T cells are necessary for ILC2 activation in house dust mite‐induced allergic airway inflammation in mice

Allergic asthma is a chronic inflammation of the airways mediated by an adaptive type 2 immune response. Upon allergen exposure, group 2 innate lymphoid cells (ILC2s) can be rapidly activated and represent an early innate source of IL‐5 and IL‐13. Here, we used a house dust mite (HDM)‐driven asthma mouse model to study the induction of ILC2s in allergic airway inflammation. In BALF, lungs, and lymph nodes, ILC2 activation is critically dependent on prior sensitization with HDM. Importantly, T cells are required for ILC2 induction, whereby T‐cell activation precedes ILC2 induction. During HDM‐driven allergic airway inflammation the accumulation of ILC2s in BALF is IL‐33 independent, although infiltrating ILC2s produce less cytokines in Il33^?/? mice. Transfer of in vitro polarized OVA‐specific OT‐II Th2 cells alone or in combination with Th17 cells followed by OVA and HDM challenge is not sufficient to induce ILC2, despite significant eosinophilic inflammation and T‐cell activation. In this asthma model, ILC2s are therefore not an early source of Th2 cytokines, but rather contribute to type 2 inflammation in which Th2 cells play a key role. Taken together, ILC2 induction in HDM‐mediated allergic airway inflammation in mice critically depends on activation of T cells.     

Bone marrow type 2 innate lymphoid cells: a local source of interleukin‐5 in interleukin‐33‐driven eosinophilia

T helper type 2 (Th2) cells, type 2 innate lymphoid cells (ILC2s) and eosinophil progenitors have previously been described to produce interleukin‐5 (IL‐5) in the airways upon allergen provocation or by direct administration of IL‐33. Eosinophilic airway inflammation is known to be associated with IL‐5‐dependent eosinophil development in the bone marrow, however, the source of IL‐5 remains unclear. T helper cells, ILC2s and CD34⁺ progenitors have been proposed to be involved in this process, therefore, we investigated whether these cells are taking part in eosinophilopoiesis by producing IL‐5 locally in the bone marrow in IL‐33‐driven inflammation. Airway exposure with IL‐33 led to eosinophil infiltration in airways and elevated eotaxin‐2/CCL24. Importantly, IL‐5 production as well as expression of the IL‐33 receptor increased in ILC2s in the bone marrow under this treatment. A small but significant induction of IL‐5 was also found in CD34⁺ progenitors but not in T helper cells. Similar results were obtained by in vitro stimulation with IL‐33 where ILC2s rapidly produced large amounts of IL‐5, which coincided with the induction of eosinophil hematopoiesis. IL‐33‐mediated eosinophil production was indeed dependent on IL‐5 as both airway and bone marrow eosinophils decreased in mice treated with anti‐IL‐5 in combination with IL‐33. Interestingly, the responsiveness of ILC2s to IL‐33 as well as IL‐33‐induced eotaxin‐2/CCL24 were independent of the levels of IL‐5. In summary, we demonstrate for the first time that IL‐33 acts directly on bone marrow ILC2s, making them an early source of IL‐5 and part of a process that is central in IL‐33‐driven eosinophilia.     

Regulatory T cells and type 2 innate lymphoid cell‐dependent asthma

Group 2 innate lymphoid cells (ILC2s) are a recently identified group of cells with the potent capability to produce Th2‐type cytokines such as interleukin (IL)‐5 and IL‐13. Several studies suggest that ILC2s play an important role in the development of allergic diseases and asthma. Activation of pulmonary ILC2s in murine models lacking T and B cells induces eosinophilia and airway hyper‐reactivity (AHR), which are cardinal features of asthma. More importantly, numerous recent studies have highlighted the role of ILC2s in asthma persistence and exacerbation among human subjects, and thus, regulation of pulmonary ILC2s is a major area of investigation aimed at curbing allergic lung inflammation and exacerbation. Emerging evidence reveals that a group of regulatory T cells, induced Tregs (iTregs), effectively suppress the production of ILC2‐driven, pro‐inflammatory cytokines IL‐5 and IL‐13. The inhibitory effects of iTregs are blocked by preventing direct cellular contact or by inhibiting the ICOS‐ICOS‐ligand (ICOSL) pathway, suggesting that both direct contact and ICOS‐ICOSL interaction are important in the regulation of ILC2 function. Also, cytokines such as IL‐10 and TGF‐β1 significantly reduce cytokine secretion by ILC2s. Altogether, these new findings uncover iTregs as potent regulators of ILC2 activation and implicate their utility as a therapeutic approach for the treatment of ILC2‐mediated allergic asthma and respiratory disease.     

