Recognition and function of Valpha14 NKT cells

Selective reduction of natural killer T cells in the bone marrow of aplastic anaemia

T cell-mediated suppression of haematopoiesis is believed to play an important role in the pathophysiology of aplastic anaemia (AA) and in the pancytopenia of some myelodysplastic syndromes (MDS). Natural-killer T (NKT) cells belong to a unique lymphocyte subset that expresses an invariant T-cell receptor (TCR), consisting of Valpha24JalphaQ, and common NK cell surface markers. NKT cells have been hypothesized to play a role in immune regulation, and many human autoimmune conditions are associated with NKT cell deficiency. Here we investigate the role of NKT cells in AA and MDS patients. Flow cytometry demonstrated that NKT cells, unlike other T-lymphocyte subpopulations, were disproportionally decreased in AA and MDS marrow. When we compared variability within the CDR3 region of Valpha24 in CD4-CD8- T cells derived from AA and healthy individuals, the CDR3 size of Valpha24 cells showed a polyclonal distribution in AA patients, while in control subjects a typical oligoclonal or monoclonal pattern was found. Southern blot and sequence analysis of Valpha24 polymerase chain reaction products revealed that the NKT cell-specific JalphaQ region was predominant in control subjects, whereas it was not, or only very weakly, detected in AA and MDS patients. These results show that NKT cells are profoundly decreased in AA and MDS, and their deficiency may, as in other human autoimmune diseases, play a role in the local immune dysregulation in AA and MDS.

Trafficking machinery of NKT cells: shared and differential chemokine receptor expression among V alpha 24(+)V beta 11(+) NKT cell subsets with distinct cytokine-producing capacity

Natural killer T (NKT) cells are important regulators of the immune system, but their trafficking machinery, including expression of chemokine receptors, has been poorly defined. Unlike other conventional T-cell populations, we show that most NKT cells express receptors for extralymphoid tissue or inflammation-related chemokines (CCR2, CCR5, and CXCR3), while few NKT cells express lymphoid tissue-homing chemokine receptors (CCR7 and CXCR5). A population with homing potential for lymph nodes (L selectin(+) CCR7(+)) exists only within a small subset of CD4 NKT cells. We show differential expression of chemokine receptors among NKT cell subsets: CCR4 is mainly expressed by a high cytokine (interleukin-4/interleukin-2)-producing (CD4) NKT subset, while CCR1, CCR6, and CXCR6 are preferentially expressed by the low cytokine-producing CD8 and CD4(-)CD8(-) subsets. In line with this, TARC/CCL17 (a CCR4 ligand) induces preferential chemotaxis of the CD4 NKT subset, while chemotactic activities of LARC/CCL20 (a CCR6 ligand) and MIP-1 alpha/CCL3 (a CCR1 ligand) are focused on the CD8 and CD4(-)CD8(-) NKT cells. We conclude that, unlike conventional naive, memory, or effector T cells, the entire NKT cell population expresses nonlymphoid tissue homing chemokine receptors, yet NKT cell subsets differ considerably from each other by displaying distinct and reciprocal expression patterns of some chemokine receptors. Our results identify chemokine receptors that are potentially important for trafficking of human blood NKT cell subsets and reveal their function (cytokine production capacity)-dependent differential trafficking potentials.

Treatment with alpha-galactosylceramide before Trypanosoma cruzi infection provides protection or induces failure to thrive

