Tonsilar NK Cells Restrict B Cell Transformation by the Epstein-Barr Virus via IFN-��

Cells of the innate immune system act in synergy to provide a first line of defense against pathogens. Here we describe that dendritic cells (DCs), matured with viral products or mimics thereof, including Epstein-Barr virus (EBV), activated natural killer (NK) cells more efficiently than other mature DC preparations. CD56^brightCD16⁻ NK cells, which are enriched in human secondary lymphoid tissues, responded primarily to this DC activation. DCs elicited 50-fold stronger interferon-γ (IFN-γ) secretion from tonsilar NK cells than from peripheral blood NK cells, reaching levels that inhibited B cell transformation by EBV. In fact, 100- to 1,000-fold less tonsilar than peripheral blood NK cells were required to achieve the same protection in vitro, indicating that innate immune control of EBV by NK cells is most efficient at this primary site of EBV infection. The high IFN-γ concentrations, produced by tonsilar NK cells, delayed latent EBV antigen expression, resulting in decreased B cell proliferation during the first week after EBV infection in vitro. These results suggest that NK cell activation by DCs can limit primary EBV infection in tonsils until adaptive immunity establishes immune control of this persistent and oncogenic human pathogen.     

Human dendritic cells respond to Helicobacter pylori, promoting NK cell and Th1-effector responses in vitro

Helicobacter pylori infection leads to chronic gastric inflammation. The current study determined the response of human APCs, NK cells, and T cells toward the bacteria in vitro. Human monocyte-derived dendritic cells (DC) were incubated with bacteria for 48 h. Intact H. pylori at a multitude of infection 5 stimulated the expression of MHC class II (4- to 7-fold), CD80, and CD86 B7 molecules (10- to 12-fold) and the CD83 costimulatory molecule (>30-fold) as well as IL-12 secretion (>50-fold) in DCs, and thereby, strongly induced their maturation and activation. CD56(+)/CD4(-) NK cells, as well as CD4(+)/CD45RA(+) naive T cells, were isolated and incubated with DCs pulsed with intact bacteria or different cellular fractions. Coculture of H. pylori-pulsed DCs with NK cells strongly potentiated the secretion of TNF-alpha and IFN-gamma. Coculture of naive T cells with H. pylori-pulsed DCs significantly enhanced TNF-alpha, IFN-gamma, and IL-2 secretion as well as T-bet mRNA levels, while GATA-3 mRNA was lowered. However, the effect appeared attenuated compared with coculture with Escherichia coli. A greater stimulation was seen with naive T cells and DCs pulsed with H. pylori membrane preparations. Intact H. pylori potently induced the maturation and activation of human monocyte-derived DC and thereby promote NK and Th1 effector responses. The strong activation of NK cells may be important for the innate immune response. Th1-polarized T cells were induced especially by incubation with membrane preparations of H. pylori, suggesting that membrane proteins may account for the specific adaptive immune response.     

Dendritic cells and NK cells stimulate bystander T cell activation in response to TLR agonists through secretion of IFN-alpha beta and IFN-gamma

Recognition of conserved features of infectious agents by innate pathogen receptors plays an important role in initiating the adaptive immune response. We have investigated early changes occurring among T cells after injection of TLR agonists into mice. Widespread, transient phenotypic activation of both naive and memory T cells was observed rapidly after injection of molecules acting through TLR3, -4, -7, and -9, but not TLR2. T cell activation was shown to be mediated by a combination of IFN-alphabeta, secreted by dendritic cells (DCs), and IFN-gamma, secreted by NK cells; notably, IFN-gamma-secreting NK cells expressed CD11c and copurified with DCs. Production of IFN-gamma by NK cells could be stimulated by DCs from TLR agonist-injected mice, and although soluble factors secreted by LPS-stimulated DCs were sufficient to induce IFN-gamma, maximal IFN-gamma production required both direct contact of NK cells with DCs and DC-secreted cytokines. In vitro, IFN-alphabeta, IL-18, and IL-12 all contributed to DC stimulation of NK cell IFN-gamma, whereas IFN-alphabeta was shown to be important for induction of T cell bystander activation and NK cell IFN-gamma production in vivo. The results delineate a pathway involving innate immune mediators through which TLR agonists trigger bystander activation of T cells.     

