Role of NK1.1+ T cells in a TH2 response and in immunoglobulin E production

Simultaneous activation of natural killer T cells and autoantibody production in mice injected with denatured syngeneic liver tissue

Denatured syngeneic liver tissue prepared by mechanical procedures was intraperitoneally injected into adult C57BL/6 mice. In parallel with a decrease in the total number of lymphocytes in the liver, spleen, and thymus from days 1-7 after the injection, the proportion of the CD4+NK1.1+CD3(int) subset of these cells (i.e. natural killer T or NKT cells) increased in the liver. Even the absolute number of these NKT cells increased in the liver on days 14 and 21. In response to the injection of denatured liver tissue, tissue damage was induced in the liver, as shown by elevated levels of serum transaminases and hepatocyte degeneration observed by electron microscopy. Sera obtained on days 7 and 14 contained autoantibodies including anti-DNA antibodies. The proportion of CD1d(high)B cells in the liver was found to decrease on days 1-7. In other words, denatured liver tissue stimulated both NKT cells and certain B cells in the liver. These results suggest that liver lymphocytes might contain not only autoreactive T cells (e.g. CD3(int) or NKT cells) but also some B cells (e.g. B-1 cells) which produce autoantibodies and that the denatured tissue had the potential to stimulate these lymphocytes and to evoke an autoimmune-like state.

Natural killer cells and their receptors

Natural killer (NK) cells have been known for a long time to be a very important component of the innate immune system. However, it is only during the last 10 years that knowledge of their receptors has emerged. Described in the present review are those receptor families killer inhibitory receptor (KIR) (belonging to the immunoglobulin superfamily), and killer lectin like receptor (KLR) CD94/NKG2, that both use HLA as a ligand and have inhibiting and activating types of receptors, and natural cytotoxic receptors (NCR) which do not associate with HLA. Association of the receptor gives rise to either an inhibiting or activating signal leading to either failure or success in lysing a target cell. The KIR receptors are very polymorphic both in the number of genes expressed in an individual and the alleles present for a gene. They would appear to have had a rapid evolution compared to the CD94/NKG2 receptors. The roles that NK cells and their receptors have with various facets of transplantation, disease, pregnancy and control of virus infection in humans are described.

Do functional subsets of leukocytes arise by divergent or linear differentiation?

The T helper type 1 (Th1)/Th2 paradigm has been extended to a wide variety of leukocyte lineages since its inception, including innate immune cells such as dendritic cells and natural killer (NK) cells. Recently, studies of human NK cells have led to the proposition of a new model of linear differentiation in which cell phenotype is controlled by regulation of proliferation versus differentiation, rather than by divergent differentiation programmes. It was suggested that this model might also apply to T cells. Here we discuss the relevance of each model to different leukocyte lineages and argue that the linear differentiation model does not apply to alpha beta T cells.

CD161+ T (NT) cells exist predominantly in human intestinal epithelium as well as in liver

It has been reported that human CD161 (NKR-P1A)+ T cells are counterparts of murine natural T (NT) cells and predominantly accumulate in the liver. However, NT cells in the human intestine have not been well analysed. The aim of this study was to assess the existence of NT cells in human intestinal epithelium and determine their phenotypical characterization. Intra-epithelial lymphocytes (IEL) were isolated from surgical specimens (jejunum, ileum and colon). The surface phenotype of IEL was analysed using a FACScan and compared with that of mononuclear cells (MNC) from other organs. CD161+ T cells were abundant in human intestinal epithelium as well as the liver. The majority of CD161+ T cells in IEL were CD8+ cells. About 50% of CD161+ T cells in hepatic lymphocytes (HL) expressed CD56, whereas only 14% of CD161+ T cells in IEL expressed CD56. The jejunum showed the greatest abundance of CD161+ T cells among the intestinal regions investigated. These results suggest that CD161+ T (NT) cells predominantly exist in human intestinal epithelium and may play an important role in local immunity.

Cryptococcal infection and Th1-Th2 cytokine balance

Cytokines have been recognized as key factors in determining host resistance to infectious pathogens. In particular, Th1-Th2 cytokine balance in hosts is profoundly associated with the outcome of infection caused by intracellular microbes. In a murine model of pulmonary and disseminated infection with Cryptococcus neoformans, an opportunistic fungal pathogen that frequently leads to fatal meningoencephalitis in severely immunocompromised hosts, expression of cytokine mRNA in the lungs from infected animals revealed Th2-dominant profiles, while administration of IL-12, which rescued mice from fatal infection, converted such balance toward Th1-dominant states in a drastic fashion. Thus, commitment of Th phenotypes critically determines host sensitivity to cryptococcal infection. In this review, we described how Th1-Th2 cytokine balance influences host protective responses to C. neoformans, and we identify the host and pathogen factors that regulate such balance.

NK T cells contribute to expansion of CD8(+) T cells and amplification of antiviral immune responses to respiratory syncytial virus

CD1d-deficient mice have normal numbers of T lymphocytes and natural killer cells but lack Valpha14(+) natural killer T cells. Respiratory syncytial virus (RSV) immunopathogenesis was evaluated in 129xC57BL/6, C57BL/6, and BALB/c CD1d(-/-) mice. CD8(+) T lymphocytes were reduced in CD1d(-/-) mice of all strains, as shown by cell surface staining and major histocompatibility complex class I tetramer analysis, and resulted in strain-specific alterations in illness, viral clearance, and gamma interferon (IFN-gamma) production. Transient activation of NK T cells in CD1d(+/+) mice by alpha-GalCer resulted in reduced illness and delayed viral clearance. These data suggest that early IFN-gamma production and efficient induction of CD8(+)-T-cell responses during primary RSV infection require CD1d-dependent events. We also tested the ability of alpha-GalCer as an adjuvant to modulate the type 2 immune responses induced by RSV glycoprotein G or formalin-inactivated RSV immunization. However, immunized CD1-deficient or alpha-GalCer-treated wild-type mice did not exhibit diminished disease following RSV challenge. Rather, some disease parameters, including cytokine production, eosinophilia, and viral clearance, were increased. These findings indicate that CD1d-dependent NK T cells play a role in expansion of CD8(+) T cells and amplification of antiviral responses to RSV.

CD1-dependent natural killer (NK1.1(+)) T cells are required for oral and portal venous tolerance induction

BACKGROUND

Local antigen presentation via either the oral (PO) or the portal venous (PV) routes results in suppression of systemic delayed-type hypersensitivity (DTH). The responsible cell populations are not well defined. Because NK1.1(+) T cells express the Fas ligand and produce high levels of the immunosuppressive cytokine, IL-4, they may play a role in both activated T-cell apoptosis and a Th1 to Th2 immune shift, thus promoting tolerance induction.

METHODS

C57BL/6 mice were tolerized to BALB/c alloantigen by PV or PO spleen cells (25 x 10(6)) on Day 0. Subcutaneous (SQ) challenge with 10 x 10(6) BALB/c cells on Day 7 was followed by footpad injection of 10 x 10(6) BALB/c cells on Day 14. Footpad swelling was measured 24 h later. A single injection of the NK1.1(+) cell-depleting antibody, PK-136, was given IP (10 mg/kg) 2 days prior to PV or PO antigen. Flow cytometry evaluated NK1.1(+) cell depletion. CD1 knockout (KO) mice, lacking NK1.1(+) T cells, were also challenged with PV and PO Balb/c in parallel experiments.

