT cells leads to a dynamic response characterized by surface receptor down-modulation and expansion. These findings alter current understanding of NKT cell biology and should aid in the rational design of NKT cell-based immunotherapies.

An anti-inflammatory role for V alpha 14 NK T cells in Mycobacterium bovis bacillus Calmette-Guérin-infected mice

The possible contribution of NKT cells to resistance to Mycobacterium tuberculosis infection remains unclear. In this paper we characterized the Valpha14 NKT cell population following infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG). BCG infection determined an early expansion of Valpha14 NKT cells in liver, lungs, and spleen, which peaked on day 8 and was sustained until day 30. However, an NK1.1(+) Valpha14 NKT population preferentially producing IFN-gamma predominated at an early stage (day 8), which was substituted by an NK1.1(-) population preferentially producing IL-4 at later stages (day 30). Despite the fact that Valpha14 NKT cell-deficient mice eliminated BCG as did control mice, they had significantly higher numbers of granulomas in liver and lungs. Additionally, while control mice developed organized small granulomas, those in Valpha14 NKT-deficient mice had signs of caseation, large cellular infiltrates, and some multinucleated macrophages, suggesting that Valpha14 NKT cells may actually work as anti-inflammatory cells by limiting excessive lymphocyte influx and tissue pathology. In agreement, we found an increased spontaneous production and mRNA expression of TNF-alpha in liver and lungs of Valpha14 NKT-deficient mice, whose neutralization in vivo by anti-TNF-alpha mAbs consistently reduced the number of granulomas in liver and lungs. Together, our results support a regulatory role for Valpha14 NKT cells in the course of BCG infection through their ability to limit the extent of inflammatory response and point to an important role for this cell subset as a regulator of the balance between protective responses and immunopathology.

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

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

IL-4 synergistically enhances both IL-2- and IL-12-induced IFN-gamma expression in murine NK cells

Interleukin-4 (IL-4) is thought to influence T and natural killer (NK) cells by down-regulating T helper 1 (Th1)-type cytokines like interferon-gamma (IFN-gamma). While investigating IL-4 regulation of IFN-gamma expression, we found that IL-4 synergized with IL-2 or IL-12 to enhance IFN-gamma production and mRNA expression in spleen-derived, IL-2-cultured NK cells, as well as negatively sorted fresh DX5+/CD3- NK cells albeit at lower levels. The positive effect of IL-4 on IL-2-induced IFN-gamma production was dependent upon signal transducer and activator of transcription 6 (Stat6) because this response was virtually abrogated in Stat6-/- mice. Notably, though, IL-12 plus IL-4 synergy on IFN-gamma expression was intact in Stat6-/- mice. In exploring possible molecular mechanisms to account for the synergistic effects of IL-4 on murine NK cells, we found that IL-2 plus IL-4 stimulation resulted in a modest increase in tyrosine phosphorylation of Stat5, while IL-12 plus IL-4 treatment resulted in a more substantial increase in tyrosine-phosphorylated Stat4. Finally, to identify regions of the IFN-gamma promoter that may be involved, NK cells from human IFN-gamma promoter/luciferase transgenic mice were treated with cytokines. NK cells from proximal (-110 to +64) promoter region mice did not respond to cytokine stimulation; however, the intact -565 to +64 IFN-gamma promoter responded synergistically to IL-2 plus IL-4 and to IL-12 plus IL-4 in NK cells. These data demonstrate a role for IL-4 in enhancing IFN-gamma expression in murine NK cells that is partially dependent on Stat6 in IL-2 costimulation and completely independent of Stat6 in IL-12 costimulations.

Innate self recognition by an invariant, rearranged T-cell receptor and its immune consequences

This review attempts to illuminate the glycolipid antigen presentation properties of CD1d, how CD1d controls the function of natural T (iNKT) cells and how CD1d and iNKT cells interact to jump-start the immune system. It is postulated that the CD1d-iNKT cell system functions as a sensor, sensing alterations in cellular lipid content by virtue of its affinity for such ligands. The presentation of a neo-self glycolipid, presumably by infectious assault of antigen-presenting cells, activates iNKT cells, which promptly release pro-inflammatory and anti-inflammatory cytokines and jump-start the immune system.

