IL‐27 stimulates human NK‐cell effector functions and primes NK cells for IL‐18 responsiveness

IL‐27, a member of the IL‐12 family of cytokines, is produced by APCs, and displays pro‐ and anti‐inflammatory effects. How IL‐27 affects human NK cells still remains unknown. In this study, we observed that mature DCs secreted IL‐27 and that blockade of IL‐27R (CD130) reduced the amount of IFN‐γ produced by NK cells during their coculture, showing the importance of IL‐27 during DC–NK‐cell crosstalk. Accordingly, human rIL‐27 stimulated IFN‐γ secretion by NK cells in a STAT1‐dependent manner, induced upregulation of CD25 and CD69 on NK cells, and displayed a synergistic effect with IL‐18. Preincubation experiments demonstrated that IL‐27 primed NK cells for IL‐18‐induced IFN‐γ secretion, which was associated with an IL‐27‐driven upregulation of T‐bet expression. Also, IL‐27 triggered NKp46‐dependent NK‐cell‐mediated cytotoxicity against Raji, T‐47D, and HCT116 cells, and IL‐18 enhanced this cytotoxic response. Such NK‐cell‐mediated cytotoxicity involved upregulation of perforin, granule exocytosis, and TRAIL‐mediated cytotoxicity but not Fas‐FasL interaction. Moreover, IL‐27 also potentiated Ab‐dependent cell‐mediated cytotoxicity against mAb‐coated target cells. Taken together, IL‐27 stimulates NK‐cell effector functions, which might be relevant in different physiological and pathological situations.     

Inhibitory effects of suplatast tosilate on the differentiation and function of monocyte-derived dendritic cells from patients with asthma

Background Dendritic cells (DCs) are antigen‐presenting cells that efficiently activate T cells. Objective We examined the effects of suplatast tosilate, which prevents T‐helper type 2 responses, on the differentiation and function of monocyte‐derived DCs (moDCs). Methods DCs were differentiated in vitro from peripheral monocytes from patients with asthma by the addition of granulocyte macrophage colony‐stimulating factor and IL‐4 in the presence or absence of suplatast tosilate. Cell surface molecules (CD1a, CD14, CD80, CD83, CD86, HLA‐DR) on immature and mature DCs were analysed with flow cytometry, and the secretion of CC chemokine ligand (CCL)17 (thymus and activation‐regulated chemokine), IL‐12p70, IL‐12p40, and IL‐10 was measured with an ELISA. We also studied the proliferative responses of allogeneic CD4⁺ T cells from healthy subjects to DCs differentiated in the presence of suplatast tosilate. In addition, the production of IFN‐γ and IL‐5 by CD4⁺ T cells after coculture with untreated DCs or suplatast tosilate‐treated DCs was measured with ELISA. Results Suplatast tosilate significantly inhibited the expression of CD1a, CD80, and CD86 on immature DCs and of CD1a, CD80, CD83, and CD86 on mature DCs. Suplatast tosilate also significantly inhibited the secretion of CCL17, IL‐12p70, and IL‐12p40; however, the secretion of IL‐10 was not affected. The proliferative responses of allogeneic CD4⁺ T cells to suplatast tosilate‐treated DCs were suppressed. Moreover, suplatast tosilate‐treated DCs had an impaired capacity to stimulate CD4⁺ T cells to produce IFN‐γ and IL‐5. Conclusion Suplatast tosilate inhibits the differentiation, maturation, and function of moDCs.     