RESULTS

The DTH to BALB/c antigen was markedly suppressed in C57BL/6 mice when this alloantigen was given by either PO or PV routes (P < 0.001, P < 0.001). The maintenance of an unaltered response to third-party C3H/HeJ demonstrated alloantigenic specificity. Administration of the anti-NK1.1 T cell monoclonal antibody, PK-136, resulted in complete restoration of in vivo DTH responsiveness in PO tolerance (P < 0.01), and partial restoration in PV tolerance (P < 0.05) in C57BL/6 mice. FACS confirmed virtually complete depletion of liver, splenic, Peyer's patch, and mesenteric lymph node NK1.1(+) lymphocytes. Development of both PO and PV tolerance was prevented in CD1 KO mice.

CONCLUSION

NK1.1(+) T cells play an essential role in antigen-specific suppression of the DTH response mediated by both oral and portal venous tolerance.

Presence of a novel subset of NKT cells bearing an invariant V(alpha)19.1-J(alpha)26 TCR alpha chain

CD1d-deficient (CD1d-/-) mouse lymphocytes were analyzed to classify the natural killer T (NKT) cells without reactivity to CD1d. The cells bearing a V(alpha)19.1-J(alpha)26 (AV19-AJ33) invariant TCR alpha chain, originally found in the peripheral blood lymphocytes, were demonstrated to be abundant in the NK1.1+ but not NK1.1- T cell population isolated from CD1d-/- mice. Moreover, more than half (11/21) of the hybrid cell lines established from CD1d-/- NKT cells expressed the V(alpha)19.1-J(alpha)26 invariant TCR alpha chain. The expression of the invariant V(alpha)19.1-J(alpha)26 mRNA was absent in beta2-microglobulin-deficient mice. Collectively, the present findings suggest the presence of a second NKT cell repertoire characterized by an invariant TCR alpha chain (V(alpha)19.1-J(alpha)26) that is selected by an MHC class I-like molecule other than CD1d.

Profiles of activated T lymphocytes in peripheral blood of Kuwaiti psoriasis vulgaris patients

We have previously reported unexpected immunological features of psoriasis among Kuwaitis, suggesting novel patterns of immune reactivity contributing to the disease. To better define this phenomenon, we herein describe profiles of major populations and immunologically activated subsets of peripheral blood lymphocytes in a cohort of Kuwaiti psoriasis vulgaris patients. Whole venous blood from fifteen psoriatic and twenty eight normal, healthy subjects was analyzed by 2-color flow cytometry for levels of major lymphocyte species and their immunologically activated subsets. When compared to normal subjects, psoriatic blood contained lower cell densities of CD2+, CD8+ (p=0.002 respectively) and B lymphocytes (CD19+) (p=0.003), with a trend toward a lower CD4+ density (p=0.072). Within each major lymphocyte population, activated lymphocytes were present at higher percentages in psoriatic than in healthy blood. These included CD4+ HLA-DR+ (p=0.002), CD4+CD25+ (p=0.043), CD4+CD54+ (p=0.005), CD8+CD25+ (p=0.015), CD8+ HLA-DR+ (p=0.046) and CD3+CD16+CD56+ (p=0.023) Additionally, psoriatic patients were found to have an expanded ratio of memory to naive T cells (CD45RO+CD45RA+) relative to control subjects; this was expected on the basis of increased immune activation. Our findings are consistent with a picture of psoriasis as a disease mediated by activated lymphocytes.

Natural killer T (NKT) cells and their role in antitumor immunity

Natural killer T (NKT) cells have become a major focus for those who study the innate immune response to tumors and infectious diseases, as well as autoimmunity. These novel T lymphocytes produce both Th1 and Th2 cytokines, recognize phospholipid and glycolipid antigens presented by CD1 molecules in a similar manner as peptides are recognized by cytotoxic T lymphocytes (CTL), and kill tumor cell targets by a perforin-dependent mechanism like NK cells and CTL. These ascribed functions thus demonstrate that NKT cells are a unique cytotoxic effector cell subpopulation with a kaleidoscope of activities. Because they can mediate antitumor effects in vivo with or without the collaboration of NK cells, the study of NKT cells in antitumor immunity may lead to novel treatments based on the ability to manipulate the generation and/or activity of these multifunctional lymphocytes.

Ocular immune privilege and CD1d-reactive natural killer T cells

PURPOSE

Immune privilege in the eye is, in part, associated with the development of an antigen-specific systemic tolerance termed anterior chamber-associated immune deviation (ACAID). Natural killer T (NKT) cells express T-cell receptor and natural killer (NK) markers and are classified as innate immune cells partly because they produce cytokines within minutes of signals. The aim of this study was to elucidate the role of murine NKT cells in the induction of T regulatory cells in anterior chamber-associated immune deviation.

METHODS

Anterior chamber-associated immune deviation T regulatory cell generation ability was examined in the following NKT cell-deficient mice: SJL mice, CDld or Jalpha281 knockout (KO) mice on C57BL/6 (B6) background, and NKT cell-depleted mice. To detect T regulatory cells, splenic T cells were harvested 7 days after anterior chamber inoculation of ovalbumin (50 microg/2 microL in Hanks balanced salt solution [HBSS]), mixed with ovalbumin-primed T cells (effector) and ovalbumin-pulsed antigen-presenting cells (stimulator), and then cotransferred into the ear pinnae of a syngeneic naive mouse (local adoptive transfer assay). Ear swelling was measured 24 hours later.

RESULTS

Anterior chamber-inoculated B6 mice developed T regulatory cells, but all natural killer T cell-deficient mice did not generate T regulatory cells unless they were reconstituted with natural killer T cells. We also found that the number of splenic natural killer T cells were increased in anterior chamber-inoculated B6 mice and those natural killer T cells produced IL-10.

CONCLUSIONS

CD1d-reactive natural killer T cells are essential for the induction of T regulatory cells in anterior chamber-associated immune deviation through their IL-10 production and are involved in the maintenance of immune privilege of the eye.

Long-term survival of corneal allografts is dependent on intact CD1d-reactive NKT cells

BALB/c mice that tolerate the allogeneic grafts develop allogeneic-specific anterior chamber-associated immune deviation. Because CD1d-reactive NKT cells are essential for anterior chamber-associated immune deviation, we postulated that the survival of C57BL/6 (B6) cornea graft in BALB/c mice was also dependent on CD1d-reactive NKT cells. The B6 corneal graft rejection rate in BALB/c vs Jalpha281 knockout (KO) mice, which lack NKT cells, was measured. While there were no difference in the early phase of rejection, the survival rates at 12 wk after grafting for BALB/c and Jalpha281 KO mice were 50 and 0%, respectively. Because anti-CD1d mAb abrogated the corneal graft survival in the wild-type mice we concluded that CD1d-reactive NKT cells were essential for graft survival. Moreover, allospecific T regulatory (Tr) cells correlated with acceptance of B6 grafts in BALB/c mice, and the adoptive transfer of these allospecific Tr cells to Jalpha281 KO mice allowed a 50% survival rate of B6 cornea grafts. In conclusion, CD1d-reactive NKT cells are required for induction of allospecific Tr cells and are essential for survival of corneal allografts. Mechanisms that contribute to cornea graft acceptance may lead to new therapies for improvement in graft survival in high-risk corneas and other transplanted tissues and grafts.