Interleukin‐33 and alveolar macrophages contribute to the mechanisms underlying the exacerbation of IgE‐mediated airway inflammation and remodelling in mice

Allergen‐specific IgE has long been regarded as a major molecular component of allergic asthma. Additionally, there is increasing evidence of the important roles of interleukin‐33 (IL‐33) in the disease. Here, we show that IL‐33 and alveolar macrophages play essential roles in the exacerbation of IgE‐mediated airway inflammation and remodelling. BALB/c mice passively sensitized with ovalbumin (OVA)‐specific IgE monoclonal antibody (mAb) were challenged with OVA seven times intratracheally. The seventh challenge exacerbated airway inflammation and remodelling compared with the fourth challenge; furthermore, markedly increased expression of IL‐33 in the lungs was observed at the fourth and seventh challenges. When anti‐IL‐33 or anti‐ST2 antibody was administered during the fourth to seventh challenge, airway inflammation and remodelling were significantly inhibited at the seventh challenge. Because increases of IL‐33⁺ and ST2⁺ alveolar macrophages and ST2⁺ CD4⁺ T cells in the lungs were observed at the fourth challenge, the roles of macrophages and CD4⁺ cells were investigated. Depletion of macrophages by 2‐chloroadenosine during the fourth to seventh challenge suppressed airway inflammation and remodelling, and IL‐33 production in the lung at the seventh challenge; additionally, anti‐CD4 mAb inhibited airway inflammation, but not airway remodelling and IL‐33 production. Meanwhile, treatment with 2‐chloroadenosine or anti‐CD4 mAb decreased IL‐33‐induced airway inflammation in normal mice; airway remodelling was repressed only by 2‐chloroadenosine. These results illustrate that macrophage‐derived IL‐33 contributes to the exacerbation of IgE‐mediated airway inflammation by mechanisms associated with macrophages and CD4⁺ cells, and airway remodelling through the activation of macrophages.     

Characterization of CC-chemokine receptor 7 expression on murine T cells in lymphoid tissues

Expression of the lymph node homing and CC‐chemokine receptor 7 (CCR7), with L‐selectin (CD62L), has been shown to divide human memory T cells into two functionally distinct subsets. We generated a polyclonal antibody against murine CCR7 and used this antibody to study CCR7 expression on murine T‐cell subsets. Using flow cytometric staining of T cells for visualisation expression of CCR7 in association with CD62L and CD44, a major population of CD4 or CD8 T cells expressing CCR7 were found to be CD62L^high CD44^low, which would suggest a naïve cell phenotype. By analogy with human studies, memory cells could be subdivided into CCR7^high CD62L^high CD44^high (central memory) and CCR7^low CD62L^low CD44^high (effector memory). The proportions of these populations were different in lymph node, blood and spleen. Functional, short‐term in vitro polyclonal stimulation of blood, spleen and lymph node cells from naive mice demonstrated that CCR7^high CD4 T cells produced predominantly interleukin (IL)‐2, whereas CCR7^low CD4 T cells produced both IL‐2 and interferon‐γ (IFN‐γ). However, in contrast to previously published reports, the CCR7^high CD8 T‐cell subpopulation produced both IFN‐γ and IL‐2. Analysis of effector T cells, induced by immunization in vivo, showed that a proportion of activated naïve CD4 T cells down‐regulated CCR7 only after multiple cell divisions, and this coincided with the down‐regulation of CD62L and production of IL‐4 and IFN‐γ. Finally, analysis of effector T cells during the phase of maximal clonal expansion of secondary immune responses in vivo indicated that the vast majority of both IL‐2‐ and IFN‐γ‐producing cells are CCR7^low, while few cytokine‐expressing CCR7^high T cells were detected. Our results support the hypothesis, developed from studies with human cells, that CCR7 may separate functionally different murine memory T‐cell subpopulations, but indicate additional complexity in that CCR7^high CD8 T cells also may produce IFN‐γ.     