Trypanosoma cruzi, a protozoan parasite, chronically infects many mammalian species and triggers a chronic inflammatory disease. Invariant Valpha14 NK T (iNKT) cells are a regulatory subset of T cells that can contribute to protection against pathogens and to control of chronic inflammatory diseases. alpha-Galactosylceramide (alpha-GalCer) is an iNKT cell-specific glycolipid Ag: a single immunization with alpha-GalCer stimulates robust IFN-gamma and IL-4 production by iNKT cells, while multiple immunizations stimulate IL-4 production, but limited IFN-gamma production. We recently demonstrated that iNKT cells help control T. cruzi infection and affect the chronic Ab response. Therefore, alpha-GalCer treatment might be used to increase protection or decrease chronic inflammation during T. cruzi infection. In this report, we show that a single dose of alpha-GalCer before T. cruzi infection decreases parasitemia. This protection is independent of IL-12, but dependent upon iNKT cell IFN-gamma. In addition, alpha-GalCer treatment of the IFN-gamma(-/-) mice exacerbates parasitemia through IL-4 production. Furthermore, a multiple dose regimen of alpha-GalCer before T. cruzi infection does not lower parasitemia and, surprisingly, after parasitemia has resolved, causes poor weight gain. These data demonstrate that during T. cruzi infection glycolipids can be used to manipulate iNKT cell responses and suggest the possibility of developing glycolipid treatments that can increase protection and possibly decrease the chronic inflammatory pathology.

The roles of IFN gamma in protection against tumor development and cancer immunoediting

Interferon-gamma (IFN gamma) is a cytokine that plays physiologically important roles in promoting innate and adaptive immune responses. The absence of IFN gamma production or cellular responsiveness in humans and experimental animals significantly predisposes the host to microbial infection, a result that validates the physiologic importance of this cytokine in preventing infectious disease. Recently, an additional role for IFN gamma in preventing development of primary and transplanted tumors has been identified. Although there now appears to be a consensus that IFN gamma promotes host responses to tumors, the mechanisms by which this cytokine achieves its effects remain unclear. In this review, we briefly discuss key issues of the molecular cell biology of IFN gamma and its receptor that are most relevant to IFN gamma-dependent anti-tumor effects and then focus on the data implicating IFN gamma as a critical immune system component that regulates tumor development. Potential mechanisms underlying IFN gamma's anti-tumor effects are discussed and a preliminary integrative model of IFN gamma's actions on tumors is proposed. Finally, the capacity of IFN gamma and lymphocytes to not only provide protection against tumor development but also to sculpt the immunogenic phenotype of tumors that develop in an immunocompetent host is presented and introduced as a "cancer immunoediting" process.

CD1d-restricted human natural killer T cells are highly susceptible to human immunodeficiency virus 1 infection

Human natural killer (NK) T cells are unique T lymphocytes that express an invariant T cell receptor (TCR) Valpha24-Vbeta11 and have been implicated to play a role in various diseases. A subset of NKT cells express CD4 and hence are potential targets for human immunodeficiency virus (HIV)-1 infection. We demonstrate that both resting and activated human Valpha24(+) T cells express high levels of the HIV-1 coreceptors CCR5 and Bonzo (CXCR6), but low levels of CCR7, as compared with conventional T cells. Remarkably NKT cells activated with alpha-galactosylceramide (alpha-GalCer)-pulsed dendritic cells were profoundly more susceptible to infection with R5-tropic, but not X4-tropic, strains of HIV-1, compared with conventional CD4(+) T cells. Furthermore, resting CD4(+) NKT cells were also more susceptible to infection. After initial infection, HIV-1 rapidly replicated and depleted the CD4(+) subset of NKT cells. In addition, peripheral blood NKT cells were markedly and selectively depleted in HIV-1 infected individuals. Although the mechanisms of this decline are not clear, low numbers or absence of NKT cells may affect the course of HIV-1 infection. Taken together, our findings indicate that CD4(+) NKT cells are directly targeted by HIV-1 and may have a potential role during viral transmission and spread in vivo.

