NK1.1+ CD4+ CD8- thymocytes with specific lymphokine secretion

NKT Cells and Other Innate T Cells: The Immune Cells That Do Not Follow the Rules

This Pillars of Immunology article is a commentary on “A subset of CD4+ thymocytes selected by MHC class I molecules,” a pivotal article by A. Bendelac, N. Killeen, D.R. Littman, and R.H. Schwartz published in Science in 1994, marking the discovery of NKT cells and paving the way for the identification and characterization of other innate T cells. https://doi.org/10.1126/science.7907820.

Antitumor Immunity Exerted by Natural Killer and Natural Killer T Cells in the Liver

The liver plays crucial roles in systemic immunity and greatly contributes to the systemic defense mechanism. Antitumor immunity in the liver is especially critical for the defense against systemic tumor cell dissemination. To achieve effective defense against metastatic tumor cells, liver immune cells with powerful cytotoxic activities construct a potent defense mechanism. In the liver, as compared with other organs, there is a significantly more intense percentage of innate immune lymphocytes, such as natural killer (NK) and NKT cells. These characteristic lymphocytes survey the portal blood transferred to the liver from the alimentary tract and eliminate malignant cells with their robust cytotoxic ability. Additionally, with their active cytokine-producing capacity, these innate lymphocytes initiate immunological sequences by adaptive immune cells. Therefore, they are crucial contributors to systemic antitumor immunity. These attractive immune cells help conduct a fundamental investigation of tumor immunity and act as a target of clinical measures for cancer therapies. This review discusses the mechanisms of these innate lymphocytes regarding recognition and cytotoxicity against tumor cells and the possibility of clinical applications for therapeutic measures.

IL-4-Producing Vγ1+/Vδ6+ γδ T Cells Sustain Germinal Center Reactions in Peyer's Patches of Mice

The mucosal immune system is the first line of defense against pathogens. Germinal centers (GCs) in the Peyer's patches (PPs) of the small intestine are constantly generated through stimulation of the microbiota. In this study, we investigated the role of γδ T cells in the GC reactions in PPs. Most γδ T cells in PPs localized in the GCs and expressed a TCR composed of Vγ1 and Vδ6 chains. By using mice with partial and total γδ T cell deficiencies, we found that Vγ1+/Vδ6+ T cells can produce high amounts of IL-4, which drives the proliferation of GC B cells as well as the switch of GC B cells towards IgA. Therefore, we conclude that γδ T cells play a role in sustaining gut homeostasis and symbiosis via supporting the GC reactions in PPs.

New Insights into Asthma Inflammation: Focus on iNKT, MAIT, and γδT Cells

Asthma is a chronic immunological disease affecting all age groups, but often starting in childhood. Although it has long been ascribed to a single pathology, recent studies have highlighted its heterogeneity due to the potential involvement of various pathogenic mechanisms. Here, we present our current understanding of the role of innate-like T (ILT) cells in asthma pathogenesis. These cells constitute a specific family mainly comprising γδT, invariant natural killer (iNKT) and mucosal-associated invariant (MAIT) T cells. They all share the ability to massively secrete a wide range of cytokines in a T-cell receptor (TCR)-dependent or -independent manner. ILT cells are prevalent in mucosal tissues, including airways, where their innate and adaptive immune functions consist primarily in protecting tissue integrity. However, ILT cells may also have detrimental effects leading to asthma symptoms. The immune mechanisms through which this pathogenic effect occurs will be discussed in this overview.

Does exercise attenuate age- and disease-associated dysfunction in unconventional T cells? Shining a light on overlooked cells in exercise immunology

Unconventional T Cells (UTCs) are a unique population of immune cells that links innate and adaptive immunity. Following activation, UTCs contribute to a host of immunological activities, rapidly responding to microbial and viral infections and playing key roles in tumor suppression. Aging and chronic disease both have been shown to adversely affect UTC numbers and function, with increased inflammation, change in body composition, and physical inactivity potentially contributing to the decline. One possibility to augment circulating UTCs is through increased physical activity. Acute exercise is a potent stimulus leading to the mobilization of immune cells while the benefits of exercise training may include anti-inflammatory effects, reductions in fat mass, and improved fitness. We provide an overview of age-related changes in UTCs, along with chronic diseases that are associated with altered UTC number and function. We summarize how UTCs respond to acute exercise and exercise training and discuss potential mechanisms that may lead to improved frequency and function.

The Variable Genomic NK Cell Receptor Locus Is a Key Determinant of CD4+ T Cell Responses During Viral Infection

Increasing evidence points to a key role for NK cells in controlling adaptive immune responses. In studies examining the role of CD1d on CD4+ T cell responses, we found that a line of CD1d-deficient mice on the C57BL/6J background had a homozygous 129 locus on chromosome 6 containing the entire NK cell gene cluster. Mice possessing this locus (C57BL/6.NKC¹²⁹) displayed a >10-fold reduction in antigen-specific CD4+ T cell responses after intracranial infection with lymphocytic choriomeningitis virus (LCMV). Neither parental strain displayed defects in viral-specific CD4+ T cell responses. Interestingly, following infection, increased numbers of NK cells accumulated in the lymph nodes of C57BL/6.NKC¹²⁹ mice and displayed enhanced in vivo functionality. Moreover, depletion of NK cells with anti-asialo-GM-1 antibody in C57BL/6.NKC¹²⁹ mice resulted in a >20-fold increase in viral-specific CD4+ T cell responses. Mechanistically, we found that dendritic cell antigen presentation and early type I IFN production were significantly decreased in C57BL/6.NKC¹²⁹ mice, but were restored in perforin-deficient C57BL/6.NKC¹²⁹ mice or following NK depletion. Together, these data reveal that the variable genomic regions containing the activating/inhibitory NK cell receptors are key determinants of antigen-specific CD4+ T cell responses, controlling type I IFN production and the antigen-presenting capacity of dendritic cells.

Complementary approaches to study NKT cells in cancer

NKT cells are a small but influential member of the T cell family, recognizing lipids presented by the non-classical MHC-like molecule CD1d rather than peptides presented by classical MHC molecules. They bridge between the innate and adaptive immune systems, serving as rapid responders but also allowing the T cell immune system to recognize lipid antigens, for example derived from tumors or bacteria. They also serve as potent regulatory cells, controlling other immune responses. Type I NKT cells use a semi-invariant T cell receptor (TCR) whereas type II use diverse TCRs. Most often, type I NKT cells promote tumor immunity whereas type II tend to suppress it, and the two subtypes crossregulate each other, forming an immunoregulatory axis. Lack of tools to study these important cells has limited the understanding of these, but newer tools have allowed great advances, especially in mouse models. These range from transgenic and knock-out mice to CD1d tetramers carrying ligands for type I or II NKT cells, to antibodies and NKT cell hybridomas. Here we describe these complementary tools and approaches and their use to study NKT cells and their role in the immunology and immunotherapy of cancer.