Effector T‐cell differentiation during viral and bacterial infections: Role of direct IL‐12 signals for cell fate decision of CD8+ T cells

To study the role of IL‐12 as a third signal for T‐cell activation and differentiation in vivo, direct IL‐12 signaling to CD8⁺ T cells was analyzed in bacterial and viral infections using the P14 T‐cell adoptive transfer model with CD8⁺ T cells that lack the IL‐12 receptor. Results indicate that CD8⁺ T cells deficient in IL‐12 signaling were impaired in clonal expansion after Listeria monocytogenes infection but not after infection with lymphocytic choriomeningitis virus, vaccinia virus or vesicular stomatitis virus. Although limited in clonal expansion after Listeria infection, CD8⁺ T cells deficient in IL‐12 signaling exhibited normal degranulation activity, cytolytic functions, and secretion of IFN‐γ and TNF‐α. However, CD8⁺ T cells lacking IL‐12 signaling failed to up‐regulate KLRG1 and to down‐regulate CD127 in the context of Listeria but not viral infections. Thus, direct IL‐12 signaling to CD8⁺ T cells determines the cell fate decision between short‐lived effector cells and memory precursor effector cells, which is dependent on pathogen‐induced local cytokine milieu.     

Interferon‐γ constrains cytokine production of group 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2s) produce a significant amount of interleukin‐5 (IL‐5), which supports eosinophil responses in various tissues; they also produce IL‐13, which induces mucus production and contributes to tissue repair or fibrosis. The ILC2s are activated by alarmins, such as IL‐33 released from epithelia, macrophages and natural killer T (NKT) cells in response to infection and allergen exposure, leading to epithelial injury. We examined gene expression in lung ILC2s and found that ILC2s expressed Ifngr1, the receptor for interferon‐γ (IFN‐γ). Interferon‐γ severely inhibited IL‐5 and IL‐13 production by lung and kidney ILC2s. To evaluate the effects in vivo, we used α‐galactosylceramide (α‐GalCer) to induce NKT cells to produce IL‐33 and IFN‐γ. Intraperitoneal injection of α‐GalCer in mice induced NKT cell activation resulting in IL‐5 and IL‐13 production by ILC2s. Administration of anti‐IFN‐γ together with α‐GalCer significantly enhanced the production of IL‐5 and IL‐13 by ILC2s in lung and kidney. Conversely, cytokine production from ILC2s was markedly suppressed after injection of exogenous IL‐33 in Il33^?/? mice pre‐treated with α‐GalCer. Hence, IFN‐γ induced or already present in tissues can impact downstream pleiotropic functions mediated by ILC2s, such as inflammation and tissue repair.     

Diversification and senescence of Foxp3+ regulatory T cells during experimental autoimmune encephalomyelitis