Hypoxia modulates phenotype,inflammatory response,and leishmanial infection of human dendritic cells

Bosseto MC, Palma PVB, Covas DT, Giorgio S. Hypoxia modulates phenotype, inflammatory response, and leishmanial infection of human dendritic cells. APMIS 2010; 118: 108–14. Development of hypoxic areas occurs during infectious and inflammatory processes and dendritic cells (DCs) are involved in both innate and adaptive immunity in diseased tissues. Our group previously reported that macrophages exposed to hypoxia were infected with the intracellular parasite Leishmania amazonensis, but showed reduced susceptibility to the parasite. This study shows that although hypoxia did not alter human DC viability, it significantly altered phenotypic and functional characteristics. The expression of CD1a, CD80, and CD86 was significantly reduced in DCs exposed to hypoxia, whereas CD11c, CD14, CD123, CD49 and HLA‐DR expression remained unaltered in DCs cultured in hypoxia or normoxia. DC secretion of IL‐12p70, the bioactive interleukin‐12 (IL‐12), a cytokine produced in response to inflammatory mediators, was enhanced under hypoxia. In addition, phagocytic activity (Leishmania uptake) was not impaired under hypoxia, although this microenviroment induced infected DCs to reduce parasite survival, consequently controlling the infection rate. All these data support the notion that a hypoxic microenvironment promotes selective pressure on DCs to assume a phenotype characterized by pro‐inflammatory and microbial activities in injured or inflamed tissues and contribute to the innate immune response.     

Ebola and Marburg virus-like particles activate human myeloid dendritic cells

The filoviruses, Ebola (EBOV) and Marburg (MARV), are potential global health threats, which cause deadly hemorrhagic fevers. Although both EBOV and MARV logarithmically replicate in dendritic cells (DCs), these viruses do not elicit DC cytokine secretion and fail to activate and mature infected DCs. Here, we employed virus-like particles (VLPs) of EBOV and MARV to investigate whether these genome-free particles maintain similar immune evasive properties as authentic filoviruses. Confocal microscopy indicated that human myeloid-derived DCs readily took up VLPs. However, unlike EBOV and MARV, VLPs induced maturation of DCs including upregulation of costimulatory molecules (CD40, CD80, CD86), major histocompatibility complex (MHC) class I and II surface antigens, and the late DC maturation marker CD83. The chemokine receptors CCR5 and CCR7 were also modulated on VLP-stimulated DCs, indicating that DC could migrate following VLP exposure. Furthermore, VLPs also elicited DC secretion of the pro-inflammatory cytokines TNF-alpha, IL-8, IL-6, and MIP-1alpha. Most significantly, in stark contrast to DC treated with intact EBOV or MARV, DC stimulated with EBOV or MARV VLPs showed enhanced ability to support human T-cell proliferation in an allogenic mixed lymphocyte response (MLR). Thus, our findings suggest that unlike EBOV and MARV, VLPs are effective stimulators of DCs and have potential in enhancing innate and adaptive immune responses.     

Asthma: The importance of dysregulated barrier immunity

Chronic asthma is an inflammatory disease of the airway wall that leads to bronchial smooth muscle hyperreactivity and airway obstruction, caused by inflammation, goblet cell metaplasia, and airway wall remodeling. In response to allergen presentation by airway DCs, T‐helper lymphocytes of the adaptive immune system control many aspects of the disease through secretion of IL‐4, IL‐5, IL‐13, IL‐17, and IL‐22, and these are counterbalanced by cytokines produced by Treg cells. Many cells of the innate immune system such as mast cells, basophils, neutrophils, eosinophils, and innate lymphoid cells also play an important role in disease pathogenesis. Barrier epithelial cells are being ever more implicated in disease pathogenesis than previously thought, as these cells have in recent years been shown to sense exposure to allergens via pattern recognition receptors and to activate conventional and inflammatory‐type DCs and other innate immune cells through the secretion of thymic stromal lymphopoietin, granulocyte‐macrophage colony stimulating factor, IL‐1, IL‐33, and IL‐25. Understanding this cytokine crosstalk between barrier epithelial cells, DCs, and immune cells provides important insights into the mechanisms of allergic sensitization and asthma progression as discussed in this review.     

