Abnormal development of intestinal intraepithelial lymphocytes and peripheral natural killer cells in mice lacking the IL-2 receptor beta chain

Dendritic cells support the in vivo development and maintenance of NK cells via IL-15 trans-presentation

IL-15 is a key component that regulates the development and homeostasis of NK cells and is delivered through a mechanism termed trans-presentation. During development, multiple events must proceed to generate a functional mature population of NK cells that are vital for tumor and viral immunity. Nevertheless, how IL-15 regulates these various events and more importantly what cells provide IL-15 to NK cells to drive these events is unclear. It is known dendritic cells (DC) can activate NK cells via IL-15 trans-presentation; however, the ability of DC to use IL-15 trans-presentation to promote the development and homeostatic maintenance of NK cell has not been established. In this current study, we show that IL-15 trans-presentation solely by CD11c(+) cells assists the in vivo development and maintenance of NK cells. More specifically, DC-mediated IL-15 trans-presentation drove the differentiation of NK cells, which included the up-regulation of the activating and inhibitory Ly49 receptors. Although these cells did not harbor a mature CD11b(high) phenotype, they were capable of degranulating and producing IFN-gamma upon stimulation similar to wild-type NK cells. In addition, DC facilitated the survival of mature NK cells via IL-15 trans-presentation in the periphery. Thus, an additional role for NK-DC interactions has been identified whereby DC support the developmental and homeostatic niche of NK cells.

Exposure to cigarette smoke suppresses IL-15 generation and its regulatory NK cell functions in poly I:C-augmented human PBMCs

Both NK cells and IL-15 play crucial roles in innate immunity against viral infections and cancer. Cigarette smoke is known to increase susceptibility to infections and certain cancers. Interleukin (IL)-15 plays an important role in immune responses by regulating proliferation, survival and functions of NK cells. Here, we examined the impact of cigarette smoke on IL-15 production and IL-15 mediated NK cell functions in human PBMCs. We report that cigarette smoke significantly suppresses the induction of IL-15 by poly I:C in human PBMCs. Serum IL-15 levels among smokers was significantly lower than non-smokers. In contrast to a profound increases in intracellular IL-15/IL-15Ralpha in poly I:C-treated PBMCs, exposure of PBMCs to smoke-conditioned media (SCM) diminished the IL-15/IL-15Ralpha production. We examined if inhibition of IL-15 production could lead to less NK cell activation. Interestingly, SCM-treated PBMCs had diminished up-regulation of NK cell activation marker, CD69, but not NKG2D compared with controls after poly I:C stimulation. We then confirmed by using IL-15 neutralizing antibody as well as exogenous IL-15 that the ploy I:C-induced NK cells activation was IL-15 mediated. More importantly, cigarette smoke significantly impaired NK cell cytolytic potential to kill K562 cancer cells which was found to be IL-15 mediated. The inhibition of IL-15 and its regulatory NK cell activities were linked to attenuated STAT3 and STAT5, but not ERK1/2 phosphorylations. We demonstrate, for the first time, that cigarette smoke compromises IL-15 production and as a result NK cell function which could link to the higher incidence of cancers or viral infections observed among smokers.

Trans-presentation of IL-15 by intestinal epithelial cells drives development of CD8alphaalpha IELs

IL-15 is crucial for the development of intestinal intraepithelial lymphocytes (IEL) and delivery is mediated by a unique mechanism known as trans-presentation. Parenchymal cells have a major role in the trans-presentation of IL-15 to IELs, but the specific identity of this cell type is unknown. To investigate whether the intestinal epithelial cells (IEC) are the parenchymal cell type involved, a mouse model that expresses IL-15Ralpha exclusively by the IECs (Villin/IL-15Ralpha Tg) was generated. Exclusive expression of IL-15Ralpha by the IECs restored all the deficiencies in the CD8alphaalpha(+)TCRalphabeta(+)and CD8alphaalpha(+)TCRgammadelta(+) subsets that exist in the absence of IL-15Ralpha. Interestingly, most of the IEL recovery was due to the preferential increase in Thy1(low) IELs, which compose a majority of the IEL population. The differentiation of Thy1(high)CD4(-)CD8(-) thymocytes into Thy1(-)CD8alphaalpha IELs was found to require IL-15Ralpha expression specifically by IECs and thus, provides evidence that differentiation of Thy1(low) IELs is one function of trans-presentation of IL-15 in the intestines. In addition to effects in IEL differentiation, trans-presentation of IL-15 by IECs also resulted in an increase in IEL numbers that was accompanied by increases in Bcl-2, but not proliferation. Collectively, this study demonstrates that trans-presentation of IL-15 by IECs alone is completely sufficient to direct the IL-15-mediated development of CD8alphaalpha(+) T cell populations within the IEL compartment, which now includes a newly identified role of IL-15 in the differentiation of Thy1(low) IELs.

Interleukin-15 enhances proteasomal degradation of bid in normal lymphocytes: implications for large granular lymphocyte leukemias

Large granular lymphocyte (LGL) leukemia is a clonal proliferative disease of T and natural killer (NK) cells. Interleukin (IL)-15 is important for the development and progression of LGL leukemia and is a survival factor for normal NK and T memory cells. IL-15 alters expression of Bcl-2 family members, Bcl-2, Bcl-XL, Bim, Noxa, and Mcl-1; however, effects on Bid have not been shown. Using an adoptive transfer model, we show that NK cells from Bid-deficient mice survive longer than cells from wild-type control mice when transferred into IL-15-null mice. In normal human NK cells, IL-15 significantly reduces Bid accumulation. Decreases in Bid are not due to alterations in RNA accumulation but result from increased proteasomal degradation. IL-15 up-regulates the E3 ligase HDM2 and we find that HDM2 directly interacts with Bid. HDM2 suppression by short hairpin RNA increases Bid accumulation lending further support for HDM2 involvement in Bid degradation. In primary leukemic LGLs, Bid levels are low but are reversed with bortezomib treatment with subsequent increases in LGL apoptosis. Overall, these data provide a novel molecular mechanism for IL-15 control of Bid that potentially links this cytokine to leukemogenesis through targeted proteasome degradation of Bid and offers the possibility that proteasome inhibitors may aid in the treatment of LGL leukemia.