The fate of Foxp3⁺ regulatory T (Treg) cells responding during autoimmunity is not well defined. We observed a marked elevation in KLRG1⁺ (where KLRG1 stands for killer cell lectin‐like receptor G1) CNS‐infiltrating Treg cells in experimental autoimmune encephalomyelitis (EAE), and assessed their origin and properties. KLRG1⁺ Treg cells showed increased activation marker expression, Foxp3 and CD25 levels, and more rapid cell cycling than KLRG1^? cells. KLRG1^? Treg cells converted into KLRG1⁺ cells and this was increased in autoimmune inflammation. Conversion was unidirectional; KLRG1⁺ Treg cells did not revert to a KLRG1^? state. KLRG1⁺ but notKLRG1^?Treg cells survived poorly, indicative of terminal differentiation. This was associated with diminished BCL2 and increased apoptosis of isolated cells. KLRG1 was also upregulated on iTreg cells after transfer and EAE induction or on iTreg cells developing spontaneously during EAE. KLRG1⁺ Treg cells produced more IL‐10 and had altered effector cytokine production compared with their KLRG1^? counterparts. Despite their differences, KLRG1⁺ and KLRG1^? Treg cells proved similarly potent in suppressing EAE. KLRG1⁺ and KLRG1^? populations were phenotypically heterogeneous, with the extent and pattern of activation marker expression dependent both on cellular location and inflammation. Our results support an extensive diversification of Treg cells during EAE, and associate KLRG1 with altered Treg‐cell function and senescence.     

Reduced numbers of circulating group 2 innate lymphoid cells in patients with common variable immunodeficiency

Recent studies identified an emerging role of group 2 and 3 innate lymphoid cells (ILCs) as key players in the generation of T‐dependent and T‐independent antibody production. In this retrospective case‐control study, CD117⁺ ILCs (including the majority of ILC2 and ILC3) were reduced in patients with common variable immunodeficiency (CVID). The reduction in CD117⁺ ILCs was distinctive to CVID and could not be observed in patients with X‐linked agammaglobulinemia. Patients with a more pronounced reduction in CD117⁺ ILC numbers showed significantly lower numbers of peripheral MZ‐like B cells and an increased prevalence of chronic, non‐infectious enteropathy. Subsequent phenotyping of ILC subsets in CVID revealed that the reduction in CD117⁺ ILC numbers is due to a reduction in ILC2 numbers. In vitro expansion of CVID ILC2 in response to IL‐2, IL‐7, IL‐25 and IL‐33 was impaired. Furthermore, upregulation of MHCII and IL‐2RA in response to IL‐2, IL‐7, IL‐25 and IL‐33 was impaired in CVID ILC2. Thus, our results indicate a dysregulation of ILC subsets with a reduction in ILC2 numbers in CVID, however, further studies are needed to explore whether ILC abnormalities are a primary finding or secondary to disease complications encountered in CVID.     

TGF‐β downregulates KLRG1 expression in mouse and human CD8+ T cells

The inhibitory receptor killer cell lectin‐like receptor G1 (KLRG1) and the integrin α_E (CD103) are expressed by CD8⁺ T cells and both are specific for E‐cadherin. However, KLRG1 ligation by E‐cadherin inhibits effector T‐cell function, whereas binding of CD103 to E‐cadherin enhances cell–cell interaction and promotes target cell lysis. Here, we demonstrate that KLRG1 and CD103 expression in CD8⁺ T cells from untreated and virus‐infected mice are mutually exclusive. Inverse correlation of KLRG1 and CD103 expression was also found in human CD8⁺ T cells‐infiltrating hepatocellular carcinomas. As TGF‐β is known to induce CD103 expression in CD8⁺ T cells, we examined whether this cytokine also regulates KLRG1 expression. Indeed, our data further reveal that TGF‐β signaling in mouse as well as in human CD8⁺ T cells downregulates KLRG1 expression. This finding provides a rationale for the reciprocal expression of KLRG1 and CD103 in different CD8⁺ T‐cell subsets. In addition, it points to the limitation of KLRG1 as a marker for terminally differentiated CD8⁺ T cells if lymphocytes from tissues expressing high levels of TGF‐β are analyzed.     

