IL-15 is expressed by dendritic cells in response to type I IFN, double-stranded RNA, or lipopolysaccharide and promotes dendritic cell activation

Myeloid heme oxygenase-1 regulates innate immunity and autoimmunity by modulating IFN-beta production

Heme oxygenase-1 (HO-1) is a key cytoprotective, antioxidant, and antiinflammatory molecule. The pathophysiological functions of HO-1 have been associated with its enzymatic activities in heme catabolism. We have examined the immune functions of HO-1 by its conditional ablation in myeloid cells (HO-1(M-KO) mice). We demonstrate that myeloid HO-1 is required for the activation of interferon (IFN) regulatory factor (IRF) 3 after Toll-like receptor 3 or 4 stimulation, or viral infection. HO-1-deficient macrophages show reduced expression of IFN-beta and of primary IRF3 target genes encoding RANTES, IP-10 and MCP-1. In the presence of polyI:C, myeloid HO-1 knockout mice infected with Listeria monocytogenes, a model dependent on IFN-beta production, showed enhanced bacterial clearance and survival, whereas control mice succumbed to infection. Moreover, after induction of experimental autoimmune encephalomyelitis, mice with myeloid-specific HO-1 deficiency developed a higher incidence and an exacerbated, nonremitting clinical disease correlating with persistent activation of antigen-presenting cells, enhanced infiltration of Th17 cells, and a nonregressing myelin-specific T cell reactivity. Notably, these defects were rectified by exogenous administration of IFN-beta, confirming that HO-1 functions directly upstream of this critical immune pathway. These results uncover a novel direct function for myeloid HO-1 in the regulation of IFN-beta production, establishing HO-1 as a critical early mediator of the innate immune response.

Myeloid heme oxygenase-1 regulates innate immunity and autoimmunity by modulating IFN-beta production

Heme oxygenase–1 (HO-1) is a key cytoprotective, antioxidant, and antiinflammatory molecule. The pathophysiological functions of HO-1 have been associated with its enzymatic activities in heme catabolism. We have examined the immune functions of HO-1 by its conditional ablation in myeloid cells (HO-1^M-KO mice). We demonstrate that myeloid HO-1 is required for the activation of interferon (IFN) regulatory factor (IRF) 3 after Toll-like receptor 3 or 4 stimulation, or viral infection. HO-1–deficient macrophages show reduced expression of IFN-β and of primary IRF3 target genes encoding RANTES, IP-10 and MCP-1. In the presence of polyI:C, myeloid HO-1 knockout mice infected with Listeria monocytogenes, a model dependent on IFN-β production, showed enhanced bacterial clearance and survival, whereas control mice succumbed to infection. Moreover, after induction of experimental autoimmune encephalomyelitis, mice with myeloid-specific HO-1 deficiency developed a higher incidence and an exacerbated, nonremitting clinical disease correlating with persistent activation of antigen-presenting cells, enhanced infiltration of Th17 cells, and a nonregressing myelin-specific T cell reactivity. Notably, these defects were rectified by exogenous administration of IFN-β, confirming that HO-1 functions directly upstream of this critical immune pathway. These results uncover a novel direct function for myeloid HO-1 in the regulation of IFN-β production, establishing HO-1 as a critical early mediator of the innate immune response.

Differential expression of constitutive and inducible proteasome subunits in human monocyte-derived DC differentiated in the presence of IFN-alpha or IL-4

Several studies strongly suggest that DC differentiated in vitro in the presence of type I IFN acquire more potent immune stimulatory properties, compared with DC differentiated in vitro with IL-4. However, little is known about the molecular mechanisms underlying this phenomenon. To address this question, we compared the Ag-processing machinery (APM) profile in human DC grown in the presence of IFN-alpha ((IFN)DC) or IL-4 ((IL-4)DC). Using a panel of APM component-specific mAb in Western blot experiments, we found that (IFN)DC preferentially express inducible proteasome subunits (LMP2, LMP7, and MECL1) both at immature and mature stages. In contrast, immature (IL-4)DC co-express both constitutive (beta1, beta2, and beta5) and inducible subunits, as shown by Western blotting analysis. In addition, immature (IFN)DC express higher levels of TAP1, TAP2, calnexin, calreticulin, tapasin, and HLA class I molecules than (IL-4)DC. The different proteasome profiles of (IFN)DC and (IL-4)DC were associated with a greater ability of (IFN)DC to present an immunodominant epitope that requires LMP7 expression for its processing. In general, these data show the impact of cytokines on APM component expression and hence the Ag-processing ability of DC.

Enhanced acute responses in an experimental exposure model to biomass smoke inhalation in chronic obstructive pulmonary disease

Chronic obstructive pulmonary diseases (COPD) may increase air pollution-related mortality. The relationship of immune mechanisms to mortality caused by fine particulates in healthy and COPD populations is incompletely understood. The objective of this study was to determine whether fine particulates from a single biomass fuel alter stress and inflammation biomarkers in people with COPD. Healthy and COPD subjects were exposed to smoke in a controlled indoor setting. Immune responses were quantified by measuring cell surface marker expression with flow-cytometric analysis and mRNA levels with quantitative reverse transcriptase-polymerase chain reactions in whole blood before and after exposure. Preexposure COPD subjects had more leukocytes, mainly CD14(+) monocytes and neutrophils, but fewer CD3(+) T cells. Fifty-seven of 186 genes were differentially expressed between healthy and COPD subjects' peripheral blood mononuclear cells (PBMCs). Of these, only nuclear factor (NF)-kappa B1, TIMP-1, TIMP-2, and Duffy genes were up-regulated in COPD subjects. At 4 hours post smoke exposure, monocyte levels decreased only in healthy subjects. Fifteen genes, particular to inflammation, immune response, and cell-to-cell signaling, were differentially expressed in COPD subjects, versus 4 genes in healthy subjects. The authors observed significant differences in subjects' PBMCs, which may elucidate the adverse effects of air pollution particulates on people with COPD.

Stimulatory effects of CpG oligodeoxynucleotide on dendritic cell-based immunotherapy of colon cancer in CEA/HLA-A2 transgenic mice

Immunostimulatory DNA containing unmethylated cytosine-guanine (CpG) motifs have been successfully used as adjuvants to enhance the immunity of vaccines designed to trigger antitumor T-cell responses. We examined the effect of a CpG oligodeoxynucleotide (CpG ODN) for its ability to potentiate the activity of tumor antigen-pulsed dendritic cells (DC) in a clinically relevant mouse model, which is transgenic for both carcinoembryonic antigen (CEA) and HLA-A2 for the treatment of colon carcinoma in a therapeutic setting. The systemic administration of CpG ODN 1826 alone had modest effect on tumor growth when tumors were palpable and had no effect with larger tumor burden. However, coadministration of CpG ODN 1826 with the vaccine provided significant increase in tumor-free survival compared with mice immunized with DC-based vaccines alone. The DC/CpG combined vaccination strategy resulted in increased secretion of Th1 cytokines and HLA-A2-restricted CEA-specific CTL responses were also enhanced. Both tumor regression and extended tumor-free survival resulting from DC/CpG combination therapy required the participation of T cells. Tumor-free mice were resistant to tumor rechallenge and immunity conferred by the vaccine was transferable in athymic nude mice. These results provide evidence that vaccination with antigen-pulsed DC with CpG ODN as adjuvant can lead to effective tumor regression and long-term survival in a murine model of colon carcinoma.