Are CD8+CD122+ cells regulatory T cells or memory T cells?

We identified CD8(+)CD122(+) regulatory T cells in the mouse. Some immunologists consider CD8(+)CD122(+) cells to be memory T cells despite our report of their regulatory function. Here, we propose a dual phenotype of these cells. Murine CD8(+)CD122(+) T cells demonstrate both memory and regulatory features in their functional profiles. Human CD8(+)CXCR3(+) T cells, which are thought to be the human counterpart of murine CD8(+)CD122(+) regulatory T cells, do not match human central memory T cells of the CD8(+)CD45RA(-)CCR7(+) phenotype. Thus, we must consider human CD8(+) regulatory T cells and murine CD8(+) regulatory T cells separately. Of human CD8(+) regulatory T cells, CD8(+)CXCR3(+) regulatory T cells can be divided into further subsets and we may be able to distinguish memory T cells and regulatory T cells. Of murine CD8(+)CD122(+) regulatory T cells, it seems to be impossible to divide CD8(+)CD122(+)CD44(+)CD62L(+) regulatory T cells into further subsets at present, indicating that this single population of cells has activities of both regulatory T cells and memory T cells.

Tumor growth decreases NK and B cells as well as common lymphoid progenitor

BACKGROUND

It is well established that chronic tumor growth results in functional inactivation of T cells and NK cells. It is less clear, however, whether lymphopoeisis is affected by tumor growth.

PRINCIPAL FINDINGS

In our efforts of analyzing the impact of tumor growth on NK cell development, we observed a major reduction of NK cell numbers in mice bearing multiple lineages of tumor cells. The decrease in NK cell numbers was not due to increased apoptosis or decreased proliferation in the NK compartment. In addition, transgenic expression of IL-15 also failed to rescue the defective production of NK cells. Our systematic characterization of lymphopoeisis in tumor-bearing mice indicated that the number of the common lymphoid progenitor was significantly reduced in tumor-bearing mice. The number of B cells also decreased substantially in tumor bearing mice.

CONCLUSIONS AND SIGNIFICANCE

Our data reveal a novel mechanism for tumor evasion of host immunity and suggest a new interpretation for the altered myeloid and lymphoid ratio in tumor bearing hosts.

TGF beta secreted by B16 melanoma antagonizes cancer gene immunotherapy bystander effect

Tumor-targeted delivery of immune stimulatory genes, such as pro-inflammatory cytokines and suicide genes, has shown to cure mouse models of cancer. Total tumor eradication was also found to occur despite subtotal tumor engineering; a phenomenon coined the "bystander effect". The bystander effect in immune competent animals arises mostly from recruitment of a cancer lytic cell-mediated immune response to local and distant tumor cells which escaped gene modification. We have previously described a Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) and Interleukin 2 (IL2) fusokine (aka GIFT2) which serves as a potent anticancer cytokine and it here served as a means to understand the mechanistic underpinnings to the immune bystander effect in an immune competent model of B16 melanoma. As expected, we observed that GIFT2 secreted by genetically engineered B16 tumor cells induces a bystander effect on non modified B16 cells, when admixed in a 1:1 ratio. However, despite keeping the 1:1 ratio constant, the immune bystander effect was completely lost as the total B16 cell number was increased from 10(4) to 10(6) which correlated with a sharp reduction in the number of tumor-infiltrating NK cells. We found that B16 secrete biologically active TGFbeta which in turn inhibited GIFT2 dependent immune cell proliferation in vitro and downregulated IL-2R beta expression and IFN gamma secretion by NK cells. In vivo blockade of B16 originating TGFbeta significantly improved the immune bystander effect arising from GIFT2. We propose that cancer gene immunotherapy of pre-established tumors will be enhanced by blockade of tumor-derived TGFbeta.

Requirement of TLR2-mediated signaling for the induction of IL-15 gene expression in human monocytic cells by HSV-1

Exposure of human monocytic cells to herpes simplex virus type 1 (HSV-1) results in immediate up-regulation of interleukin (IL)-15 gene expression. However, the receptor involved in this induction is not known. Here, we provide evidence that this induction depends on TLR2-mediated signaling pathway. Through the use of small interfering RNAs (siRNAs), we demonstrate that HSV-1-induced up-regulation of IL-15 gene expression in monocytic THP1 cells requires the presence of the adaptors MyD88, IRAK1, and TRAF6. Interestingly, TIRAP/Mal, an adaptor molecule specifically recruited to TLR2 and TLR4, was also required for maximal up-regulation of IL-15. This response was completely abrogated by anti-TLR2, but not anti-TLR4, blocking mAbs in both primary monocytes and THP1 cells. Furthermore, THP1 cells rendered defective in TLR2 expression by disrupting the expression of Sp1, a major transcription factor involved in TLR2 promoter activity, were unable to up-regulate IL-15 gene expression in response to HSV-1. In addition, HSV-1-induced NF-kappaB activation was significantly reduced after neutralization of TLR2 and the adaptor proteins. Altogether, these results unequivocally show that HSV-1 induces TLR2-dependent activation of IL-15 gene expression, which requires the recruitment of both MyD88 and TIRAP/Mal and the activation of IRAK1 and TRAF6 leading to NF-kappaB translocation to the nucleus.

IL-15 does not affect IEL development in the thymus but regulates homeostasis of putative precursors and mature CD8 alpha alpha+ IELs in the intestine

Mice devoid of the IL-15 system lose over 90% of CD8alphaalpha(+) TCRalphabeta and TCRgammadelta intestinal intraepithelial lymphocytes (iIELs). Previous work revealed that IL-15Ralpha and IL-15 expressed by parenchymal cells, but not by bone marrow-derived cells, are required for normal CD8alphaalpha(+) iIEL homeostasis. However, it remains unclear when and how the IL-15 system affects CD8alphaalpha(+) iIELs through their development. This study found that IL-15Ralpha is dispensable for the thymic stage of CD8alphaalpha(+) TCRalphabeta and TCRgammadelta iIEL development but is required for the maintenance and/or differentiation of the putative lineage marker negative precursors in the intestinal epithelium, especially for the most mature CD8 single positive subset. Moreover, the IL-15 system directly supports the survival of mature CD8alphaalpha(+) iIEL in vivo. Taken together, this study suggests that regulation of CD8alphaalpha(+) iIEL homeostasis by the IL-15 system does not occur in the thymus but involves mature cells and putative precursors in the intestine.