Influenza matrix 1‐specific human CD4+FOXP3+ and FOXP3− regulatory T cells can be detected long after viral clearance

Control and termination of infection with Influenza A virus is associated with increased IL‐10 production in mouse models. Notably, IL‐10 can be produced by Treg. Therefore, we investigated whether the population of IL‐10‐producing influenza‐specific CD4⁺ T cells comprised Treg as they are potent suppressors of the adaptive immune response. Influenza‐specific IL‐10‐producing T cells were detected in all human donors displaying influenza‐specific immunity. Isolation of Matrix 1 protein‐specific IL‐10‐producing T‐cell clones revealed that a substantial proportion of these T‐cell clones displayed the capacity to suppress effector cells, functionally identifying them as Treg. Both FOXP3⁺ and FOXP3^? CD4⁺ Treg were isolated and all were able to exert their suppressive capacity when stimulated with cognate antigen, including influenza virus‐infected cells. In vitro suppression was not mediated by IL‐10 but involved interference with the IL‐2 axis. The isolated Treg suppressed amongst others the IL‐2 production of influenza‐specific T‐helper cells as well as partially prevented the upregulation of the high‐affinity IL‐2 receptor on CD8 effector cells. So far the induction of virus‐specific Treg has only been studied in the context of chronic viral infections. This study demonstrates that virus‐specific Treg can also be induced by viruses that are rapidly cleared in humans.     

IL‐33 Receptor (ST2) Signalling is Important for Regulation of Th2‐Mediated Airway Inflammation in a Murine Model of Acute Respiratory Syncytial Virus Infection

T1/ST2, an orphan receptor with homology with the interleukin (IL)‐1 receptor family, is the ligand‐binding component of the receptor for the cytokine IL‐33, a newly identified cytokine known to amplify the Th2 cell‐dominant immune responses. The function of IL‐33/ST2 signalling during respiratory syncytial virus (RSV) infection is not fully known. In this study, following intranasal infection with RSV, BALB/c mice showed a marked increase in the production of IL‐33, with an elevated expression of ST2 mRNA as well as a massive infiltration of CD45⁺ST2⁺ cells in the lungs, suggesting that during the early phase of RSV infection, IL‐33 target cells which express ST2 on cell surface, may play a critical role for the development of RSV‐induced airway inflammation. Indeed, blocking ST2 signalling using anti‐ST2 monoclonal antibody diminished not only RSV‐induced eosinophil recruitment, but also the amounts of Th2‐associated cytokines, particularly IL‐13, and Th17‐type cytokine IL‐17A in the lungs of infected mice. However, anti‐ST2 antibody treatment did not affect the production of Th1‐type cytokine IFN‐γ as well as pulmonary viral growth and clearance. These results indicate that IL‐33/ST2 signalling is involved in RSV‐induced, Th2‐associated airway inflammation but not protective immunity.     

Disruption of the Notch pathway aggravates airway inflammation by inhibiting regulatory T cell differentiation via regulation of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) regulate immunity and promote tolerance in asthma. Notch signalling is a highly conserved pathway that regulates the immune response; however, its role in pDC-mediated asthmatic airway inflammation is unclear. This study clarified the effects of Notch signalling on pDC-mediated airway inflammation using murine models of ovalbumin-sensitized allergic asthma. RBP-J-deficient pDCs (RBP-J^−/− pDCs) were co-cultured with naïve CD4⁺ T cells and supernatants and T cell subtypes were analysed. RBP-J^−/− pDCs were intranasally transferred to the airways of ovalbumin-sensitized recipient mice. Lung samples of all mice were subjected to tests for histopathology, cytokine profile of bronchoalveolar lavage fluid, airway hyperactivity and expression of T helper type 1 (Th1)/Th2 cells, regulatory T cells and type 2 innate lymphoid cells (ILC2s). The results showed that pDCs with and without RBP-J deficiency significantly differed in expression levels of cluster of differentiation 83 (CD83), but not CD80, CD86 and major histocompatibility complex class II. Co-culturing pDCs with naïve T cells revealed a poorer immunosuppressive effect of RBP-J^−/− pDCs. This may be attributed to the lower expression levels of inducible co-stimulator ligand and lower production of interleukin 10 in RBP-J^−/− pDCs than in control pDCs, which impeded T cell activation and Treg suppression. RBP-J^−/− pDCs were associated with high ILC2 expression and severe Th2 immune responses and airway inflammation. Therefore, Notch signalling is critical for pDC-dependent immunoregulation, and RBP-J deficiency reduces pDC-based immunosuppression via T cell activation and Th cell differentiation. Thus, this pathway may be a therapeutic target for pDC-based anti-asthma immunotherapy.     