Celiac disease: from oral tolerance to intestinal inflammation, autoimmunity and lymphomagenesis

Celiac disease is a multifactorial disorder and provides a privileged model to decipher how the interplay between environmental and genetic factors can alter mucosal tolerance to a food antigen, lead to chronic intestinal inflammation, and ultimately promote T-cell lymphomagenesis. Here we summarize how HLA-DQ2/8 molecules, the main genetic risk factor for this disease can orchestrate a CD4(+) T-cell adaptive immune response against gluten, and discuss recent data which shed light on the innate and adaptive immune stimuli that collaborate to induce a proinflammatory TH1 response, a massive expansion of intraepithelial lymphocytes, and a cytolytic attack of the epithelium. The intestinal immune response driven in genetically predisposed patients by chronic exposure to gluten emerges as the pathological counterpart of normal acute intestinal responses to intracellular pathogens.

Targeting poly(I:C) to the TLR3-independent pathway boosts effector CD8 T cell differentiation through IFN-alpha/beta

Poly(I:C) is an adjuvant used for antitumor treatment and vaccines because of its prominent effects on CD8 T cells and NK cells. Poly(I:C) binds TLR3 and this interaction is thought to be central for driving cell-mediated immune responses. We investigated the importance of TLR3 in poly(I:C)-mediated endogenous CD8 T cell responses using the pathogenic T cell stimulant Staphylococcus aureus enterotoxin A. While the responsive CD8 T cells expanded comparably in both wild-type and TLR3(-/-) mice, differentiation of effector CD8 T cells was enhanced by poly(I:C) in the TLR3(-/-) mice. A higher percentage of Ag-specific CD8 T cells became IFN-gamma and TNF-alpha producers in the absence of TLR3 signaling. Consistent with this boosted response was the observation that TLR3-deficient cells synthesized less IL-10 compared with TLR3-sufficient cells in response to poly(I:C). Ultimately, however, the fundamental mechanism of CD8 effector T cell differentiation through the TLR3-independent pathway was shown to be completely IFN-alpha/beta-dependent. Administration of IFN-alpha/beta-neutralizing Abs abolished the poly(I:C) effects in TLR3(-/-) mice. These findings reveal specific roles of how dsRNA receptors shape CD8 T cell responses, which should be considered as poly(I:C) is authenticated as a therapeutic adjuvant used in vaccines.

Antiviral-activated dendritic cells: a paracrine-induced response state

Infection of immature dendritic cells (DCs) by virus stimulates their maturation into APC. Infected DCs can also expose uninfected DCs to a panoply of cytokines/chemokines via paracrine signaling. Mathematical modeling suggests that a high rate of paracrine signaling is likely to occur among DCs located in three-dimensional space. Relatively little is known about how secreted factors modify the early response to virus infection. We used a transwell experimental system that allows passage of secreted factors, but not direct contact, between virus-infected DCs and uninfected DCs to investigate paracrine signaling responses. Paracrine signaling from infected DCs induced an antiviral-primed DC state distinct from that of mature virus-infected DCs that we refer to as antiviral-activated DCs (AVDCs). AVDCs had increased surface MHC class II and CD86 levels, but in contrast to virus-infected DCs, their MHC class I levels were unchanged. Imaging flow cytometry showed that AVDCs had an increased rate of phagocytosis compared with naive DCs. Experiments with IFN-beta cytokine indicated that it may be responsible for CD86, but not MHC class II regulation in AVDCs. Both IFN-inducible and IFN-independent genes are up-regulated in AVDCs. Notably, AVDCs are relatively resistant to virus infection in comparison to naive DCs and achieve accelerated and augmented levels of costimulatory molecule expression with virus infection. AVDCs show a distinct antiviral-primed state of DC maturation mediated by DC paracrine signaling. Although further in vivo study is needed, the characteristics of the AVDC suggest that it is well suited to play a role in the early innate-adaptive transition of the immune system.

Effect of interleukin-15 on depressed splenic dendritic cell functions following trauma-hemorrhage

Although trauma-hemorrhage (T-H) induces suppressed splenic dendritic cell (DC) maturation and antigen presentation capacity, it remains unclear whether IL-15 modulates splenic DC functions. The aim of this study therefore was to investigate the effect of IL-15 on splenic DC functions after T-H. Male C3H/HeN mice (6-8 wk old) were randomly assigned to T-H or sham operation. T-H was induced by midline laparotomy and approximately 90 min of hemorrhagic shock (blood pressure 35 mmHg), followed by fluid resuscitation (4x the shed blood volume in the form of Ringer lactate). Two hours later, mice were killed, splenic DCs were isolated, and the effects of exogenous IL-15 on their costimulatory factors, major histocompatibility class II expression, ability to produce cytokines, and antigen presentation were measured. The results indicate that IL-15 production capacity of splenic DCs was reduced following T-H. Ex vivo exposure to IL-15 attenuated the suppressed production of TNF-alpha, IL-6, and IFN-gamma from splenic DCs following T-H. In addition, expression of surface antigen studies demonstrate that exogenous IL-15 attenuated T-H-induced downregulation of the activation of DC. The suppressed splenic DC antigen presentation function following T-H was also attenuated by IL-15 treatment. Moreover, IL-15 enhanced IL-12-induced IFN-gamma production and antigen presentation by splenic DCs. These data suggest that ex vivo treatment with IL-15 following T-H provides beneficial effects on splenic DCs. The depression in IL-15 production by splenic DCs could contribute to the host's enhanced susceptibility to infections following T-H.

Dendritic cells drive memory CD8 T-cell homeostasis via IL-15 transpresentation

Interleukin-15 (IL-15) is crucial for the development of naive and memory CD8 T cells and is delivered through a mechanism called transpresentation. Previous studies showed that memory CD8 T cells require IL-15 transpresentation by an as yet unknown cell of hematopoietic origin. We hypothesized that dendritic cells (DCs) transpresent IL-15 to CD8 T cells, and we examined this by developing a transgenic model that limits IL-15 transpresentation to DCs. In this study, IL-15 transpresentation by DCs had little effect on restoring naive CD8 T cells but contributed to the development of memory-phenotype CD8 T cells. The generation of virus-specific, memory CD8 T cells was partially supported by IL-15Ralpha(+) DCs through the preferential enhancement of a subset of KLRG-1(+)CD27(-) CD8 T cells. In contrast, these DCs were largely sufficient in driving normal homeostatic proliferation of established memory CD8 T cells, suggesting that memory CD8 T cells grow more dependent on IL-15 transpresentation by DCs. Overall, our study clearly supports a role for DCs in memory CD8 T-cell homeostasis but also provides evidence that other hematopoietic cells are involved in this function. The identification of DCs fulfilling this role will enable future studies to better focus on mechanisms regulating T-cell homeostasis.

Human natural killer cells

Natural killer (NK) cells were discovered more than 30 years ago. NK cells are large granular lymphocytes that belong to the innate immune system because unlike T or B lymphocytes of the adaptive or antigen-specific immune system, NK cells do not rearrange T-cell receptor or immunoglobulin genes from their germline configuration. During the past 2 decades there has been a substantial gain in our understanding of what and how NK-cells "see," lending important insights into their functions and purpose in normal immune surveillance. The most recent discoveries in NK-cell receptor biology have fueled translational research that has led to remarkable results in treating human malignancy.

Type I IFN-induced, NKT cell-mediated negative control of CD8 T cell priming by dendritic cells

We investigated the negative effect of type I IFN (IFN-I) on the priming of specific CD8 T cell immunity. Priming of murine CD8 T cells is down-modulated if Ag is codelivered with IFN-I-inducing polyinosinic:polycytidylic acid (pI/C) that induces (NK cell- and T/B cell-independent) acute changes in the composition and surface phenotype of dendritic cells (DC). In wild-type but not IFN-I receptor-deficient mice, pI/C reduces the plasmacytoid DC but expands the CD8(+) conventional DC (cDC) population and up-regulates surface expression of activation-associated (CD69, BST2), MHC (class I/II), costimulator (CD40, CD80/CD86), and coinhibitor (PD-L1/L2) molecules by cDC. Naive T cells are efficiently primed in vitro by IFN-I-stimulated CD8 cDC (the key APC involved in CD8 T cell priming) although these DC produced less IL-12 p40 and IL-6. pI/C (IFN-I)-mediated down modulation of CD8 T cell priming in vivo was not observed in NKT cell-deficient CD1d(-/-) mice. CD8 cDC from pI/C-treated mice inefficiently stimulated IFN-gamma, IL-4, and IL-2 responses of NKT cells. In vitro, CD8 cDC that had activated NKT cells in the presence of IFN-I primed CD8 T cells that produced less IFN-gamma but more IL-10. The described immunosuppressive effect of IFN-I thus involves an NKT cell-mediated change in the phenotype of CD8 cDC that favors priming of IL-10-producing CD8 T cells. In the presence of IFN-I, NKT cells hence impair the competence of CD8 cDC to prime proinflammatory CD8 T cell responses.