Chlamydia pneumoniae and Chlamydia Trachomatis Infection Differentially Modulates Human Dendritic Cell Line (MUTZ) Differentiation and Activation

Chlamydia trachomatis and Chlamydia pneumoniae are important human pathogens that infect the urogenital/anorectal and respiratory tracts, respectively. Whilst the ability of these bacteria to infect epithelia is well defined, there is also considerable evidence of infection of leucocytes, including dendritic cells (DCs). Using a human dendritic cell line (MUTZ), we demonstrate that the infection and replication of chlamydiae inside DCs is species and serovar specific and that live infection with C. pneumoniae is required to upregulate costimulatory markers CD80, CD83 and human leucocyte antigen (HLA)‐DR on MUTZ cells, as well as induce secretion of interleukin (IL)‐2, IL‐6, IL‐8, IL‐12 (p70), interferon‐gamma and tumour necrosis factor‐alpha Conversely, C. trachomatis serovar D failed to upregulate DC costimulatory markers, but did induce secretion of high concentrations of IL‐8. Interestingly, we also observed that infection of MUTZ cells with C. pneumoniae or C. trachomatis serovar L2, whilst not replicative, remained infectious and upregulated lymph node migratory marker CCR7 mRNA. Taken together, these data confirm the findings of other groups using primary DCs and demonstrate the utility of MUTZ cells for further studies of chlamydial infection.     

NK cells are primed by ANRS MVAHIV‐infected DCs,via a mechanism involving NKG2D and membrane‐bound IL‐15, to control HIV‐1 infection in CD4+ T cells

Natural killer (NK) cells are the major antiviral effector cell population of the innate immune system. It has been demonstrated that NK‐cell activity can be modulated by the interaction with dendritic cells (DCs). The HIV‐1 vaccine candidate Modified Vaccinia Ankara encoding an HIV polypeptide (MVA_HIV), developed by the French National Agency for Research on AIDS (ANRS), has the ability to prime NK cells to control HIV‐1 infection in DCs. However, whether or not MVA_HIV‐primed NK cells are able to better control HIV‐1 infection in CD4⁺ T cells, and the mechanism underlying the specific priming, remain undetermined. In this study, we show that MVA_HIV‐primed NK cells display a greater capacity to control HIV‐1 infection in autologous CD4⁺ T cells. We also highlight the importance of NKG2D engagement on NK cells and DC‐produced IL‐15 to achieve the anti‐HIV‐1 specific priming, as blockade of either NKG2D or IL‐15 during MVA_HIV‐priming lead to a subsequent decreased control of HIV‐1 infection in autologous CD4⁺ T cells. Furthermore, we show that the decreased control of HIV‐1 infection in CD4⁺ T cells might be due, at least in part, to the decreased expression of membrane‐bound IL‐15 (mbIL‐15) on DCs when NKG2D is blocked during MVA_HIV‐priming of NK cells.     

High Functional CD70 Expression on α‐Type 1‐Polarized Dendritic Cells from Patients with Chronic Lymphocytic Leukaemia

Antigen‐loaded dendritic cells (DCs) used as anticancer vaccine holds promise for therapy, but needs to be optimized. The most frequently described DC vaccine is being matured with a cocktail containing prostaglandin E₂ (PGE₂DC). However, even though PGE₂DCs express both costimulatory and migratory receptors, their IL‐12p70‐prodcution is low, leading to an insufficient Th1 immune response. As an alternative, α‐type‐1 polarized DCs (αDC1s) have shown a superior production of IL‐12p70 and subsequent activation of effector cells. From chronic lymphocytic leukaemia (CLL) patients, αDC1s can be generated to induce a functional Th1‐immune response. Yet, another costimulatory receptor, CD70, appears to be essential for optimal DC function by promotion of T cell survival and function. So far, PGE₂ is suggested as one of the most important factors for the induction of CD70 expression on DCs. Therefore, we wanted to investigate whether αDC1s have the ability to express functional CD70. We found that CD70 expression on αDC1s could be upregulated in the same manner as PGE₂DCs. In an allogeneic mixed leucocyte reaction, we found that antibody‐blocking of CD70 on αDC1s from controls reduced effector cell proliferation although this could not be found when using CLL αDC1s. Nevertheless, CD70‐blocking of αDC1s from both controls and patients with CLL had a negative influence on the production of both IL‐12p70 and the Th1 cytokine IFN‐γ, while the production of the Th2 cytokine IL‐5 was enhanced. Together, this study further suggests that αDC1s should be considered as a suitable candidate for clinical antitumour vaccine strategies in patients with CLL.     