Distinction between IL-13+ and IFN-gamma+ natural killer cells and regulation of their pool size by IL-4

The hypothesis that distinct subsets of NK cells produce type 2 and type 1 cytokines in resting naive lymphocytes was tested analyzing cytokine production at the single-cell level. Two non-overlapping IL-13+ and IFN-gamma+ subsets were identified in adult and neonatal NK cells. IL-2 maintained their relative proportion. Accumulation of the former was induced by IL-4, but not IL-13, and inhibited by IL-12; that of the latter was induced by IL-12 and inhibited by IL-4 and IL-13. IL-4 induced preferential proliferation of the pre-existing peripheral IL-13+ cells, whereas IL-12 had minimal effect on proliferation of the IFN-gamma+ NK cells. The IL-13+ cells (CD161+ only) are phenotypically distinct from the IFN-gamma+ ones (CD56+) before and after culture under any condition analyzed, and produce IL-13 in response to NK-sensitive target cells and PMA+Ca(2+) ionophore, whereas also FcgammaRIIIA and IL-2+IL-12 stimulate IFN-gamma production. These data define the existence and regulation of two distinct resting peripheral NK cell subsets producing type 1 and type 2 cytokines, and suggest possible roles for IL-13+ NK cells in allergy.

Highly increased numbers of leukocytes in inflamed gingiva from patients with HIV infection

BACKGROUND

HIV infection increases susceptibility for marginal periodontitis, with horizontal and rapid loss of periodontal soft tissues and alveolar bone.

OBJECTIVES

To examine whether numbers, distribution and some properties of mast cells, neutrophils and macrophages are normal in chronically inflamed gingiva of HIV-positive patients.

METHODS

Gingival biopsies were stained for mast cell tryptase and chymase, neutrophil elastase, CD68, human transforming growth factor beta(1), HLA-DR, Fc gamma RI, Fc gamma RII and Fc gamma RIII and calprotectin.

RESULTS

Patients at all stages of HIV infection showed radically increased numbers of mast cells and neutrophils throughout the connective tissue, and of macrophages below the oral gingival epithelium (P < 0.05).

CONCLUSION

HIV infection is associated with increased numbers of mast cells, macrophages and neutrophils in the chronic periodontal lesion. This may predispose for tissue destruction through the release of inflammatory mediators and effector molecules. The unusually heavy cell infiltrate throughout the gingival connective tissue may contribute to the diverging pattern of periodontal tissue loss in HIV-positive patients.

Immunology of vaccination

An ideal vaccine is relatively easy to define, but few real vaccines approach the ideal and no vaccines exist for many organisms, for which a vaccine is the only realistic protective strategy in the foreseeable future. Many difficulties account for the failure to produce these vaccines. All micro-organisms deploy evasion mechanisms that interfere with effective immune responses and, for many organisms, it is not clear which immune responses provide effective protection. However, recent advances in methods for studying immune response to pathogens have provided a better understanding of immune mechanisms, including immunological memory, and led to the realisation that the initiation of immune responses is a key event requiring triggering through 'danger' signals. Based on these findings, the development of novel adjuvants, vectors and vaccine formulations allowing stimulation of optimal and prolonged protective immunity should lead to the introduction of vaccines for previously resistant organisms.

Immunological approach in the evaluation of regional lymph nodes of patients with squamous cell carcinoma of the head and neck

In cancer, regional lymph node (LN) cells are one of the first components of the immune system to have contact with tumor cells or their products. Therefore, the phenotype and functional properties of hematopoietic cells present within the tumor-draining LN are important to understanding their role in the control of malignant cells. Based on the locoregional metastatic behavior of squamous cell carcinoma of the head and neck (SCCH&N) region, we analyzed tumor-draining lymph nodes from SCCH&N patients to obtain insights into regional tumor immunity. Using a three-color fluorescent labeling technique, surface antigen expression was visualized in mononuclear cells of lymph nodes that were obtained from head and neck cancer patients and compared to mononuclear cells of normal lymph nodes. Cell cycle analyses were performed using propidium iodide. Proliferation after phytohemagglutinin stimulation was measured by a sodium tetrazolium-based assay. LN histology was correlated with flow cytometric findings. Regional lymph nodes of head and neck cancer patients undergo morphologic and functional changes. Flow cytometry revealed a decrease in CD8(+) T cells and in some lymph nodes the presence of second or third populations of larger cells with distinct size and granularity that expressed both T (gammadelta/alphabeta) and different natural killer cell markers. Moreover, cell cycle analyses and proliferation assays showed a diminished response to mitogenic stimuli. These changes were found in both metastatic and hyperplastic lymph nodes from head and neck cancer patients; however, no alterations were found in control lymph nodes or peripheral blood mononuclear cells from noncancer patients. The immune alterations detected in lymphocytes present within the draining lymph nodes of head and neck cancer patients may improve our understanding of how tumor cells escape host immunosurveillance. However, this dysfunction in local draining lymph nodes may not be detected systemically.

The IL-4 production capability of different strains of naive CD4(+) T cells controls the direction of the T(h) cell response

The qualitative nature of an immune response raised against infectious pathogens depends upon the phenotypes of T(h) cell subsets, which secrete distinct types of cytokines. Genetic background is known to greatly influence the nature of the T(h) cell response. However, the precise nature of this influence still remains unclear. In the present study, we demonstrate that CD62L(+), CD44(low) and CD4(+) naive T cells from BALB/c mice are capable of producing significant amounts of IL-4, while naive T cells from B10.D2 mice exhibit no IL-4 production. The addition of exogenous IL-4 into the B10.D2 induction culture recovered T(h)2 development, thereby indicating that the potential of naive T cells to secrete IL-4 at primary activation is likely to substantially influence development of T(h)2. Regulation of the IL-4 gene in naive T cells differs from that in cells committed towards becoming T(h)2 cells, based on the observation that naive T cells from STAT6-deficient mice having a BALB/c background produce detectable amounts of IL-4. The IL-4 promoter region was found to be equally histone acetylated in both BALB/c and B10.D2 naive T cells by primary TCR activation. Interestingly, the expression levels of transcription factors NF-AT and GATA-3, which regulate promoter activity, differ between BALB/c and B10.D2 cells. These results suggest that the differences in expression level between the two transcriptional factors may affect the potential of naive T cells to secrete IL-4, which may subsequently influence the development of T(h) cell phenotypes.

Intrinsic defects in the T-cell lineage results in natural killer T-cell deficiency and the development of diabetes in the nonobese diabetic mouse

T-cell-mediated autoimmune diabetes in nonobese diabetic (NOD) mice is closely associated with natural killer T (NKT)-cell deficiency. To determine whether intrinsic defects of the T-cell lineage contribute to the pathogenesis of the disease and NKT cell deficiency, we reconstituted the T-cell compartment in NOD.scid or BALB.scid mice with T-cells from NOD, nonobese diabetes-resistant (NOR), or AKR thymic precursor cells and examined the development of the NKT cell population. NKT cells developed well from AKR thymic precursor cells but not from other precursor cells in both recipient strains. Insulitis and diabetes developed only in the NOD.scid recipients of NOD or NOR precursor cells. When thymic precursor cells of beta2-microglobulin gene-deficient AKR mice, which have a deficient NKT population, were introduced into NOD.scid recipients, both CD4(+) and CD8(+) T-cell populations developed and the recipient mice developed insulitis and diabetes. We conclude that NKT cells originate from a T-cell-committed thymic precursor population and that the deficiency in the NKT cell population in NOD mice results from intrinsic defects within the T-cell lineage and plays a major role in the development of autoimmune diabetes in the presence of both the NOD thymus and antigen-presenting cells.