Prophylactic treatment with fms-like tyrosine kinase-3 ligand after burn injury enhances global immune responses to infection

Severely burned patients are susceptible to infections with opportunistic organisms due to altered immune responses and frequent wound contamination. Immunomodulation to enhance systemic and local responses to wound infections may be protective after burn injury. We previously demonstrated that pretreatments with fms-like tyrosine kinase-3 (Flt3) ligand (Flt3L), a dendritic cell growth factor, increase the resistance of mice to a subsequent burn injury and wound infection by a dendritic cell-dependent mechanism. This study was designed to test the hypothesis that Flt3L administration after burn injury decreases susceptibility to wound infections by enhancing global immune cell activation. Mice were treated with Flt3L after burn injury and examined for survival, wound and systemic bacterial clearance, and immune cell activation after wound inoculation with Pseudomonas aeruginosa. To gain insight into the local effects of Flt3L at the burn wound, localization of Langerhans cells was examined. Mice treated with Flt3L had significantly greater numbers of CD25-expressing T cells and CD69-expressing T and B cells, neutrophils, and macrophages after, but not before, infection. Overall leukocyte apoptosis in response to infection was decreased with Flt3L treatment. Survival and local and systemic bacterial clearance were enhanced by Flt3L. Langerhans cells appeared in the dermis of skin bordering the burn wound, and further increased in response to wound infection. Flt3L augmented the appearance of Langerhans cells in response to both injury and infection. These data suggest that dendritic cell enhancement by Flt3L treatments after burn injury protects against opportunistic infections through promotion of local and systemic immune responses to infection.

IL-15 transpresentation augments CD8+ T cell activation and is required for optimal recall responses by central memory CD8+ T cells

Although the adaptive immune system has a remarkable ability to mount rapid recall responses to previously encountered pathogens, the cellular and molecular signals necessary for memory CD8(+) T cell reactivation are poorly defined. IL-15 plays a critical role in memory CD8(+) T cell survival; however, whether IL-15 is also involved in memory CD8(+) T cell reactivation is presently unclear. Using artificial Ag-presenting surfaces prepared on cell-sized microspheres, we specifically addressed the role of IL-15 transpresentation on mouse CD8(+) T cell activation in the complete absence of additional stimulatory signals. In this study we demonstrate that transpresented IL-15 is significantly more effective than soluble IL-15 in augmenting anti-CD3epsilon-induced proliferation and effector molecule expression by CD8(+) T cells. Importantly, IL-15 transpresentation and TCR ligation by anti-CD3epsilon or peptide MHC complexes exhibited synergism in stimulating CD8(+) T cell responses. In agreement with previous studies, we found that transpresented IL-15 preferentially stimulated memory phenotype CD8(+) T cells; however, in pursuing this further, we found that central memory (T(CM)) and effector memory (T(EM)) CD8(+) T cells responded differentially to transpresented IL-15. T(CM) CD8(+) T cells undergo Ag-independent proliferation in response to transpresented IL-15 alone, whereas T(EM) CD8(+) T cells are relatively unresponsive to transpresented IL-15. Furthermore, upon Ag-specific stimulation, T(CM) CD8(+) T cell responses are enhanced by IL-15 transpresentation, whereas T(EM) CD8(+) T cell responses are only slightly affected, both in vitro and in vivo. Thus, our findings distinguish the role of IL-15 transpresentation in the stimulation of distinct memory CD8(+) T cell subsets, and they also have implications for ex vivo reactivation and expansion of Ag-experienced CD8(+) T cells for immunotherapeutic approaches.

Regulatory T cells control dendritic cell/NK cell cross-talk in lymph nodes at the steady state by inhibiting CD4+ self-reactive T cells

The CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) play an important role in the control of peripheral tolerance by directly inhibiting conventional T cell proliferative and effector functions. However, the mechanisms by which Treg regulate the homeostasis of lymph nodes remain unclear. In this study, we show in a mouse model that Treg control two major checkpoints dictated by the interaction between self-reactive CD4(+) T cells and resident dendritic cell (DC) in secondary lymphoid organs. First, Treg inhibit the production of CCR5 ligands, limiting the CCR5-dependent recruitment of DC in the lymph nodes. Second, Treg prevent the DC exposure of IL-15Ralpha, markedly interfering in the DC-mediated NK cell proliferation in vivo. Therefore, the DC/T cell autoreactivity leading to NK cell triggering could potentially be controlled by the coinhibition of both IL-15Ralpha and CCR5 in autoimmune disorders in which NK cells play a deleterious role.

The critical role of IL-15 in the antitumor effects mediated by the combination therapy imatinib and IL-2

The synergistic antitumor effects of the combination therapy imatinib mesylate (IM) and IL-2 depended upon NK1.1- expressing cells and were associated with the accumulation of CD11c(int)B220(+)NK1.1(+) IFN-producing killer dendritic cells (IKDC) into tumor beds. In this study, we show that the antitumor efficacy of the combination therapy was compromised in IL-15 and IFN-type 1R loss-of-function mice. IL-15Ralpha was required for the proliferation of IKDC during IM plus IL-2 therapy. Trans-presentation of IL-15/IL-15Ralpha activated IKDC to express CCR2 and to respond to type 1 IFN by producing CCL2. Moreover, the antitumor effects of the combination therapy correlated with a CCL2-dependent recruitment of IKDC, but not B220(-) NK cells, into tumor beds. Altogether, the IL-15-driven peripheral expansion and the CCL-2-dependent intratumoral chemoattraction of IKDC are two critical parameters dictating the antitumor efficacy of IM plus IL-2 in mice.

IL-15Ralpha chaperones IL-15 to stable dendritic cell membrane complexes that activate NK cells via trans presentation

Natural killer (NK) cells are innate immune effectors that mediate rapid responses to viral antigens. Interleukin (IL)-15 and its high affinity IL-15 receptor, IL-15Ralpha, support NK cell homeostasis in resting animals via a novel trans presentation mechanism. To better understand how IL-15 and IL-15Ralpha support NK cell activation during immune responses, we have used sensitive assays for detecting native IL-15 and IL-15Ralpha proteins and developed an assay for detecting complexes of these proteins. We find that IL-15 and IL-15Ralpha are preassembled in complexes within the endoplasmic reticulum/Golgi of stimulated dendritic cells (DCs) before being released from cells. IL-15Ralpha is required for IL-15 production by DCs, and IL-15 that emerges onto the cell surface of matured DCs does not bind to neighboring cells expressing IL-15Ralpha. We also find that soluble IL-15-IL-15Ralpha complexes are induced during inflammation, but membrane-bound IL-15-IL-15Ralpha complexes, rather than soluble complexes, support NK cell activation in vitro and in vivo. Finally, we provide in vivo evidence that expression of IL-15Ralpha specifically on DCs is critical for trans presenting IL-15 and activating NK cells. These studies define an unprecedented cytokine-receptor biosynthetic pathway in which IL-15Ralpha serves as a chaperone for IL-15, after which membrane-bound IL-15Ralpha-IL-15 complexes activate NK cells via direct cell-cell contact.