Binding of human papilloma virus L1 virus-like particles to dendritic cells is mediated through heparan sulfates and induces immune activation

Immunization using human papilloma virus (HPV)-L1 virus-like particles (VLPs) induces a robust and effective immune response, which has recently resulted in the implementation of the HPV-L1 VLP vaccination in health programs. However, during infection, HPV can escape immune surveillance leading to latency and disease. Dendritic cells (DCs) induce effective immune responses after vaccination, but might also induce immune modulation during infection. The interaction of HPV-L1 VLPs with mucosal DCs determines the immune response. However, little is known about the receptors on mucosal DC subsets involved in HPV-L1 VLP binding. Therefore, we set out to investigate the interaction of HPV-L1 VLPs with the different mucosal DC subsets; the subepithelial DCs and Langerhans cells (LCs). We observed strong binding of HPV-L1 VLPs to both DCs and LCs. We did not observe an involvement for C-type lectins such as dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) and langerin. The HPV-L1 VLP binding to DCs was mediated through heparan sulfates, since it was abrogated by heparinase-II treatment. The heparan sulfate proteoglycan syndecan-3 binds VLPs and is expressed on both DCs and LCs. Binding of VLPs to DCs, but not to LCs, strongly correlated with the levels of heparan sulfates and syndecan-3, suggesting that syndecan-3 is the main receptor for HPV-L1 VLPs on DCs. VLP interaction with DCs resulted in the up-regulation of co-stimulatory molecules and the production of the cytokines IL-6, IL-8, IL-10 and IL-12p40. Our results support an important role for syndecan-3 as a HPV receptor on DCs, which could be important for both vaccine development and understanding HPV pathogenesis.     

Activation of the aryl hydrocarbon receptor affects activation and function of human monocyte‐derived dendritic cells

Aryl hydrocarbon receptor (AhR) is well known for mediating the toxic effects of dioxin‐containing pollutants, but has also been shown to be involved in the natural regulation of the immune response. In this study, we investigated the effect of AhR activation by its endogenous ligands 6‐formylindolo[3,2‐b]carbazole (FICZ) and 2‐(1′H‐indole‐3′‐carbonyl)‐thiazole‐4‐carboxylic acid methyl ester (ITE) on the differentiation, maturation and function of monocyte‐derived DCs in Behçet's disease (BD) patients. In this study, we showed that AhR activation by FICZ and ITE down‐regulated the expression of co‐stimulatory molecules including human leucocyte antigen D‐related (HLA‐DR), CD80 and CD86, while it had no effect on the expression of CD83 and CD40 on DCs derived from BD patients and normal controls. Lipopolysaccharide (LPS)‐treated dendritic cells (DCs) from active BD patients showed a higher level of interleukin (IL)‐1β, IL‐6, IL‐23 and tumour necrosis factor (TNF)‐α production. FICZ or ITE significantly inhibited the production of IL‐1β, IL‐6, IL‐23 and TNF‐α, but induced IL‐10 production by DCs derived from active BD patients and normal controls. FICZ or ITE‐treated DCs significantly inhibited the T helper type 17 (Th17) and Th1 cell response. Activation of AhR either by FICZ or ITE inhibits DC differentiation, maturation and function. Further studies are needed to investigate whether manipulation of the AhR pathway may be used to treat BD or other autoimmune diseases.     

