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

Two novel NKG2D ligands of the mouse H60 family with differential expression patterns and binding affinities to NKG2D

H60, originally described as a dominant minor histocompatibility Ag, is an MHC class I-like molecule that serves as a ligand for the NKG2D receptor. In the present study, we identified two novel mouse chromosome 10-encoded NKG2D ligands structurally resembling H60. These ligands, which we named H60b and H60c, encode MHC class I-like molecules with two extracellular domains. Whereas H60b has a transmembrane region, H60c is a GPI-anchored protein. Recombinant soluble H60b and H60c proteins bound to NKG2D with affinities typical of cell-cell recognition receptors (K(d) = 310 nM for H60b and K(d) = 8.7 muM for H60c). Furthermore, expression of H60b or H60c rendered Ba/F3 cells susceptible to lysis by NK cells, thereby establishing H60b and H60c as functional ligands for NKG2D. H60b and H60c transcripts were detected only at low levels in tissues of healthy adult mice. Whereas H60b transcripts were detectable in various tissues, H60c transcripts were detected mainly in the skin. Infection of mouse embryonic fibroblasts with murine cytomegalovirus induced expression of H60b, but not H60c or the previously known H60 gene, indicating that transcriptional activation of the three types of H60 genes is differentially regulated. The present study adds two new members to the current list of NKG2D ligands.

Innate lymphocyte and dendritic cell cross-talk: a key factor in the regulation of the immune response

Dendritic cells (DC) are specialized in the presentation of antigens and the initiation of specific immune responses. They have been involved recently in supporting innate immunity by interacting with various innate lymphocytes, such as natural killer (NK), NK T or T cell receptor (TCR)-gammadelta cells. The functional links between innate lymphocytes and DC have been investigated widely and different studies demonstrated that reciprocal activations follow on from NK/DC interactions. The cross-talk between innate cells and DC which leads to innate lymphocyte activation and DC maturation was found to be multi-directional, involving not only cell-cell contacts but also soluble factors. The final outcome of these cellular interactions may have a dramatic impact on the quality and strength of the down-stream immune responses, mainly in the context of early responses to tumour cells and infectious agents. Interestingly, DC, NK and TCR-gammadelta cells also share similar functions, such as antigen uptake and presentation, as well as cytotoxic and tumoricidal activity. In addition, NK and NK T cells have the ability to kill DC. This review will focus upon the different aspects of the cross-talk between DC and innate lymphocytes and its key role in all the steps of the immune response. These cellular interactions may be particularly critical in situations where immune surveillance requires efficient early innate responses.

Neuroendocrine factors alter host defense by modulating immune function

An increasing body of evidence demonstrates that there is bidirectional communication between the neuroendocrine and immune systems. Interaction between these systems results in a variety of outcomes, including the well documented "sickness behavior" elicited by cytokines of the immune system that can enter the brain and activate second messengers that modify neuronal activity. Crosstalk between the neuroendocrine and immune systems can also result in production of factors by the nervous and endocrine systems that alter immune cell function and subsequent modulation of immune responses against infectious agents and other pathogens. Continued exposure to molecules produced by the neuroendocrine system has also been known to increase susceptibility and/or severity of disease. Furthermore, neuroendocrine factors are thought to play a major role in gender-specific differences in development of certain disorders, including autoimmune/inflammatory diseases that have a two to tenfold higher incidence in females compared to males. Neuroendocrine factors can affect immune cells at the level of gene transcription but have also been shown to modify immune cell activity by interacting with intracellular molecules, resulting in modified ability of these cells to mount a potent immune response. In this review, we will consider various effects of the neuroendocrine system and its proteins on specific populations of immune cells and associated responses in host immunity against pathogens. We will further discuss how this modification of immune cell activity by the neuroendocrine system can contribute to susceptibility/severity of disease development.

Expression of bacterial genes and induction of INF-gamma in human myeloid dendritic cells during persistent infection with Chlamydophila pneumoniae

The interactions between human monocyte-derived dendritic cells (DCs) and Chlamydophila pneumoniae (Cpn) infection were investigated. Cpn infection induced the maturation and functional activation of DCs, and Cpn antigens were present in all of the subpopulations during the maturation process. Chlamydial antigens were detected in DCs during an observation period of 28 days. The exponential production of infectious elementary bodies was not observed. Chlamydial transcripts of the 16S rRNA gene, groEL-1 and omcB genes were expressed, as determined by a quantitative real-time PCR, but the expression of the ftsK gene was limited. DC cultures produced IFN-gamma, but the presence of IFN-gamma in the culture medium was not the major factor that decreased the growth of Cpn, as was shown by neutralization of the IFN-gamma. A cell population identified as producing IFN-gamma had no markers for T, B, natural killer, monocyte cells or macrophages but displayed DC morphology and the expression of specific DC markers, such as CD11c and HLA-DR. These results reveal a persistent infection of DCs with the expression of some, but not cell division-related genes and the production of IFN-gamma that may contribute to the pathomechanism of chronic inflammatory diseases associated with persistent Cpn infection.

Impaired TRAIL-dependent cytotoxicity of CD1c-positive dendritic cells in chronic hepatitis C virus infection

Dendritic cells (DCs) play a central role in antiviral immunity. Conflicting data on DC function have been reported for hepatitis C virus (HCV) infection. In addition to antigen presentation and cytokine secretion, a subset of human DCs displays direct cytotoxic activity. It has been suggested that measles virus and human immunodeficiency virus (HIV) may enhance cytotoxicity of DCs potentially leading to apoptosis of activated T cells and subsequent down-regulation of antiviral immune responses. We demonstrate that CD1c-positive myeloid DCs, but not BDCA-4-positive plasmacytoid DCs, are able to kill different target cells mainly via tumour necrosis factor-related apoptosis-inducing ligand. The ability of CD1c+ DCs to lyze target cells was found to be completely impaired in patients with chronic hepatitis C (10 chronic HCV patients vs 10 healthy controls; P < 0.001) but not in patients with primary biliary cirrhosis. Successful antiviral therapy of chronic hepatitis C rescued the cytotoxicity of DCs. Myeloid DCs of HCV patients and healthy controls had a similar phenotype and endocytotic activity, however, the frequency of mDCs in the peripheral blood was lower (P = 0.004) and the allostimulatory function was weaker (P < 0.001) in chronic hepatitis C. Thus, in contrast to HIV and measles virus studies on monocyte-derived DCs, freshly isolated myeloid DCs of patients with hepatitis C do not show an increased but a completely abolished cytotoxic activity. The impaired DC cytotoxicity could represent a novel mechanism for the increased prevalence of autoimmunity in HCV infection.