IL‐2 is positively involved in the development of colitogenic CD4+ IL‐7Rαhigh memory T cells in chronic colitis

IL‐2 and IL‐7 share a common γ‐chain receptor and are critical for T‐cell homeostasis. We aimed to clarify the reciprocal roles of IL‐2 and IL‐7 in the development and persistence of chronic colitis. We performed a series of adoptive transfers of IL‐2^?/? CD4⁺CD45RB^high T cells into RAG‐2^?/? mice and assessed the role of IL‐2 in the induction of IL‐7Rα on colitogenic CD4⁺ T cells and the development of chronic colitis. RAG‐2^?/? mice transferred with WT but not with IL‐2^?/? CD4⁺CD45RB^high T cells developed Th1/Th17‐mediated colitis. Consistently, re‐expression of IL‐7Rα was severely impaired on IL‐2^?/? but not on WT CD4⁺ T cells from the transferred mice. To exclude a contribution of the preclinical autoimmunity of IL‐2^?/?mice, WT Ly5.1⁺ or IL‐2^?/? Ly5.2⁺ CD4⁺CD45RB^high T cells from GFP mice previously transplanted with the same number of WT and IL‐2^?/? BM cells were transferred into RAG‐2^?/? mice. RAG‐2^?/? mice transferred with IL‐2^?/?‐derived CD4⁺CD45RB^high T cells did not develop colitis, but their splenic CD4⁺ T cells changed from effector‐memory to central‐memory type. These results show that IL‐2 is critically involved in the establishment and maintenance of IL‐7‐dependent colitogenic memory CD4⁺IL‐7Rα^high T cells.     

Memory precursor phenotype of CD8+ T cells reflects early antigenic experience rather than memory numbers in a model of localized acute influenza infection

The mechanistic basis of memory T‐cell development is poorly defined. Phenotypic markers that define precursors at effector stages have been characterized for acute systemic infections with high antigen load. We asked whether such markers can identify memory precursors from early effectors (d6) to late memory (>d500) for two immunodominant CD8⁺ responses during the course of a localized low‐load influenza infection in mice. CD8⁺ T cells stained with the D^bNP₃₆₆ and D^bPA₂₂₄ tetramers were characterized as IL‐7Rα^hi, IL‐7Rα^hiCD62L^hi or IL‐7Rα^hiKLRG1^lo. While the D^bNP₃₆₆‐ and D^bPA₂₂₄‐specific responses were comparable in size, decay kinetics and memory precursor frequency, their expansion characteristics differed. This correlated with a divergence in the IL‐7Rα^hi, IL‐7Rα^hiCD62L^hi and IL‐7Rα^hiKLRG1^lo phenotypes on effector, but not naïve, CD8⁺ populations. That effect was abrogated by priming with viruses engineered to present equivalent levels of NP₃₆₆ and PA₂₂₄ peptides, indicating that memory phenotypes reflect early antigenic experience rather than memory potential. Thus, the IL‐7Rα^hiKLRG1^lo phenotype had a poor predictive value in identifying memory precursors in the spleen and at the site of infection. Greater consistency in influenza‐specific IL‐7Rα^hiKLRG1^loCD8⁺ T‐cell numbers was found in draining lymph nodes, suggesting that this may be the preferential site for memory establishment and maintenance following localized virus infections.     