Monocyte chemoattractant protein-1-dependent increase of V alpha 14 NKT cells in lungs and their roles in Th1 response and host defense in cryptococcal infection

To elucidate the role of NKT cells in the host defense to cryptococcal infection, we examined the proportion of these cells, identified by the expression of CD3 and NK1.1, in lungs after intratracheal infection with Cryptococcus neoformans. This population increased on day 3 after infection, reached a peak level on days 6-7, and decreased thereafter. In Valpha14 NKT cell-deficient mice, such increase was significantly attenuated. The proportion of Valpha14 NKT cells, detected by binding to alpha-galactosylceramide-loaded CD1d tetramer, and the expression of Valpha14 mRNA increased after infection with a similar kinetics. The delayed-type hypersensitivity response and differentiation of the fungus-specific Th1 cells was reduced in Valpha14 NKT cell-deficient mice, compared with control mice. Additionally, elimination of this fungal pathogen from lungs was significantly delayed in Valpha14 NKT cell-deficient mice. Production of monocyte chemoattractant protein (MCP)-1 in lungs, detected at both mRNA and protein levels, increased on day 1, reached a peak level on day 3, and decreased thereafter, which preceded the increase in NKT cells. Finally, the increase of total and Valpha14(+) subset of NKT cells after infection was significantly reduced in MCP-1-deficient mice. Our results demonstrated that NKT cells, especially Valpha14(+) subset, accumulated in a MCP-1-dependent manner in the lungs after infection with C. neoformans and played an important role in the development of Th1 response and host resistance to this fungal pathogen.

Regulation of CD1 function and NK1.1(+) T cell selection and maturation by cathepsin S

NK1.1(+) T cells develop and function through interactions with cell surface CD1 complexes. In I-A(b) mice lacking the invariant chain (Ii) processing enzyme, cathepsin S, NK1.1(+) T cell selection and function are impaired. In vitro, thymic dendritic cells (DCs) from cathepsin S(-/-) mice exhibit defective presentation of the CD1-restricted antigen, alpha-galactosylceramide (alpha-GalCer). CD1 dysfunction is secondary to defective trafficking of CD1, which colocalizes with Ii fragments and accumulates within endocytic compartments of cathepsin S(-/-) DCs. I-A(k), cathepsin S(-/-) mice do not accumulate class II-associated Ii fragments and accordingly do not display CD1 abnormalities. Thus, function of CD1 is critically linked to processing of Ii, revealing MHC class II haplotype and cathepsin S activity as regulators of NK T cells.

Selective loss of natural killer T cells by apoptosis following infection with lymphocytic choriomeningitis virus

Natural killer T (NKT) cells, a unique subpopulation of T cells, coexpress markers also present on NK cells and recognize the major histocompatibility complex class I-like CD1d1 molecule. We studied the effect of an acute virus infection on NKT cells. Mice were infected with the nonhepatotropic Armstrong strain of lymphocytic choriomeningitis virus (LCMV), and at various times postinfection, mononuclear cells from the liver, peritoneum, and spleen were isolated. It was found that within 2 to 3 days, there was a selective loss of NKT cells from the liver with an apparent rapid recovery within 8 to 14 days. There was no increase in peritoneal or splenic NKT cells, indicating that NKT cells did not traffic to these tissues. This loss of NKT cells was independent of gamma interferon (IFN-gamma) and interleukin 12 (IL-12) production, but did occur in mice treated with poly(I-C), a classical inducer of IFN-alpha/beta. The reduction in NKT cells was CD28 and fas/fasL independent and occurred via apoptosis. It was not observed in LCMV-infected DNA fragmentation factor 45-deficient mice, and an increase in active caspase 3-specific staining was found in liver NKT cells from LCMV-infected and poly(I-C)-treated mice compared to uninfected wild-type mice. Interestingly, it was also found that liver NKT cells from LCMV-infected mice were themselves infected. These results suggest that the loss of NKT cells following an acute LCMV infection could be due to the induction of IFN-alpha/beta resulting in NKT-cell apoptosis and is important for the host's immune response to LCMV.

Glycolipid targets of CD1-mediated T-cell responses

Members of the CD1 family of antigen-presenting molecules bind and present a variety of mammalian and microbial glycolipids for specific recognition by T cells. CD1 proteins accomplish their antigen-presenting function by binding the alkyl chains of the antigens within a deep, hydrophobic groove on the membrane distal surface of CD1, making the hydrophilic elements of the antigen available for contact with the variable regions of antigen-specific T-cell receptors. Most models of CD1-restricted T cells function in infectious, neoplastic, or autoimmune diseases and are based on the premise that CD1-restricted T-cell responses are initiated by alterations in cellular glycolipid content. Although a growing number of self, altered self and foreign glycolipid antigens have been identified, the cellular mechanisms that could lead to the generation of antigenic glycolipids within cells, or control the presentation of particular classes of altered self or microbial glycolipids in disease states have only recently come under investigation. Here we review the structures of known glycolipid antigens for T cells and discuss how the chemical nature of these antigens, which is quite different from that of peptides, influences their recognition by T cells.

Clinical application of NKT cell assays to the prediction of type 1 diabetes

Type 1 diabetes is a disease characterised by disturbed glucose homeostasis, which results from autoimmune destruction of the insulin-producing beta cells in the pancreas. The autoimmune attack, while not yet fully characterised, exhibits components of both mis-targeting and failed tolerance induction. The involvement of non-classical lymphocytes in the induction and maintenance of peripheral tolerance has recently been recognised and natural killer T (NKT) cells appear to play such a role. NKT cells are a subset of T cells that are distinct in being able to produce cytokines such as IL-4 and IFN-gamma extremely rapidly following activation. These lymphocytes also express some surface receptors, and the lytic activity, characteristic of NK cells. Deficiencies in NKT cells have been identified in animal models of type 1 diabetes, and a causal association has been demonstrated by adoptive transfer experiments in diabetes-prone NOD mice. Preliminary work suggests that a similar relationship may exist between deficiencies in NKT cells and type 1 diabetes in humans, although the techniques reported to date would be difficult to translate to clinical use. Here, we describe methods appropriate to the clinical assessment of NKT cells and discuss the steps required in the assessment and validation of NKT cell assays as a predictor of type 1 diabetes.

Dendritic cell maturation overrules H-2D-mediated natural killer T (NKT) cell inhibition: critical role for B7 in CD1d-dependent NKT cell interferon gamma production

Given the broad expression of H-2 class Ib molecules on hematopoietic cells, antigen presentation pathways among CD1d expressing cells might tightly regulate CD1d-restricted natural killer T (NKT) cells. Bone marrow-derived dendritic cells (BM-DCs) and not adherent splenocytes become capable of triggering NK1.1(+)/T cell receptor (TCR)(int) hepatic NKT cell activation when (a) immature BM-DCs lack H-2D(b)-/- molecules or (b) BM-DCs undergo a stress signal of activation. In such conditions, BM-DCs promote T helper type 1 predominant CD1d-restricted NKT cell stimulation. H-2 class Ia-mediated inhibition involves more the direct H-2D(b) presentation than the indirect Qa-1(b) pathway. Such inhibition can be overruled by B7/CD28 interactions and marginally by CD40/CD40L or interleukin 12. These data point to a unique regulatory role of DCs in NKT cell innate immune responses and suggest that H-2 class Ia and Ib pathways differentially control NKT cell recognition of DC antigens.