Uterine NK cells in murine pregnancy

Murine uterine natural killer (uNK) cells are transient, short-lived, terminally differentiated lymphocytes found in decidualized endometrium. Cells expressing natural killer cell surface markers are present in uteri of infant mice. Terminal uNK cell differentiation coincides with mesometrial decidual development subsequent to blastocyst implantation and begins about gestation day 5. uNK cells proliferate rapidly and, within 3 days, senescent uNK cells appear in normal implantation sites. Mid-gestation, senescent cells become dominant and uNK cell numbers decline until term when remaining cells are shed with the placenta. Transplantable uNK cell progenitors occur outside the uterus, suggesting that blood cell homing augments any in-utero progenitors. Early in healthy pregnancies, uNK cells produce cytokines and angiogenic molecules. Their lytic capacity in normal gestation and in pregnancy failure is incompletely defined. A significant shift recently occurred in thinking about major uNK cell functions. Activated uNK cells are now considered critical for appropriate endometrial angiogenesis in early implantation site development and in non-gestational endometrium. Because analogous cells appear in the endometria of women during each menstrual cycle and become abundant in early pregnancy, studies involving experimental pregnancy termination in genetically manipulated mice continue to have great importance for understanding regulation at the human maternal-fetal interface.

Proteasome activator and antigen-processing aminopeptidases are regulated by virus-induced type I interferon in the hepatitis C virus-infected liver

Many components of the class I antigen-processing pathway are thought to be regulated solely by interferon-gamma (IFN-gamma). Herein, we report type I IFN-mediated induction of proteasome activator (PA28) subunits alpha and beta, endoplasmic reticulum aminopeptidase 1 (ERAP1), ERAP2, and leucine aminopeptidase (LAP). This mechanism was initiated by either synthetic RNA (poly(I-C)) or by hepatitis C virus (HCV) RNA-mediated induction of type I IFN and abrogated by blocking of type I IFN. In serial liver biopsies of chimpanzees with acute HCV infection, increases in PA28 subunit and aminopeptidase mRNA levels correlated with intrahepatic type I IFN responses and preceded intrahepatic IFN-gamma responses by several weeks. Thus, viral RNA-induced type I IFN regulates the antigen-processing machinery early during viral infection and prior to IFN-gamma response. This mechanism may contribute to the high effectiveness of type I IFN-based therapies if administered early during acute HCV infection.

Interferon type I responses in primary and secondary infections

The mammalian host responds to a microbial infection with a rapid innate immune reaction that is dominated by type I interferon (IFN-I) release. Most cells of vertebrates can respond to microbial attack with IFN-I production, but the cell type responsible for most of the systemic IFN-I release is thought to be plasmacytoid dendritic cells (pDCs). Besides its anti-microbial and especially anti-viral properties IFN-I also exerts a regulatory role on many facets of the sequential adaptive immune response. One of these is being the recently described partial, systemic activation of the vast majority of B and T lymphocytes in mice, irrespective of antigen reactivity. The biological significance of this partial activation of lymphocytes is at present speculative. Secondary infections occurring within a short time span of a primary infection fail to elicit a similar lymphocyte activation response due to a refractory period in systemic IFN-I production. This period of exhaustion in IFN-I responses is associated with an increased susceptibility of the host to secondary infections. The latter correlates with well-established clinical observations of heightened susceptibility of patients to secondary microbial infections after viral episodes.

IL-4 suppresses dendritic cell response to type I interferons

Cytokines play an important role in modulating the development and function of dendritic cells (DCs). Type I IFNs activate DCs and drive anti-viral responses, whereas IL-4 is the prototype of a Th2 cytokine. Evidence suggests that type I IFNs and IL-4 influence each other to modulate DC functions. We found that two type I IFNs, IFN-alpha and IFN-beta, stimulated a similar costimulatory profile in myeloid resting DCs. IL-4 suppressed the response of myeloid DCs to both type I IFNs in vitro and in vivo by impairing the up-regulation of MHC and costimulatory molecules and the production of cytokines, such as IL-6 and IL-15, and anti-viral genes, such as Mx-1, upon type I IFN stimulation. In dissecting the mechanism underlying this inhibition, we characterized the positive feedback loop that is triggered by IFN-alpha in primary DCs and found that IL-4 inhibited the initial phosphorylation of STAT1 and STAT2 (the transducers of signaling downstream of IFN-alpha and -beta receptors (IFNARs)) and reduced the up-regulation of genes involved in the amplification of the IFN response such as IRF-7, STAT1, STAT2, IFN-beta, and the IFNARs in vitro and in vivo. Therefore, IL-4 renders myeloid DCs less responsive to paracrine type I IFNs and less potent in sustaining the autocrine positive loop that normally amplifies the effects of type I IFNs. This inhibition could explain the increased susceptibility to viral infections observed during Th2-inducing parasitoses.

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.

Interleukin-15 increases vaccine efficacy through a mechanism linked to dendritic cell maturation and enhanced antibody titers

Interleukin-15 (IL-15) is generally considered to sustain T-cell memory and to be a growth factor for natural killer cells. Previous data from our laboratory demonstrated that IL-15 is also an important factor for developing human dendritic cells. For this study, we investigated the effects of IL-15 on antibody responses in mice to a recombinant staphylococcal enterotoxin B (SEB) vaccine (STEBVax) in a preclinical model of toxic shock syndrome induced by SEB. We observed that mouse spleen cells treated with IL-15 in ex vivo culture gained a dendritic cell-like phenotype. Administration of IL-15 to mice also resulted in an increased number of mature CD11c+ dendritic cells in mouse spleens. A significant, IL-15 dose-dependent increase in antigen-specific antibody was observed after coadministration with the vaccine and an aluminum-based adjuvant (alhydrogel). Furthermore, the coadministration of IL-15 with STEBVax and alhydrogel also protected mice from lethal toxic shock above the levels that obtained without IL-15. Thus, the vaccine response enhanced by IL-15 appears to be mediated by mature dendritic cells and results in prevalent seroconversion to Th2-dependent antibodies. This suggests a potential use of IL-15 as an adjuvant for antibody-dependent responses to vaccines.

Genetic control directed toward spontaneous IFN-alpha/IFN-beta responses and downstream IFN-gamma expression influences the pathogenesis of a murine psoriasis-like skin disease

Psoriasis is an inflammatory skin disease, onset and severity of which are controlled by multiple genetic factors; aberrant expression of and responses to several cytokines including IFN-alpha/IFN-beta and IFN-gamma are associated with this "type 1" disease. However, it remains unclear whether genetic regulation influences these cytokine-related abnormalities. Mice deficient for IFN regulatory factor-2 (IRF-2) on the C57BL/6 background (IRF-2(-/-)BN mice) exhibited accelerated IFN-alpha/IFN-beta responses leading to a psoriasis-like skin inflammation. In this study, we found that this skin phenotype disappeared in IRF-2(-/-) mice with the BALB/c or BALB/c x C57BL/6 F(1) backgrounds. Genome-wide scan revealed two major quantitative trait loci controlled the skin disease severity. Interestingly, these loci were different from that for the defect in CD4(+) dendritic cells, another IFN-alpha/IFN-beta-dependent phenotype of the mice. Notably, IFN-gamma expression as well as spontaneous IFN-alpha/IFN-beta responses were up-regulated several fold spontaneously in the skin in IRF-2(-/-)BN mice but not in IRF-2(-/-) mice with "resistant" backgrounds. The absence of such IFN-gamma up-regulation in IRF-2(-/-)BN mice lacking the IFN-alpha/IFN-beta receptor or beta(2)-microglobulin indicated that accelerated IFN-alpha/IFN-beta signals augmented IFN-gamma expression by CD8(+) T cells in the skin. IFN-gamma indeed played pathogenic roles as skin inflammation was delayed and was much more infrequent when IRF-2(-/-)BN mice lacked the IFN-gamma receptor. Our current study thus revealed a novel genetic mechanism that kept the skin immune system under control and prevented skin inflammation through regulating the magnitude of IFN-alpha/IFN-beta responses and downstream IFN-gamma production, independently of CD4(+) dendritic cells.