Gamma interferon production by hepatic NK T cells during Escherichia coli infection is resistant to the inhibitory effects of oxidative stress

The reductive-oxidative status of tissues regulates the expression of many inflammatory genes that are induced during gram-negative bacterial infections. The cytokine gamma interferon (IFN-gamma) is a potent stimulus for host inflammatory gene expression, and oxidative stress has been shown to inhibit its production in mice challenged with Escherichia coli bacteria. The objective of the present study was to characterize the cells that produced IFN-gamma in a mouse bacterial peritonitis model and determine the effects of oxidative stress on their activation. The liver contained large numbers of IFN-gamma-expressing lymphocytes following challenge with viable E. coli bacteria. The surface phenotypes of IFN-gamma-expressing hepatic lymphocytes were those of natural killer (NK) cells (NK1.1(+) CD3(-)), conventional T cells (NK1.1(-) CD3(+)), and NK T cells (NK1.1(+) CD3(+)). Treating mice with diethyl maleate to deplete tissue thiols significantly impaired IFN-gamma production by NK cells, conventional T cells, and CD1d-restricted NK T cells in response to E. coli challenge. However, IFN-gamma expression by a subset of NK T cells, which did not bind alpha-galactosylceramide-CD1d tetramers, was resistant to the inhibitory effects of tissue oxidative stress. Stress-resistant IFN-gamma-expressing cells were also predominantly CD8(+) and bore gamma delta T-cell antigen receptors. The residual IFN-gamma response by NK T cells may explain previous reports of hepatic gene expression following gram-negative bacterial challenge in thiol-depleted mice. The finding also demonstrates that innate immune cells differ significantly in their responses to altered tissue redox status.

A role for innate immunity in type 1 diabetes?

Two arms of the immune system, innate and adaptive immunity, differ in their mode of immune recognition. The innate immune system recognizes a few highly conserved structures on a broad range of microorganisms. On the other hand, recognition of self or autoreactivity is generally confined to the adaptive immune response. Whilst autoimmune features are relatively common, they should be distinguished from autoimmune disease that is infrequent. Type 1 diabetes is an immune-mediated disease due to the destruction of insulin secreting cells mediated by aggressive immune responses, including activation of the adaptive immune system following genetic and environmental interaction. Hypotheses for the cause of the immune dysfunction leading to type 1 diabetes include self-reactive T-cell clones that (1) escape deletion in the thymus, (2) escape from peripheral tolerance or (3) escape from homeostatic control with an alteration in the immune balance leading to autoimmunity. Evidence, outlined in this review, raises the possibility that changes in the innate immune system could lead to autoimmunity, by either priming or promoting aggressive adaptive immune responses. Hostile microorganisms are identified by genetically determined surface receptors on innate effector cells, thereby promoting clearance of these invaders. These innate effectors include a few relatively inflexible cell populations such as monocytes/macrophages, dendritic cells (DC), natural killer (NK) cells, natural killer T (NKT) cells and gammadelta T cells. Recent studies have identified abnormalities in some of these cells both in patients with type 1 diabetes and in those at risk of the disease. However, it remains unclear whether these abnormalities in innate effector cells predispose to autoimmune disease. If they were to do so, then modulation of the innate immune system could be of therapeutic value in preventing immune-mediated diseases such as type 1 diabetes.

Role of NK1.1+ and AsGm-1+ cells in oral immunoregulation of experimental colitis