Tumour immunity: effector response to tumour and role of the microenvironment

Substantial evidence shows that inflammation promotes oncogenesis and, occasionally, participates in cancer rejection. This paradox can be accounted for by a dynamic switch from chronic smouldering inflammation promoting cancer-cell survival to florid, tissue-disruptive inflammatory reactions that trigger cancer-cell destruction. Clinical and experimental observations suggest that the mechanism of this switch recapitulates the events associated with pathogen infection, which stimulate immune cells to recognise danger signals and activate immune effector functions. Generally, cancers do not have danger signals and, therefore, they cannot elicit strong immune reactions. Synthetic molecules have been developed that mimic pathogen invasion at the tumour site. These compounds activate dendritic cells to produce proinflammatory cytokines, which in turn trigger cytotoxic mechanisms leading to cancer death. Simultaneously, dendritic cells capture antigen shed by dying cancer cells, undergo activation, and stimulate antigen-specific T and B cells. This process results in massive amplification of the antineoplastic inflammatory process. Thus, although anti-inflammatory drugs can prevent onset of some malignant diseases, induction of T cells specific for tumour antigen by active immunisation, combined with powerful activation signals within the cancer microenvironment, might yield the best strategy for treatment of established cancers.

Evolving views on the genealogy of B cells

Many fundamental concepts about immune system development have changed substantially in the past few years, and rapid advances with animal models are presenting prospects for further discovery. However, continued progress requires a clearer understanding of the relationships between haematopoietic stem cells and the progenitors that replenish each type of lymphocyte pool. Blood-cell formation has traditionally been described in terms of discrete developmental branch points, and a single route is given for each major cell type. As we discuss in this Review, recent findings suggest that the process of B-cell formation is much more dynamic.

Characterization of the immature dendritic cells and cytotoxic cells both expanded after activation of invariant NKT cells with alpha-galactosylceramide in vivo

Invariant natural killer T (iNKT) cells can perform multiple functions characteristic of both innate and acquired immunity. Activation of iNKT cells in vivo by repeated alpha-GalCer injections can induce immune tolerance, but the mechanisms responsible for such immunoregulation remain unclear. We prepared alpha-GalCer-liposomes, a single injection of which into mice resulted in the expansion of splenic CD11c(low)CD45RB(high) cells, which consists of two populations, CD180(+) and CD49b(+). Expansion of these cells was not observed in alpha-GalCer-liposome-treated mice deficient in IL-10 or iNKT cells. MHC and co-stimulatory molecules were down-regulated in CD11c(low)CD180(+) cells compared with conventional dendritic cells (cDCs), suggesting that the former possess characteristics of immature DCs. Meanwhile, the CD11c(low)CD49b(+) cells expressed IL-10 and Ctla4, and possessed greater lytic activity than resting NK cells. These observations suggest that both immature DCs (CD11c(low)CD180(+)) and cytotoxic cells (CD11c(low)CD49b(+)) might be expanded by alpha-GalCer-activated iNKT cells and could therefore be involved in immune tolerance.

Adenovirus E3/19K promotes evasion of NK cell recognition by intracellular sequestration of the NKG2D ligands major histocompatibility complex class I chain-related proteins A and B

The adenovirus (Ad) early transcription unit 3 (E3) encodes multiple immunosubversive functions that are presumed to facilitate the establishment and persistence of infection. Indeed, the capacity of E3/19K to inhibit transport of HLA class I (HLA-I) to the cell surface, thereby preventing peptide presentation to CD8(+) T cells, has long been recognized as a paradigm for viral immune evasion. However, HLA-I downregulation has the potential to render Ad-infected cells vulnerable to natural killer (NK) cell recognition. Furthermore, expression of the immediate-early Ad gene E1A is associated with efficient induction of ligands for the key NK cell-activating receptor NKG2D. Here we show that while infection with wild-type Ad enhances synthesis of the NKG2D ligands, major histocompatibility complex class I chain-related proteins A and B (MICA and MICB), their expression on the cell surface is actively suppressed. Both MICA and MICB are retained within the endoplasmic reticulum as immature endoglycosidase H-sensitive forms. By analyzing a range of cell lines and viruses carrying mutated versions of the E3 gene region, E3/19K was identified as the gene responsible for this activity. The structural requirements within E3/19K necessary to sequester MICA/B and HLA-I are similar. In functional assays, deletion of E3/19K rendered Ad-infected cells more sensitive to NK cell recognition. We report the first NK evasion function in the Adenoviridae and describe a novel function for E3/19K. Thus, E3/19K has a dual function: inhibition of T-cell recognition and NK cell activation.

Interleukin-15 liver gene transfer increases the number and function of IKDCs and NK cells

The surface phenotype CD3-NK1.1+DX5+CD11c(int)B220+GR1- has been recently ascribed to a novel subset of mouse leukocytes termed interferon (IFN)-producing killer dendritic cells (IKDCs) that shares functions with natural killer (NK) cells and DCs. Interleukin-15 (IL-15) is critical for NK cells but its relationship with IKDC remained unexplored. An expression cassette encoding human IL-15 (hIL-15) has been transferred by hydrodynamic injection into the liver of mice, resulting in transient expression of the cytokine that is detectable during the first 48 h. hIL-15 hydrodynamic gene transfer resulted in an expansion of NK cells and IKDCs. Relative expansions of IKDCs were more dramatic in the IL-15 gene-transferred hepatic tissue than in the spleen. Adoptively transferred DX5+ cells comprising both NK cells and IKDCs proliferated in response to hydrodynamic injection of hIL-15, indicating that quantitative increases are at least in part the result of proliferation from already differentiated cells. Expansion is accompanied by enhanced cytolytic activity and increased expression of TRAIL and CD137 (4-1BB), without augmenting interferon-gamma production. The effects of a single hydrodynamic injection surpassed those of two intraperitoneal doses of the recombinant protein. The novel functional link between circulating IL-15 and IKDCs opens new possibilities to study the biology and applications of this minority cell subset.