Enhanced oxidative phosphorylation in NKT cells is essential for their survival and function

Cellular metabolism and signaling pathways are key regulators to determine conventional T cell fate and function, but little is understood about the role of cell metabolism for natural killer T (NKT) cell survival, proliferation, and function. We found that NKT cells operate distinct metabolic programming from CD4 T cells. NKT cells are less efficient in glucose uptake than CD4 T cells with or without activation. Gene-expression data revealed that, in NKT cells, glucose is preferentially metabolized by the pentose phosphate pathway and mitochondria, as opposed to being converted into lactate. In fact, glucose is essential for the effector functions of NKT cells and a high lactate environment is detrimental for NKT cell survival and proliferation. Increased glucose uptake and IFN-γ expression in NKT cells is inversely correlated with bacterial loads in response to bacterial infection, further supporting the significance of glucose metabolism for NKT cell function. We also found that promyelocytic leukemia zinc finger seemed to play a role in regulating NKT cells' glucose metabolism. Overall, our study reveals that NKT cells use distinct arms of glucose metabolism for their survival and function.

CD8dim but not CD8bright cells positive to CD56 dominantly express KIR and are cytotoxic during visceral leishmaniasis

This study reports a structural and functional heterogeneity of CD8⁺CD56⁺NKT cells, which usually decrease quantitatively during visceral leishmaniasis. Based on fluorescence intensity of CD8 receptors on CD56⁺NKT cells, two populations of CD8⁺CD56⁺NKT cells have been identified. These cells were recognized as CD8^dimCD56⁺NKT and CD8^brightCD56⁺NKT cells. We further analyzed the functional nature of CD8^dim and CD8^bright positive CD56⁺NKT cells. In comparison to CD8^brightCD56⁺NKT cells, a significantly higher percentage of CD8^dimCD56⁺NKT cells expressed KIR during VL. The percentage of CD8^dimCD56⁺NKT cells expressing KIR was found 4 fold higher in VL as compared to healthy subjects. But, the difference was insignificant in case of CD8^brightCD56⁺NKT cells. CD8⁺CD56⁺NKT cells release granzyme B to kill the infected cells. A categorical difference was also observed in the function of CD8^dimCD56⁺NKT and CD8^brightCD56⁺NKT cells during visceral leishmaniasis. The percentage of granzyme B expressing CD8^dimCD56⁺NKT cells was 2.83 fold higher in VL compared to healthy subjects. But, there was no significant difference in granzyme B expressing CD8^brightCD56⁺NKT cells in samples from healthy and VL subjects. However, within VL subject, the percentage of granzyme B expressing CD8^dimCD56⁺NKT cells was 5.7 fold higher in comparison to CD8^brightCD56⁺NKT cells. This study concludes that CD8^dimCD56⁺NKT cells are more cytotoxic than CD8^brightCD56⁺NKT cells during VL.

Frequency of CD4+CD161+ T Cell and Interleukin-10 Expression in Inflammatory Bowel Diseases

Mucosal immune dysregulation associated with T cells plays a critical role in the development of inflammatory bowel diseases (IBD). However, the definite significances of these cells in IBD still remain unclear. Therefore, we investigated the population and expression of CD4⁺CD161⁺ T cells in the colonic lamina propria mononuclear cells (LPMCs) in patients with IBD by analyses using flow cytometry and immunohistochemistry. Interleukin-10 (IL-10) mRNA levels in both LPMCs and CD4⁺ T cells in lamina propria (LP-CD4⁺ T cells) were measured using a real-time quantitative reverse transcription-polymerase chain reaction. IL-10 production was investigated with immunohistochemistry. The results revealed that the population of CD4⁺CD161⁺ T cells was significantly decreased in active ulcerative colitis (UC) compared with inactive UC (P < 0.05). The CD4⁺CD161⁺ T cell population was inversely correlated with disease activity in patients with UC (r = −0.6326, P = 0.0055), but there was no significant correlation in those with Crohn’s disease. Over-expression of IL-10 mRNA in both LPMCs and LP-CD4⁺ T cells were detected in active UC. Immunohistochemistry revealed decreased frequency of CD161⁺ cells and increased IL-10 positive cells in active UC. The frequency of CD4⁺CD161⁺ T cells and IL-10 expression was supposed to be associated with the pathological status of mucosal immunoregulation in IBD.

Phenyl Glycolipids with Different Glycosyl Groups Exhibit Marked Differences in Murine and Human iNKT Cell Activation

Glycosphingolipids (GSLs) bearing the α-galactosyl headgroup and the acyl chain terminated with a phenyl derivative were found to be more potent than α-galactosyl ceramide (αGalCer) to stimulate both murine and human invariant natural killer T (iNKT) cells and to induce an antibody isotope switch to IgG. In this study, we replaced the galactosyl group with glucose (αGlc) and its fluoro-analogs and found that phenyl GSLs with αGlc (C34-Glc) and its fluoro-analog 6F-C34-Glc were stronger than those with αGal in stimulating human iNKT cells but weaker in mice. Their activities have a strong correlation with the binding avidities of the ternary interaction between the iNKT-cell receptor (iNKTCR) and CD1d-GSL complex. It was the iNKTCR rather than CD1d that dictated the species-specific responses. C34-Glc was further used as an adjuvant for a SSEA4-crm-197 vaccine, and after immunization in mice, the vaccine was highly effective against Lewis lung carcinoma.

Proliferatory defect of invariant population and accumulation of non-invariant CD1d-restricted natural killer T cells in the joints of RA patients

OBJECTIVES

While numerical and functional defects of invariant NKT cells have been demonstrated in rheumatoid arthritis (RA), the detailed characterization of proliferative and secretory responses following CD1d-mediated presentation is lacking; the presence of non-invariant populations has never been assessed in human autoimmunity. We have evaluated both invariant and non-invariant populations in the blood and synovial fluid from patients to assess feasibility of NKT cell-directed manipulations in RA.

METHODS

NKT cell populations were quantified by anti-CD4/anti-Vα24 staining and/or CD1d tetramers. Proliferation was measured in cultures of mononuclear cells following stimulations with αGalCer and cytokine secretion determined by multi-bead assay.

RESULTS

We have confirmed a proliferative defect of iNKT cells in both peripheral blood and synovial fluid from RA patients, but no changes in baseline frequencies. Moreover, we have detected an enlargement of non-invariant cell pool in synovial fluid samples. In addition, we noted an evident Th2 shift following exposure to αGalCer and pronounced IL-6 secretion.

CONCLUSIONS

While RA patients suffer from defective proliferative responses of invariant NKT cells, non-invariant cells accumulate at the site of inflammation. While stimulation with αGalCer results in reduced TNF-α and increased suppressive IL-10, abundantly produced IL-6 could potentially contribute to the induction of Th17 cells in the joints.