MHC class I chain-related molecules induced on monocytes by IFN-gamma promote NK cell activation

NKG2D receptor-ligand interaction triggers NK cell-mediated cytolysis and IFN-gamma secretion. IFN-gamma produced by NK cells has been found to promote the interaction between NK cells and monocytes; however, the underlying mechanism remains elusive. We demonstrate here that IFN-gamma exclusively induced or upregulated the expression of MHC class I chain-related (MIC) molecules, which are ligands of the NKG2D receptor, on the surface of human monocytes of the PBMC population. The IFN-gamma-induced MIC molecules on monocytes played an essential role in triggering the activation of NK cells because mAb-mediated masking of the MIC molecules and the inhibition of cell-to-cell contact using transwell inserts significantly abolished NK cell activation. Meanwhile, membrane-bound IL-15 (mIL-15) was concomitantly induced with MIC molecules on IFN-gamma-treated monocytes and played an essential role in protecting NK cells cocultured with monocytes from MIC-induced NKG2D down-modulation. Therefore, we conclude that the IFN-gamma-induced MIC molecules participated in monocyte/NK cell interaction and that this interaction also involved mIL-15.

Molecular and Functional Characterization of IL-15 in Rainbow TroutOncorhynchus mykiss:A Potent Inducer of IFN-γ Expression in Spleen Leukocytes

IL-15 is a member of the common gamma-chain family of cytokines that possess a heterogeneous repertoire of activities on various cells of the immune system. We report here the first functional characterization of a fish IL-15 in rainbow trout. The trout IL-15 gene is 6-kb long and contains six exons and five introns that transcribe into a 1.2-kb mRNA containing seven out-of-frame AUG initiation codons and translate into a 193-aa peptide. Potential sites for transcriptional activators and repressors have been identified in the trout IL-15 gene. Like IL-15 from other species, trout IL-15 is closely linked to an INPP4B gene, but there is also a BCL10 gene located between the IL-15 and INPP4B genes. Three alternative splicing variants of the trout IL-15 gene have also been identified and their expression in vivo was studied. Trout IL-15 expression is present in all the tissues and cell lines studied. Recombinant trout IFN-gamma selectively increased IL-15 expression but had little effect on other cytokines such as IL-1 beta and IL-11. Recombinant trout IL-15 preferentially stimulated splenic leukocytes from healthy fish, where it induced a large increase in IFN-gamma expression, with little, if any, effect on IL-1 beta expression. This effect was quite long-lived, and was still apparent 24 h poststimulation. Although the exact cell types being affected have still to be determined, it is clear that once produced IL-15 will have a profound affect on the ability of the fish immune system to activate antimicrobial defenses and genes induced themselves by IFN-gamma.

Dendritic cells prime natural killer cells by trans-presenting interleukin 15

Natural killer (NK) cells are important effector cells in the control of infections. The cellular and molecular signals required for NK cell activation in vivo remain poorly defined. By using a mouse model for the inducible ablation of dendritic cells (DCs), we showed that the in vivo priming of NK cell responses to viral and bacterial pathogens required the presence of CD11c(high) DCs. After peripheral Toll-like receptor (TLR) stimulation, NK cells were recruited to local lymph nodes, and their interaction with DCs resulted in the emergence of effector NK cells in the periphery. NK cell priming was dependent on the recognition of type I IFN signals by DCs and the subsequent production and trans-presentation of IL-15 by DCs to resting NK cells. CD11c(high) DC-derived IL-15 was necessary and sufficient for the priming of NK cells. Our data define a unique in vivo role of DCs for the priming of NK cells, revealing a striking and previously unappreciated homology to T lymphocytes of the adaptive immune system.

DAP12 signaling directly augments proproliferative cytokine stimulation of NK cells during viral infections

NK cells vigorously proliferate during viral infections. During the course of murine CMV infection, this response becomes dominated by the preferential proliferation of NK cells that express the activation receptor Ly49H. The factors driving such selective NK cell proliferation have not been characterized. In this study, we demonstrate that preferential NK cell proliferation is dependent on DAP12-mediated signaling following the binding of Ly49H to its virally encoded ligand, m157. Ly49H signaling through DAP12 appears to directly augment NK cell sensitivity to low concentrations of proproliferative cytokines such as IL-15. The impact of Ly49H-mediated signaling on NK cell proliferation is masked in the presence of high concentrations of proproliferative cytokines that nonselectively drive all NK cells to proliferate.

Exhaustion of type I interferon response following an acute viral infection

Viral infections often cause a period of heightened susceptibility to a secondary infection but the cause of this phenomenon is unknown. We found that a primary viral infection in mice rapidly triggers an IFN-I-dependent partial activation state in the majority of B and T lymphocytes, which reverts to a resting phenotype within 5 days. When a secondary infection with an unrelated virus occurred 5 to 9 days after the primary infection, no recurrence of marked activation of lymphocytes was observed. This was not due to an inherent inability of the previously activated cells to undergo renewed partial activation, because they responded when challenged with virus after transfer into "naive" recipients. Instead, the failure to respond optimally resided in the original host's incapacity to mount an IFN-I response to the secondary infection during this time period. Thus, transient immunosuppression through exhaustion of IFN-I production during an acute viral infection creates a time period of enhanced susceptibility to secondary infection.

Type-I interferons and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease characterized by the production of autoantibodies directed against nuclear antigens and chronic inflammation affecting multiple tissues. Complex genetic disorders are at the origin of the disease in humans and in SLE-prone mice, leading to the escape of auto-reactive B-lymphocytes from central and peripheral control checkpoints that operate normally in healthy organisms. Although necessary, autoimmune B-cells are not sufficient and additional mechanisms such as T-cell help are clearly needed for the disease to occur. The role of type-I interferons (type-I IFNs), and in particular IFNalpha, as prominent cofactors for SLE was suggested years ago. Leading observations in patients and recent data in SLE-prone mice have now established IFNalpha as a major actor in SLE. Several systemic clinical symptoms and laboratory findings can indeed be interpreted as downstream effects of a high IFNalpha production, and point to this cytokine as a link between the expansion of autoimmune B-cells and the stimulation of other components of the immune system. Consequently, a vicious circle is established with overt immune-cell activation and inflammatory infiltrates culminating in the selective destruction of tissue targets, notably the kidney. These notions can now be transplanted to the clinic and designate IFNalpha as a new promising therapeutic target.

Essential roles of DC-derived IL-15 as a mediator of inflammatory responses in vivo

Interleukin (IL)-15 is expressed in a variety of inflammatory diseases. However, the contribution of dendritic cell (DC)–derived IL-15 to the development of diseases is uncertain. Using established models of Propionibacterium acnes (P. acnes)– and zymosan-induced liver inflammation, we observed granuloma formation in the livers of wild-type (WT) and RAG-2^−/− mice but not in those of IL-15^−/− mice. We demonstrate that this is likely caused by an impaired sequential induction of IL-12, IFN-γ, and chemokines necessary for monocyte migration. Likewise, lethal endotoxin shock was not induced in P. acnes– and zymosan-primed IL-15^−/− mice or in WT mice treated with a new IL-15–neutralizing antibody. In both systems, proinflammatory cytokine production was impaired. Surprisingly, neither granuloma formation, lethal endotoxin shock, nor IL-15 production was induced in mice deficient for DCs, and adoptive transfer of WT but not IL-15^−/− DCs restored the disease development in IL-15^−/− mice. Collectively, these data indicate the importance of DC-derived IL-15 as a mediator of inflammatory responses in vivo.