Mononuclear phagocyte-derived IL-10 suppresses the innate IL-12/IFN-gamma axis in lung-challenged aged mice

Previously, we reported that IL-10-producing mononuclear phagocytes increase in lungs of aged mice, causing impaired innate cytokine expression. Since dendritic cells (DCs) contribute to innate NK cell and adaptive T cell immunity, we tested the hypothesis that age-related IL-10 might influence DC function with effects on NK and T cell activation. The results showed that DC recruitment to sites of lung inflammation was normal in aged mice (>20 mo). However, IFN-gamma-producing NK cells in LPS-challenged lungs were decreased in aged as compared with young mice, which was associated with increased IL-10(+)CD11b(+)Gr-1(low)CD11c(-) cells consistent with mononuclear phagocytes. In vivo or in vitro blockade of IL-10 signaling restored IFN-gamma-producing NK cells. This restoration was reversed by IL-12 neutralization, indicating that IL-10 suppressed sources of IL-12 in aged mice. To probe DC function in adaptive immunity, we transferred young naive OVA-specific TCR transgenic T cells to old mice. Following challenge with OVA plus LPS, Ag presentation in the context of MHC-I and MHC-II occurred with similar kinetics and intensity in draining lymph nodes of young and old recipients as measured by proliferation. Despite this, aged hosts displayed impaired induction of IFN-gamma(+)CD4(+), but not IFN-gamma(+)CD8(+), effector T cells. Blockade of IL-10 signaling reversed age-associated defects. These studies indicate that the innate IL-12/IFN-gamma axis is not intrinsically defective in lungs of aged mice, but is rather suppressed by enhanced production of mononuclear phagocyte-derived IL-10. Our data identify a novel mechanism of age-associated immune deficiency.     

Early responding dendritic cells direct the local NK response to control herpes simplex virus 1 infection within the cornea

Dendritic cells (DCs) regulate both innate and adaptive immune responses. In this article, we exploit the unique avascularity of the cornea to examine a role for local or very early infiltrating DCs in regulating the migration of blood-derived innate immune cells toward HSV-1 lesions. A single systemic diphtheria toxin treatment 2 d before HSV-1 corneal infection transiently depleted CD11c(+) DCs from both the cornea and lymphoid organs of CD11c-DTR bone marrow chimeric mice for up to 24 h postinfection. Transient DC depletion significantly delayed HSV-1 clearance from the cornea through 6 d postinfection. No further compromise of viral clearance was observed when DCs were continuously depleted throughout the first week of infection. DC depletion did not influence extravasation of NK cells, inflammatory monocytes, or neutrophils into the peripheral cornea, but it did significantly reduce migration of NK cells and inflammatory monocytes, but not neutrophils, toward the HSV-1 lesion in the central cornea. Depletion of NK cells resulted in similar loss of viral control to transient DC ablation. Our findings demonstrate that resident corneal DCs and/or those that infiltrate the cornea during the first 24 h after HSV-1 infection contribute to the migration of NK cells and inflammatory monocytes into the central cornea, and are consistent with a role for NK cells and possibly inflammatory monocytes, but not polymorphonuclear neutrophils, in clearing HSV-1 from the infected cornea.     