Revival of CD8+ Treg-mediated suppression

Despite their first recognition almost 40 years ago, CD8(+) 'suppressor' T cells remain poorly characterized. Recent studies of these lymphocytes, now popularly referred to as regulatory CD8(+) T cells (CD8(+) Tregs), have helped clarify their important role in the regulation of autoimmune disease. Here, we review progress related to the identification, phenotype and function of CD8(+) Tregs. We also focus on a newly described subset, CD8alphaalpha(+)TCRalphabeta(+) Tregs, which in mice recognize a T-cell receptor-derived peptide in the context of the class Ib major histocompatibility complex molecule Qa-1. These Tregs target only activated T cells and complement the suppression provided by CD4(+)Foxp3(+) Tregs. Investigations leading to the detailed identification, expansion, maintenance and function of CD8alphaalpha(+) Tregs should result in new therapeutic strategies for human inflammatory diseases.

Identification of the DNA binding element of the human ZNF300 protein

The human ZNF300 gene is a member of the KRAB/C₂H₂ zinc finger gene family, the members of which are known to be involved in various developmental and pathological processes. Here, we show that the ZNF300 gene encodes a 68-kDa nuclear protein that binds DNA in a sequence-specific manner. The ZNF300 DNA binding site, C(t/a)GGGGG(c/g)G, was defined via a random oligonucleotide selection assay, and the DNA binding site was further confirmed by electrophoretic mobility shift assays. A potential ZNF300 binding site was found in the promoter region of the human IL-2Rβ gene. The results of electrophoretic mobility shift assays indicated that ZNF300 bound to the ZNF300 binding site in the IL-2Rβ promoter in vitro. Transient co-transfection assays showed that ZNF300 could activate the IL-2Rβ promoter, and that the activation was abrogated by the mutation of residues in the ZNF300 binding site. Identifying the DNA binding site and characterizing the transcriptional regulation property of ZNF300 would provide critical insights into its potential as a transcriptional regulator.

Humanized immune system (HIS) mice as a tool to study human NK cell development

The study of human hematopoiesis is conditioned by access to nondiseased human tissue samples that harbor the cellular substrates for this developmental process. Technical and ethical concerns limit the availability to tissues derived from the fetal and newborn periods, while adult samples are generally restricted to peripheral blood. Access to a small animal model that faithfully recapitulates the process of human hematopoiesis would provide an important tool. Natural killer (NK) cells comprise between 10% and 15% of human peripheral blood lymphocytes and appear conserved in several species. NK cells are implicated in the recognition of pathogen-infected cells and in the clearance of certain tumor cells. In this chapter, we discuss NK cell developmental pathways and the use of humanized murine models for the study of human hematopoiesis and, in particular, human NK cell development.

Role of natural killer cells in the pathogenesis and progression of multiple sclerosis

Natural killer (NK) cells are a subset of lymphocytes which have long been alleged to play an immunoregulatory role in the prevention of autoimmune diseases. Here, we briefly review NK cell features and the major findings from studies on NK cells in human and animals susceptible to multiple sclerosis (MS). Although most studies in human seem to suggest an association between disease and deficiencies in NK cells, it is also clear that NK cells can be both protective and pathogenic in MS models. These contrasting observations could result from differences in experimental procedures as well as from differences in NK cell subset targeted. Whatever the case, the functional features of these cells and their potential role in regulation of autoimmunity suggest that NK cell-based therapies might be an interesting approach for the treatment of multiple sclerosis.

NK dendritic cells expanded in IL-15 exhibit antitumor responses in vivo

NK dendritic cells (NKDC) are a novel subtype of DC with NK cell properties. IL-15 is a pleiotropic cytokine that plays an obligate role in the proliferation and survival of NK cells. We hypothesized that IL-15 is also essential for NKDC development. NKDC were nearly absent in IL-15(-/-) mice, but restored by administration of exogenous IL-15. Treatment of wild-type mice with IL-15 caused a 2- to 3-fold expansion of both NK cells and NKDC. After 7 days of culture with IL-15, sorted splenic NKDC expanded 10-fold while NK cells increased 5-fold. NKDC expanded in IL-15 retained their cytolytic capacity but lost the ability to stimulate naive T cells. Meanwhile, NKDC expanded in IL-15 produced 10 times more IFN-gamma as fresh NKDC and conferred protection in a tumor prevention model. Thus, IL-15 is essential to the proliferation and survival of NKDC and IL-15 expanded NKDC possess antitumor properties.

Interleukin 15-mediated survival of natural killer cells is determined by interactions among Bim, Noxa and Mcl-1

Interleukin 15 (IL-15) promotes the survival of natural killer (NK) cells by preventing apoptosis through mechanisms unknown at present. Here we identify Bim, Noxa and Mcl-1 as key regulators of IL-15-dependent survival of NK cells. IL-15 suppressed apoptosis by limiting Bim expression through the kinases Erk1 and Erk2 and mechanisms dependent on the transcription factor Foxo3a, while promoting expression of Mcl-1, which was necessary and sufficient for the survival of NK cells. Withdrawal of IL-15 led to upregulation of Bim and, accordingly, both Bim-deficient and Foxo3a-/- NK cells were resistant to cytokine deprivation. Finally, IL-15-mediated inactivation of Foxo3a and cell survival were dependent on phosphotidylinositol-3-OH kinase. Thus, IL-15 regulates the survival of NK cells at multiple steps, with Bim and Noxa being key antagonists of Mcl-1, the critical survivor factor in this process.