Type I interferons directly regulate lymphocyte recirculation and cause transient blood lymphopenia

Early viral infection is often associated with lymphopenia, a transient reduction of blood lymphocyte counts long before the onset of clinical symptoms. We have investigated lymphopenia in mice infected with vesicular stomatitis virus (VSV) or treated with the Toll-like receptor (TLR) agonists poly(I:C) and R-848. In all cases analyzed, lymphopenia was critically dependent on type I interferon receptor (IFNAR) signaling. With the use of bone marrow-chimeric mice, radioresistant cells, such as stroma and endothelium, could be excluded as type I interferon (IFN-alpha/beta) targets for the induction of lymphopenia. Instead, adoptive transfer experiments and studies in conditionally gene-targeted mice with a B- or T-cell-specific IFNAR deletion demonstrated that IFN-alpha/beta exerted a direct effect on lymphocytes that was necessary and largely sufficient to induce lymphopenia. Furthermore, after treatment with R-848, we found that other cytokines such as TNF-alpha also played a role in T-cell lymphopenia. Investigation of the molecular mechanism revealed that lymphopenia was mainly independent of G protein-coupled receptors (GPCRs) and chemokines. In an adhesion assay, B cells of poly(I:C)-treated mice showed moderately increased adhesion to ICAM-1 but not to VCAM-1. In conclusion, our data identify a new effect of direct IFN-alpha/beta stimulation of lymphocytes that profoundly affects lymphocyte redistribution.

Positive and negative regulation of Natural Killer cells: therapeutic implications

Natural Killer (NK) cells can mediate numerous anti-tumor and anti-viral effector functions as well as play important immunoregulatory roles in various disease states. Promoting the ability of NK cells to respond in an immunotherapeutic setting has often been sought by the addition of NK cell-stimulating factors. However, such therapies are often found to be insufficient, which may in part be due to the presence of inhibitory influences on the NK cell. NK cells can respond to a plethora of cytokines which are generated by numerous cell types and these interactions can markedly affect NK cell survival and activity. NK cells also possess multiple activating and inhibiting receptors which can alter their function. Whether the NK cell will become activated or not can depend on a complex balance of activating and inhibitory signals received by the cell and modulation of these signals may shift the balance on NK activation. This review discusses the various activating and inhibitory stimuli which can act on NK cells, and suggests that future NK cell-based therapies consider not only activating stimuli but also removal of possible inhibitory elements which could prevent optimal NK cell function and/or survival.

Modification of TLR-induced activation of human dendritic cells by type I IFN: synergistic interaction with TLR4 but not TLR3 agonists

Upon detection of direct and indirect signs of infection, dendritic cells (DC) undergo functional changes that modify their ability to elicit immune responses. Type I interferon (IFN-alpha/beta), which includes a large family of closely related infection-inducible cytokines, represents one indirect signal that can act as a DC stimulus. We have investigated the ability of IFN-alpha/beta subtypes to affect DC function and to influence DC responses to Toll-like receptor (TLR) agonists (i.e., direct infection-associated signals). Subtle differences were observed among 15 subtypes of IFN-alpha/beta in the ability to stimulate expression of maturation markers and chemokines by human monocyte-derived DC, with IFN-omega being the most unique in its effects. Pre-treatment with IFN-alpha/beta did not alter the ability of DC to mature in response to subsequent contact with TLR agonists, but did modulate their secretion of chemokines. Conversely, IFN-alpha/beta was shown to act synergistically with TLR4 but not TLR3 agonists for the induction of maturation and chemokine production when DC were exposed to IFN-alpha/beta and TLR ligands simultaneously. Taken together, these results indicate a complex role for IFN-alpha/beta in regulating DC function during the course an infection, which varies according to IFN-alpha/beta subtype and the timing of exposure to other stimuli.

The adjuvant effects of the toll-like receptor 3 ligand polyinosinic-cytidylic acid poly (I:C) on antigen-specific CD8+ T cell responses are partially dependent on NK cells with the induction of a beneficial cytokine milieu

Poly (I:C), a TLR3 ligand, has shown promise as a vaccine adjuvant to CD8(+) T cell responses. The underlying mechanisms involved in creating this adjuvant response in vivo, however, have not been well defined. In this study, we explored the contribution of NK cells and inflammatory cytokines in mediation the poly (I:C) adjuvant effects. Enhanced antigen-specific CD8(+) T cell responses were observed only when poly (I:C) was administered within 4h of peptide vaccination. Poly (I:C) treatment was associated with a rapid induction of inflammatory cytokines in the serum, including IL-6, IL-10, MCP-1, TNF-alpha, IFN-alpha, and IFN-gamma, and selective increases in the numbers of NK (NK1.1(+)CD11b(+)) cells and Mvarphi (NK1.1(-)CD11b(+)), but not NK T (CD3(+)NK1.1(+)) cells. NK cells were required for the adjuvant effects of poly (I:C). Poly (I:C) treatment in TNF-alpha, type I IFNR, IFN-gamma, IL-6, IL-12Rbeta2, or IL-15 gene-deficient mice revealed a reciprocal interaction and interdependence in the induction of these cytokines, where the absence of one cytokine impacted on the production of others. Further, the adjuvant effects of poly (I:C) were dependent on the endogenous levels of type I IFNs, TNF-alpha, IFN-gamma, IL-12, and IL-15. IFN-alpha and IFN-beta, but not TNF-alpha or IL-6, were able to mimic the adjuvant effects of poly (I:C). We conclude that the adjuvant effects of poly (I:C) on antigen-specific CD8(+) T cells appeared to be exquisitely dependent on the rapid induction of certain beneficial cytokines produced in part by NK cells.

Converting IL-15 to a superagonist by binding to soluble IL-15R{alpha}

IL-15 is normally presented in vivo as a cell-associated cytokine bound to IL-15Ralpha. We show here that the biological activity of soluble IL-15 is much improved after interaction with recombinant soluble IL-15Ralpha; after injection, soluble IL-15/IL-15Ralpha complexes rapidly induce strong and selective expansion of memory-phenotype CD8(+) cells and natural killer cells. These findings imply that binding of IL-15Ralpha to IL-15 may create a conformational change that potentiates IL-15 recognition by the betagamma(c) receptor on T cells. The enhancing effect of IL-15Ralpha binding may explain why IL-15 normally functions as a cell-associated cytokine. Significantly, the results with IL-2, a soluble cytokine, are quite different; thus, IL-2 function is markedly inhibited by binding to soluble IL-2Ralpha.

The interleukin-15/interleukin-15 receptor system as a model for juxtacrine and reverse signaling

Interleukin-15 (IL-15) is a pleiotropic cytokine of the 4 alpha-helix bundle family, which binds to a receptor complex that displays common elements with the IL-2 receptor and a unique high-affinity alpha chain. This review focuses on juxtacrine and reverse signaling levels in the IL-15/IL-15R system. Specifically, we discuss how agonistic stimulation of membrane-bound IL-15 induces phosphorylation of members of the MAP kinase family and of focal adhesion kinase (FAK), thereby upregulating processes including cytokine secretion, cell adhesion and migration. In addition, we explore IL-15 trans-presentation and intracellular signaling, and define promising molecular targets for future pharmacological intervention in infectious diseases and immunological disorders. These frontiers in IL-15/IL-15Ralpha research serve as highly instructive examples for key concepts, unsolved problems and therapeutic opportunities in juxtacrine and reverse signaling in general.