T cell‐derived IFN‐γ downregulates protective group 2 innate lymphoid cells in murine lupus erythematosus

Innate lymphoid cells (ILCs) are important regulators of the immune response and play a crucial role in the restoration of tissue homeostasis after injury. GATA‐3⁺ IL‐13‐ and IL‐5‐producing group 2 innate lymphoid cells (ILC2s) have been shown to promote tissue repair in barrier organs, but despite extensive research on ILCs in the recent years, their potential role in autoimmune diseases is still incompletely understood. In the present study, we investigate the role of ILC2s in the MRL/MpJ‐Fas^lpr (MRL‐lpr) mouse model for severe organ manifestation of systemic lupus erythematosus (SLE). We show that in these MRL‐lpr mice, progression of lupus nephritis is accompanied with a reduction of ILC2 abundance in the inflamed renal tissue. Proliferation/survival and cytokine production of kidney‐residing ILC2s was suppressed by IFN‐γ and, to a lesser extent, by IL‐27 which were produced by activated T cells and myeloid cells in the nephritic kidney, respectively. Most importantly, restoration of ILC2 numbers by IL‐33‐mediated expansion ameliorated lupus nephritis and prevented mortality in MRL‐lpr mice. In summary, we show here that development of SLE‐like kidney inflammation leads to a downregulation of the renal ILC2 response and identify an ILC2‐expanding therapy as a promising treatment approach for autoimmune diseases.     

Enrichment of IL‐17A+IFN‐γ+ and IL‐22+IFN‐γ+ T cell subsets is associated with reduction of NKp44+ILC3s in the terminal ileum of Crohn's disease patients

Crohn's disease (CD) is a chronic inflammatory condition of the human gastrointestinal tract whose aetiology remains largely unknown. Dysregulated adaptive immune responses and defective innate immunity both contribute to this process. In this study, we demonstrated that the interleukin (IL)‐17A⁺interferon (IFN)‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets accumulated specifically in the inflamed terminal ileum of CD patients. These cells had higher expression of Ki‐67 and were active cytokine producers. In addition, their proportions within both the IL‐17A‐producer and IL‐22‐producer populations were increased significantly. These data suggest that IL‐17A⁺IFN‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets might represent the pathogenic T helper type 17 (Th17) population in the context of intestinal inflammation for CD patients. In the innate immunity compartment we detected a dramatic alteration of both phenotype and function of the intestinal innate lymphoid cells (ILCs), that play an important role in the maintenance of mucosal homeostasis. In the inflamed gut the frequency of the NKp44^–CD117^–ILC1s subset was increased significantly, while the frequency of NKp44⁺ILC3s was reduced. Furthermore, the frequency of human leucocyte antigen D‐related (HLA‐DR)‐expressing‐NKp44⁺ILC3s was also reduced significantly. Interestingly, the decrease in the NKp44⁺ILC3s population was associated with an increase of pathogenic IL‐17A⁺IFN‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets in the adaptive compartment. This might suggest a potential link between NKp44⁺ILC3s and the IL‐17A⁺IFN‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets in the terminal ileum of CD patients.     

Plasmacytoid dendritic cells induce a distinct cytokine pattern in virus-specific CD4+ memory T cells that is modulated by CpG oligodeoxynucleotides

Inherent properties of dendritic cell (DC) subsets are important in the regulation of naïve T‐cell differentiation (e.g. Th1 versus Th2 cells), whereas effector memory T cells are believed to produce a fixed cytokine repertoire independent of the type of antigen presenting cell. Here we show that two distinct human DC subsets, plasmacytoid DC (PDC) and myeloid CD11c+ DC, induced autologous mumps virus‐specific memory CD4⁺ T cells to produce markedly different cytokine patterns upon antigen stimulation. PDC stimulated the T cells to produce γ‐interferon (IFN‐γ) and interleukin‐(IL)‐10, whereas CD11c+ DC induced lower levels of IFN‐γ, virtually no IL‐10, but significant levels of IL‐5. Analysis of intracellular cytokine production showed simultaneous production of IL‐10 and IFN‐γ in mumps‐specific T cells activated by PDC, a cytokine pattern similar to that described for Th1‐like regulatory cells. Introduction of CpG oligodeoxynucleotides in PDC/T‐cell co‐cultures had synergistic effect on virus‐dependent IFN‐γ production, whereas the other cytokines remained unchanged. Together, our results show that the type of DC involved in reactivation of previously primed T cells may have significant impact on the resulting cytokine response and suggest that targeting of viral antigens and adjuvant to specific DC subsets should be considered in the design of therapeutic antiviral vaccines.