Novel insights into the relationships between dendritic cell subsets in human and mouse revealed by genome-wide expression profiling

Genome-wide expression profiling of mouse and human leukocytes reveal conserved transcriptional programs of plasmacytoid or conventional dendritic cell subsets.

Background

Dendritic cells (DCs) are a complex group of cells that play a critical role in vertebrate immunity. Lymph-node resident DCs (LN-DCs) are subdivided into conventional DC (cDC) subsets (CD11b and CD8α in mouse; BDCA1 and BDCA3 in human) and plasmacytoid DCs (pDCs). It is currently unclear if these various DC populations belong to a unique hematopoietic lineage and if the subsets identified in the mouse and human systems are evolutionary homologs. To gain novel insights into these questions, we sought conserved genetic signatures for LN-DCs and in vitro derived granulocyte-macrophage colony stimulating factor (GM-CSF) DCs through the analysis of a compendium of genome-wide expression profiles of mouse or human leukocytes.

Results

We show through clustering analysis that all LN-DC subsets form a distinct branch within the leukocyte family tree, and reveal a transcriptomal signature evolutionarily conserved in all LN-DC subsets. Moreover, we identify a large gene expression program shared between mouse and human pDCs, and smaller conserved profiles shared between mouse and human LN-cDC subsets. Importantly, most of these genes have not been previously associated with DC function and many have unknown functions. Finally, we use compendium analysis to re-evaluate the classification of interferon-producing killer DCs, lin^-CD16⁺HLA-DR⁺ cells and in vitro derived GM-CSF DCs, and show that these cells are more closely linked to natural killer and myeloid cells, respectively.

Conclusion

Our study provides a unique database resource for future investigation of the evolutionarily conserved molecular pathways governing the ontogeny and functions of leukocyte subsets, especially DCs.

Innate Valpha14(+) natural killer T cells mature dendritic cells, leading to strong adaptive immunity

The observation that the glycolipid alpha-galactosylceramide (alpha-GalCer) is a potent stimulator of natural killer T (NKT) cells has provided an important means for investigating NKT cell biology. alpha-GalCer is presented on CD1d to the invariant NKT receptor, leading to interleukin-12 (IL-12) production by dendritic cells (DCs) and to NK cell activation. We review our research on the tumor-protective properties of alpha-GalCer, particularly the major role played by DCs. We compared administration of alpha-GalCer on mature DCs with soluble glycolipid and found that DCs induced more prolonged interferon-gamma (IFN-gamma) production by NKT cells and better protection against B16 melanoma. Human alpha-GalCer-loaded DCs also expanded NKT cell numbers in cancer patients. alpha-GalCer-activated NKT cells were then found to induce DC maturation in vivo. The maturing DCs produced IL-12, upregulated co-stimulatory molecules, and induced adaptive immunity to captured cellular antigens, including prolonged, combined CD4(+)/CD8(+) T-cell immunity to dying tumor cells. Surprisingly, co-stimulator-poor tumor cells, if directly loaded with alpha-GalCer ('tumor/Gal') and injected intravenously, also induced strong NKT- and NK-cell responses. The latter killed the tumor/Gal, which were subsequently cross presented by CD1d on DCs to elicit DC maturation and prolonged adaptive T-cell immunity, which lasted 6-12 months. These findings help explain tumor protection via alpha-GalCer and urge development of the DC-NKT axis to provide innate and adaptive immunity to human cancers.

NOD/Shi-scid IL2rgamma(null) (NOG) mice more appropriate for humanized mouse models

"Humanized mice," in which various kinds of human cells and tissues can be engrafted and retain the same functions as in humans, are extremely useful because human diseases can be studied directly. Using the newly combined immunodeficient NOD-scid IL2rgamma(null) mice and Rag2(null) IL2rgamma(null) humanized mice, it has became possible to expand applications because various hematopoietic cells can be differentiated by human hematopoietic stem cell transplantation, and the human immune system can be reconstituted to some degree. This work has attracted attention worldwide, but the development and use of immunodeficient mice in Japan are not very well known or understood. This review describes the history and characteristics of the NOD/Shi-scid IL2rgamma(null) (NOG) and BALB/cA-Rag2(null) IL2rgamma(null) mice that were established in Japan, including our unpublished data from researchers who are currently using these mice. In addition, we also describe the potential development of new immunodeficient mice that can be used as humanized mice in the future.

The lipopolysaccharide adjuvant effect on T cells relies on nonoverlapping contributions from the MyD88 pathway and CD11c+ cells

Bacterial LPS is a natural adjuvant that induces profound effects on T cell clonal expansion, effector differentiation, and long-term T cell survival. In this study, we delineate the in vivo mechanism of LPS action by pinpointing a role for MyD88 and CD11c(+) cells. LPS induced long-term survival of superantigen-stimulated CD4 and CD8 T cells in a MyD88-dependent manner. By tracing peptide-stimulated CD4 T cells after adoptive transfer, we showed that for LPS to mediate T cell survival, the recipient mice were required to express MyD88. Even when peptide-specific CD4 T cell clonal expansion was dramatically boosted by enforced OX40 costimulation, OX40 only synergized with LPS to induce survival when the recipient mice expressed MyD88. Nevertheless, these activated, but moribund, T cells in the MyD88(-/-) mice acquired effector properties, such as the ability to synthesize IFN-gamma, demonstrating that effector differentiation is not automatically coupled to a survival program. We confirmed this notion in reverse fashion by showing that effector differentiation was not required for the induction of T cell survival. Hence, depletion of CD11c(+) cells did not affect LPS-driven specific T cell survival, but CD11c(+) cells were paramount for optimal effector T cell differentiation as measured by IFN-gamma potential. Thus, LPS adjuvanticity is based on MyD88 promoting T cell survival, while CD11c(+) cells support effector T cell differentiation.