Natural killer T cells are required for lipopolysaccharide-mediated enhancement of atherosclerosis in apolipoprotein E-deficient mice

Lipopolysaccharide (LPS) has been shown to accelerate atherosclerosis and to increase the prevalence of IL-4-producing natural killer T (NKT) cells in various tissues. However, the role of NKT cells in the development of LPS-induced atherosclerotic lesions has not been fully tested in NKT cell-deficient mice. Here, we examined the lesion development in apolipoprotein E knockout (apoE-KO) mice and apoE-KO mice on an NKT cell-deficient, CD1d knockout (CD1d-KO) background (apoE-CD1d double knockout; DKO). LPS (0.5 μg/g body weight/wk) or phosphate-buffered saline (PBS) was intraperitoneally administered to apoE-KO and DKO mice (8-wk old) for 5 wk and atherosclerotic lesion areas were quantified thereafter. Consistent with prior reports, NKT cell-deficient DKO mice showed milder atherosclerotic lesions than apoE-KO mice. Notably, LPS administration significantly increased the lesion size in apoE-KO, but not in DKO mice, compared to PBS controls. Our findings suggest that LPS, and possibly LPS-producing bacteria, aggravate the development of atherosclerosis primarily through NKT cell activation and subsequent collaboration with NK cells.

Avidity of CD1d-ligand-receptor ternary complex contributes to T-helper 1 (Th1) polarization and anticancer efficacy

Invariant natural killer T cell (NKT) cells (iNKT cells) produce both T-helper 1 (Th1) and T-helper 2 cytokines in response to α-Galactosylceramide (α-GalCer) stimulation and are thought to be the important effectors in the regulation of both innate and adaptive immunity involved in autoimmune disorders, microbial infections, and cancers. However, the anticancer effects of α-GalCer were limited in early clinical trial. In this study, several analogs of α-GalCer, containing phenyl groups in the lipid tails were found to stimulate murine and human iNKT cells to secrete Th1-skewed cytokines and exhibit greater anticancer efficacy in mice than α-GalCer. We explored the possibility of different Vβ usages of murine Vα14 iNKT or human Vα24 iNKT cells, accounting for differential cytokine responses. However, T-cell receptor Vβ analysis revealed no significant differences in Vβ usages by α-GalCer and these phenyl glycolipid analogs. On the other hand, these phenyl glycolipids showed greater binding avidity and stability for iNKT T-cell receptor when complexed with CD1d. These findings suggest that CD1d-phenyl glycolipid complexes may interact with the same population of iNKT cells but with higher avidity and stability to drive Th1 polarization. Thus, this study provides a key to the rational design of Th1 biased CD1d reactive glycolipids in the future.

Invariant NKT cell anergy is induced by a strong TCR-mediated signal plus co-stimulation

Vα14 TCR expressing invariant NK T (iNKT) cells recognize α-galactosylceramide (αGC)/CD1d complex and produce large amounts of various cytokines before the onset of the adaptive immunity. After stimulation with a high dose (2-5 μg) of αGC in vivo, iNKT cells in the spleen and liver become anergic in terms of the proliferation and cytokine production to subsequent stimulation. In this study, we monitor how iNKT anergy is induced. Anergized iNKT cells dramatically reduced the expression of IL-2Rα, and exogenous IL-2 restored the ability to proliferate and produce IL-4 but not to produce IFN-γ. Anergized iNKT cells expressed high levels of programmed death-1 (PD-1). However, iNKT cells in PD-1-deficient mice became anergic as a result of αGC injection, as do normal mice. Furthermore, anti-PD-1 blocking mAb was unable to restore their responsiveness. When iNKT cells were stimulated with immobilized anti-CD3 in the presence or absence of anti-CD28, they produced cytokines in a dose-dependent manner. Unlike in naive CD4 T cells, the strong TCR-mediated signaling with co-stimulation renders them anergic to any subsequent stimulation with αGC and spleen dendritic cells (DCs). Moreover, iNKT cells also became anergic after stimulation with phorbol-12-myristate-13-acetate + ionophore. Finally, the injection of αGC-pulsed DCs was more potent in inducing anergy than B cells. These results indicate that strong TCR-mediated activation with co-stimulation provides signals that induce the anergic state in iNKT cells.

Requirement for invariant chain in macrophages for Mycobacterium tuberculosis replication and CD1d antigen presentation

Mycobacterium tuberculosis is an intracellular bacterium that persists in phagosomes of myeloid cells. M. tuberculosis-encoded factors support pathogen survival and reduce fusion of phagosomes with bactericidal lysosomal compartments. It is, however, not entirely understood if host factors that mediate endosomal fusion affect M. tuberculosis intracellular localization and survival. Neither is it known if endosomal fusion influences induction of host immune reactivity by M. tuberculosis-infected cells. Lysosomal degradation of M. tuberculosis appears to be pivotal for making available lipid substrates for assembly into lipid-CD1d complexes to allow activation of CD1d-restricted invariant natural killer T (iNKT) cells. To clarify the role for endosomal fusion in M. tuberculosis survival and induction of host CD1d-mediated immune defense, we focused our studies on the invariant chain (Ii). Ii regulates endosome docking and fusion and thereby controls endosomal transport. Through direct binding, Ii also directs intracellular transport of the class II major histocompatibility complex and CD1d. Our findings demonstrate that upon infection of Ii-knockout (Ii(-/-)) macrophages, M. tuberculosis is initially retained in early endosomal antigen 1-positive lysosomal-associated membrane protein 1-negative phagosomes, which results in slightly impaired pathogen replication. The absence of Ii did not affect the ability of uninfected and infected macrophages to produce nitric oxide, tumor necrosis factor alpha, or interleukin-12. However, induction of cell surface CD1d was impaired in infected Ii(-/-) macrophages, and CD1d-restricted iNKT cells were unable to suppress bacterial replication when they were cocultured with M. tuberculosis-infected Ii(-/-) macrophages. Thus, while the host factor Ii is not essential for the formation of the M. tuberculosis-containing vacuole, its presence is crucial for iNKT cell recognition of infected macrophages.

Type 2 innate immune responses and the natural helper cell

The T helper type 2 (Th2) immune response, characterized by the production of interleukin-4 (IL-4), IL-5 and IL-13, is a critical immune response against helminths invading cutaneous or mucosal sites. It also plays a critical role in the pathophysiology of allergic diseases such as asthma and allergic diarrhoea. The Th2 cytokines are induced soon after helminth infection, even before a pathogen-specific adaptive immune response is established. Recent studies have shed light on such innate Th2 cytokine production by formerly uncharacterized innate immune cells such as natural helper cells capable of producing Th2 cytokines in response to IL-25 and IL-33 independently of adaptive immune responses. These cells produce large amounts of Th2 cytokines, most notably IL-5 and IL-13, leading to eosinophilia and goblet cell hyperplasia. We discuss here the mechanisms of innate production of Th2 cytokines in host immune responses against helminth infection as well as allergic immune responses and the similarities and differences between recently identified Th2-cytokine producing cells.