NK1.1 and AsGm-1 expressing cells play a role in immunomodulation. Our purpose was to determine the role of NK1.1+ and AsGm-1+ expressing cells in the inflammatory/tolerance paradigm in experimental colitis. Oral tolerance towards colitis-extracted proteins had previously been shown to alleviate experimental colitis. Colitis was induced in C57/B6 mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Oral tolerance was induced via five oral doses of proteins extracted from TNBS-colitis colonic wall. Clinical, macroscopic, and microscopic scores were used for colitis assessment. To evaluate the putative role of AsGm-1 in tolerance induction, depletion of AsGm-1 expressing cells was performed. To evaluate the mechanism of tolerance induction, liver-associated NKT lymphocytes were harvested 14 days following tolerance induction, and cultured with concanavalin A (con A) and colitis-extracted proteins. T cell subsets were measured by flow cytometry. Cytokine expression was measured by intracellular staining and enzyme-linked immunosorbent assay (ELISA). Orally tolerized mice exhibited significant alleviation of the clinical, macroscopic, and microscopic parameters of colitis, with increased CD4+ILA+/CD4+IFNgamma+ lymphocyte ratio, increased IL-4, and decreased IFNgamma and IL-12 serum levels. In contrast, orally fed mice that were AsGm-1 depleted showed evidence of severe colitis. These mice exhibited significant decreased CD4 +IL4+/CD4+IFNgamma+ ratios, and an increase in IFNgamma and IL-12, with decreased IL-4 levels. NKT cells harvested from tolerized mice secreted high levels of antiinflammatory cytokines. In contrast, in nontolerized mice, NKT cells mainly secreted proinflammatory cytokines. In a tolerized environment, both NK1.1 and AsGm-1 expressing cells are essential for disease alleviation. In contrast, in a nontolerized environment, AsGm-1 expressing cells support an antiinflammatory immune paradigm, while NKT lymphocytes support a proinflammatory shift.

Regulation of murine cerebral malaria pathogenesis by CD1d-restricted NKT cells and the natural killer complex

NKT cells are specialized cells coexpressing NK and T cell receptors. Upon activation they rapidly produce high levels of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) and are therefore postulated to influence T(H)1/T(H)2 immune responses. The precise role of the CD1/NKT cell pathway in immune response to infection remains unclear. We show here that CD1d-restricted NKT cells from distinct genetic backgrounds differentially influence T(H)1/T(H)2 polarization, proinflammatory cytokine levels, pathogenesis, and fatality in the P. berghei ANKA/rodent model of cerebral malaria. The functional properties of CD1d-restricted NKT cells vary according to expression of loci of the natural killer complex (NKC) located on mouse chromosome 6, which is shown here to be a significant genetic determinant of murine malarial fatalities.

U5A2-13, an antigen originally found on mouse NK-like T cells, is an early inducible cell surface antigen during lymphoid activation

We have previously reported a monoclonal antibody (mAb), U5A2-13 mAb, which originally recognizes a phenotypically and functionally similar population of natural killer (NK)-like T cells. In this study, we found that U5A2-13 antigen (U5A2-13) was expressed not only on NK-like T cells but also on T and B cells during activation. In contrast to the low levels of U5A2-13 on freshly harvested T and B cells, the activation of these cells by various stimuli resulted in high levels of expression of U5A2-13 in vitro and in vivo. Similar to CD69, U5A2-13 is also expressed in most mouse lymphoid cell lines but not in nonhematopoietic cells. U5A2-13 on T cells reached maximal expression by 24h after stimulation and returned to baseline levels after 3 days. However, U5A2-13 differed from CD69 since its expression profile was different on CD4(+)- and CD8(+)-activated T cells, phorbol ester-activated EL-4 cells, and activated splenocytes in CD69-deficient mice. In addition, immunoprecipitation study indicated that U5A2-13 is not identical to CD69. Importantly, the U5A2-13-positive population of CD4(+) T cells exhibited significant levels of cytokine producing activity upon stimulation. Overall, U5A2-13 is an early inducible cell surface antigen that could be involved in lymphocyte activation.