Role of Peyer's patches in the induction of Helicobacter pylori-induced gastritis

Helicobacter pylori is a Gram-negative spiral bacterium that causes gastritis and peptic ulcer and has been implicated in the pathogenesis of gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. Although Th1 immunity is involved in gastritis and the accumulation of H. pylori-specific CD4(+) T cells in the H. pylori-infected gastric mucosa in human patients, how T cells are primed with H. pylori antigens is unknown because no apparent lymphoid tissues are present in the stomach. We demonstrate here that Peyer's patches (PPs) in the small intestine play critical roles in H. pylori-induced gastritis; no gastritis is induced in H. pylori-infected mice lacking PPs. We also observed that the coccoid form of H. pylori is phagocytosed by dendritic cells in PPs. We propose that H. pylori converts to the coccoid form in the anaerobic small intestine and stimulates the host immune system through PPs.

Mature natural killer cell and lymphoid tissue-inducing cell development requires Id2-mediated suppression of E protein activity

The Id2 transcriptional repressor is essential for development of natural killer (NK) cells, lymphoid tissue–inducing (LTi) cells, and secondary lymphoid tissues. Id2 was proposed to regulate NK and LTi lineage specification from multipotent progenitors through suppression of E proteins. We report that NK cell progenitors are not reduced in the bone marrow (BM) of Id2^−/− mice, demonstrating that Id2 is not essential for NK lineage specification. Rather, Id2 is required for development of mature (m) NK cells. We define the mechanism by which Id2 functions by showing that a reduction in E protein activity, through deletion of E2A, overcomes the need for Id2 in development of BM mNK cells, LTi cells, and secondary lymphoid tissues. However, mNK cells are not restored in the blood or spleen of Id2^−/−E2A^−/− mice, suggesting a role for Id2 in suppression of alternative E proteins after maturation. Interestingly, the few splenic mNK cells in Id2^−/− and Id2^−/−E2A^−/− mice have characteristics of thymus-derived NK cells, which develop in the absence of Id2, implying a differential requirement for Id2 in BM and thymic mNK development. Our findings redefine the essential functions of Id2 in lymphoid development and provide insight into the dynamic regulation of E and Id proteins during this process.

Intraepithelial lymphocytes: their shared and divergent immunological behaviors in the small and large intestine

At the front line of the body's immunological defense system, the gastrointestinal tract faces a large number of food-derived antigens, allergens, and nutrients, as well as commensal and pathogenic microorganisms. To maintain intestinal homeostasis, the gut immune system regulates two opposite immunological reactions: immune activation and quiescence. With their versatile immunological features, intraepithelial lymphocytes (IELs) play an important role in this regulation. IELs are mainly composed of T cells, but these T cells are immunologically distinct from peripheral T cells. Not only do IELs differ immunologically from peripheral T cells but they are also comprised of heterogeneous populations showing different phenotypes and immunological functions, as well as trafficking and developmental pathways. Though IELs in the small and large intestine share common features, they have also developed differences as they adjust to the two different environments. This review seeks to shed light on the immunological diversity of small and large intestinal IELs.

Interleukin-2 gene variation impairs regulatory T cell function and causes autoimmunity

Autoimmune diseases are thought to result from imbalances in normal immune physiology and regulation. Here, we show that autoimmune disease susceptibility and resistance alleles on mouse chromosome 3 (Idd3) correlate with differential expression of the key immunoregulatory cytokine interleukin-2 (IL-2). In order to test directly that an approximately twofold reduction in IL-2 underpins the Idd3-linked destabilization of immune homeostasis, we show that engineered haplodeficiency of Il2 gene expression not only reduces T cell IL-2 production by twofold but also mimics the autoimmune dysregulatory effects of the naturally occurring susceptibility alleles of Il2. Reduced IL-2 production achieved by either genetic mechanism correlates with reduced function of CD4(+) CD25(+) regulatory T cells, which are critical for maintaining immune homeostasis.

Interferon-producing killer dendritic cells (IKDCs) arise via a unique differentiation pathway from primitive c-kitHiCD62L+ lymphoid progenitors

Interferon-producing killer dendritic cells (IKDCs) have only recently been described and they share some properties with plasmacytoid dendritic cells (pDCs). We now show that they can arise from some of the same progenitors. However, IKDCs expressed little or no RAG-1, Spi-B, or TLR9, but responded to the TLR9 agonist CpG ODN by production of IFNgamma. The RAG-1(-)pDC2 subset was more similar to IKDCs than RAG-1(+) pDC1s with respect to IFNgamma production. The Id-2 transcriptional inhibitor was essential for production of IKDCs and natural killer (NK) cells, but not pDCs. IKDCs developed from lymphoid progenitors in culture but, unlike pDCs, were not affected by Notch receptor ligation. While IKDCs could be made from estrogen-sensitive progenitors, they may have a slow turnover because their numbers did not rapidly decline in hormone-treated mice. Four categories of progenitors were compared for IKDC-producing ability in transplantation assays. Of these, Lin(-)Sca-1(+)c-Kit(Hi)Thy1.1(-)L-selectin(+) lymphoid progenitors (LSPs) were the best source. While NK cells resemble IKDCs in several respects, they develop from different progenitors. These observations suggest that IKDCs may arise from a unique differentiation pathway, and one that diverges early from those responsible for NK cells, pDCs, and T and B cells.

The extrathymic T-cell differentiation in the murine gut

The gut epithelial border is in continuous contact with exogenous antigens and harbors a distinctive and very abundant CD8 alpha alpha intraepithelial T-lymphocyte effector population. We describe here the characteristics of these cells that distinguish them from all other T-cell types in the body as well as their functions in local protection. We also describe how these cells differentiate from local precursors present in the gut cryptopatches (CPs) following a pathway of T-cell differentiation unique to the gut wall. Finally, we describe the origin of the precursors of CD8 alpha alpha T cells, which come from the bone marrow in athymic mice but are first imprinted in the thymus in euthymic mice. Indeed, CD3(-)CD4(-)CD8(-) T-cell-committed precursors can leave the thymus before T-cell receptor rearrangements and then colonize the gut CPs, proceeding with their differentiation within the gut wall.