Dendritic cell subsets in health and disease

The dendritic cell (DC) system of antigen-presenting cells controls immunity and tolerance. DCs initiate and regulate immune responses in a manner that depends on signals they receive from microbes and their cellular environment. They allow the immune system to make qualitatively distinct responses against different microbial infections. DCs are composed of subsets that express different microbial receptors and express different surface molecules and cytokines. Our studies lead us to propose that interstitial (dermal) DCs preferentially activate humoral immunity, whereas Langerhans cells preferentially induce cellular immunity. Alterations of the DC system result in diseases such as autoimmunity, allergy, and cancer. Conversely, DCs can be exploited for vaccination, and novel vaccines that directly target DCs in vivo are being designed.

The chemokine CCL6 promotes innate immunity via immune cell activation and recruitment

Septic syndrome is a consequence of innate immune failure. Recent studies showed that the CC chemokine CCL6 enhanced antimicrobial immunity during experimental sepsis through an unknown mechanism. The present study demonstrates that transgenic CCL6 expression abolishes mortality in a septic peritonitis model via the modulation of resident peritoneal cell activation and, more importantly, through the recruitment of IFN-producing NK cells and killer dendritic cells into the peritoneum. Thus, CCL6 attenuates the immune failure during sepsis, in part, through a protective type 1-cytokine mediated mechanism.

The BXH2 mutation in IRF8 differentially impairs dendritic cell subset development in the mouse

Among dendritic cell (DC) subsets, CD8alpha(+) DCs and plasmacytoid DCs (pDCs) produce high levels of IL12 and type I interferons (IFNs), respectively, and confer early innate immunity. Development of CD8alpha(+) DCs and pDCs requires the interferon regulatory factor 8 (IRF8). Recently, a spontaneous point mutation was identified in the Irf8/Icsbp gene in the BXH2 mouse, which exhibits an immunodeficient phenotype similar to the IRF8 knockout (KO) mouse. We show that this mutation, designated IRF8(R294C), abolishes the development of CD8alpha(+) DCs without impairing pDC development, and eliminates production of IL12p40, while retaining that of type I IFNs. Electrophoretic mobility shift and chromatin immunoprecipitation assays indicated that IRF8(R294C) failed to interact with partner transcription factors and did not bind certain promoters that require partner interactions. Together, this work indicates that IRF8-partner interactions play different roles in CD8alpha(+) DCs and pDCs, revealing a mechanistic separation that underlies development of these DC subsets.

Interleukin-21 activates human natural killer cells and modulates their surface receptor expression

Interleukin (IL)-21 is a novel cytokine that has been shown to enhance proliferation and activation of CD8+ T cells, enhance natural killer (NK) cell activity and costimulate anti-CD40-driven B-cell proliferation in mice. Several studies have furthermore demonstrated antitumour effects of IL-21 administration in mouse models. In this study we have investigated how IL-21 affects the survival and cytotoxicity of human NK cells and modulates their expression of surface receptors and of the effector molecules granzyme B and perforin. In contrast to murine NK cells, where IL-21 alone cannot sustain survival, IL-21 and IL-2 were equally efficient in sustaining survival of human NK cells. In the absence of other cytokines, IL-21 had little effect on expression of a panel of surface receptors on human NK cells. However, IL-21 synergized with IL-2 to up-regulate several surface receptors, including NKG2A, CD25, CD86 and CD69. The CD25+ CD86+ NK cells were CD56(bright) and were large and granular. Expression of the effector molecules perforin and granzyme A and B was up-regulated by IL-21 at both mRNA and protein levels. Furthermore, IL-21 increased the cytotoxicity of NK cells against K562 target cells. These findings suggest that IL-21 modulates NK cell activity through induction of intracellular effector molecules as well as modulation of surface receptor expression.

Alveolar macrophages are the primary interferon-alpha producer in pulmonary infection with RNA viruses

Type I interferons (IFNs) are critical for antiviral responses. Here we generated a knockin mouse in which green fluorescence protein (GFP) was expressed under the control of the Ifna6 promoter. Virus-induced expression of GFP recapitulated various IFN-alpha subtypes. Systemic infection of the mice with Newcastle disease virus (NDV) increased GFP(+) plasmacytoid dendritic cells (pDCs) via the Toll-like receptor system, and GFP(+) conventional dendritic cells (cDCs) and macrophages via the RIG-I-like helicase system. By contrast, lung infection with NDV led to IFN-alpha production in alveolar macrophages (AMs) and cDCs, but not in pDCs. Specific depletion of AMs caused a marked defect in the initial viral elimination in the lung. pDCs produced IFN-alpha in the absence of AM-mediated viral recognition, suggesting that pDCs function when the first defense line is broken. Thus, AMs act as a type I IFN producer that is important for the initial responses to viral infection in the lung.

Developmental pathways that generate natural-killer-cell diversity in mice and humans

Natural killer (NK) cells are large granular lymphocytes capable of producing inflammatory cytokines and spontaneously killing malignant, infected or 'stressed' cells. These NK-cell functions are controlled by cell-surface receptors that titrate stimulatory and inhibitory signals. However, we remain puzzled about where and when NK cells develop and differentiate, and this has fuelled the debate over the diversification of the peripheral NK-cell pool: are NK cells functionally homogeneous or are there subsets with specialized effector functions? In this Review, we consider the developmental relationships and biological significance of the diverse NK-cell subsets in mice and humans, and discuss how new humanized mouse models may help to characterize them further.