Prostaglandin D2 inhibits the production of IFN-gamma by invariant NK T cells: consequences in the control of B16 melanoma

Invariant NK T (iNKT) cells are a subset of innate/memory lymphocytes that recognize lipid Ags presented by CD1d-expressing APCs such as dendritic cells (DCs). Upon primary stimulation through their TCR, iNKT cells promptly produce large amounts of IFN-gamma and/or IL-4 that play critical roles in the regulation of innate and adaptive immune responses. To date, the role of environmental factors on iNKT cell functions has been poorly investigated. In this study, we addressed the question of whether PGD2, a potent eicosanoid lipid mediator involved in immune responses and inflammation, could be important in DC/iNKT cell cross-talk. We show that PGD2 dramatically reduced the production of IFN-gamma, but not IL-4, by iNKT cells in response to the superagonist alpha-galactosylceramide (alpha-GalCer) both in vitro and in vivo. This effect is mediated by the D prostanoid receptor 1 (DP1) expressed by DCs and iNKT cells and requires protein kinase A activation. We also report that PGD2 and BW245C (a selective DP1 agonist) reduce the protective effects of alpha-GalCer in B16F10-induced melanoma metastasis, an effect that depends on IFN-gamma production by iNKT cells. As a whole, these data reveal novel pathways regulating iNKT cell biologic functions and confirm the immunoregulatory roles of PGD2 on the innate response.     

Immature human dendritic cells infected with Leishmania infantum are resistant to NK-mediated cytolysis but are efficiently recognized by NKT cells

Dendritic cells (DC) play an important role in innate and adaptive immunity, interacting with T cells, NK, and NKT cells. A critical step in the interaction of the parasitic protozoa Leishmania with their host is the evasion of both innate and adaptive immunity, producing a long-lasting chronic infection. There is growing evidence that these parasites can modify the Ag-presenting and immunoregulatory functions of DCs. The cells and mechanisms involved in innate immune response against Leishmania are still poorly understood. In this study, we investigated how Leishmania infantum infection affects DC interactions with NK and invariant NKT (iNKTs) cells in humans. We found that infected immature DCs (iDCs) do not up-regulate HLA class I molecules. Despite this, iDCs become resistant to killing mediated by autologous NK cells due to the up-regulation of HLA-E expression, which protects target cells from NK-mediated lysis through interaction with the inhibitory receptor CD94/NKG2A. Furthermore, iDCs infected with L. infantum up-regulate CD1d cell surface expression and consequently can be efficiently recognized and killed by iNKT cells that produce IFN-gamma. These data suggest that L. infantum could be able to evade NK recognition; in contrast, iNKTs may play an important role in the immune response against Leishmania.     

Dendritic cells in innate immune responses against HIV

Dendritic cells (DCs) were recently found to be innate immunity effectors against tumoral cells and viruses. (i) In response to most viruses, including HIV, plasmacytoid DCs are responsible for most of the type I IFN secretion, which is strongly anti-viral and induces TH1 type responses. Myeloid DCs secrete IL-12, which is also important for TH1-type and cytotoxic responses. In HIV patient blood, both DC population numbers decrease as early as the primary stage. Plasmacytoid DC numbers correlate with type I IFN secretion, which is a prognosis predictor, particularly under treatment. IL-12 secretion is also defective. Immunotherapies to replace the defective cytokines or to restore a potentially defective DC-T lymphocyte feed-back might help patients restore their immune responses under antiviral therapy. (ii) After measles and other viral infections, or incubation with dsRNA, DCs become cytotoxic and consequently exhibit natural killer function, through upregulation of type I IFN secretion which enhances TRAIL expression. In HIV infection, this mechanism was not demonstrated yet, but it might a) be responsible for the massive apoptosis of uninfected lymphocytes, and b) increase specific immunity through cross-presentation of antigens from infected cells killed by DCs. (iii) DCs direct expansion and effector functions of NK cells in the absence of adaptive-type cytokines and modulate NKT cell IFN-gamma production. Reciprocally, NK activation triggers DC maturation. HIV-1 Tat inhibits NK cell cytotoxicity directly and probably through inhibition of IL-12 secretion by DC. Therefore, understanding the functions of DCs in innate immune responses and in pathogenesis will help obtain better HIV replication control.     