Familial NK cell deficiency associated with impaired IL-2- and IL-15-dependent survival of lymphocytes

We previously reported the clinical phenotype of two siblings with a novel inherited developmental and immunodeficiency syndrome consisting of severe intrauterine growth retardation and the impaired development of specific lymphoid lineages, including transient CD8 alphabeta T lymphopenia and a persistent lack of blood NK cells. We describe here the elucidation of a plausible underlying pathogenic mechanism, with a cellular phenotype of impaired survival of both fresh and herpesvirus saimiri-transformed T cells, in the surviving child. Clearly, NK cells could not be studied. However, peripheral blood T lymphocytes displayed excessive apoptosis ex vivo. Moreover, the survival rates of CD4 and CD8 alphabeta T cell blasts generated in vitro, and herpesvirus saimiri-transformed T cells cultured in vitro, were low, but not nil, following treatment with IL-2 and IL-15. In contrast, Fas-mediated activation-induced cell death was not enhanced, indicating a selective excess of cytokine deprivation-mediated apoptosis. In keeping with the known roles of IL-2 and IL-15 in the development of NK and CD8 T cells in the mouse model, these data suggest that an impaired, but not abolished, survival response to IL-2 and IL-15 accounts for the persistent lack of NK cells and the transient CD8 alphabeta T lymphopenia documented in vivo. Impaired cytokine-mediated lymphocyte survival is likely to be the pathogenic mechanism underlying this novel form of inherited and selective NK deficiency in humans.

Enforced Expression of Bcl-2 Partially Restores Cell Numbers but Not Functions of TCRγδ Intestinal Intraepithelial T Lymphocytes in IL-15-Deficient Mice

IL-15 knockout (KO) mice have severely reduced numbers of TCRgammadelta intestinal intraepithelial T lymphocytes (i-IEL), suggesting requirements of IL-15 signaling in the development or maintenance of i-IEL. To determine an involvement of survival signals via Bcl-2 in IL-15-mediated homeostasis of TCRgammadelta i-IEL, we introduced a bcl-2 transgene into IL-15 KO mice. In situ apoptosis of TCRgammadelta i-IEL was decreased in Bcl-2 transgenic (Tg) x IL-15 KO mice compared with IL-15 KO mice. The enforced expression of Bcl-2 partially restored the numbers of TCRgammadelta i-IEL in IL-15 KO mice. However, effector functions of TCRgammadelta i-IEL, including cytokine production and cytotoxic activity, were not recovered in Bcl-2 Tg x IL-15 KO mice. Importantly, TCRgammadelta i-IEL in Bcl-2 Tg x IL-15 KO mice expressed a reduced level of eomesodermin, a transcription factor critical for effector functions of NK cells and CD8(+) T cells. Similar to the case of TCRgammadelta i-IEL, enforced expression of Bcl-2 restored the numbers but not the functions of NK cells in IL-15 KO mice. These results suggest that Bcl-2-mediated survival signal is involved in the IL-15-mediated homeostasis of TCRgammadelta i-IEL and NK cells, but other signals from IL-15 are critical for inducing transcription factors, such as eomesodermin for their effector functions.

Reciprocal regulation between natural killer cells and autoreactive T cells

The initiation and the progression of autoimmune diseases stem from complex interactions that involve cells of both the innate and the adaptive immune system. As we discuss here, natural killer (NK) cells, which are components of the innate immune system, can inhibit or promote the activation of autoreactive T cells during the initiation of autoimmunity. After they have been activated, autoreactive T cells contribute to the homeostatic contraction of NK-cell populations. The dynamic interaction between NK cells and autoreactive T cells might indicate the transition from the innate immune triggering of autoimmunity to the progressive phase of the disease. Understanding the mechanisms and signals that control the reciprocal regulation of NK cells and autoreactive T cells could have important implications for treatment in the clinic.

Characterization of immunodeficiency in a patient with growth hormone insensitivity secondary to a novel STAT5b gene mutation

STAT5 proteins are components of the common growth hormone and interleukin 2 family of cytokines' signaling pathway. Mutations in the STAT5b gene, described in 2 patients, lead to growth hormone insensitivity that resembles Laron syndrome. Clinical immunodeficiency was also present, although immunologic defects have not been well characterized thus far. Here we describe a 16-year-old girl who suffered generalized eczema and recurrent infections of the skin and respiratory tract since birth. She also suffered severe chronic lung disease and multiple episodes of herpetic keratitis. Clinical features of congenital growth hormone deficiency were observed, such as persistently low growth rate, severely delayed bone age, and postnatal growth failure resulting from growth hormone resistance. This combined phenotype of growth hormone insensitivity and immunodeficiency was attributable to a homozygous C-->T transition that resulted in a nonsense mutation at codon 152 in exon 5 of the STAT5b gene. This novel mutation determined a complete absence of protein expression. The main immunologic findings were moderate T-cell lymphopenia (1274/mm3), normal CD4/CD8 ratio, and very low numbers of natural killer (18/mm3) and gammadelta T (5/mm3) cells. T cells presented a chronically hyperactivated phenotype. In vitro T-cell proliferation and interleukin 2 signaling were impaired. CD4+ and CD25+ regulatory T cells were significantly diminished, and they probably contributed to the signs of homeostatic mechanism deregulation found in this patient. This new case, in accordance with 2 previously reported cases, definitely demonstrates the significant role of the STAT5b protein in mediating growth hormone actions. Furthermore, the main immunologic findings bring about an explanation for the clinical immunodeficiency features and reveal for the first time the relevant role of STAT5b as a key protein for T-cell functions in humans.