CpG-C ISS-ODN activation of blood-derived B cells from healthy and chronic immunodeficiency virus-infected macaques

Cytosine-phosphate-guanine class C (CpG-C) immunostimulatory sequence oligodeoxynucleotides (ISS-ODNs) activate human B cells and dendritic cells (DCs), properties that suggest potential use as a novel adjuvant to enhance vaccine efficacy. After demonstrating that the CpG-C ISS-ODN C274 activates macaque DCs, we examined in vitro activation of macaque B cells by C274 as a prelude to evaluation of this molecule as an adjuvant in the testing of candidate human immunodeficiency virus vaccines in the rhesus macaque-simian immunodeficiency virus (SIV) model. C274 induced macaque CD20(+) B cells to proliferate more strongly than CD40 ligand or CpG-B ISS-ODN. C274 enhanced B cell survival; increased viability was most evident after 3-7 days of culture. Increased expression of CD40, CD80, and CD86 by B cells was apparent within 24 h of exposure to C274 and persisted for up to 1 week. C274-stimulated, B cell-enriched and peripheral blood mononuclear cell suspensions from naïve and immunodeficiency virus-infected monkeys secreted several cytokines [e.g., interleukin (IL)-3, IL-6, IL-12, interferon-alpha] and chemokines [e.g., monocyte chemoattractant protein-1/CC chemokine ligand 2 (CCL2), macrophage-inflammatory protein-1alpha/CCL3, IL-8/CXC chemokine ligand 8]. In comparison, exposure of macaque B cells to SIV had minimal impact on surface phenotype, despite inducing cytokine and chemokine production in cells from infected and uninfected animals. These observations emphasize the need to identify strategies to optimally boost immune function, as immunodeficiency viruses themselves only partially activate B cells and DCs. The ability of C274 to stimulate B cells and DCs in healthy and infected monkeys suggests its possible use as a broad-acting adjuvant to be applied in the rhesus macaque model for the development of preventative and therapeutic vaccines.

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.

Direct Stimulation of T Cells by Type I IFN Enhances the CD8+T Cell Response during Cross-Priming

Type I IFN (IFN-alphabeta), which is produced rapidly in response to infection, plays a key role in innate immunity and also acts as a stimulus for the adaptive immune response. We have investigated how IFN-alphabeta induces cross-priming, comparing CD8+ T cell responses generated against soluble protein Ags in the presence or absence of IFN-alphabeta. Injection of IFN-alpha was found to prolong the proliferation and expansion of Ag-specific CD8+ T cells, which was associated with marked up-regulation of IL-2 and IL-15 receptors on Ag-specific cells and expression of IL-15 in the draining lymph node. Surprisingly, neither IL-2 nor IL-15 was required for IFN-alpha-induced cross-priming. Conversely, expression of the IFN-alphabetaR by T cells was shown to be necessary for effective stimulation of the response by IFN-alpha. The finding that T cells represent direct targets of IFN-alphabeta-mediated stimulation reveals an additional mechanism by which the innate response to infection promotes adaptive immunity.

Importance of signaling via the IFN-alpha/beta receptor on host cells for the realization of the therapeutic benefits of cyclophosphamide for mice bearing a large MOPC-315 tumor

Here we show that low-dose cyclophosphamide (CY), that depends for its therapeutic effectiveness on the immunopotentiating activity of the drug for T cell-mediated tumor-eradicating immunity, is curative for approximately 80% of wild-type (WT) mice bearing a large s.c. MOPC-315 tumor, but only for approximately 10% of IFN-alpha/betaR-/- mice bearing a large s.c. MOPC-315 tumor. Histopathological examination of the s.c. tumors of such mice on day 4 after the chemotherapy revealed that the low dose of CY led to accumulation of T lymphocytes in both the WT and the IFN-alpha/betaR-/- mice. However, in the CY treated tumor bearing WT mice the T lymphocytes were present throughout the tumor mass and in direct contact with tumor cells, but in the CY treated tumor bearing IFN-alpha/betaR-/- mice most of the T lymphocytes remained in blood vessels. In addition to being important for CY-induced transendothelial migration of T lymphocytes into the tumor mass, we show here that signaling via the IFN-alpha/betaR is also important for CY-induced control of metastatic tumor progression in the spleen and liver of the tumor bearing mice. Finally, CY cured tumor bearing WT mice were resistant to a subsequent challenge with MOPC-315 tumor cells, but the few CY cured tumor bearing IFN-alpha/betaR-/- mice were not. Thus, signaling via the IFN-alpha/betaR on host cells in MOPC-315 tumor bearers is important for CY-induced: (a) transendothelial migration of T lymphocytes into the tumor mass and the eradication of the primary tumor, (b) control of metastatic tumor progression, and (c) resistance to a subsequent tumor challenge.

Interferon-alpha/beta upregulate IL-15 expression in vitro and in vivo: analysis in human hepatocellular carcinoma cell lines and in chronic hepatitis C patients during interferon-alpha/beta treatment

Type I interferon (IFN) possesses antiviral and antitumor activities and also having an immune regulatory effect, activating cellular immune response and upregulating several cytokines. Recent study has shown that type I IFN upregurates the dendritic cell production of IL-15 capable of activating natural killer cells and CD8+ memory T lymphocytes. However, it is still unknown if type I IFN induces IL-15 production in non-immune cells and if type I IFN affects IL-15 production in vivo. The present study investigated the effect of type I IFNs on IL-15 expression in hepatocellular carcinoma (HCC) cell lines in vitro and in patients with chronic hepatitis C in vivo. When three HCC cell lines, Huh7, HepG2, and JHH4 were cultured in vitro, IFN upregulation of IL-15 expression was observed at both the mRNA and protein levels. In experiments using Huh7 cells, upregulation of IL-15 expression occurred within 24 h of the start of IFN stimulation, and both IFN-alpha and -beta dose-dependently increased IL-15 production in the range from 100 U/ml to 10,000 U/ml of concentration. IFN-beta showed stronger activity in IL-15 production induction in vitro than IFN-alpha. For in vivo examination, sera were obtained from 21 chronic hepatitis C patients treated with IFN and 29 healthy individuals, and the serum IL-15 level was quantified by ELISA. The serum IL-15 level of chronic hepatitis C patients before IFN treatment was similar to that of the healthy controls and significantly increased only during the IFN administration period. These results confirm that IFN-alpha/beta induce IL-15 production and also suggest that IL-15 may be associated with type I IFN-induced immune response.

Two interleukin (IL)-15 homologues in fish from two distinct origins

Here, we report two distinct genes in teleosts that are homologous to interleukin (IL)-15. The two genes, isolated from fugu (Takifugu rubripes), resemble to mammalian IL-15 but differ from IL-2 and IL-21 in their amino acid sequences, the possessing of an extraordinary long signal peptide and more widespread tissue localization. In addition, multiple out-of-frame AUG codons, the negative translational regulators of mammalian IL-15 genes were also detected in the 5'-UTR of the two genes. Fugu IL-15 homologues also contain four conserved cysteines allowing the formation of two disulfide bridges along with four predicted alpha-helices. Genomic analysis showed that one of the fugu IL-15 homologues possessed six coding exons and exhibited a similar exon-intron organization and synteny structure to that of mammalian and chicken IL-15 genes. Conversely, the other fugu IL-15 homologue possesses four exons and exhibits a different synteny structure with that of IL-15, suggesting that the two genes were derived from two different origins. Moreover, the two genes also differ from each other in tissue localizations and in their expression in response to mitogens. The existence of these two IL-15 homologues in telesots was further supported by their characterization in zebrafish Danio rerio, and the green-spotted pufferfish Tetraodon nigroviridis. The discovery of two distinct IL-15 homologues in fish will assist investigations into the evolution of these genes and their relative contribution to the fish immune system.