NKp30-dependent cytolysis of filovirus-infected human dendritic cells

Understanding how protective innate immune responses are generated is crucial to defeating highly lethal emerging pathogens. Accumulating evidence suggests that potent innate immune responses are tightly linked to control of Ebola and Marburg filoviral infections. Here, we report that unlike authentic or inactivated Ebola and Marburg, filovirus-derived virus-like particles directly activated human natural killer (NK) cells in vitro, evidenced by pro-inflammatory cytokine production and enhanced cytolysis of permissive target cells. Further, we observed perforin- and CD95L-mediated cytolysis of filovirus-infected human dendritic cells (DCs), primary targets of filovirus infection, by autologous NK cells. Gene expression knock-down studies directly linked NK cell lysis of infected DCs to upregulation of the natural cytotoxicity receptor, NKp30. These results are the first to propose a role for NK cells in the clearance of infected DCs and the potential involvement of NKp30-mediated cytolysis in control of viral infection in vivo. Further elucidation of the biology of NK cell activation, specifically natural cytotoxicity receptors like NKp30 and NKp46, promises to aid our understanding of microbial pathology.     

Inhibition of myeloid dendritic cell accessory cell function and induction of T cell anergy by alcohol correlates with decreased IL-12 production

Alcohol consumption inhibits accessory cell function and Ag-specific T cell responses. Myeloid dendritic cells (DCs) coordinate innate immune responses and T cell activation. In this report, we found that in vivo moderate alcohol intake (0.8 g/kg of body weight) in normal volunteers inhibited DC allostimulatory capacity. Furthermore, in vitro alcohol treatment during DC differentiation significantly reduced allostimulatory activity in a MLR using naive CD4(+) T cells, and inhibited tetanus toxoid Ag presentation by DCs. Alcohol-treated DCs showed reduced IL-12, increased IL-10 production, and a decrease in expression of the costimulatory molecules CD80 and CD86. Addition of exogenous IL-12 and IL-2, but not neutralization of IL-10, during MLR ameliorated the reduced allostimulatory capacity of alcohol-treated DCs. Naive CD4(+) T cells primed with alcohol-treated DCs showed decreased IFN-gamma production that was restored by exogenous IL-12, indicating inhibition of Th1 responses. Furthermore, CD4(+) T cells primed with alcohol-treated DCs were hyporesponsive to subsequent stimulation with the same donor-derived normal DCs, suggesting the ability of alcohol-treated DCs to induce T cell anergy. LPS-induced maturation of alcohol-treated immature DCs partially restored the reduced allostimulatory activity, whereas alcohol given only during DC maturation failed to inhibit DC functions, suggesting that alcohol primarily impairs DC differentiation rather than maturation. NFkappaB activation, a marker of DC maturation was not affected by alcohol. Taken together, alcohol both in vitro and in vivo can impair generation of Th1 immune responses via inhibition of DC differentiation and accessory cell function through mechanisms that involve decreased IL-12 induction.     

Distinctive lack of CD48 expression in subsets of human dendritic cells tunes NK cell activation

CD48 is a glycosyl phosphatidylinositol anchor protein known to be virtually expressed by all human leukocytes. Its ligand, 2B4, is a signaling lymphocyte activation molecule-related receptor involved in NK cell activation. Because dendritic cells (DCs) are strong inducers of NK cell functions, we analyzed the expression of CD48 in different human DC subsets. We observed that monocytes differentiating in DCs promptly down-regulate CD48. Similarly, DCs isolated from inflamed lymph nodes generally do not express CD48. Plasmocytoid DCs do not express CD48 either, whereas myeloid DCs harbored in blood, bone marrow, and thymus express it. In addition, we showed that CD48 expression in DCs affects NK cell functions during NK/DC cross-talk, because NK cells obtained from normal donors and from X-linked lymphoproliferative disease patients are, respectively, triggered or inhibited by DCs expressing surface CD48. Remarkably, IFN-gamma production by lymph node NK cells, in contrast to blood NK cells, can be negatively modulated by 2B4/CD48 interactions, indicating a 2B4 inhibitory pathway in lymph node NK cells. Therefore, the CD48 deficiency of DCs harbored in inflamed lymph nodes that we report in this study might be relevant to successfully activate lymph node NK cells in the early phase of the immune response. Our results show that distinct subsets of human DCs, differently from all other mononuclear hemopoietic cells, specifically do not express CD48. Moreover, the expression of CD48 depends on the anatomic location of DCs and might be related to the tissue-specific 2B4 function (activating or inhibitory) of the NK cells with which they interact.     