Expansion of lung V alpha 14 NKT cells by administration of alpha-galactosylceramide-pulsed dendritic cells

NKT cells, a novel murine lymphoid lineage bearing an invariant T cell receptor encoded by V alpha 14 and J alpha 281 gene segments, recognize a specific ligand glycolipid, alpha-galactosylceramide (alpha-GalCer) in a CD1d-dependent manner. Recent research has revealed that activated V alpha 14 NKT cells have dramatic antitumor effects against a wide variety of tumor cell lines in vivo and in vitro. Here, we demonstrate strong in vivo antitumor effects brought about by treatment with alpha-GalCer-pulsed dendritic cells in comparison with in vitro-activated V alpha 14 NKT cells. Furthermore, we show a significant expansion of endogenous V alpha 14 NKT cells in the lung following the administration of alpha-GalCer-pulsed dendritic cells. The feasibility of immunotherapy with alpha-GalCer-pulsed dendritic cells is discussed.

Allogeneic MHC class I ligands and their role in positive and negative regulation of human cytotoxic effector cells

The allogeneic mixed lymphocyte culture (MLC) has served as an important experimental system for elucidating the cellular and molecular basis of human lymphocyte responses. Complex mixtures of lymphocytes are stimulated by disparate alloantigens, inducing cellular activation and generating a cytokine milieu that is an excellent breeding ground for the proliferation and differentiation of many distinct lymphocyte subsets. Cloning of individual lymphocytes following alloactivation has allowed various cytotoxic lymphocytes to be isolated and characterized with respect to phenotype and specificity. These analyses have revealed that all types of cytotoxic effector cells are regulated by interactions with MHC-peptide ligands, however, the consequences of these interactions can result in opposite functional outcomes. In this review we summarize how allogeneic MHC class I-peptide ligands positively or negatively regulate the activities of four distinct groups of cytotoxic lymphocytes and how this information might be transferred into clinical use.

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.

CD4(+) regulatory T cells

There is now compelling evidence that CD4(+) T cells that specialize in the suppression of immune responses play a key role in the control of immune pathology. Recently, there have been a number of reports that have provided information on the generation of CD4(+) regulatory T cells in the thymus and in the periphery. These cells have also been identified in humans, paving the way for analysis of the function of CD4(+) regulatory T cells in immune-mediated disease.

A major fraction of human bone marrow lymphocytes are Th2-like CD1d-reactive T cells that can suppress mixed lymphocyte responses

Murine bone marrow (BM) NK T cells can suppress graft-vs-host disease, transplant rejection, and MLRs. Human BM contains T cells with similar potential. Human BM was enriched for NK T cells, approximately 50% of which recognized the nonpolymorphic CD1d molecule. In contrast to the well-characterized blood-derived CD1d-reactive invariant NK T cells, the majority of human BM CD1d-reactive T cells used diverse TCR. Healthy donor invariant NK T cells rapidly produce large amounts of IL-4 and IFN-gamma and can influence Th1/Th2 decision-making. Healthy donor BM CD1d-reactive T cells were Th2-biased and suppressed MLR and, unlike the former, responded preferentially to CD1d(+) lymphoid cells. These results identify a novel population of human T cells which may contribute to B cell development and/or maintain Th2 bias against autoimmune T cell responses against new B cell Ag receptors. Distinct CD1d-reactive T cell populations have the potential to suppress graft-vs-host disease and stimulate antitumor responses.

Tumor-induced immune dysfunctions caused by myeloid suppressor cells

In the late 1970s, several findings suggested that accessory cells distinct from lymphocytes might suppress immune reactivity in tumor-bearing hosts. Studies in animal models and patients later confirmed that cells driven to act as dominant immune suppressors by growing cancers could subvert the immune system. These cells have also been termed natural suppressors, a functional definition connoting their ability to hamper various T- and B-lymphocyte responses without prior activation and independently from antigen and MHC restriction. These properties were attributed to distinct cell populations. The phenotypic discrepancies, together with the lack of antigen specificity, have generated serious restraints to research on tumor-induced suppression. Recent evidence indicates that suppressor cells are closely related to immature myeloid precursors and can be found in several situations that can exert adverse effects on the immunotherapy of cancer. The present review is an attempt to address the nature and properties of immature myeloid suppressors and their relationship to dendritic cells and macrophages, with the aim of clarifying the complex network of tumor-induced, negative regulators of the immune system.