Low doses of natural killer T cells provide protection from acute graft-versus-host disease via an IL-4-dependent mechanism

CD4(+) natural killer T (NKT) cells, along with CD4(+)CD25(+) regulatory T cells (Tregs), are capable of controlling aberrant immune reactions. We explored the adoptive transfer of highly purified (> 95%) CD4(+)NKT cells in a murine model of allogeneic hematopoietic cell transplantation (HCT). NKT cells follow a migration and proliferation pattern similar to that of conventional T cells (Tcons), migrating initially to secondary lymphoid organs followed by infiltration of graft-versus-host disease (GVHD) target tissues. NKT cells persist for more than 100 days and do not cause significant morbidity or mortality. Doses of NKT cells as low as 1.0 × 10(4) cells suppress GVHD caused by 5.0 × 10(5) Tcons in an interleukin-4 (IL-4)-dependent mechanism. Protective doses of NKT cells minimally affect Tcon proliferation, but cause significant reductions in interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) production by donor Tcons and in skin, spleen, and gastrointestinal pathology. In addition, NKT cells do not impact the graft-versus-tumor (GVT) effect of Tcons against B-cell lymphoma-1 (BCL-1) tumors. These studies elucidate the biologic function of donor-type CD4(+)NKT cells in suppressing GVHD in an allogeneic transplantation setting, demonstrating clinical potential in reducing GVHD in HCT.

Mechanism of regulation of autoimmunity by iNKT cells

iNKT cells, CD1d dependent natural killer T cells are a unique population of T cells. The capacity of iNKT cells to produce regulatory cytokines first provided an indication of their regulatory potential. Later on, in experimental models as well as in patients afflicted with an auto-immune disease, such as Type 1 diabetes mellitus, multiple sclerosis, and systemic lupus erythematosus along with others, a deficit in iNKT cell number was observed, suggesting the role these cells may possibly have in the prevention of auto-immune diseases. More importantly, experimental strategies which focused on increasing the volume or stimulation of iNKT cells in laboratory animals, demonstrated an improved level of protection against the development of auto-immune diseases. This article reviews the mechanism of protection against autoimmunity by iNKT cells, discusses the obstacles against and indications for the potential use of iNKT cell manipulation in the treatment of human auto-immune diseases.

Alpha-GalCer ameliorates listeriosis by accelerating infiltration of Gr-1+ cells into the liver

Alpha-galactosylceramide (alpha-GalCer) activates invariant (i)NKT cells, which in turn stimulate immunocompetent cells. Although activation of iNKT cells appears critical for regulation of immune responses, it remains elusive whether protection against intracellular bacteria can be induced by alpha-GalCer. Here, we show that alpha-GalCer treatment ameliorates murine listeriosis, and inhibits inflammation following Listeria monocytogenes infection. Liver infiltration of Gr-1+ cells and gamma/delta T cells was accelerated by alpha-GalCer treatment. Gr-1+ cell and gamma/delta T-cell depletion exacerbated listeriosis in alpha-GalCer-treated mice, and this effect was more pronounced after depletion of Gr-1+ cells than that of gamma/delta T cells. Although GM-CSF and IL-17 were secreted by NKT cells after alpha-GalCer treatment, liver infiltration of Gr-1+ cells was not prevented by neutralizing mAb. In parallel to the numerical increase of CD11b+Gr-1+ cells in the liver following alpha-GalCer treatment, CD11b-Gr-1+ cells were numerically reduced in the bone marrow. In addition, respiratory burst in Gr-1+ cells was enhanced by alpha-GalCer treatment. Our results indicate that alpha-GalCer-induced antibacterial immunity is caused, in part, by accelerated infiltration of Gr-1+ cells and to a lesser degree of gamma/delta T cells into the liver. We also suggest that the infiltration of Gr-1+ cells is caused by an accelerated supply from the bone marrow.

Alpha-galactosylceramide promotes killing of Listeria monocytogenes within the macrophage phagosome through invariant NKT-cell activation

alpha-Galactosylceramide (alpha-GalCer) has been exploited for the treatment of microbial infections. Although amelioration of infection by alpha-GalCer involves invariant natural killer T (iNKT)-cell activation, it remains to be determined whether macrophages (Mphi) participate in the control of microbial pathogens. In the present study, we examined the participation of Mphi in immune intervention in infection by alpha-GalCer using a murine model of listeriosis. Phagocytic and bactericidal activities of peritoneal Mphi from C57BL/6 mice, but not iNKT cell-deficient mice, were enhanced after intraperitoneal injection of alpha-GalCer despite the absence of iNKT cells in the peritoneal cavity. High levels of gamma interferon (IFN-gamma) and nitric oxide (NO) were detected in the peritoneal cavities of mice treated with alpha-GalCer and in culture supernatants of peritoneal Mphi from mice treated with alpha-GalCer, respectively. Although enhanced bactericidal activity of peritoneal Mphi by alpha-GalCer was abrogated by endogenous IFN-gamma neutralization, this was only marginally affected by NO inhibition. Similar results were obtained by using a listeriolysin O-deficient strain of Listeria monocytogenes. Moreover, respiratory burst in Mphi was increased after alpha-GalCer treatment. Our results suggest that amelioration of listeriosis by alpha-GalCer is, in part, caused by enhanced killing of L. monocytogenes within phagosomes of Mphi activated by IFN-gamma from iNKT cells residing in an organ(s) other than the peritoneal cavity.

Natural helper cells: a new player in the innate immune response against helminth infection

The Th2-type immune response, characterized by the production of IL-4, IL-5, and IL-13, is a critical immune response against helminths invading cutaneous or mucosal sites. Th2 cytokines are induced soon after helminth infection, even before a pathogen-specific adaptive immune response is established. Although the expulsion and clearance of helminths usually requires pathogen-specific Th2-mediated immunity, early induction of Th2 cytokines during the innate immune phase is important for host protection from helminth invasion. Recent studies have shed light on such Th2 cytokine production by formerly uncharacterized innate immune cells such as a newly identified natural helper cell. We discuss here the mechanisms of innate production of Th2 cytokines in host immune responses against helminth infection.