Vitamin D3upregulated protein 1 (VDUP1) is a regulator for redox signaling and stress-mediated diseases

Vitamin D(3) upregulated protein 1 (VDUP1) is a 46-kDa multifunctional protein, initially isolated in HL-60 cells as a protein of which expression is upregulated by vitamin D(3) administration. Subsequently, it was identified independently by investigators from diverse scientific backgrounds as a thioredoxin binding protein that negatively regulates the expression and the activity of thioredoxin, and is thus involved in redox regulation. Further studies have revealed that VDUP1 plays multiple roles in a wide range of cellular processes such as proliferation or apoptosis. Recently, it has been reported that VDUP1 is also involved in the immune system via positive regulation of natural killer development. In addition, VDUP1 has been revealed to be associated with the fatty acid utilization. In the present review, we discuss the novel aspects of VDUP1 function as well as the historical background of VDUP1. Future studies will explore the diagnostic and therapeutic potential of modulating the function of VDUP1 in vivo.

Both integrated and differential regulation of components of the IL-2/IL-2 receptor system

Interleukin-2 was discovered in 1976 as a T-cell growth factor. It was the first type I cytokine cloned and the first for which a receptor component was cloned. Its importance includes its multiple actions, therapeutic potential, and lessons for receptor biology, with three components differentially combining to form high, intermediate, and low-affinity receptors. IL-2Ralpha and IL-2Rbeta, respectively, are markers for double-negative thymocytes and regulatory T-cells versus memory cells. gamma(c), which is shared by six cytokines, is mutated in patients with X-linked severe-combined immunodeficiency. We now cover an under-reviewed area-the regulation of genes encoding IL-2 and IL-2R components, with an effort to integrate/explain this knowledge.

Trans-presentation of donor-derived interleukin 15 is necessary for the rapid onset of acute graft-versus-host disease but not for graft-versus-tumor activity

The "holy grail" of allogeneic stem cell transplantation is to preserve the graft-versus-tumor (GVT) effect while eliminating graft-versus-host disease (GVHD). Endogenous donor-derived interleukin 15 (IL-15) has been implicated in the pathogenesis of acute GVHD, yet the mechanism by which it impacts this lethal process remains unclear. Using the well-described and clinically relevant C57BL/6 --> B6D2F1 murine model of acute GVHD, we demonstrate that in trans presentation of IL-15 by donor bone marrow-derived cells is required for the rapid onset of acute GVHD. Recipients of IL-15-/- C57BL/6 bone marrow cells show diminished type 1 polarization of T cells, yet there is no decrease in donor T-cell reconstitution. A molecular basis for these findings is provided with the observation that expression of T-bet, the master control gene for type 1 T-cell functions, is necessary for IL-15-mediated acute GVHD lethality. Finally, we demonstrate that in the absence of donor-derived IL-15, the GVT effect is maintained. These findings thus establish a mechanism by which endogenous donor-derived IL-15 impacts the pathobiology of acute GVHD and GVT activity.

Human natural killer cell development and biology

Natural killer cells are important innate immune effector cells with potentially broad applications in the treatment of human malignancy due to their ability to lyse neoplastic cells without the need for tumor-specific antigen recognition. Human NK cells can be divided into two functional subsets based on their surface expression of CD56; CD56(bright) immunoregulatory cells and CD56(dim) cytotoxic cells. In addition to functional differences, these NK cell subsets can be modulated differently by interleukin (IL)-2, which has permitted the development of lower dose, better tolerated IL-2 regimens for the in vivo expansion and activation of NK cells. The importance of early hematopoietic growth factors, such as c-kit ligand and flt-3 ligand, and their synergy with IL-15 in the development of human NK cells in the bone marrow has permitted the investigation of novel cytokine combinations for optimizing in vivo expansion of NK cell in the clinic. The importance of lymph nodes as a site for NK cell development has recently been elucidated. Furthermore, progress in the field of how NK cell recognize target cells via activating and inhibitory receptors, and how the balance of signals from these receptors can modulate NK cell activity has revolutionized our understanding of the selective killing of tumor cells by NK cells while sparing normal cells. In this review, we summarize current understanding of NK cell biology, and highlight how such knowledge may be translated to optimize the efficacy of using autologous or allogeneic NK cell for the immunotherapy of cancer.

Evidence for discrete stages of human natural killer cell differentiation in vivo

Human natural killer (NK) cells originate from CD34(+) hematopoietic progenitor cells, but the discrete stages of NK cell differentiation in vivo have not been elucidated. We identify and functionally characterize, from human lymph nodes and tonsils, four NK cell developmental intermediates spanning the continuum of differentiation from a CD34(+) NK cell progenitor to a functionally mature NK cell. Analyses of each intermediate stage for CD34, CD117, and CD94 cell surface expression, lineage differentiation potentials, capacity for cytokine production and natural cytotoxicity, and ETS-1, GATA-3, and T-BET expression provide evidence for a new model of human NK cell differentiation in secondary lymphoid tissues.

Diverse functions of IL-2, IL-15, and IL-7 in lymphoid homeostasis

IL-2, IL-15, and IL-7 are cytokines that are critical for regulating lymphoid homeostasis. These cytokines stimulate similar responses from lymphocytes in vitro, but play markedly divergent roles in lymphoid biology in vivo. Their distinct physiological functions can be ascribed to distinct signaling pathways initiated by proprietary cytokine receptor chains, differential expression patterns of the cytokines or their receptor chains, and/or signals occurring in distinct physiological contexts. Recently, the discovery of a novel mechanism of cytokine signaling, trans-presentation, has provided further insights into the different ways these cytokines function. Trans-presentation also raises several novel cell biological and cellular implications concerning how cytokines support lymphoid homeostasis.

Interferon-producing killer dendritic cells provide a link between innate and adaptive immunity

Natural killer (NK) cells and dendritic cells (DCs) are, respectively, central components of innate and adaptive immune responses. We describe here a third DC lineage, termed interferon-producing killer DCs (IKDCs), distinct from conventional DCs and plasmacytoid DCs and with the molecular expression profile of both NK cells and DCs. They produce substantial amounts of type I interferons (IFN) and interleukin (IL)-12 or IFN-gamma, depending on activation stimuli. Upon stimulation with CpG oligodeoxynucleotides, ligands for Toll-like receptor (TLR)-9, IKDCs kill typical NK target cells using NK-activating receptors. Their cytolytic capacity subsequently diminishes, associated with the loss of NKG2D receptor (also known as Klrk1) and its adaptors, Dap10 and Dap12. As cytotoxicity is lost, DC-like antigen-presenting activity is gained, associated with upregulation of surface major histocompatibility complex class II (MHC II) and costimulatory molecules, which formally distinguish them from classical NK cells. In vivo, splenic IKDCs preferentially show NK function and, upon systemic infection, migrate to lymph nodes, where they primarily show antigen-presenting cell activity. By virtue of their capacity to kill target cells, followed by antigen presentation, IKDCs provide a link between innate and adaptive immunity.