Temporal regulation of interleukin-12p70 (IL-12p70) and IL-12-related cytokines in splenic dendritic cell subsets during Leishmania donovani infection

Dendritic cells (DC) play an essential role in initiating and directing T-cell responses, in part by production of interleukin-12p70 (IL-12p70), IL-23, and IL-27. However, comparative studies on the capacity for cytokine production of DC subsets are rare. Here, we compare splenic CD8alpha+, CD4+, and double-negative (DN) DC, isolated 5 h to 28 days after Leishmania donovani infection, for (i) production of IL-12p70, (ii) accumulation of IL-12/23p40, IL-12p35, IL-23p19, and IL-27p28 mRNAs, and (iii) their capacity to direct CD4+ T-cell differentiation. At 5 h, conventional DC (cDC) accumulated mRNA for IL-12/23p40 (CD8alpha>CD4>DN), IL-23p19 (CD4>CD8alpha>DN), and IL-27p28 (CD8alpha>CD4>DN), in an infection dose-dependent manner. IL-12p70 was restricted to CD8alpha+ cDC, reflecting the subset-specific accumulation of IL-12p35 mRNA. In contrast, cDC from mice infected for 14 to 28 days accumulated little mRNA for IL-12p40 and IL-12p19, though IL-27p28 mRNA remained detectable (CD8alpha>DN>CD4). IL-12p70 secretion by CD8alpha+ cDC was also absent, reflecting deficient IL-12/23p40, rather than IL-12p35, mRNA accumulation. The capacity of CD8alpha+ cDC isolated early after infection to direct Th1 cell differentiation was mediated through IL-12/23p40, whereas this ability in CD4+ and DN cDC was independent of IL-12/23p40 and did not result from overexpression of Delta 4 Notch-like ligand. However, DN cDC produced gamma interferon (IFN-gamma) and also contained a rare population of CD11c(hi) DX5+ IFN-gamma-producing cells. Our data illustrate the extensive diversity in, and temporal regulation of, splenic cDC subsets during infection and suggest caution in interpreting data obtained with unfractionated or minimally purified DC.

Tumor stress, cell death and the ensuing immune response

A cornucopia of physiological and pathological circumstances including anticancer chemotherapy and radiotherapy can induce cell death. However, the immunological consequences of tumor cell demise have remained largely elusive. The paradigm opposing 'apoptosis versus necrosis' as to their respective immunogenicity does not currently hold to predict long-term immunity. Moreover, the notion that tumor cells may be 'stressed' before death to be recognized by immune cells deserves to be underlined. 'Eat-me', 'danger' and 'killing' signals released by stressed tumor under the pressure of cytotoxic compounds may serve as links between the chemotherapy-elicited response of tumor cells and subsequent immune responses. This review will summarize the state-of-the-art of cancer immunity and describe how tumor cell death dictates the links between innate and acquired immunity.

A role for natural killer cells in intestinal inflammation caused by infection with Salmonella enterica serovar Typhimurium

Acute gastroenteritis caused by Salmonella infection is a significant public health problem. Using a mouse model of this condition, the authors demonstrated previously that the cytokine gamma interferon (IFN-gamma) is required for a normal intestinal inflammatory response to the pathogen. In the present study, these experiments are extended to show that natural killer (NK) cells constitute an early source of intestinal IFN-gamma during Salmonella infection, and that these cells have a significant impact on intestinal inflammation. It was found that infection of mice with Salmonella increased both intestinal IFN-gamma production and the numbers of NK cells in the intestine and mesenteric lymph nodes. NK cells, along with other types of lymphocytes, produced IFN-gamma in response to the bacteria in vitro, while antibody-mediated depletion of NK cells in vivo resulted in a significant reduction in Salmonella-induced intestinal IFN-gamma expression. In a mouse strain lacking NK cells and T and B lymphocytes, intestinal production of IFN-gamma and Salmonella-induced intestinal inflammation were both significantly decreased compared with a strain deficient only in T and B cells. The authors' observations point to an important function for NK cells and NK-derived IFN-gamma in regulating the intestinal inflammatory response to Salmonella.

The 'kiss of death' by dendritic cells to cancer cells

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) specialized in the stimulation of naïve T lymphocytes, which are key components of antiviral and antitumor immunity. DCs are 'sentinels' of the immune system endowed with the mission to (1) sense invading pathogens as well as any form of tissue distress and (2) alert the effectors of the immune response. They represent a very heterogeneous population including subsets characterized by their anatomical locations and specific missions. Beyond their unique APC features, DCs exhibit a large array of effector functions that play critical roles in the induction and regulation of the cell-mediated as well as humoral immune responses. In the course of the antitumor immune response, DCs are unique in engulfing tumor cells killed by natural killer (NK) cells and cross-presenting tumor-associated antigens to cytotoxic T lymphocytes (CTLs). However, while DCs mediate antitumor immune responses by stimulating tumor-specific CTLs and NK cells, direct tumoricidal mechanisms have been recently evoked. This review addresses the other face of DCs to directly deliver apoptotic signals to stressed cells, their role in tumor cell death, and its implication in the design of DC-based cancer immunotherapies.

Interactions of tumor cells with dendritic cells: balancing immunity and tolerance

Dendritic cells (DCs) are antigen-presenting cells specialized to initiate and maintain immunity and tolerance. DCs initiate immune responses in a manner that depends on signals they receive from pathogens, surrounding cells and their products. Most tumors are infiltrated by DCs. Thus, interactions between DCs and dying tumor cells may determine the balance between immunity and tolerance to tumor cells. In addition, DCs also display non-immunologic effects on tumors and the tumor microenvironment. Therefore, improved understanding of the cross talk between tumor cells and DCs may suggest new approaches to improve cancer therapy.

Putative IKDCs are functionally and developmentally similar to natural killer cells, but not to dendritic cells

Interferon-producing killer dendritic cells (IKDCs) have been described as possessing the lytic potential of NK cells and the antigen-presenting capacity of dendritic cells (DCs). In this study, we examine the lytic function and antigen-presenting capacity of mouse spleen IKDCs, including those found in DC preparations. IKDCs efficiently killed NK cell targets, without requiring additional activation stimuli. However, in our hands, when exposed to protein antigen or to MHC class II peptide, IKDCs induced little or no T cell proliferation relative to conventional DCs or plasmacytoid DCs, either before or after activation with CpG, or in several disease models. Certain developmental features indicated that IKDCs resembled NK cells more than DCs. IKDCs, like NK cells, did not express the transcription factor PU.1 and were absent from recombinase activating gene-2–null, common γ-chain–null (Rag2^−/−Il2rg^−/−) mice. When cultured with IL-15 and -18, IKDCs proliferated extensively, like NK cells. Under these conditions, a proportion of expanded IKDCs and NK cells expressed high levels of surface MHC class II. However, even such MHC class II⁺ IKDCs and NK cells induced poor T cell proliferative responses compared with DCs. Thus, IKDCs resemble NK cells functionally, and neither cell type could be induced to be effective antigen-presenting cells.