The specialized iNKT cell system recognizes glycolipid antigens and bridges the innate and acquired immune systems with potential applications for cancer therapy

Invariant NKT (iNKT) cells bridge innate and acquired immunity and play an important role in both protective and regulatory responses. The nature of the response is dictated by the initial cytokine environment: interaction with IL-10-producing cells induces negative regulatory T(h)2/regulatory T cell-type iNKT cells, while that with IL-12-producing cells results in pro-inflammatory T(h)1-type responses. Particularly, in the anti-tumor response, iNKT cells mediate adjuvant activity by their production of IFN-gamma, which in turn activates both innate and acquired immune systems. Thus, upon activation of iNKT cells, both MHC(-) and MHC(+) tumor cells can be efficiently eliminated. On the basis of these mechanisms, iNKT cell-targeted adjuvant cell therapies have been developed and have shown great promise in initial clinical trials on cancer patients.

The contrasting roles of NKT cells in tumor immunity

NKT cells are true T cells that serve as a bridge between the innate and adaptive immune system, acting as first responders. They recognize lipid antigens rather than peptides, and respond to these when presented by a non-classical class I MHC molecule, CD1d. NKT cells can play a pathogenic role in asthma or a protective role against several autoimmune diseases, in part based on their cytokine profile. In cancer, they can play opposite roles, contributing to anti-tumor immunity or suppressing it. The protective NKT cells were found to be primarily type I NKT cells defined by use of a semi-invariant T cell receptor involving Valpha14Jalpha18 in mice and Valpha24Jalpha18 in humans and responding to alpha-galactosylceramide, and the most protective were among the minority that are CD4-. The suppressive NKT cells were found to be CD4+ and to be primarily type II NKT cells, that have diverse T-cell receptors and respond to other lipids. Further, the type I and type II NKT cells were found to counter-regulate each other, forming a new immunoregulatory axis. This axis may have broad implications beyond cancer, as NKT cells play a role in steering other adaptive immune responses. The balance along this axis could affect immunity to tumors and infectious diseases and responses to vaccines.

Phosphodiesterase 7A inhibitor ASB16165 suppresses proliferation and cytokine production of NKT cells

A possible involvement of phosphodiesterase 7A (PDE7A) in proliferation and function of NKT cells was examined using ASB16165, a selective inhibitor for PDE7A. Stimulation of isolated murine NKT cells with anti-CD3 antibody plus IL-2 induced not only cell proliferation but production of cytokines including IFN-gamma, TNF-alpha, IL-17 and IL-22. ASB16165 significantly inhibited the CD3/IL-2-stimulated cell proliferation and production of all the cytokines examined. Forskolin (an activator of adenylyl cyclase) and dibutyryl cAMP also exerted inhibitory effects on the cell proliferation and cytokine production of NKT cells. In addition, Rp-8-Br-cAMPS, an inhibitor of protein kinase A (PKA), reversed the suppressive effects of ASB16165 against NKT cells. These results suggest that PKA/cAMP as well as PDE7A is involved in regulation of cell proliferation and cytokine production of NKT cells, and that the inhibitory effects of ASB16165 in NKT cells shown here are mediated by increase in cellular cAMP level. Our findings also raise the possibility that PDE7A inhibitor including ASB16165 may be useful for treatment of the diseases in which NKT cells have pathogenic roles.

Prognostic value of CD57(+) T lymphocytes in the peripheral blood of patients with advanced gastric cancer

BACKGROUND

Natural killer (NK)-like T cells comprising CD56(+) T cells and CD57(+) T cells belong to a subset of CD1d-independent NKT cells playing an important role in regulating immune responses. Although NK-like T cells are reported to increase in patients with advanced gastric carcinomas, it remains unknown how NK-like T cells are involved in disease progression in gastric cancer patients.

METHODS

The proportions of Th1 cells (interferon [IFN]-gamma-producing CD4(+) T cells), Th2 cells (IL-4-producing CD4(+) T cells), and NK-like T cells (CD56(+) T cells and CD57(+) T cells) in the peripheral blood of 48 gastric cancer patients and 20 healthy controls were measured by two-color flow cytometry analysis and by intracellular cytokine analysis to investigate an association of these immune cells with the survival rate of gastric cancer patients.

RESULTS

Univariate analysis showed that Th1 cells and CD57(+) T cells, as well as some clinicopathological factors, significantly influenced the survival rate. CD57-high (> or ==18%) patients survived for a significantly shorter period after surgery compared to CD57-low patients (P = 0.046; Kaplan-Meier, log-rank test) in the stage III-IV patients, but not in the stage I-II patients. Further, multivariate analysis showed that lymphatic invasion was a statistically significant independent risk factor in all the gastric cancer patients, but the proportion of CD57(+) T cells as well as depth of tumor were statistically significant independent risk factors in patients with advanced carcinomas (stage III-IV).

CONCLUSION

An increased proportion (> or ==18%) of CD57(+) T cells in the peripheral blood of patients with advanced gastric carcinomas could indicate a poor prognosis.

beta-Glycosphingolipids as immune modulators

beta-Glycosphingolipids have emerged as a family of potential ligands for natural killer T (NKT)-regulatory lymphocytes. This subset of regulatory lymphocytes has been implicated in the regulation of autoimmune processes. The major histocompatibility complex (MHC) Class I-like CD1d glycoprotein is a member of the CD1 family of antigen-presenting molecules and is responsible for selection of NKT cells. beta-Glycolipids have been shown to alter immune responses in the opposing settings of autoimmune diseases or cancer. In this review, we discuss the potential use of beta-glycoshpingolipids for NKT-based immunotherapy.

A critical function for CD200 in lung immune homeostasis and the severity of influenza infection

The lung must maintain a high threshold of immune 'ignorance' to innocuous antigens to avoid inflammatory disease that depends on the balance of positive inflammatory signals and repressor pathways. We demonstrate here that airway macrophages had higher expression of the negative regulator CD200 receptor (CD200R) than did their systemic counterparts. Lung macrophages were restrained by CD200 expressed on airway epithelium. Mice lacking CD200 had more macrophage activity and enhanced sensitivity to influenza infection, which led to delayed resolution of inflammation and, ultimately, death. The administration of agonists that bind CD200R, however, prevented inflammatory lung disease. Thus, CD200R is critical for lung macrophage immune homeostasis in the resting state and limits inflammatory amplitude and duration during pulmonary influenza infection.

Liver invariant NKT cells and listeriosis

The invariant (i) NKT cells represent unique T lymphocytes expressing TCRValpha14. Although iNKT cells have been regarded as T lymphocytes expressing NK1.1, they do not consistently express this marker. NK1.1 allows recognition of "missing-self" and thus controls inhibition/activation of iNKT cells. It is thus tempting to assume that iNKT cells participate in the regulation of host immune responses during microbial infection by controlling NK1.1 expression. These findings shed light on the unique role of iNKT cells in microbial infection and provide an evidence for unique aspects of the NK1.1 on these cells as a regulatory molecule.

NKT cells in tumor immunity: opposing subsets define a new immunoregulatory axis

NKT cells are true Ag-specific T cells that also have innate properties and form a bridge between the innate and adaptive immune systems. Distinct NKT cell subsets play positive and negative regulatory roles and define a new immunoregulatory axis with broad implications for tumor immunity and other immunological and disease settings.