An indispensable role of type-1 IFNs for inducing CTL-mediated complete eradication of established tumor tissue by CpG-liposome co-encapsulated with model tumor antigen

We have evaluated the capacity of a novel, nanoparticle-based tumor vaccine to eradicate established tumors in mice. C57BL/6 mice were intradermally (i.d.) inoculated with ovalbumin (OVA)-expressing EG-7 tumor cells. When the tumor size reached 7-8 mm, the tumor-bearing mice were i.d. injected near the tumor-draining lymph node (DLN) with liposomes encapsulated with unmethylated cytosine-phosphorothioate-guanine containing oligodeoxynucleotides (CpG-ODN) (CpG-liposomes) co-encapsulated with OVA. This vaccination protocol markedly prevented the growth of the established tumor mass and approximately 50% of tumor-bearing mice became completely cured. Tumor eradication correlated with the generation of OVA/H-2K(b)-tetramer(+) CTLs in the tumor DLN and at the tumor site with specific cytotoxicity toward EG-7 cells. Interestingly, tetramer(+) CTLs failed to be induced in lymph node-deficient Aly/Aly mice. Thus, tetramer(+) CTLs appeared to be generated in the tumor DLN and subsequently migrated into the tumor site. In vivo antibody blocking experiments revealed that CD8(+) T cells, but not CD4(+) T, NK or NKT cells, were the major effector cells mediating tumor eradication. CTL induction was also inhibited when vaccinated tumor-bearing mice were treated with both anti-IFN-alpha and anti-IFN-beta mAbs but not with anti-IFN-alpha or anti-IFN-beta mAb alone. Neither IFN-gamma(-/-) nor IL-12(-/-) mice showed impaired induction of tetramer(+) CTLs. Thus, these findings revealed that CpG-ODN-induced IFN-alpha/beta, but not IL-12 or IFN-gamma, is critical for the generation of tumor-specific CTLs in response to vaccination. These results highlight the potential utility of CpG-liposomes co-encapsulated with protein tumor antigens as therapeutic vaccines in cancer patients.

Interferon-alpha2a is sufficient for promoting dendritic cell immunogenicity

Type I interferons (IFNs) are widely used therapeutically. IFN-alpha2a in particular is used as an antiviral agent, but its immunomodulatory properties are poorly understood. Dendritic cells (DCs) are the only antigen-presenting cells able to prime naive T cells and therefore play a crucial role in initiating the adaptive phase of the immune response. We studied the effects of IFN-alpha2a on DC maturation and its role in determining Th1/Th2 equilibrium. We found that IFN-alpha2a induced phenotypic maturation of DCs and increased their allostimulatory capacity. When dendritic cells were stimulated simultaneously by CD40 ligation and IFN-alpha2a, the production of interleukin (IL)-10 and IL-12 was increased. In contrast, lipopolysaccharide (LPS) stimulation in the presence of IFN-alpha2a mainly induced IL-10 release. The production of IFN-gamma and IL-5 by the responder naive T cells was also amplified in response to IFN-alpha2a-treated DCs. Furthermore, IL-12 production by IFN-alpha2a-treated DCs was enhanced further in the presence of anti-IL-10 antibody. Different results were obtained when DCs were treated simultaneously with IFN-alpha2a and other maturation factors, in particular LPS, and then stimulated by CD40 ligation 36 h later. Under these circumstances, IFN-alpha2a did not modify the DC phenotype, and the production of IL-10/IL-12 and IFN-gamma/IL-5 by DCs and by DC-stimulated naive T cells, respectively, was inhibited compared to the effects on DCs treated with maturation factors alone. Altogether, this work suggests that IFN-alpha2a in isolation is sufficient to promote DC activation, however, other concomitant events, such as exposure to LPS during a bacterial infection, can inhibit its effects. These results clarify some of the in vivo findings obtained with IFN-alpha2a and have direct implications for the design of IFN-alpha-based vaccines for immunotherapy.

IL-15 and IL-15R in leucocytes from patients with systemic lupus erythematosus

OBJECTIVE

To assess the functional status of the IL-15/IL-15Ralpha cytokine system in different leucocyte subsets from patients with systemic lupus erythematosus (SLE).

METHODS

Eighteen patients with SLE (10 with inactive and eight with active disease) and 14 healthy individuals were studied. Serum levels and in vitro production of IL-15 were determined. In addition, the expression of IL-15 receptor alpha (IL-15Ralpha) and membrane-bound IL-15 was assessed and the in vitro effects of IL-15 on CD69 and CD64 expression, interferon-gamma and TNF-alpha synthesis, respiratory burst induction and apoptosis were studied.

RESULTS

Serum levels of IL-15 were significantly increased in inactive and active patients with SLE. Accordingly, the in vitro synthesis and release of IL-15 by monocytes in response to IFN-gamma+lipopolysaccharide was significantly enhanced in SLE patients with active disease, as was the percentage of membrane-bound IL-15+ monocytes. On the other hand, enhanced basal expression of IL-15Ralpha was detected in leucocytes from SLE patients, with defective induction upon stimulation with phytohaemagglutinin or phorbol myristate acetate/ionomycin. Furthermore, diminished induction of CD69 expression and interferon-gamma and TNF-alpha synthesis by recombinant human IL-15 was detected in peripheral blood mononuclear cells from SLE, and there was defective induction of CD64 and priming for respiratory burst in neutrophils. The anti-apoptotic effect of IL-15 was diminished in leucocytes from SLE patients.

CONCLUSION

Our data indicate that there is enhanced synthesis of IL-15 by immune cells from SLE patients, with a poor response to this cytokine by different leucocyte subsets. This abnormal function of IL-15/IL-15Ralpha may contribute significantly to the pathogenesis of SLE.

Restoration by IL-15 of MHC class I antigen-processing machinery in human dendritic cells inhibited by tumor-derived gangliosides

We have recently reported that MHC class I Ag-processing machinery (APM) component expression in dendritic cells (DC) might be down-regulated by tumor cells. However, the tumor-derived factors responsible for inhibition of the APM component expression in DC generated in the tumor microenvironment as well as potential protective mechanism have not yet been investigated. In this article, we demonstrate that expression of several MHC class I APM components, including MB1 (beta5), LMP2, LMP7, LMP10, and ERp57, is significantly down-regulated in human DC generated in the presence of primary oral squamous cell carcinoma cell lines or coincubated with purified gangliosides. Suppression of MHC class I APM component expression in DC generated in the presence of tumor cells was significantly attenuated by the inhibition of glucosyl transferase in tumor cells, suggesting that tumor-induced MHC class I APM component down-regulation in DC was mediated in part by oral squamous cell carcinoma-derived gangliosides. Furthermore, rIL-15 restored both tumor cell-induced and ganglioside-induced MHC class I APM component expression in DC, as well as their ability to present Ags to autologous Ag-specific T cells. These results demonstrate that IL-15 restores MHC class I APM component expression in DC down-regulated by tumor-derived gangliosides.

Shared alterations in NK cell frequency, phenotype, and function in chronic human immunodeficiency virus and hepatitis C virus infections

Human immunodeficiency virus (HIV) and hepatitis C virus (HCV) cause clinically important persistent infections. The effects of virus persistence on innate immunity, including NK cell responses, and the underlying mechanisms are not fully understood. We examined the frequency, phenotype, and function of peripheral blood CD3- CD56+ NK subsets in HIV+ and HCV+ patients and identified significantly reduced numbers of total NK cells and a striking shift in NK subsets, with a marked decrease in the CD56(dim) cell fraction compared to CD56(bright) cells, in both infections. This shift influenced the phenotype and functional capacity (gamma interferon production, killing) of the total NK pool. In addition, abnormalities in the functional capacity of the CD56(dim) NK subset were observed in HIV+ patients. The shared NK alterations were found to be associated with a significant reduction in serum levels of the innate cytokine interleukin 15 (IL-15). In vitro stimulation with IL-15 rescued NK cells of HIV+ and HCV+ patients from apoptosis and enhanced proliferation and functional activity. We hypothesize that the reduced levels of IL-15 present in the serum during HIV and HCV infections might impact NK cell homeostasis, contributing to the common alterations of the NK pool observed in these unrelated infections.