NKT-associated markers and perforin in hyperplastic thymuses from patients with Myasthenia gravis

Immunohistochemical expression of natural killer T (NKT) cell-associated markers (Valpha24 and CD56) and perforin in relation to CD44-highly positive (CD44(high)) cells was studied in hyperplastic thymuses from patients with myasthenia gravis (MG) whose symptoms dramatically improved after thymectomy and compared with non-MG control thymuses. In the control thymuses, Valpha24-positive (Valpha24(+)) and CD56-positive (CD56(+)) cells were sparsely distributed in the medullary area only. In contrast, in hyperplastic MG thymus, Valpha24(+) and CD56(+) cells were more frequent in connective tissue, appeared to have penetrated the thymic parenchyma, and most coexpressed CD44(high). Perforin-positive cells were not present in the control thymus, but were in the connective tissue and perilobular cortical areas in the hyperplastic MG thymus. Most of these perforin-positive cells were CD44(high) and were located near blood vessels. They appeared to have migrated directly from the vascular system and penetrated the thymic parenchyma. Some perforin-positive cells coexpressed Valpha24, CD56, or both. These findings suggest that in this particular type of MG thymus, NKT-like cells may have increased via a CD44- and perforin-mediated mechanism, leading to an imbalance in the immune system that favored an antibody-mediated autoimmunity against the acetylcholine receptor.

Loss of IFN-gamma production by invariant NK T cells in advanced cancer

Invariant NK T cells express certain NK cell receptors and an invariant TCRalpha chain specific for the MHC class I-like CD1d protein. These invariant NK T cells can regulate diverse immune responses in mice, including antitumor responses, through mechanisms including rapid production of IL-4 and IFN-gamma, but their physiological functions remain uncertain. Invariant NK T cells were markedly decreased in peripheral blood from advanced prostate cancer patients, and their ex vivo expansion with a CD1d-presented lipid Ag (alpha-galactosylceramide) was diminished compared with healthy donors. Invariant NK T cells from healthy donors produced high levels of both IFN-gamma and IL-4. In contrast, whereas invariant NK T cells from prostate cancer patients also produced IL-4, they had diminished IFN-gamma production and a striking decrease in their IFN-gamma:IL-4 ratio. The IFN-gamma deficit was specific to the invariant NK T cells, as bulk T cells from prostate cancer patients produced normal levels of IFN-gamma and IL-4. These findings support an immunoregulatory function for invariant NK T cells in humans mediated by differential production of Th1 vs Th2 cytokines. They further indicate that antitumor responses may be suppressed by the marked Th2 bias of invariant NK T cells in advanced cancer patients.

Cytokine cross-talk between mother and the embryo/placenta

Cytokines are regulatory glycoproteins that can affect virtually every cell type in the body and have pleiotropic regulatory effects on hematopoietic, endocrine, nervous and immune systems. Chemokines, although considered as members of the cytokine superfamily, are establishing their own identity. Chemokines mediate leukocyte migration through specific G protein coupled receptors in various tissues. Recently, much evidence has suggested that cytokines and chemokines play a very important role in the reproduction, i.e. embryo implantation, endometrial development, and trophoblast growth and differentiation by modulating the immune and endocrine systems. The close correlation between the embryo and endometrium and between the placenta and decidua are mediated by sex steroid hormones, cytokines and chemokines. As a result of this closely related cross-talk, pregnancy is successfully maintained.

A rare example of three abundant conformers in one retro model of the cisplatin-DNA d(GpG) intrastrand cross link. Unambiguous evidence that guanine O6 to carrier amine ligand hydrogen bonding is not important. possible effect of the Lippard base pair step adjacent to the lesion on carrier ligand hydrogen bonding in DNA adducts

Guanine O6 to carrier ligand hydrogen bonding is a central feature of many hypotheses advanced to explain the anticancer activity of cis-type anticancer drugs, cis-PtA(2)X(2) (A(2) = diamine or two amines). Early structural evidence suggested that cis-Pt(NH(3))(2)(d(GpG)) (the cross-link model for the key cisplatin-DNA adduct) and other cis-PtA(2)(d(GpG)) adducts exist exclusively or mainly as the HH1 conformer with head-to-head (HH) bases. The dynamic motion of the d(GpG) in these adducts is too rapid to permit definitive characterization of both the conformation and the H-bonding. Hence, we use retro models having A(2) ligands designed to slow the motion. Here, we employ Me(2)ppz (N,N'-dimethylpiperazine), which lacks NH groups. Me(2)ppz is unique in having sp(3) N-methyl groups directly in the coordination plane, allowing the coexistence of multiple conformers but hindering dynamic motion in Me(2)ppzPt(d(GpG)) and Me(2)ppzPt(GpG) retro models. Dynamic processes are decreased enough in Me(2)ppzPt(d(GpG)) to permit HPLC separation of three abundant forms. After HPLC separation, the three re-equilibrate, proving that the three forms must be conformers and that Me(2)ppz has little influence on conformer distribution. This marks the first reported characterization of three abundant conformers for one cis-PtA(2)(d(GpG)) adduct. From NMR evidence, the Me(2)ppzPt(d(GpG)) HH1 conformer has uncanted bases. Another conformer, one of two recently discovered conformer types, has head-to-tail (HT) bases with Delta chirality. For this Delta HT1 form, several lines of evidence establish that the dinucleotide moieties have essentially identical structures in d(GpG) (and GpG) adducts of Me(2)ppzPt and other cis-PtA(2) complexes. For example, the shifts of the highly structure-sensitive G H8 NMR signals are almost identical for the Delta HT1 form of all adducts. In previous models, the stabilization of the Delta HT1 form could be attributed to G O6 H-bonding to A(2) NH groups. Such H-bonds are not possible for Me(2)ppz. The unambiguous conclusions are that G O6 H-bonding is weak and that neither canting nor H-bonding is essential in HH forms. These two features are present in almost all other small models but are essentially absent in the cross-link base pair (bp) step in duplexes. We conclude from our work that the forces favoring canting and H-bonding are weak, and we hypothesize that steric effects within the Lippard bp step adjacent to this cross-link bp step easily overcome these forces.

Characterization of the phenotype and function of CD8(+), alpha / beta(+) NKT cells from tumor-bearing mice that show a natural killer cell activity and lyse multiple tumor targets

Natural Killer (NK) T cells are a specialized T cell population that co-expresses receptors of the NK lineage with the alpha / beta TCR receptor and other T cell surface markers. Their functions, regulation and relationship to other cells in the immune system are not fully understood. This report demonstrates that tumor-bearing C57BL / 6 mice have a population of NKT cells that co-express CD8 and CD161 (NK1.1) surface markers. These cells are maintained in long-term culture with T helper 2 (Th2) cytokine interleukin-4 (IL-4), but produce large amounts of Th1 cytokine interferon-gamma (IFN-gamma) following activation. NK1.1(+)CD8(+) T cells show a potent NK-like cytotoxic activity against multiple tumor targets, and lysis is independent of major histocompatibility complex (MHC)-class I or non-classical MHC-class I molecules (Qa, TL). The NK1.1(+)CD8(+) T cells express Vbeta14 chain of the TCR. These NKT cells are not CD1d restricted, and their cytotoxic activity is CD1d independent. Therefore, they represent a unique subset of T cells with an unknown restriction element which produce large quantities of IFN-gamma following expansion with IL-4. Furthermore, their cytotoxic activity is enhanced by B7 co-stimulatory molecules present on tumor cells. CD161(+) T cells that are expanded in tumor-bearing hosts may function as a part of the innate immune system with potential role(s) in tumor surveillance.