Activation of invariant NKT cells exacerbates experimental visceral leishmaniasis

We report that natural killer T (NKT) cells play only a minor physiological role in protection from Leishmania donovani infection in C57BL/6 mice. Furthermore, attempts at therapeutic activation of invariant NKT (iNKT) cells with α-galactosylceramide (α-GalCer) during L. donovani infection exacerbated, rather than ameliorated, experimental visceral leishmaniasis. The inability of α-GalCer to promote anti-parasitic immunity did not result from inefficient antigen presentation caused by infection because α-GalCer–loaded bone marrow–derived dendritic cells were also unable to improve disease resolution. The immune-dampening affect of α-GalCer correlated with a bias towards increased IL-4 production by iNKT cells following α-GalCer stimulation in infected mice compared to naïve controls. However, studies in IL-4–deficient mice, and IL-4 neutralisation in cytokine-sufficient mice revealed that α-GalCer–induced IL-4 production during infection had only a minor role in impaired parasite control. Analysis of liver cell composition following α-GalCer stimulation during an established L. donovani infection revealed important differences, predominantly a decrease in IFNγ⁺ CD8⁺ T cells, compared with control-treated mice. Our data clearly illustrate the double-edged sword of NKT cell–based therapy, showing that in some circumstances, such as when sub-clinical or chronic infections exist, iNKT cell activation can have adverse outcomes.

Natural killer T (NKT) cells are a unique subset of T cells that can produce large quantities of inflammatory cytokines very rapidly upon stimulation. They are known to be strongly stimulated by a molecule called α-galactosylceramide (α-GalCer) that is derived from a marine sponge, and in this way α-GalCer is hoped to provide effective immunotherapy for a wide range of diseases. We attempted to stimulate NKT cells with α-GalCer in mice infected with Leishmania donovani, a protozoan parasite that causes a chronic disease known as visceral leishmaniasis in humans. L. donovani characteristically causes an acute resolving infection in the liver where NKT cells are abundant. Therefore, we hypothesised that by stimulating these cells with α-GalCer we would improve the rate of hepatic disease resolution. However, while α-GalCer administered prior to infection had no effect on hepatic parasite burden, α-GalCer administered during an established infection exacerbated hepatic disease, associated with a decrease in IFNγ-producing CD8⁺ T cells. These results are important as they demonstrate that therapies aimed at modulating NKT cell function are not always beneficial, and adverse consequences may occur in certain circumstances, such as in the presence of persistent and/or sub-clinical infections.

H2-D(d)-mediated upregulation of interleukin-4 production by natural killer T-cell and dendritic cell interaction

Natural killer T (NKT) cells are capable of subserving apparently opposite functions, the interferon-gamma (IFN-gamma)-mediated enhancement of host defence and interleukin-4 (IL-4) -mediated immune regulation. Although dendritic cells (DCs) potently activate NKT cells, DC regulation of the IL-4-IFN-gamma balance via NKT-cell activation is not well characterized. In the present study, we examined the effect of DC treatment with CpG oligodeoxynucleotide (ODN), a Toll-like receptor 9 ligand, on the induction of NKT-cell cytokine production. CpG-ODN-conditioned and alpha-galactosylceramide (alpha-GalCer)-loaded myeloid DCs (CpG-DCs) from BALB/c mice showed enhanced ability to induce NKT-cell production of IL-4, but not IFN-gamma, compared to alpha-GalCer-loaded control DCs (not treated with CpG-ODN). The CpG-DCs expressed significantly higher levels of H2-D(d) than control DCs, and blocking of the H2-D(d) and Ly49 receptor interaction during antigen presentation completely abolished the enhanced ability of the CpG-DCs to induce NKT-cell production of IL-4. These findings demonstrate that DC recognition of the CpG motif leads to induction of enhanced IL-4 production by NKT cells via interaction of the augmented H2-D(d) with Ly49 receptors on NKT cells.

Th1 or Th2 balance regulated by interaction between dendritic cells and NKT cells

If Th1 or Th2 polarization could be artificially manipulated, effective immune responses would be generated depending on nature of the targets. In this study we attempted to regulate CD40 expressions on dendritic cells (DCs) in order to modify the T cell response. It was found that reducing agents selectively inhibited surface expression of CD40 on DCs. This finding may provide a new strategy of DC-mediated modulation of the Th1/Th2 balance. It was also shown that NKT-produced Th1/Th2 cytokine balance was under control of negative feedback loop through DCs. Th1 cytokine-pretreated DCs mainly induced Th2 cytokine production, whereas Th2 cytokine-pretreated DCs induced Th1 cytokine production by alpha-galactosylceramide-stimulated NKT cells. The negative feedback regulation system could be applicable to therapeutics of various diseases based on immunological disorders.

The role of NKT cells in tumor immunity

NKT cells are a relatively newly recognized member of the immune community, with profound effects on the rest of the immune system despite their small numbers. They are true T cells with a T cell receptor (TCR), but unlike conventional T cells that detect peptide antigens presented by conventional major histocompatibility (MHC) molecules, NKT cells recognize lipid antigens presented by CD1d, a nonclassical MHC molecule. As members of both the innate and adaptive immune systems, they bridge the gap between these, and respond rapidly to set the tone for subsequent immune responses. They fill a unique niche in providing the immune system a cellular arm to recognize lipid antigens. They play both effector and regulatory roles in infectious and autoimmune diseases. Furthermore, subsets of NKT cells can play distinct and sometimes opposing roles. In cancer, type I NKT cells, defined by their invariant TCR using Valpha14Jalpha18 in mice and Valpha24Jalpha18 in humans, are mostly protective, by producing interferon-gamma to activate NK and CD8(+) T cells and by activating dendritic cells to make IL-12. In contrast, type II NKT cells, characterized by more diverse TCRs recognizing lipids presented by CD1d, primarily inhibit tumor immunity. Moreover, type I and type II NKT cells counter-regulate each other, forming a new immunoregulatory axis. Because NKT cells respond rapidly, the balance along this axis can greatly influence other immune responses that follow. Therefore, learning to manipulate the balance along the NKT regulatory axis may be critical to devising successful immunotherapies for cancer.