CD11cloB220+ interferon-producing killer dendritic cells are activated natural killer cells

Interferon-producing killer dendritic cells (IKDCs) are a recently described subset of CD11c^loB220⁺ cells that share phenotypic and functional properties of DCs and natural killer (NK) cells (Chan, C.W., E. Crafton, H.N. Fan, J. Flook, K. Yoshimura, M. Skarica, D. Brockstedt, T.W. Dubensky, M.F. Stins, L.L. Lanier, et al. 2006. Nat. Med. 12:207–213; Taieb, J., N. Chaput, C. Menard, L. Apetoh, E. Ullrich, M. Bonmort, M. Pequignot, N. Casares, M. Terme, C. Flament, et al. 2006. Nat. Med. 12:214–219). IKDC development appears unusual in that cytokines using the interleukin (IL)-2 receptor β (IL-2Rβ) chain but not those using the common γ chain (γ_c) are necessary for their generation. By directly comparing Rag2^−/−γ_c^−/y, Rag2^−/−IL-2Rβ^−/−, Rag2^−/−IL-15^−/−, and Rag2^−/−IL-2^−/− mice, we demonstrate that IKDC development parallels NK cell development in its strict IL-15 dependence. Moreover, IKDCs uniformly express NK-specific Ncr-1 transcripts (encoding NKp46), whereas NKp46⁺ cells are absent in Ncr1^gfp/+γ_c^−/y mice. Distinguishing features of IKDCs (CD11c^loB220⁺MHC-II⁺) were carefully examined on developing NK cells in the bone marrow and on peripheral NK cells. As B220 expression was heterogeneous, defining B220^lo versus B220^hi NK1.1⁺ NK cells could be considered as arbitrary, and few phenotypic differences were noted between NK1.1⁺ NK cells bearing different levels of B220. CD11c expression did not correlate with B220 or major histocompatibility complex (MHC) class II (MHC-II) expression, and most MHC-II⁺ NK1.1⁺ cells did not express B220 and were thus not IKDCs. Finally, CD11c, MHC-II, and B220 levels were up-regulated on NK1.1⁺ cells upon activation in vitro or in vivo in a proliferation-dependent fashion. Our data suggest that the majority of CD11c^loB220⁺ “IKDC-like” cells represent activated NK cells.

Development and function of murine B220+CD11c+NK1.1+ cells identify them as a subset of NK cells

Lymphoid organs contain a B220⁺CD11c⁺NK1.1⁺ cell population that was recently characterized as a novel dendritic cell (DC) subset that functionally overlaps with natural killer (NK) cells and plasmacytoid DCs (PDCs). Using Siglec-H and NK1.1 markers, we unambiguously dissected B220⁺CD11c⁺ cells and found that PDCs are the only professional interferon (IFN)-α–producing cells within this heterogeneous population. In contrast, B220⁺CD11c⁺NK1.1⁺ cells are a discrete NK cell subset capable of producing higher levels of IFN-γ than conventional NK cells. Unlike DCs, only a minute fraction of B220⁺CD11c⁺NK1.1⁺ cells in the spleen expressed major histocompatibility complex class II ex vivo or after stimulation with CpG. Consistent with being a NK cell subset, B220⁺CD11c⁺NK1.1⁺ cells depended primarily on interleukin 15 and common cytokine receptor γ chain signaling for their development. In terms of function, expression of distinctive cell surface receptors, and location in lymphoid organs, NK1.1⁺B220⁺CD11c⁺ appear to be the murine equivalent of human CD56^bright NK cells.

Present role and future potential of type I interferons in adjuvant therapy of high-risk operable melanoma

Few molecular therapeutic approaches have been so rigorously investigated in relation to the pathophysiology and outcome of human diseases as type I interferons. Historically, IFNs were discovered after the phenomenon of 'interference' was first described by Isaacs and Lindenmann in 1957, and for years IFNs (IFNalpha) were considered as potential "antiviral penicillins" until the broader spectrum of effects upon normal cell physiology, the natural and adaptive immune systems, and tumor growth and proliferation were described. Interferon beta (IFNbeta) was the second human gene after insulin to be cloned, and it codes for the first cytokine used to treat human malignancies. Despite the progress in understanding and treating cancer over the last 25 years, IFN alpha (IFNalpha) remains the most commonly used biologically active cytokine in the treatment of solid tumors, and for some like melanoma, the only successful agent. In this review we discuss the role of type I interferons in the pathophysiology and treatment of melanoma, with emphasis on the 22 years of work conducted at the University of Pittsburgh. We discuss potential mechanisms that partially explain the clinical benefit, and set the groundwork for building upon, the design of more effective treatments for this disease.

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.

Monocyte derived dendritic cells generated by IFN-alpha acquire mature dendritic and natural killer cell properties as shown by gene expression analysis

BACKGROUND

Dendritic cell (DC) vaccines can induce antitumor immune responses in patients with malignant diseases, while the most suitable DC culture conditions have not been established yet. In this study we compared monocyte derived human DC from conventional cultures containing GM-CSF and IL-4/TNF-alpha (IL-4/TNF-DC) with DC generated by the novel protocol using GM-CSF and IFN-alpha (IFN-DC).

METHODS

To characterise the molecular differences of both DC preparations, gene expression profiling was performed using Affymetrix microarrays. The data were conformed on a protein level by immunophenotyping, and functional tests for T cell stimulation, migration and cytolytic activity were performed.

RESULTS

Both methods resulted in CD11c+ CD86+ HLA-DR+ cells with a typical DC morphology that could efficiently stimulate T cells. But gene expression profiling revealed two distinct DC populations. Whereas IL-4/TNF-DC showed a higher expression of genes envolved in phagocytosis IFN-DC had higher RNA levels for markers of DC maturity and migration to the lymph nodes like DCLAMP, CCR7 and CD49d. This different orientation of both DC populations was confined by a 2.3 fold greater migration in transwell experiments (p = 0.01). Most interestingly, IFN-DC also showed higher RNA levels for markers of NK cells such as TRAIL, granzymes, KLRs and other NK cell receptors. On a protein level, intracytoplasmatic TRAIL and granzyme B were observed in 90% of IFN-DC. This translated into a cytolytic activity against K562 cells with a median specific lysis of 26% at high effector cell numbers as determined by propidium iodide uptake, whereas IL-4/TNF-DC did not induce any tumor cell lysis (p = 0.006). Thus, IFN-DC combined characteristics of mature DC and natural killer cells.