Pathophysiology of immune-mediated (type 1) diabetes mellitus: potential for immunotherapy

Type 1 diabetes mellitus is a chronic T cell-mediated disease resulting from autoimmune destruction of pancreatic beta-cells. This process leads to progressive and irreversible failure of insulin secretion. Development of the disease involves both genetic and environmental factors. Genetic predisposition is mainly connected with the human leucocyte antigen (HLA) region, which encodes structures responsible for antigen presentation. A comprehensive molecular understanding of the pathogenesis of the disease is essential for the design of rational and well tolerated means of prevention. This paper describes recent experimental and clinical findings and elucidates the current possibilities for immunotherapy of type 1 diabetes. The nature of breakdown of self-tolerance and the mechanisms involved in its recovery are discussed.

The source of early IFN-gamma that plays a role in Th1 priming

When naive CD4 T cells are primed, they rapidly differentiate into polarized Th1 and/or Th2 phenotypes. A major factor in producing such polarization is the early production of cytokines (IL-12 and IFN-gamma in the case of Th1 cells and IL-4 in the case of Th2 cells). One issue that remains unresolved is the source of the early IFN-gamma that synergizes with IL-12 to fully polarize CD4 T cells into Th1 cells. We have examined this question by injecting mice with anti-CD3 and examining cells from normal and various MHC-knockout mice. We found that IFN-gamma is induced rapidly in a small subset of CD8 T cells. This subset is absent in mice that lack beta2-microglobulin, but not in K(b)D(b)-double-knockout mice, indicating that these CD8 T cells are dependent on nonclassical MHC class Ib molecules. The early burst of IFN-gamma polarizes CD4 T cells toward Th1 cells, in part by stimulating the release of IL-12 from APC. We also use TAP- and CD1-knockout mice to show that such cells are not CD1-restricted NK T cells, nor are they dependent on TAP-1 transport for surface expression of the relevant MHC class Ib molecule. Therefore, they arise on MHC class Ib molecules that do not depend on TAP-1 transporters.

Tolerance to islet autoantigens in type 1 diabetes

Tolerance to beta cell autoantigens represents a fragile equilibrium. Autoreactive T cells specific to these autoantigens are present in most normal individuals but are kept under control by a number of peripheral tolerance mechanisms, among which CD4(+) CD25(+) CD62L(+) T cell-mediated regulation probably plays a central role. The equilibrium may be disrupted by inappropriate activation of autoantigen-specific T cells, notably following to local inflammation that enhances the expression of the various molecules contributing to antigen recognition by T cells. Even when T cell activation finally overrides regulation, stimulation of regulatory cells by CD3 antibodies may reset the control of autoimmunity. Other procedures may also lead to disease prevention. These procedures are essentially focused on Th2 cytokines, whether used systemically or produced by Th2 cells after specific stimulation by autoantigens. Protection can also be obtained by NK T cell stimulation. Administration of beta cell antigens or CD3 antibodies is now being tested in clinical trials in prediabetics and/or recently diagnosed diabetes.

Resistance to malarial infection is achieved by the cooperation of NK1.1(+) and NK1.1(-) subsets of intermediate TCR cells which are constituents of innate immunity

We previously reported that the major expanding lymphocytes were intermediate TCR (TCR(int)) cells (mainly NK1.1(-)) during malarial infection in mice. Cell transfer experiments of TCR(int) cells indicated that these T cells mediated resistance to malaria. However, TCR(int) cells always contain NK1.1(+)TCR(int) cells (i.e., NKT cells) and controversial results (NKT cells were effective or not for resistance to malaria) have been reported by different investigators. In this study, we used CD1d((-/-)) mice, which almost completely lack NKT cells in the liver and other immune organs. Parasitemia was prolonged in the blood of CD1d((-/-)) mice and the expansion of lymphocytes in the liver of these mice was more prominent after an injection of Plasmodium yoelii-infected erythrocytes. However, these mice finally recovered from malaria. In contrast to B6 mice, CD4(-)8(-) NKT cells as well as NK1.1(-)CD3(int) cells expanded in CD1d((-/-)) mice after malarial infection, instead of CD4(+) (and CD8(+)) NKT cells. These newly generated CD4(-)8(-)NKT cells in CD1d((-/-)) mice did not use an invariant chain of Valpha14Jalpha281 for TCRalpha. Other evidence was that severe thymic atrophy and autoantibody production were accompanied by malarial infection, irrespective of the mice used. These results suggest that both NK1.1(-) and NK1.1(+) subsets of TCR(int) cells (i.e., constituents of innate immunity) are associated with resistance to malaria and that an autoimmune-like state is induced during malarial infection.

Maternal tolerance is not critically dependent on interleukin-4

Pregnant animals can generate and maintain immune responses to fetal antigens. This however, does not usually lead to fetal loss. At least two types of immune response are recognized. T helper type 1 (Th1) responses support the generation of cellular cytotoxicity. In contrast, Th2-type responses support the production of non-cytotoxic antibody and suppress the Th1-type. One attempt to explain why the fetus is not generally rejected has been to suggest that during pregnancy Th2-type responses are dominant. These responses rely heavily on interleukin-4 (IL-4) for both functions. This work focuses on maternal immunity to the male antigen H-Y, which is expressed in male fetuses. When injected with male spleen cells, female mice of certain strains mount a cytotoxic immune response to H-Y. However, pregnant females immunized in this way do not deliver litters with fewer males. To help delineate the possible role of IL-4 in such maternal tolerance, female mice genetically deficient in IL-4 were studied. The results show that: (1) deficiency in maternal IL-4 does not affect fertility, (2) deficiency in IL-4 is not associated with selective loss of male offspring in unimmunized mice, (3) pregnancy does not obliterate anti-H-Y reactivity in immunized mice and (4) maternal immunity to H-Y in the absence of IL-4 does not result in loss of male offspring. The results suggest that IL-4-dependent Th2-type responses are not critical to maternal tolerance. Other cytokines must be examined for their role in this phenomenon.

CD8+ T cells control the TH phenotype of MBP-reactive CD4+ T cells in EAE mice

Trimolecular interactions between the T cell antigen receptor and MHC/peptide complexes, together with costimulatory molecules and cytokines, control the initial activation of naive T cells and determine whether the helper precursor cell differentiates into either T helper (TH)1 or TH2 effector cells. We now present evidence that regulatory CD8(+) T cells provide another level of control of TH phenotype during further evolution of immune responses. These regulatory CD8(+) T cells are induced by antigen-triggered CD4(+) TH1 cells during T cell vaccination and, in vitro, distinguish mature TH1 from TH2 cells in a T cell antigen receptor Vbeta-specific and Qa-1-restricted manner. In vivo, protection from experimental autoimmune encephalomyelitis (EAE) induced by T cell vaccination depends on CD8(+) T cells, and myelin basic protein-reactive TH1 Vbeta8(+) clones, but not TH2 Vbeta8(+) clones, used as vaccine T cells, protect animals from subsequent induction of EAE. Moreover, in vivo depletion of CD8(+) T cells during the first episode of EAE results in skewing of the TH phenotype toward TH1 upon secondary myelin basic protein stimulation. These data provide evidence that CD8(+) T cells control autoimmune responses, in part, by regulating the TH phenotype of self-reactive CD4(+) T cells.