The role of subsets of CD4+ T cells in autoimmunity

It is generally considered that T cells which are reactive with self-antigens are effectively eliminated by two processes: clonal deletion and the induction of T cell anergy. More recently, it has been shown that some potentially autoreactive T cells remain unactivated because the self-antigens for which they are specific are not presented on competent antigen-presenting cells. All these mechanisms of self-tolerance may be regarded as passive in the sense that the autoreactive cells are either deleted or are intrinsically non-responsive. If this view of self-tolerance is adopted, then one would predict that rendering animals relatively lymphopoenic should not give rise to autoimmune disease. This prediction is not verified by experiment. Rats rendered relatively lymphopoenic by adult thymectomy followed by repeated low dose gamma-irradiation develop a high incidence of autoimmune diabetes. Furthermore, it has been shown that the reconstitution of these rats with a specific subset of CD4+ T cells from syngeneic donors prevents the development of this disease. The protective cells have the CD45RClow phenotype, they are resistant to adult thymectomy and the majority of them appear to be non-activated in the donor rats. In contrast, the CD45RChigh CD4+ subset does not provide protection from diabetes. Instead, on injection into athymic rats, it gives rise to pathological changes in a variety of organs: stomach, pancreas, liver, thyroid and lung. In addition, the CD45RClow CD4+ subset prevents these manifestations of autoimmunity in these circumstances. Recently, we have shown that CD4+ CD8- thymocytes are a highly potent source of cells that have the ability to control autoimmune diabetes in rats. It appears that the thymus has three distinct functions: positive selection; negative selection; and the generation of a population of cells that seem specialized for the control of autoimmunity.

Endoplasmic reticulum stress, hepatocyte CD1d and NKT cell abnormalities in murine fatty livers

The liver regulates lipid homeostasis and is enriched with natural killer T (NKT) cells that respond to lipid antigens. Optimal maturation and activation of NKT cells requires their interaction with lipid antigens that are presented by cluster of differentiation-1 (CD-1) molecules on antigen-presenting cells. Hepatocytes express CD1d and present lipid antigens to NKT cells. Depletion and dysregulation of hepatic NKT cells occurs in mice with fatty livers. Herein, we assess whether reduced CD1d content on steatotic hepatocytes contributes to fatty liver-associated NKT cell abnormalities. We show that despite expressing normal levels of CD1d mRNA, fatty hepatocytes from ob/ob mice have significantly less CD1d on their plasma membranes than normal hepatocytes. This has functional significance because ob/ob hepatocytes are less able to activate CD1d-restricted T-cell responses in vitro, and CD1d-reactive NKT cells are reduced in ob/ob livers. Events in the endoplasmic reticulum (ER) normally regulate CD1d trafficking to plasma membranes. Hepatic steatosis has been associated with ER stress. To determine if ER stress reduces CD-1 accumulation on hepatocytes, we evaluated hepatic ER stress in ob/ob mice and treated cultured hepatocytes and lean mice with tunicamycin to induce ER stress. Lipid accumulation and ER stress occurred in the livers of both ob/ob and tunicamycin-treated mice. Tunicamycin caused dose-dependent decreases in hepatocyte CD1d, inhibited hepatocyte activation of CD1d-restricted T-cell responses, depleted liver populations of CD1d-reactive NKT cells and promoted Th-1 polarization of hepatic cytokine production. In conclusion, ER stress-related decreases in hepatocyte CD1d contribute to NKT cell dysregulation in fatty livers.

IL-18 time-dependently modulates Th1/Th2 cytokine production by ligand-activated NKT cells

While IL-18 synergizes with IL-12 to induce a Th1 immune response, it also promotes a Th2 response. Here we investigate the modulatory role of IL-18 on the Th1/Th2 cytokine response. The injection of alpha-galactosylceramide (alpha-GalCer), a ligand for NKT cells, elevated mouse serum levels of both IFN-gamma and IL-4. When the mice were treated 2 h before alpha-GalCer challenge with IL-18, IFN-gamma production but not IL-4 production was remarkably up-regulated. In contrast, pretreatment with IL-18 6 h before the challenge enhanced IL-4 production. However, this IL-18-enhanced IL-4 production was not elicited in mice injected with anti-CD3 Ab. Liver mononuclear cells (MNC) produced a similar cytokine production pattern when MNC from mice treated with IL-18 either 2 h or 6 h before challenge were stimulated with alpha-GalCer in vitro. Expression of SOCS1 and SOCS3 was notably up-regulated in the liver MNC from mice pretreated 6 h before with IL-18; in particular, SOCS3 expression was confined to the liver NKT cells. Inhibition of SOCS3 by RNA interference up-regulated the phosphorylation of STAT3 and suppressed in vitro IL-4 production by IL-18-primed liver MNC stimulated with alpha-GalCer, but it did not affect IFN-gamma production. These results suggest that IL-18 time-dependently modulates Th1/Th2 cytokine production in ligand-activated NKT cells by regulating/inducing SOCS3 expression.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

IL-21 enhances dendritic cell ability to induce interferon-gamma production by natural killer T cells

Interleukin (IL)-21 shows pleiotropic effects on the proliferation, differentiation, and effector functions of leukocytes. However, the influence of IL-21 on dendritic cell (DC) activation of natural killer T (NKT) cells has not yet been elucidated. In the present study, we examined the effect of IL-21 on murine myeloid DC ability to induce NKT cell production of interferon-gamma (IFN-gamma) and IL-4. Pretreatment of DCs with IL-21 and alpha-galactosylceramide (alpha-GalCer), an NKT cell-specific ligand, resulted in the enhanced ability of the DCs to induce NKT cell production of IFN-gamma but not IL-4 in vitro compared to DCs pretreated with alpha-GalCer alone. A similar effect of IL-21 was observed when DCs pretreated with IL-21 and alpha-GalCer in vitro were transferred into naïve mice. Direct administration of IL-21 to the mice also enhanced IFN-gamma production after injection of alpha-GalCer. Thus, IL-21 can modify DC ability to selectively enhance NKT cell production of IFN-gamma upon stimulation with alpha-GalCer.

Successful Islet Transplantation to Two Recipients From a Single Donor by Targeting Proinflammatory Cytokines in Mice

BACKGROUND

Currently, the inability to achieve successful islet transplantation from one donor to one recipient is a major obstacle facing clinical islet transplantation. We herein determined whether this limitation could be overcome by targeting pro-inflammatory cytokines with the prevention of immediate islet graft loss in association with engraftment in mice.

METHODS

Isolated islets were grafted into the liver of streptozotocin-induced diabetic mice and the role of proinflammatory cytokines in the engraftment of islets was evaluated with the use of interferon (IFN)-gamma-/- mice and monoclonal antibodies against proinflammatory cytokines.

RESULTS

Hyperglycemia in streptozotocin-induced diabetic mice receiving 200 syngenic islets, which were isolated from a single mouse pancreas, was ameliorated when IFN-gamma-/-, but not wild-type mice, were used as recipients. The treatment with anti-IFN-gamma antibody produced normoglycemia in diabetic wild-type mice receiving 200, but not 100 islets. However, when anti-tumor necrosis factor-alpha and anti-interleukin-1beta antibodies were administered in conjunction with anti-IFN-gamma antibody, wild-type diabetic mice receiving 100 islets became normoglycemic after transplantation. In addition, the favorable effect of the combined use of antibodies was similarly achieved in mice receiving islet allografts when rejection was prevented with anti-CD4 antibody treatment.