Primary immune responses by cord blood CD4(+) T cells and NK cells inhibit Epstein-Barr virus B-cell transformation in vitro

Epstein-Barr virus (EBV) transformation of B cells from fetal cord blood in vitro varies depending on the individual sample. When a single preparation of EBV was simultaneously used to transform fetal cord blood samples from six different individuals, the virus transformation titer varied from less than zero to 10(5.9). We show that this variation in EBV transformation is associated with a marked primary immune response in cord blood samples predominately involving CD4(+) T cells and CD16(+) CD56(+) NK cells. After virus challenge both CD4(+) T cells and NK cells in fetal cord blood cultures expressed the lymphocyte activation marker CD69. The cytotoxic response against autologous EBV-infected lymphoblastoid cell line (LCL) targets correlated with the number of CD16(+) CD69(+) cells and was inversely correlated with the virus transformation titer. Although NK activity was detected in fresh cord blood and increased following activation by the virus, killing of autologous LCLs was detected only following activation by exposure to the virus. Both activated CD4(+) T cells and CD16(+) NK cells were independently able to kill autologous LCLs. Both interleukin-2 and gamma interferon were produced by CD4(+) T cells after virus challenge. The titer of EBV was lower when purified B cells were used than when whole cord blood was used. Addition of monocytes restored the virus titer, while addition of resting T cells or EBV-activated CD4(+) T-cell blasts reduced the virus titer. We conclude that there are primary NK-cell and Th1-type CD4(+) T-cell responses to EBV in fetal cord blood that limit the expansion of EBV-infected cells and in some cases eliminate virus infection in vitro.     

Activating immunity in the liver. II. IFN-beta attenuates NK cell-dependent liver injury triggered by liver NKT cell activation

Dendritic cell (DC)-dependent activation of liver NKT cells triggered by a single i.v. injection of a low dose (10-100 ng/mouse) of alpha-galactosyl ceramide (alphaGalCer) into mice induces liver injury. This response is particularly evident in HBs-tg B6 mice that express a transgene-encoded hepatitis B surface Ag in the liver. Liver injury following alphaGalCer injection is suppressed in mice depleted of NK cells, indicating that NK cells play a role in NK T cell-initiated liver injury. In vitro, liver NKT cells provide a CD80/86-dependent signal to alphaGalCer-pulsed liver DC to release IL-12 p70 that stimulates the IFN-gamma response of NKT and NK cells. Adoptive transfer of NKT cell-activated liver DC into the liver of nontreated, normal (immunocompetent), or immunodeficient (RAG(-/-) or HBs-tg/RAG(-/-)) hosts via the portal vein elicited IFN-gamma responses of liver NK cells in situ. IFN-beta down-regulates the pathogenic IL-12/IFN-gamma cytokine cascade triggered by NKT cell/DC/NK cell interactions in the liver. Pretreating liver DC in vitro with IFN-beta suppressed their IL-12 (but not IL-10) release in response to CD40 ligation or specific (alphaGalCer-dependent) interaction with liver NKT cells and down-regulated the IFN-gamma response of the specifically activated liver NKT cells. In vivo, IFN-beta attenuated the NKT cell-triggered induction of liver immunopathology. This study identifies interacting subsets of the hepatic innate immune system (and cytokines that up- and down-regulate these interactions) activated early in immune-mediated liver pathology.     