CONCLUSION

Our results suggest that IFN-DC not only stimulate adaptive but also mediate innate antitumor immune responses. Therefore, IFN-DC should be evaluated in clinical vaccination trials. In particular, this could be relevant for patients with diseases responsive to a treatment with IFN-alpha such as Non-Hodgkin lymphoma or chronic myeloid leukemia.

Interleukin-12: biological properties and clinical application

Interleukin-12 (IL-12) is a heterodimeric protein, first recovered from EBV-transformed B cell lines. It is a multifunctional cytokine, the properties of which bridge innate and adaptive immunity, acting as a key regulator of cell-mediated immune responses through the induction of T helper 1 differentiation. By promoting IFN-gamma production, proliferation, and cytolytic activity of natural killer and T cells, IL-12 induces cellular immunity. In addition, IL-12 induces an antiangiogenic program mediated by IFN-gamma-inducible genes and by lymphocyte-endothelial cell cross-talk. The immunomodulating and antiangiogenic functions of IL-12 have provided the rationale for exploiting this cytokine as an anticancer agent. In contrast with the significant antitumor and antimetastatic activity of IL-12, documented in several preclinical studies, clinical trials with IL-12, used as a single agent, or as a vaccine adjuvant, have shown limited efficacy in most instances. More effective application of this cytokine, and of newly identified IL-12 family members (IL-23 and IL-27), should be evaluated as therapeutic agents with considerable potential in cancer patients.

Dendritic cells in the kidney

Dendritic cells (DC) in nonlymphoid organs function at the crossroads of innate and adaptive immunity, self-tolerance, and tissue homeostasis. This review provides an overview of the study of DC in the kidney, tracing its history leading to the current knowledge of the origins, migration, and function of renal DC. Together, these studies suggest that renal DC play a critical role in the health and disease of the kidney, opening the way to direct targeting of renal DC for therapeutic benefit.

Global unresponsiveness as a mechanism of natural killer cell tolerance in mixed xenogeneic chimeras

Mixed xenogeneic chimerism induces T- and B-cell tolerance in mice receiving T-cell-depleted rat bone marrow cells (BMC) following nonmyeloablative conditioning that includes alphabeta and gammadelta T cell and Natural killer (NK) cell-depleting mAbs. NK-cell depletion is essential to permit marrow engraftment, but NK-cell tolerance has not been previously assessed in mixed xenogeneic chimeras. We assessed NK-cell tolerance in rat --> mouse mixed xenogeneic chimeras using in vivo(125)I-5iodo-2-deoxyuridine assays. Additional rapid marrow rejection mechanisms resulted in a requirement for 10-fold more rat than ss2 microglobulin knockout (ss2M(-/-)) (MHC class I-deficient) mouse BMC to achieve engraftment in NK-cell-depleted mice. Both 12-week mixed xenogeneic chimeras and conditioned controls showed reduced resistance to engraftment of ss2M(-/-) mouse and rat BMC. While conditioned control mice recovered NK-cell-mediated resistance to ss2M(-/-) and rat BMC by 16 weeks, mixed chimeras lacked resistance to either, similar to NK-cell-deficient Ly49A transgenic mice. Thus, global NK-cell unresponsiveness is induced by mixed xenogeneic chimerism. Our data suggest that NK-cell anergy is induced by interactions with xenogeneic hematopoietic cells that express activating but not inhibitory ligands for recipient NK cells.

Mechanisms of dendritic cell-based vaccination against infection

Due to their unique capacity to initiate and regulate adaptive immune responses, dendritic cells (DC) represent the most potent antigen-presenting cells of the immune system. Immature DC reside in peripheral tissues, where they sample and process antigens and efficiently sense a large variety of signals from the surrounding environment. Toll-like receptors (TLR) expressed by DC play a critical role in the detection of invading pathogens as well as in triggering the subsequent immune responses. The differential expression of TLR by different DC subsets may correlate with the induction of different patterns of adaptive immune responses. The rapidly expanding and fundamental knowledge of DC biology furthers promising perspectives for the development of vaccination strategies in different fields. For example, the immunotherapeutic potential of antigen-pulsed DC for the treatment of cancer has been confirmed in a number of experimental tumour models. Furthermore, DC have been shown to serve as natural adjuvants in different models of infectious diseases, mediating protection against various types of pathogens. Using murine leishmaniasis as an example, we have demonstrated that DC, once properly conditioned ex vivo, mediate complete and durable protection against infection. Critical parameters determining the efficiency of DC-based vaccination against microbial pathogens include the origin of DC, the choice of antigen to be used for DC loading, the route of immunization and the state of DC maturation and activation. In the present review, we discuss the necessity to define the mechanisms responsible for the immunostimulatory capacity of DC in vivo, in order to exploit their full potential as vaccination tools.

Development of dendritic-cell lineages

Dendritic cells (DCs) are a heterogenous population of bone-marrow-derived immune cells. Although all DCs share a common ability to process and present antigen to naive T cells for the initiation of an immune response, they differ in surface markers, migratory patterns, localization, and cytokine production. DCs were originally considered to be myeloid cells, but recent findings have demonstrated that DCs can develop not only from myeloid- but also from lymphoid-committed progenitors. The common feature of the progenitors capable of developing into DCs is the surface expression of Flt3 receptor. The development of different populations of DCs is differentially regulated by various transcription factors and cytokines. This review summarizes the recent advances made in the field of DC development.