CONCLUSIONS

These findings clearly demonstrate that successful islet transplantation from one donor to two recipients is feasible by targeting pro-inflammatory cytokines in mice, thus suggesting a potential application in clinical islet transplantation if similar mechanisms of islet graft loss could be mediated in humans.

gammadelta T-cell receptors: functional correlations

The gammadelta T-cell receptors (TCRs) are limited in their diversity, suggesting that their natural ligands may be few in number. Ligands for gammadeltaTCRs that have thus far been determined are predominantly of host rather than foreign origin. Correlations have been noted between the Vgamma and/or Vdelta genes a gammadelta T cell expresses and its functional role. The reason for these correlations is not yet known, but several different mechanisms are conceivable. One possibility is that interactions between particular TCR-V domains and ligands determine function or functional development. However, a recent study showed that at least for one ligand, receptor specificity is determined by the complementarity-determining region 3 (CDR3) component of the TCR-delta chain, regardless of the Vgamma and/or Vdelta. To determine what is required in the TCR for other specificities and to test whether recognition of certain ligands is connected to cell function, more gammadeltaTCR ligands must be defined. The use of recombinant soluble versions of gammadeltaTCRs appears to be a promising approach to finding new ligands, and recent results using this method are reviewed.

Streptococcus agalactiae GAPDH is a virulence-associated immunomodulatory protein

Certain extracellular proteins produced by several pathogenic microorganisms interfere with the host immune system facilitating microbial colonization and were thus designated virulence-associated immunomodulatory proteins. In this study, a protein with B lymphocyte stimulatory activity was isolated from culture supernatants of Streptococcus agalactiae strain NEM316. This protein, with an apparent molecular mass of 45 kDa, was identified as GAPDH by N-terminal amino acid sequencing. The gapC gene was cloned and expressed in Escherichia coli for the production of a recombinant histidyl-tagged protein. The recombinant GAPDH (rGAPDH), purified in an enzymatically active form, induced in vitro an up-regulation of CD69 expression on B cells from normal and BCR transgenic mice. In addition, rGAPDH induced an increase in the numbers of total, but not of rGAPDH-specific, splenic Ig-secreting cells in C57BL/6 mice treated i.p. with this protein. These in vitro- and in vivo-elicited B cell responses suggest that the B cell stimulatory effect of rGAPDH is independent of BCR specificity. A S. agalactiae strain overexpressing GAPDH showed increased virulence as compared with the wild-type strain in C57BL/6 mice. This virulence was markedly reduced in IL-10-deficient and anti-rGAPDH antiserum-treated mice. These results suggest that IL-10 production, which was detected at higher concentrations in the serum of rGAPDH-treated mice, is important in determining the successfulness of the host colonization by S. agalactiae and they highlight the direct role of GAPDH in this process. Taken together, our data demonstrate that S. agalactiae GAPDH is a virulence-associated immunomodulatory protein.

Advances in the understanding of acute graft-versus-host disease

Allogeneic stem cell transplantation (SCT) remains the definitive immunotherapy for malignancy. However, morbidity and mortality due to graft-vs.-host disease (GVHD) remains the major barrier to its advancement. Emerging experimental data highlights the immuno-modulatory roles of diverse cell populations in GVHD, including regulatory T cells, natural killer (NK) cells, NK T cells, gammadelta T cells, and antigen presenting cells (APC). Knowledge of the pathophysiology of GVHD has driven the investigation of new rational strategies to both prevent severe GVHD and treat steroid-refractory GVHD. Novel cytokine inhibitors, immune-suppressant agents known to preserve or even promote regulatory T-cell function and the depletion of specific alloreactive T-cell sub-populations all promise significant advances in the near future. As our knowledge and therapeutic options expand, the ability to limit GVHD whilst preserving anti-microbial and tumour responses becomes a realistic prospect.

Type 1 and 2 T helper cell-mediated colitis

PURPOSE OF REVIEW

Abrogation of mucosal T cell homeostasis by exaggerated not only T helper 1, but also T helper 2 cells is a major problem that leads to intestinal inflammation. In this regard, it is important to understand these different aspects of mucosal inflammation.

RECENT FINDINGS

Both T helper 1 and 2 cells play central roles in the induction of mucosal immune responses including secretory IgA antibody production, which would be the most beneficial aspect for the host defense mechanism. T helper 1- and 2-type responses, however, exhibit other roles in the abrogation of intestinal homeostasis. Although it has been shown that T helper 1-type immune responses are key players in the induction of intestinal inflammation in mice colitis models and also in inflammatory bowel diseases in humans, studies in murine colitis models clearly show that T helper 2-type responses are also involved in the pathophysiology of the intestinal inflammation. Both regulatory type T cells and T helper 17 cells are involved to down- or upregulate aberrant T helper 1 and 2 cell responses.

SUMMARY

Understanding the cellular and molecular mechanisms of crosstalk among T helper 1, 2, 17 and T regulatory 1 cells is central for the prevention or treatment of inflammatory bowel diseases.

The NK1.1+T cells alive in irradiated mice play an important role in a Th1/Th2 balance

PURPOSE

Ionizing radiation is known to reduce the helper T (Th) 1 like function, resulting in a Th1/Th2 imbalance. We studied whether NK1.1+T cells which were the most resistant against gamma-irradiation impact on the imbalanced immune response after irradiation.

MATERIALS AND METHODS

C57BL/6 mice received a whole-body gamma-irradiation (WBI) of 4 Gy. The primary T cells were separated by magnetic cell sorter (MACS) using the anti-CD90.2 antibody. The apoptotic cells were detected by propidium iodide (PI) staining. To determine the Th1 and Th2 cell functions, the production of interferon (IFN)-gamma and interleukin (IL)-4 were analysed by a reverse transcriptase-polymerase chain reaction (RT-PCR) and an enzyme linked immunosorbent assay (ELISA). NK1.1+T cells were detected by flow cytometry. For depletion of the NK1.1+T cells in the WBI mice, anti-asialo GM1 antiserum was injected.

RESULTS

The CD90.2 positive cells of the WBI mice produced significantly more Th2 type cytokines and also produced Th1 type cytokines at a not lower level than normal mice, and contained a higher absolute number of NK1.1+T cells. Also, the proportion of the NK1.1+T cells increased in the WBI mice. We found that the NK1.1+T cells were resistant to radiation-induced apoptosis in comparison with the conventional T cells. The depletion of NK1.1+T cells in WBI mice resulted in higher production of IgE and IL-4 and lower secretion of IL-12p70.

CONCLUSION

Our findings revealed that NK1.1+T cells that survive at an early stage after irradiation play an important role in the balance of the immune responses at a late stage after irradiation.