Natural killer cells and dendritic cells: rendezvous in abused tissues

Natural killer (NK) cells and dendritic cells (DCs) are two types of specialized cell of the innate immune system, the reciprocal interaction of which results in a potent, activating cross-talk. For example, DCs can prime resting NK cells, which, in turn, after activation, might induce DC maturation. However, NK cells negatively regulate the function of DCs also by killing immature DCs in peripheral tissues. Moreover, a subset of NK cells, after migration to secondary lymphoid tissues, might have a role in the editing of mature DCs based on the selective killing of mature DCs that do not express optimal surface densities of MHC class I molecules. So, cognate interactions between NK cells and DCs provide a coordinated mechanism that is involved not only in the regulation of innate immunity, but also in the promotion of appropriate downstream adaptive responses for defence against pathogens.     

NKp46 and NKG2D recognition of infected dendritic cells is necessary for NK cell activation in the human response to influenza infection

At an early phase of viral infection, contact and cooperation between dendritic cells (DCs) and NK cells activates innate immunity, and also influences recruitment, when needed, of adaptive immunity. Influenza, an adaptable fast-evolving virus, annually causes acute, widespread infections that challenge the innate and adaptive immunity of humanity. In this study, we dissect and define the molecular mechanisms by which influenza-infected, human DCs activate resting, autologous NK cells. Three events in NK cell activation showed different requirements for soluble mediators made by infected DCs and for signals arising from contact with infected DCs. IFN-alpha was mainly responsible for enhanced NK cytolysis and also important for CD69 up-regulation, whereas IL-12 was necessary for enhancing IFN-gamma production. Increased CD69 expression and IFN-gamma production, but not increased cytolysis, required recognition of influenza-infected DCs by two NK cell receptors: NKG2D and NKp46. Abs specific for these receptors or their known ligands (UL16-binding proteins 1-3 class I-like molecules for NKG2D and influenza hemagglutinin for NKp46) inhibited CD69 expression and IFN-gamma production. Activation of NK cells by influenza-infected DCs and polyinosinic:polycytidylic acid (poly(I:C))-treated DCs was distinguished. Poly(I:C)-treated DCs did not express the UL16-binding protein 3 ligand for NKG2D, and in the absence of the influenza hemagglutinin there was no involvement of NKp46.     

Critical role of MHC class I-related chain A and B expression on IFN-alpha-stimulated dendritic cells in NK cell activation: impairment in chronic hepatitis C virus infection

Dendritic cells (DCs) augment effector functions of NK cells, but the underlying mechanisms are not fully understood. Here we show in an in vitro coculture system that human monocyte-derived DCs enhance IFN-gamma production, CD69 expression, and K562 cytolytic ability of NK cells when DCs are prestimulated with various maturation stimuli such as IFN-alpha or LPS. Of interest is the finding that NK cell activation mediated by LPS-stimulated DCs was dependent on IL-12 produced in DC/NK coculture, but that IFN-alpha-stimulated DC-mediated activation was not. Alternatively, MHC class I-related chain A and B (MICA/B), ligands for NKG2D activating receptor, were found to be induced on DCs upon IFN-alpha stimulation and to be responsible for the NK activation because mAb-mediated masking of MICA/B as well as inhibition of direct cell-to-cell contact using transwell insert completely abolished DC-dependent NK cell activation by IFN-alpha. Finally, DCs recovered from chronic hepatitis C virus-infected patients showed defects in the induction of MICA/B and impaired ability to activate NK cells in response to IFN-alpha stimulation. These findings suggested that MICA/B induction on DCs may be one of the mechanisms by which IFN-alpha activates NK cells; this impairment might affect IFN-alpha responsiveness in hepatitis C virus infection.     