Expansion of cytolytic CD8(+) natural killer T cells with limited capacity for graft-versus-host disease induction due to interferon gamma production

T cells with natural killer cell phenotype and function (NKT cells) have been described in both human and murine tissues. In this study, culture conditions were developed that resulted in the expansion of CD8(+) NKT cells from bone marrow, thymus, and spleen by the timed addition of interferon-gamma (IFN-gamma), interleukin 2 (IL-2), and anti-CD3 monoclonal antibody. After 14 to 21 days in culture, dramatic expansion of CD3(+), CD8(+), alphabetaT-cell receptor(+) T cells resulted with approximately 20% to 50% of the cells also expressing the NK markers NK1.1 and DX5. The CD8(+) NKT cells demonstrated lytic activity against several tumor target cells with more than 90% lysis by day 14 to day 21 of culture. Cytotoxicity was observed against both syngeneic and allogeneic tumor cell targets with the greatest lytic activity by the cells expressing either NK1.1 or DX5. The expanded CD8(+) NKT cells produce T(H)1-type cytokines with high levels of IFN-gamma and tumor necrosis factor alpha. Expansion of the CD8(+) NKT cells was independent of CD1d. Ly49 molecules were expressed on only a minority of cells. A single injection of expanded CD8(+) NKT cells was capable of protecting syngeneic animals from an otherwise lethal dose of Bcl1 leukemia cells. Expanded CD8(+) NKT cells produced far less graft-versus-host disease (GVHD) than splenocytes across major histocompatibility barriers, even when 10 times the number of CD8(+) NKT cells as compared to splenocytes were injected. This reduction in GVHD was related to IFN-gamma production since cells expanded from IFN-gamma knock-out animals caused acute lethal GVHD, whereas cells expanded from animals defective in fas ligand, fas, IL-2, and perforin did not. These data indicate that CD8(+) NKT cells expanded in this fashion could be useful for preserving graft-versus-leukemia activity without causing GVHD.

SAP controls T cell responses to virus and terminal differentiation of TH2 cells

SH2D1A, which encodes signaling lymphocyte activation molecule (SLAM)-associated protein (SAP), is altered in patients with X-linked lymphoproliferative disease (XLP), a primary immunodeficiency. SAP-deficient mice infected with lymphocytic choriomeningitis virus had greatly increased numbers of CD8+ and CD4+ interferon-gamma-producing spleen and liver cells compared to wild-type mice. The immune responses of SAP-deficient mice to infection with Leishmania major together with in vitro studies showed that activated SAP-deficient T cells had an impaired ability to differentiate into T helper 2 cells. The aberrant immune responses in SAP-deficient mice show that SAP controls several distinct key T cell signal transduction pathways, which explains in part the complexity of the XLP phenotypes.

Th1-Th2 cytokine kinetics in the bronchoalveolar lavage fluid of mice infected with Cryptococcus neoformans of different virulences

Th1 immune response plays an important role in protection against infection with Cryptococcus neoformans in mice. We investigated the effect of virulence of C. neoformans on cytokine production in the lung of a mouse model of pulmonary cryptococcosis. BALB/c mice were inoculated intratracheally with a high or low virulence strain of C. neoformans, followed by serial measurements of Th1 and Th2 cytokine concentrations in the bronchoalveolar lavage (BAL) fluid using appropriate enzyme-linked immunosorbent assay kits. The number of colony-forming units (CFU) increased with time, and all mice infected with the highly virulent strain were dead at 28 days after inoculation. In contrast, the number of microorganisms diminished with time in the mice infected with the low virulence strain during the 4-week study. The numbers of neutrophils and lymphocytes in the BAL fluid paralleled those of CFU. High neutrophil counts were observed in the BAL fluid of mice infected with the highly virulent strain, while lymphocyte counts were increased only in the later part of the study in mice infected with the high and low virulence strains. The concentrations of Th2 cytokine, interleukin (IL)-4 were significantly higher in mice infected with the highly virulent strain at days 14 and 21 of infection, whereas the level of Th1 cytokine, interferon-gamma, was significantly higher in the latter strain at days 7 and 14. Our results suggest that strain-specific difference in the organism's ability to induce (or evade) the host immune system contributes to the outcome of infection.

NK T cell-induced protection against diabetes in V alpha 14-J alpha 281 transgenic nonobese diabetic mice is associated with a Th2 shift circumscribed regionally to the islets and functionally to islet autoantigen

The onset of autoimmune diabetes is related to defective immune regulation. Recent studies have shown that NK T cells are deficient in number and function in both diabetic patients and nonobese diabetic (NOD) mice. NK T cells, which are CD1d restricted, express a TCR with an invariant V alpha 14-J alpha 281 chain and rapidly produce large amounts of cytokines. V alpha 14-J alpha 281 transgenic NOD mice have increased numbers of NK T cells and are protected against diabetes onset. In this study we analyzed where and how NK T cells interfere with the development of the anti-islet autoimmune response. NK T cells, which are usually rare in lymph nodes, are abundant in pancreatic lymph nodes and are also present in islets. IL-4 mRNA levels are increased and IFN-gamma mRNA levels decreased in islets from diabetes-free V alpha 14-J alpha 281 transgenic NOD mice; the IgG1/IgG2c ratio of autoantibodies against glutamic acid decarboxylase is also increased in these mice. Treatment with IL-12 (a pro-Th1 cytokine) or anti-IL-4 Ab abolishes the diabetes protection in V alpha 14-J alpha 281 NOD mice. The protection from diabetes conferred by NK T cells is thus associated with a Th2 shift within islets directed against autoantigen such as glutamic acid decarboxylase. Our findings also demonstrate the key role of IL-4.

Cutting edge: regulation of uterine NKT cells by a fetal class I molecule other than CD1

The peri-implantation uterus contains an expanded population of NK1.1(+) V alpha 14(+) TCR(int) (NKT) lymphocytes. Although these cells bear the above features in common with other NKT cells populations in thymus, bone marrow, liver, and spleen, they differ from these other populations in terms of an altered V beta repertoire and absence of a CD4(+) component. In this study, we demonstrate that the uterine population also differs from other NKT cell populations because they recognize a class I/class I-like molecule other than CD1, whereas most previously described V alpha 14(+) NKT cells are CD1-restricted. Moreover, the class I/class I-like molecule leading to the uterine NKT cell expansion may be supplied by the fetus. These data demonstrate a novel mechanism whereby the fetus is capable of modulating the maternal immune system.

Requirement for natural killer T (NKT) cells in the induction of allograft tolerance

In this study, we investigated the role of Valpha14 natural killer T (NKT) cells in transplant immunity. The ability to reject allografts was not significantly different between wild-type (WT) and Valpha14 NKT cell-deficient mice. However, in models in which tolerance was induced against cardiac allografts by blockade of lymphocyte function-associated antigen-1/intercellular adhesion molecule-1 or CD28/B7 interactions, long-term acceptance of the grafts was observed only in WT but not Valpha14 NKT cell-deficient mice. Adoptive transfer with Valpha14 NKT cells restored long-term acceptance of allografts in Valpha14 NKT cell-deficient mice. The critical role of Valpha14 NKT cells to mediate immunosuppression was also observed in vitro in mixed lymphocyte cultures in which lymphocyte function-associated antigen-1/intercellular adhesion molecule-1 or CD28/B7 interactions were blocked. Experiments using IL-4- or IFN-gamma-deficient mice suggested a critical contribution of IFN-gamma to the Valpha14 NKT cell-mediated allograft acceptance in vivo. These results indicate a critical contribution of Valpha14 NKT cells to the induction of allograft tolerance and provide a useful model to investigate the regulatory role of Valpha14 NKT cells in various immune responses.