Binding of human papilloma virus L1 virus-like particles to dendritic cells is mediated through heparan sulfates and induces immune activation

Immunization using human papilloma virus (HPV)-L1 virus-like particles (VLPs) induces a robust and effective immune response, which has recently resulted in the implementation of the HPV-L1 VLP vaccination in health programs. However, during infection, HPV can escape immune surveillance leading to latency and disease. Dendritic cells (DCs) induce effective immune responses after vaccination, but might also induce immune modulation during infection. The interaction of HPV-L1 VLPs with mucosal DCs determines the immune response. However, little is known about the receptors on mucosal DC subsets involved in HPV-L1 VLP binding. Therefore, we set out to investigate the interaction of HPV-L1 VLPs with the different mucosal DC subsets; the subepithelial DCs and Langerhans cells (LCs). We observed strong binding of HPV-L1 VLPs to both DCs and LCs. We did not observe an involvement for C-type lectins such as dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) and langerin. The HPV-L1 VLP binding to DCs was mediated through heparan sulfates, since it was abrogated by heparinase-II treatment. The heparan sulfate proteoglycan syndecan-3 binds VLPs and is expressed on both DCs and LCs. Binding of VLPs to DCs, but not to LCs, strongly correlated with the levels of heparan sulfates and syndecan-3, suggesting that syndecan-3 is the main receptor for HPV-L1 VLPs on DCs. VLP interaction with DCs resulted in the up-regulation of co-stimulatory molecules and the production of the cytokines IL-6, IL-8, IL-10 and IL-12p40. Our results support an important role for syndecan-3 as a HPV receptor on DCs, which could be important for both vaccine development and understanding HPV pathogenesis.     

NK cell‐extrinsic IL‐18 signaling is required for efficient NK‐cell activation by vaccinia virus

NK cells are important for the control of vaccinia virus (VV) in vivo. Recent studies have shown that multiple pathways are required for effective activation of NK cells. These include both TLR‐dependent and ‐independent pathways, as well as the NKG2D activating receptor that recognizes host stress‐induced NKG2D ligands. However, it remains largely unknown what controls the upregulation of NKG2D ligands in response to VV infection. In this study using C57BL/6 mice, we first showed that IL‐18 is critical for NK‐cell activation and viral clearance. We then demonstrated that IL‐18 signaling on both NK cells and DCs is required for efficient NK‐cell activation upon VV infection in vitro. We further showed in vivo that efficient NK‐cell activation in response to VV is dependent on DCs and IL‐18 signaling in non‐NK cells, suggesting an essential role for NK cell‐extrinsic IL‐18 signaling in NK‐cell activation. Mechanistically, IL‐18 signaling in DCs promotes expression of Rae‐1, an NKG2D ligand. Collectively, our data reveal a previously unrecognized role for NK cell‐extrinsic IL‐18 signaling in NK‐cell activation through upregulation of NKG2D ligands. These observations may provide insights into the design of effective NK‐cell‐based therapies for viral infections and cancer.     

Early liaisons between cells of the innate immune system in inflamed peripheral tissues

The crosstalk between natural killer (NK) cells and myeloid dendritic cells (DCs) results in NK-cell activation and DC maturation. Activated NK cells acquire the ability to kill DCs that have failed to undergo complete maturation ('DC editing'). Recent studies have revealed that this crosstalk can be promoted by pathogen-derived products that activate different innate immune cell types directly and simultaneously through their Toll-like receptors (TLRs). These cells include NK cells and DCs, as well as plasmacytoid DCs (PDCs) and mast cells. This crosstalk can have a great impact on the quality and strength of the subsequent adaptive immune response. Thus, NK cells have an important role in the defense against pathogens, acting as regulatory cells as well as effector cells.     