The role of dendritic cells in the immunopathogenesis of psoriasis

Psoriasis vulgaris is a chronic inflammatory skin disease that is marked by a complex interplay of dendritic cells (DCs), T-cells, cytokines, and downstream transcription factors as part of a self-sustaining type 1 cytokine network. As integral players of the immune system, DCs represent antigen-presenting cells that are crucial for efficient activation of T-cells and B-cells. DCs have also been linked to distinct chronic inflammatory conditions, including psoriasis. In the setting of psoriasis therapy, DC/T cell interactions serve as a potential target for biologic response modifiers. Here we describe the major DC subsets as well as the immunologic involvement of DCs within the context of psoriatic lesions.

Promiscuity and the single receptor: NKG2D

NKG2D (natural-killer group 2, member D) is a powerful activating receptor expressed by natural killer (NK) cells and T cells that regulates immune responses during infection, cancer and autoimmunity. NKG2D ligands comprise a diverse array of MHC-class-I-related proteins that are upregulated by cellular stress. Why is it beneficial for the host to have so many ligands for the same receptor? In this Opinion article, we propose that although competition with viruses is the most likely evolutionary drive for this diversity, there might be other explanations.

NK cells rapidly remove B16F10 tumor cells in a perforin and interferon-gamma independent manner in vivo

Natural killer (NK) cells have been shown critical in reducing tumor lung metastasis in various murine cancer models. Effector molecules such as perforin and IFN-gamma may play important roles in inhibition of metastasis. However, most of these conclusions were based on experiments that involved quantitation of metastatic colonies several weeks after tumor challenge. The roles of NK cells and their effector molecules (perforin and IFN-gamma) in the initial immune responses against tumor metastasis in lungs are still unknown. By using the B16F10 melanoma tumor model combined with confocal microscopy, we observed an increase in numbers of B16F10 cells in NK-depleted mice at 60 min post tumor inoculation, but this effect was independent of perforin or IFN-gamma. In addition, NK cell numbers in lungs after tumor injection rapidly increased suggesting a redistribution of NK cells in the lungs. However, NK cells were not found in contact with tumor cells until day 6 or later. Our data indicate that during early responses against B16F10 cells, NK cells use another mechanism(s) besides perforin and IFN-gamma to prevent tumor metastasis.

Cytokines and other immunological biomarkers in children's environmental health studies

Environmental exposures (e.g. pesticides, air pollution, and environmental tobacco smoke) during prenatal and early postnatal development have been linked to a growing number of childhood diseases including allergic disorders and leukemia. Because the immune response plays a critical role in each of these diseases, it is important to study the effects of toxicants on the developing immune system. Children's unique susceptibility to environmental toxicants has become an important focus of the field of immunotoxicology and the use of immune biomarkers in molecular epidemiology of children's environmental health is a rapidly expanding field of research. In this review, we discuss how markers of immune status and immunotoxicity are being applied to pediatric studies, with a specific focus on the various methods used to analyze T-helper-1/2 (Th1/Th2) cytokine profiles. Furthermore, we review recent data on the effects of children's environmental exposures to volatile organic compounds, metals, and pesticides on Th1/Th2 cytokine profiles and the associations of Th1/Th2 profiles with adverse health outcomes such as pediatric respiratory diseases, allergies, cancer and diabetes. Although cytokine profiles are increasingly used in children's studies, there is still a need to acquire distribution data for different ages and ethnic groups of healthy children. These data will contribute to the validation and standardization of cytokine biomarkers for future studies. Application of immunological markers in epidemiological studies will improve the understanding of mechanisms that underlie associations between environmental exposures and immune-mediated disorders.

Inflammatory arthritis can be reined in by CpG-induced DC-NK cell cross talk

Unmethylated CpG-oligodeoxynucleotides (ODNs) are generally thought of as potent adjuvants with considerable therapeutic potential to enhance immune responses against microbes and tumors. Surprisingly, certain so-called stimulatory CpG-ODNs strongly inhibited the effector phase of inflammatory arthritis in the K/BxN serum transfer system, either preventively or therapeutically. Also unexpected was that the inhibitory influence did not depend on the adaptive immune system cells mobilized in an immunostimulatory context. Instead, they relied on cells of the innate immune system, specifically on cross talk between CD8α⁺ dendritic cells and natural killer cells, resulting in suppression of neutrophil recruitment to the joint, orchestrated through interleukin-12 and interferon-γ. These findings highlight potential applications of CpG-ODNs and downstream molecules as antiinflammatory agents.

Role of endogenous IFN-gamma in macrophage programming induced by IL-12 and IL-18

Besides the established role of interleukin-12 (IL-12) and IL-18 on interferon-gamma (IFN-gamma) production by natural killer (NK), T, and B cells, the effects of these cytokines on macrophages are largely unknown. Here, we investigated the role of IL-12/IL-18 on nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production by CD11b(+) adherent peritoneal cells, focusing on the involvement of endogenously produced IFN-gamma. C57BL/6 cells released substantial amounts of NO when stimulated with IFN-gamma or lipopolysaccharide (LPS), but failed to respond to IL-12 or IL-18 or both. However, IL-12/IL-18 pretreatment was able to program these cells to release 6-8-fold more NO and TNF-alpha in response to LPS or Trypanosoma cruzi stimulation, with NO levels directly correlating with macrophage resistance to intracellular parasite growth. Analysis of IL-12/IL-18-primed cells from mice deficient in IFN-gamma, IFNGR, and IFN regulatory factor-1 (IRF-1) revealed that these molecules were essential for LPS-induced NO release, but TNF-alpha production was IFN-gamma independent. Conversely, the myeloid differentiation factor 88 (MyD88)-dependent pathway was indispensable for IL-12/IL-18-programmed LPS-induced TNF-alpha production, but not for NO release. Contaminant T and NK cells largely modulated the IL-12/IL-18 programming of LPS-induced NO response through IFN-gamma secretion. Nevertheless, a small population of IFN-gamma(+) cells with a macrophage phenotype was also identified, particularly in the peritoneum of chronically T. cruzi-infected mice, reinforcing the notion that macrophages can be an alternative source of IFN-gamma. Taken together, our data contribute to elucidate the molecular basis of the IL-12/IL-18 autocrine pathway of macrophage activation, showing that endogenous IFN-gamma plays an important role in programming the NO response, whereas the TNF-alpha response occurs through an IFN-gamma-independent pathway.