Oral QS-21 requires early IL-4 help for induction of mucosal and systemic immunity

The highly purified saponin derivative, QS-21, from the Quillaja saponaria Molina tree has been proved to be safe for parenteral administration and represents a potential alternative to bacterial enterotoxin derivatives as a mucosal adjuvant. Here we report that p.o. administration of QS-21 with the vaccine protein tetanus toxoid elicited strong serum IgM and IgG Ab responses, which were only slightly enhanced by further oral immunization. The IgG Ab subclass responses were predominantly IgG1 followed by IgG2b for the 50-microg p.o. dose of QS-21, whereas the 250-microg p.o. dose also induced IgG2a and IgG3 Abs. Low oral QS-21 doses induced transient IgE Ab responses 7 days after the primary immunization, whereas no IgE Ab responses were seen in mice given the higher QS-21 dose. Further, low but not high p.o. QS-21 doses triggered Ag-specific secretory IgA (S-IgA) Ab responses. Th cell responses showed higher IFN-gamma (Th1-type) and lower IL-5, IL-6, and IL-10 (Th2-type) secretion after the high QS-21 p.o. dose than after low doses. Interestingly, the mucosal adjuvant activity of low oral QS-21 doses was diminished in IL-4(-/-) mice, suggesting a role for this cytokine in the initiation of mucosal immunity by oral QS-21. In summary, our results show that oral QS-21 enhances immunity to coadministered Ag and that different doses of QS-21 lead to distinct patterns of cytokine and serum Ab responses. We also show that an early IL-4 response is required for the induction of mucosal immunity by oral QS-21 as adjuvant.

Cytokine dependency of human B cell cycle progression elicited by ligands which coengage BCR and the CD21/CD19/CD81 costimulatory complex

Coengagement of BCR and the C3dg binding CD21/CD19/CD81 costimulatory complex can profoundly reduce the BCR binding threshold for eliciting B cell S phase entry, provided cytokine is present. IL-4 is substantially better than IL-2, IL-13, and TNF-alpha at exhibiting synergy with BCR:CD21 coengaging ligand (anti-IgM:anti-CD21:dextran) in promoting B cell DNA synthesis. Synergy between IL-4 and anti-IgM:anti-CD21:dextran (a) is not explained by the viability-promoting function of IL-4, (b) occurs when the anti-CD21 moiety engages either C3dg binding or non-C3dg binding domains, (c) does not reflect reversal of FcgammaRII-mediated negative regulation, and (d) involves differing temporal requirements for BCR and IL-4R signal transduction during the activation process. The IL-4R signaling pathway appears to synergize directly with the BCR:CD21 signaling pathway(s) in promoting the progression of resting B cells past an early G1 checkpoint, as well as to promote independently the progression of activated B cells past a later G1 to S checkpoint.

IL-18 enhances IL-4 production by ligand-activated NKT lymphocytes: a pro-Th2 effect of IL-18 exerted through NKT cells

NKT cells are a remarkably versatile population whose functional capacities are determined by cytokines present in their microenvironment. In this study, we provide evidence for a new immunoregulatory effect of the proinflammatory cytokine IL-18 on NKT cells. We found that IL-18, mainly known for its involvement in NK cell activation and in Th 1 immune responses, substantially enhanced IL-4 production as well as the percentage of IL-4(+) cells among NKT lymphocytes activated by their specific ligand alpha-galactosylceramide (alpha-GalCer). The effect of IL-18 on IL-4 production by activated NKT cells took place both in vivo and in vitro and was not affected by IL-12 which increased IFN-gamma secretion in the same conditions. We show that NKT cells are the main targets for IL-18-induced IL-4 production since it occurred neither in NKT-deficient mice nor after stimulation of Th2 lymphocytes. Finally, we provide evidence that the IL-4 promptly generated by NKT cells in response to IL-18 plus alpha-galactosylceramide in vivo can effectively contribute to the adaptive Th2 immune response by up-regulating the early activation marker CD69 on B cells. Our data support the notion that, in contrast to the exclusive IFN-gamma inducer IL-12, IL-18 acts in a more subtle manner as a costimulatory factor in both pro-Th1 and pro-Th2 responses depending on the nature of the stimulation and the target cells.

Activation of Valpha14(+) natural killer T cells by alpha-galactosylceramide results in development of Th1 response and local host resistance in mice infected with Cryptococcus neoformans

We examined the effect of alpha-galactosylceramide (alpha-GalCer) on the synthesis of gamma interferon (IFN-gamma) and local resistance in mice infected intravenously with Cryptococcus neoformans. The level of IFN-gamma in serum increased on day 3, reached a peak level on day 7, and decreased to the basal level on day 14 postinfection in mice treated with alpha-GalCer, while in vehicle-treated mice, no increase was detected at any time points except for a small increase on day 7. Such effects were not observed in NKT-KO mice. In CD4KO mice, minor synthesis of IFN-gamma was detected on day 3 in sera but was completely abolished by day 7. The alpha-GalCer-induced IFN-gamma production on day 3 was partially reduced in mice depleted of NK cells by treatment with anti-asialo-GM(1) antibody (Ab). Spleen cells obtained from infected and alpha-GalCer-treated mice on day 7 produced a large amount of IFN-gamma upon restimulation with live organisms, while only a marginal level of production was detected in splenocytes from infected and vehicle-treated mice. Such effects were abolished in CD4KO and NKT-KO mice. Finally, the fungal loads in the lungs and spleen on days 7 and 14 were significantly reduced in alpha-GalCer-treated mice compared to those in control mice. In NKT-KO mice, local resistance elicited by alpha-GalCer was completely abolished, although no obvious exacerbation of infection was detected. Furthermore, treatment with anti-IFN-gamma monoclonal Ab mostly abrogated the protective effect of this agent. Thus, our results indicated that activation of Valpha14(+) NKT cells resulted in an increased Th1 response and local resistance to C. neoformans through production of IFN-gamma.

Decreases in interleukin-4 secretion by invariant CD4(-)CD8(-)V alpha 24J alpha Q T cells in peripheral blood of patientswith relapsing-remitting multiple sclerosis

The cytokine profile of invariant CD4(-)CD8(-)V alpha 24J alpha Q T cells from patients with multiple sclerosis (MS) was compared with that of healthy controls. CD4(-)CD8(-)V alpha 24(+) T cells from the peripheral blood of 12 patients with relapsing-remitting MS (RR-MS), 5 patients with progressive MS (CP-MS), and 9 control individuals were directly sorted into single wells and expanded in vitro for analysis of IL-4 and IFN-gamma secretion; 315 V alpha 24J alpha Q T cell clones were generated and their T cell receptor (TCR) sequenced. T cell functionality was determined by examining cytokine secretion upon TCR cross-linking. RR-MS patients exhibited lower frequencies of IL-4 secreting CD4(-)CD8(-)V alpha 24J alpha Q T cell clones than patients with CP-MS and controls. No differences in IFN-gamma secretion were observed between the groups. An IL-4 positive cytokine profile could be correlated to the cloning efficiency of the V alpha 24J alpha Q T cells. We conclude that alterations in cytokine secretion patterns of CD4(-)CD8(-)V alpha 24J alpha Q T cells may influence the immune system and thus contribute to relapsing-remitting MS.