Reciprocal crosstalk between dendritic cells and natural killer cells under the effects of PGE2 in immunity and immunopathology

The reciprocal activating crosstalk between dendritic cells (DCs) and natural killer (NK) cells plays a pivotal role in regulating immune defense against viruses and tumors. The cytokine-producing capacity, Th-cell polarizing ability and chemokine expression, migration and stimulatory functions of DCs are regulated by activated NK cells. Conversely, the innate and effector functions of NK cells require close interactions with activated DCs. Cell membrane-associated molecules and soluble mediators, including cytokines and prostaglandins (PGs), contribute to the bidirectional crosstalk between DCs and NK cells. One of the most well-known and well-studied PGs is PGE2. Produced by many cell types, PGE2 has been shown to affect various aspects of the immune and inflammatory responses by acting on all components of the immune system. There is emerging evidence that PGE2 plays crucial roles in DC and NK cell biology. Several studies have shown that DCs are not only a source of PGE2, but also a target of its immunomodulatory action in normal immune response and during immune disorders. Although NK cells appear to be unable to produce PGE2, they are described as powerful PGE2-responding cells, as they express all PGE2 E-prostanoid (EP) receptors. Several NK cell functions (lysis, migration, proliferation, cytokine production) are influenced by PGE2. This review highlights the effects of PGE2 on DC–NK cell crosstalk and its subsequent impact on immune regulations in normal and immunopathological processes.     

Cover Picture: Eur. J. Immunol. 11/11

The cover shows a modified electron microscopic image of HPV16‐virus‐like particle (HPV16‐VLP)‐internalization by NK cells. The colour added to the cover image is purely for aesthetic purposes and has no biological significance. The original, unmodified image is from Renoux et al. (pp. 3240–3252) in which the authors demonstrate that HPV16‐VLPs are taken up by NK cells by macropinocytosis. CD16 is shown to play a central role in the NK cell response to HPV16, being shown to be required for viral uptake, and for granzyme and cytokine release.     

Co‐operative suppression of inflammatory responses in human dendritic cells by plant proanthocyanidins and products from the parasitic nematode Trichuris suis

Interactions between dendritic cells (DCs) and environmental, dietary and pathogen antigens play a key role in immune homeostasis and regulation of inflammation. Dietary polyphenols such as proanthocyanidins (PAC) may reduce inflammation, and we therefore hypothesized that PAC may suppress lipopolysaccharide (LPS) ‐induced responses in human DCs and subsequent T helper type 1 (Th1) ‐type responses in naive T cells. Moreover, we proposed that, because DCs are likely to be exposed to multiple stimuli, the activity of PAC may synergise with other bioactive molecules that have anti‐inflammatory activity, e.g. soluble products from the helminth parasite Trichuris suis (TsSP). We show that PAC are endocytosed by monocyte‐derived DCs and selectively induce CD86 expression. Subsequently, PAC suppress the LPS‐induced secretion of interleukin‐6 (IL‐6) and IL‐12p70, while enhancing secretion of IL‐10. Incubation of DCs with PAC did not affect lymphocyte proliferation; however, subsequent interferon‐γ production was markedly suppressed, while IL‐4 production was unaffected. The activity of PAC was confined to oligomers (degree of polymerization ≥ 4). Co‐pulsing DCs with TsSP and PAC synergistically reduced secretion of tumour necrosis factor‐α, IL‐6 and IL‐12p70 while increasing IL‐10 secretion. Moreover, both TsSP and PAC alone induced Th2‐associated OX40L expression in DCs, and together synergized to up‐regulate OX40L. These data suggest that PAC induce an anti‐inflammatory phenotype in human DCs that selectively down‐regulates Th1 response in naive T cells, and that they also act cooperatively with TsSP. Our results indicate a novel interaction between dietary compounds and parasite products to influence immune function, and may suggest that combinations of PAC and TsSP can have therapeutic potential for inflammatory disorders.     