Enhanced complement sensitivity of NK-T cells in murine thymus and spleen associated with presence of serum immunoglobulin

In vitro treatment of thymocytes and splenocytes with rabbit complement (C') alone induced significant reductions in the proportion of NK-T cells in murine system. The reduction appeared to be prominent in the thymic NK-T cells compared to that in splenic NK-T cells. No reductions were detected in other populations, such as T, B and NK cells. Thus, NK-T cells lineage-specifically showed the enhanced C' sensitivity. However, NK-T cells in T cell receptor (TCR) transgenic mice of RAG-/- background that lack B cells and antibodies exhibited no C' sensitivity. On the other hand those from the same TCR transgenic mice of RAG intact background that have a normal population of B cells and antibodies showed the C' sensitivity similar to that in normal mice. These findings suggest that the enhanced C' sensitivity observed in the NK-T cell population is associated with the NK-T specific autoantibodies. Indeed, we found that a subset of NK-T cells in the thymus bound mouse immunoglobulins. Similar observations were obtained with several strains of lupus model mice, some of which show a decrease of NK-T cells with aging. Possible roles of the enhanced C' sensitivity of NK-T cells in pathophysiological conditions in various mouse strains including lupus models are discussed.

Homeostasis of V alpha 14i NKT cells

CD1d-reactive natural killer T (NKT) cells with an invariant V alpha 14 rearrangement (V alpha 14i) are a distinct subset of T lymphocytes that likely have important immune-regulatory functions. Little is known regarding the factors responsible for their peripheral survival. Using alpha-galactosylceramide-containing CD1d tetramers to detect V alpha 14i NKT cells, we show here that the expansion of V alpha 14i NKT cells in lymphopenic mice was not dependent on CD1d expression and was unaffected by the presence of host NKT cells. Additionally, we found that IL-15 was important in the expansion and/or survival of V alpha 14i NKT cells, with IL-7 playing a lesser role. These results demonstrate that the homeostatic requirements for CD1d-restricted NKT cells, which are CD4(+) or CD4(-)CD8(-), resemble those of CD8(+) memory T cells. We propose that this expansion and/or survival in the periphery of V alpha 14i NKT cells is affected by competition for IL-15, and that IL-15-requiring cells-such as NK cells and CD8(+) memory cells-may define the V alpha 14i NKT cell niche.

Adenovirus-mediated in vivo B7-1 gene transfer induces anti-tumor immunity against pre-established primary tumor and pulmonary metastasis of rat osteosarcoma

We have previously reported that an osteosarcoma vaccine generated by ex vivo transfection of B7-1 cDNA induces protective as well as curative immunity against B7-1-negative parental osteosarcoma. Because establishment of human osteosarcoma cell lines, which is a prerequisite for ex vivo gene transfer, is rarely successful, we, in the present study, investigated the therapeutic efficacy of adenovirus-mediated in vivo B7-1 gene transfer to pre-established primary tumor as well as pulmonary metastasis of osteosarcoma. Adenovirus-mediated rat B7-1 gene transfer induced (a) expression of B7-1 molecules in osteosarcoma cells by both in vitro and in vivo infection procedures, (b) curative immunity against pre-established primary osteosarcoma and, subsequently, hosts gained protection against additional challenge of parental B7-1-negative osteosarcoma cells, (c) systemic immunity against pre-established pulmonary metastasis, and (d) activation of regional lymph node CD4(+) T cells, expansion of dendritic cells and natural killer cells and the secretion of interferon-gamma. These findings collectively support the therapeutic value of adenovirus-mediated in vivo gene transfer on osteosarcoma, which is of greater simplicity than cell-based B7-1 vaccine, and represent an attractive strategy for therapy of patients with metastatic osteosarcama who acquired resistance to current therapeutic protocols.

Mechanisms of immune privilege for tumor cells by regulatory cytokines produced by innate and acquired immune cells

In murine tumors, innate immunity act as a trigger for the development of acquired immunity. The innate immune cells, natural killer (NK) and natural T (NKT) cells, generate the acquired immune cells, cytotoxic T lymphocytes (CTLs) and T helper (Th) 1 cells, by releasing interferon (IFN)-gamma. Regulatory T cells co-infiltrate with these tumoricidal effectors. In the innate phase, T cell receptor (TCR) gammadelta-bearing T (gammadelta T) and TCRalphabeta intermediate T cells are the regulators that suppress NK and NKT cells by elaborating interleukin (IL)-4, IL-10 and transforming growth factor (TGF)-beta. The acquired phase has Th3/T regulatory 1-like cells that inhibit CTLs and Th1 cells by TGF-beta. Thus, cytokines from regulatory T cells exert profound effects on tumor growth.