Effects of interleukin-15 on antifungal responses of human polymorphonuclear leukocytes against Fusarium spp. and Scedosporium spp

Fusarium spp. and Scedosporium spp. have emerged as important fungal pathogens that are frequently resistant to antifungal compounds. We investigated the effects of human interleukin-15 (IL-15) on human polymorphonuclear leukocyte (PMNL) activity against Fusarium solani and Fusarium oxysporum as well as Scedosporium prolificans and Scedosporium apiospermum. IL-15 (100 ng/ml) significantly enhanced PMNL-induced hyphal damage of both Fusarium spp. and S. prolificans after incubation for 22 h (P < 0.01) but not S. apiospermum. In addition, IL-15 enhanced PMNL oxidative respiratory burst evaluated as superoxide anion production in response to S. prolificans but not to the other fungi after 2 h incubation. IL-15 increased interleukin-8 (IL-8) release from PMNLs challenged with hyphae of F. solani and S. prolificans (P< or = 0.04). Release of tumor necrosis factor-alpha was not affected. The species-dependent enhancement of hyphal damage and induction of IL-8 release suggest that IL-15 plays an important role in the immunomodulation of host response to these emerging fungal pathogens.

A human CD34(+) subset resides in lymph nodes and differentiates into CD56bright natural killer cells

In humans, T cells differentiate in thymus and B cells develop in bone marrow (BM), but the natural killer (NK) precursor cell(s) and site(s) of NK development are unclear. The CD56bright NK subset predominates in lymph nodes (LN) and produces abundant cytokines compared to the cytolytic CD56dim NK cell that predominates in blood. Here, we identify a novel CD34dimCD45RA(+) hematopoietic precursor cell (HPC) that is integrin alpha4beta7bright. CD34dimCD45RA(+)beta7bright HPCs constitute <1% of BM CD34(+) HPCs and approximately 6% of blood CD34(+) HPCs, but >95% of LN CD34(+) HPCs. They reside in the parafollicular T cell regions of LN with CD56bright NK cells, and when stimulated by IL-15, IL-2, or activated LN T cells, they become CD56bright NK cells. The data identify a new NK precursor and support a model of human NK development in which BM-derived CD34dimCD45RA(+)beta7bright HPCs reside in LN where endogenous cytokines drive their differentiation to CD56bright NK cells in vivo.

Biology of IL-21 and the IL-21 receptor

Interleukin-21 (IL-21) is the newest member of the common gamma-chain family of cytokines, which includes IL-2, IL-4, IL-7, IL-9, IL-13, and IL-15. Its private receptor, IL-21R, has been shown to activate the Janus kinase/signal transducers and activators of transcription signaling pathway upon ligand binding. Initial studies have demonstrated that IL-21 has pleiotropic effects on the proliferation, differentiation, and effector functions of B, T, natural killer, and dendritic cells. More recently, the potential therapeutic capacity of IL-21 in the treatment of cancers has been widely investigated. The biological role of IL-21 in the immune system is complex, as IL-21 has been shown to have the ability to both promote and inhibit immune responses. Overall, the current data point to IL-21 being a novel immunomodulatory cytokine, whose regulation of any given immune response is highly dependent on the surrounding environmental context.

Cytokines and immunodeficiency diseases: critical roles of the gamma(c)-dependent cytokines interleukins 2, 4, 7, 9, 15, and 21, and their signaling pathways

In this review, we discuss the role of cytokines and their signaling pathways in immunodeficiency. We focus primarily on severe combined immunodeficiency (SCID) diseases as the most severe forms of primary immunodeficiencies, reviewing the different genetic causes of these diseases. We focus in particular on the range of forms of SCID that result from defects in cytokine-signaling pathways. The most common form of SCID, X-linked SCID, results from mutations in the common cytokine receptor gamma-chain, which is shared by the receptors for interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21, underscoring that X-linked SCID is indeed a disease of defective cytokine signaling. We also review the signaling pathways used by these cytokines and the phenotypes in humans and mice with defects in the cytokines or signaling pathways. We also briefly discuss other cytokines, such as interferon-gamma and IL-12, where mutations in the ligand or receptor or signaling components also cause clinical disease in humans.

Contrasting Effects of Low-Dose IL-2 on Vaccine-Boosted Simian Immunodeficiency Virus (SIV)-Specific CD4+and CD8+T Cells in Macaques Chronically Infected with SIVmac251

IL-2, the first cytokine discovered with T cell growth factor activity, is now known to have pleiotropic effects on T cells. For example, it can promote growth, survival, and differentiation of Ag-selected cells, or facilitate Ag-induced cell death of T cells when Ag persists, and in vivo, it is thought to contribute to the regulation of the size of adaptive T cell response. IL-2 is deficient in HIV-1 infection and has been used in the management of HIV-1-infected individuals undergoing antiretroviral therapy. In this study, we investigated how continuous low-dose IL-2 affected the CD4+ and CD8+ T cell response induced by two inoculations of a canarypox recombinant SIV-based vaccine candidate in healthy macaques chronically infected with SIVmac251. These macaques had normal levels of CD4+ T cells at the beginning of antiretroviral therapy treatment. Vaccination in the presence of IL-2 significantly augmented Gag-specific CD8+ T cell responses, but actually reduced Gag-specific CD4+ T cell responses. Although IL-2 at low doses did not change the overall concentration of circulating CD4+ or CD8+ T cells, it expanded the frequency of CD4+CD25+ T cells. Depletion of the CD4+CD25+ T cells in vitro, however, did not result in a reconstitution of Gag-specific CD4+ responses or augmentation of SIV-specific CD8+ T cell responses. Thus, we conclude that the decrease in virus-specific CD4+ T cell response may be due to IL-2-promoted redistribution of cells from the circulation, or due to Ag-induced cell death, rather than suppression by a T regulatory population.