Human papillomavirus L1L2-E7 virus-like particles partially mature human dendritic cells and elicit E7-specific T-helper responses from patients with cervical intraepithelial neoplasia or cervical cancer in vitro

We evaluated the ability of autologous dendritic cells (DC) pulsed with recombinant human papillomavirus 16 L1L2-E7 virus-like particles (VLPs) to stimulate E7-specific CD4+ T-cell responses from normal donors and patients with cervical intraepithelial neoplasia lesions or cervical carcinoma in vitro. Exposure to VLPs partially matured DCs, as evidenced by upregulated expression of costimulatory and major histocompatibility complex molecules and the reduced capacity of treated DCs to process exogenous antigens. However, VLP treatment failed to promote strong expression of the CD83 or CCR7 markers or to modulate interleukin-12p70 secretion, indicators of terminal DC maturation. Notably, both normal donor- and patient-derived DCs behaved similarly after exposure to VLPs. A single round of in vitro stimulation of CD4+ T cells with DCs exposed to L1L2-E7 VLPs promoted specific anti-E7 responses in the majority of donors. In particular, DCs exposed to VLPs effectively stimulated type 1 biased E7-specific CD4+ T-cell responses in patients with premalignant cervical intraepithelial neoplasia I-III lesions, but type 2 or Treg biased responses in patients with cervical cancer. Given the high rate of CD4+ T-cell responses (14 [93%] of 15 patients) against DC-L1L2-E7 VLP stimulation, this vaccine modality could serve as a foundation for developing a general treatment option for patients with human papillomavirus 16-associated malignancies.     

Presence and maturity of dendritic cells in melanoma lymph node metastases

Immune avoidance mechanisms play a key role in the successful dissemination of melanoma. One mechanism whereby this could be achieved is by interfering with dendritic cell (DC) presentation of tumour‐associated antigens to naïve T cells. In particular, immature DCs characterized by the absence of accessory molecules are known to be immunosuppressive and to be involved in the induction of tolerance. The present study has investigated the presence and activation status of DCs within melanoma metastases in the regional lymph nodes. Using image analysis techniques, the expression of Factor XIIIa (FXIIIa), CD40, CD83 and HLA‐DR and the morphological features of DCs were examined in paraffin sections from 26 lymph nodes containing melanoma metastases. DCs expressing FXIIIa were found in 70% of the lymph nodes. The number of DCs identified was generally small but there were more concentrated areas of DCs designated as hotspots. In these areas of high FXIIIa staining, the percentage area occupied by DCs varied between 0.1% and 10%. The majority of FXIIIa‐positive cells did not express the DC maturation markers CD83 or CD40 and morphologically were rounded with few dendrites, indicating that they were immature. The cells did, however, express high levels of HLA‐DR, suggesting that they have the ability to present antigen but lack the accessory molecules required to initiate an immune response. Immature DCs, characterized by phenotypic and morphological features, are therefore present within the tumour deposits in lymph nodes infiltrated by melanoma and may specifically modulate the anti‐melanoma immune response. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

CD2–CD58 interactions are pivotal for the activation and function of adaptive natural killer cells in human cytomegalovirus infection

The existence and expansion of adaptive NK‐cell subsets have been linked to HCMV infection. Phenotypically, a majority of adaptive NK cells expresses the activating receptor NKG2C and CD57. Some of the molecular factors driving the expansion of NKG2C⁺CD57⁺ NK cells in HCMV infection have been identified. The direct interaction of adaptive NK cells with HCMV‐infected cells, preceding the expansion, however, remains less studied. Recently, adaptive NK cells were reported to express higher levels of the co‐activating receptor CD2. We explored whether CD2 was directly involved in the response of adaptive NK cells to HCMV. In a co‐culture system of human PBMCs and productively infected fibroblasts, we observed an upregulation of CD69, CD25, and HLA‐DR on all NK cells. However, only in adaptive NK cells was this increase largely blocked by antibodies against CD2 and CD58. Functionally, this blockade also resulted in diminished production of IFN‐γ and TNF‐α by adaptive human NK cells in response to HCMV‐infected cells. Our results demonstrate that binding of CD2 to upregulated CD58 on infected cells is a critical event for antibody‐mediated activation and subsequent effector functions of adaptive NKG2C⁺CD57⁺ NK cells during the antiviral response.