Innate immune response to malaria: rapid induction of IFN-gamma from human NK cells by live Plasmodium falciparum-infected erythrocytes

To determine the potential contribution of innate immune responses to the early proinflammatory cytokine response to Plasmodium falciparum malaria, we have examined the kinetics and cellular sources of IFN-gamma production in response to human PBMC activation by intact, infected RBC (iRBC) or freeze-thaw lysates of P. falciparum schizonts. Infected erythrocytes induce a more rapid and intense IFN-gamma response from malaria-naive PBMC than do P. falciparum schizont lysates correlating with rapid iRBC activation of the CD3(-)CD56(+) NK cell population to produce IFN-gamma. IFN-gamma(+) NK cells are detectable within 6 h of coculture with iRBC, their numbers peaking at 24 h in most donors. There is marked heterogeneity between donors in magnitude of the NK-IFN-gamma response that does not correlate with mitogen- or cytokine-induced NK activation or prior malaria exposure. The NK cell-mediated IFN-gamma response is highly IL-12 dependent and appears to be partially IL-18 dependent. Exogenous rIL-12 or rIL-18 did not augment NK cell IFN-gamma responses, indicating that production of IL-12 and IL-18 is not the limiting factor explaining differences in NK cell reactivity between donors or between live and dead parasites. These data indicate that NK cells may represent an important early source of IFN-gamma, a cytokine that has been implicated in induction of various antiparasitic effector mechanisms. The heterogeneity of this early IFN-gamma response between donors suggests a variation in their ability to mount a rapid proinflammatory cytokine response to malaria infection that may, in turn, influence their innate susceptibility to malaria infection, malaria-related morbidity, or death from malaria.     

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

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

Prolonged antitumor NK cell reactivity elicited by CXCL10-expressing dendritic cells licensed by CD40L+ CD4+ memory T cells

Immunotherapy using dendritic cells (DCs) has the potential to activate both T cells and NK cells. We previously demonstrated the long-lasting antitumor responses by NK cells following immunization with bone marrow-derived DCs. In the current study, we demonstrate that long-term antitumor NK responses require endogenous DCs and a subset of effector memory CD4(+) T (CD4(+) T(EM)) cells. One month after DC immunization, injection of a tumor into DC-immunized mice leads to an increase in the expression of CXCL10 by endogenous DCs, thus directing NK cells into the white pulp where the endogenous DCs bridged CD4(+) T(EM) cells and NK cells. In this interaction, CD4(+) T(EM) cells express CD40L, which matures the endogenous DCs, and produce cytokines, such as IL-2, which activates NK cells. These findings suggest that DC vaccination can sustain long-term innate NK cell immunity but requires the participation of the adaptive immune system.     

CD1d mediates T-cell-dependent resistance to secondary infection with encephalomyocarditis virus (EMCV) in vitro and immune response to EMCV infection in vivo

The innate and adaptive immune responses have evolved distinct strategies for controlling different viral pathogens. Encephalomyocarditis virus (EMCV) is a picornavirus that can cause paralysis, diabetes, and myocarditis within days of infection. The optimal innate immune response against EMCV in vivo requires CD1d. Interaction of antigen-presenting cell CD1d with distinct natural killer T-cell ("NKT") populations can induce rapid gamma interferon (IFN-gamma) production and NK-cell activation. The T-cell response of CD1d-deficient mice (lacking all NKT cells) against acute EMCV infection was further studied in vitro and in vivo. EMCV persisted at higher levels in CD1d-knockout (KO) splenocyte cultures infected in vitro. Furthermore, optimal resistance to repeat cycles of EMCV infection in vitro was also shown to depend on CD1d. However, this was not reflected in the relative levels of NK-cell activation but rather by the responses of both CD4(+) and CD8(+) T-cell populations. Repeated EMCV infection in vitro induced less IFN-gamma and alpha interferon (IFN-alpha) from CD1d-deficient splenocytes than with the wild type. Furthermore, the level of EMCV replication in wild-type splenocytes was markedly and specifically increased by addition of blocking anti-CD1d antibody. Depletion experiments demonstrated that dendritic cells contributed less than the combination of NK and NKT cells to anti-EMCV responses and that none of these cell types was the main source of IFN-alpha. Finally, EMCV infection in vivo produced higher levels of viremia in CD1d-KO mice than in wild-type animals, coupled with significantly less lymphocyte activation and IFN-alpha production. These results point to the existence of a previously unrecognized mechanism of rapid CD1d-dependent stimulation of the antiviral adaptive cellular immune response.