Interleukins 2 and 15 Regulate Ets1 Expression via ERK1/2 and MNK1 in Human Natural Killer Cells

Interleukins (IL)-2 and IL-15 regulate natural killer (NK) cell proliferation, survival, and cytolytic activity. Ets1 is a transcription factor expressed early in NK cell differentiation. Because IL-2Rbeta, IL-2Rgamma, IL-15, and Ets1 knock-out mice similarly lack NK cells, we explored a molecular connection between IL-2R signaling and Ets1. Here we report the post-transcriptional regulation of Ets1 by IL-2R signaling in human NK cells. IL-2 and IL-15 stimulation leads to increased Ets1 protein levels with no significant change in mRNA levels. Pulse and pulse-chase experiments show that IL-2 stimulation results in both a marked increase in the nascent translation of Ets1 and an increased protein half-life. Pharmacological inhibition of MEK specifically blocks IL-2- and IL-15-induced translation, whereas p38, phosphatidylinositol 3-kinase, and mTOR inhibitors had no effect on Ets1 levels. Fli1, an Ets family member, exhibited a different mechanism of regulation, illustrating the specificity of IL-2R beta and gamma subunit signaling on the regulation of Ets1 expression. Expression of a dominant negative form of MNK1, a regulator of the translation initiation factor eIF4E, blocks the expression of Ets1 as do the dominant negative forms of the common IL-2R beta and gamma chains. Expression of Ets1 is regulated similarly in normal peripheral human NK cells. Taken together, our findings provide a direct link between IL-2R subunit signaling and Ets1 expression and helps to explain the interdependence of the IL-2R subunits and Ets1 for NK cell development and function.

VDUP1 Is Required for the Development of Natural Killer Cells

Vitamin D3 upregulated protein 1 (VDUP1) is a stress-response gene that is upregulated by 1,25(OH)2D3 in tumor cells. The in vivo roles of VDUP1 were investigated by producing mice lacking VDUP1 (VDUP1-/- mice). VDUP1-/- mice showed minimal changes in the development of T and B cells, but there was a profound reduction in the numbers of natural killer (NK) cells. As well, these mice showed decreased NK activity. In the VDUP1-/- mice, the expression of CD122 was reduced, demonstrating that VDUP1 is required for CD122 expression and NK maturation. In addition, severe lymphoid hyperplasia in the small intestine was observed in VDUP1-/- mice. Taken together, these results suggest that VDUP1 is a critical factor for the development and function of NK cells in vivo.

Interleukin-2, Interleukin-15, and Their Roles in Human Natural Killer Cells

Natural killer (NK) cells are CD56+CD3- large granular lymphocytes that constitute a key component of the human innate immune response. In addition to their potent cytolytic activity, NK cells elaborate a host of immunoregulatory cytokines and chemokines that play a crucial role in pathogen clearance. Furthermore, interactions between NK and other immune cells are implicated in triggering the adaptive, or antigen-specific, immune response. Interleukin-2 (IL-2) and IL-15 are two distinct cytokines with partially overlapping properties that are implicated in the development, homeostasis, and function of NK cells. This review examines the pervasive effects of IL-2 and IL-15 on NK cell biology, with an emphasis on recent discoveries and lingering challenges in the field.

STAT5 is required for thymopoiesis in a development stage-specific manner

Diverse cytokines necessary for normal lymphopoiesis and lymphocyte homeostasis activate STAT5 in responder cells. Although STAT5 has been suggested to be a central molecular effecter of IL-7 function, its essential role during IL-7-dependent T cell development in vivo remained unclear. Using Stat5(-/-) mice we now show that STAT5 is essential for various functions ascribed to IL-7 in vivo. STAT5 is required for embryonic thymocyte production, TCRgamma gene transcription, and Peyer's patch development. In sharp contrast, normal STAT5 is dispensable for adult thymopoiesis. In peripheral lymphocytes, STAT5 is primarily required for the generation and/or maintenance of gammadelta T cells and TCRgammadelta(+) intraepithelial lymphocytes. Collectively, these results demonstrate that STAT5 is critical for many, but not all, aspects of steady state lymphoid lineage development and maintenance and suggest the existence of previously undocumented cytokine signaling traits and/or cytokine milieu during adult thymopoiesis.

Accumulation of gammadelta T cells in the lungs and their regulatory roles in Th1 response and host defense against pulmonary infection with Cryptococcus neoformans

The present study was designed to elucidate the role of gammadelta T cells in the host defense against pulmonary infection with Cryptococcus neoformans. The gammadelta T cells in lungs commenced to increase on day 1, reached a peak level on day 3 or 6, and then decreased on day 10 after intratracheal infection. The increase of these cells was similar in monocyte chemoattractant protein (MCP)-1-deficient mice, although that of NK and NKT cells was significantly reduced. The number of live microorganisms in lungs on days 14 and 21 was significantly reduced in mice depleted of gammadelta T cells by a specific mAb compared with mice treated with control IgG. Similarly, elimination of this fungal pathogen was promoted in gammadelta T cell-deficient (TCR-delta(-/-)) mice compared with control littermate mice. Finally, lung and serum levels of IFN-gamma on days 7 and 14 and on day 7 postinfection, respectively, were significantly higher in TCR-delta(-/-) mice than in littermate mice, whereas levels of TGF-beta showed the opposite results. IL-4 and IL-10 were not different between these mice. IFN-gamma production by draining lymph node cells upon restimulation with cryptococcal Ags was significantly higher in the infected TCR-delta(-/-) mice than in control mice. Our results demonstrated that gammadelta T cells accumulated in the lungs in a manner different from NK and NKT cells after cryptococcal infection and played a down-modulatory role in the development of Th1 response and host resistance against this fungal pathogen.