New roles for CD14 and IL-ß linking inflammatory dendritic cells to IL-17 production in memory CD4+ T cells.

Interleukin (IL)-1ß has proven to be crucial in the differentiation of human and mouse Th17 cells. Although it has become evident that IL-1ß has potent IL-17-inducing effects on CD4+ T cells directly, it has not yet been explored whether IL-1ß can also prime dendritic cells (DCs) for a Th17 instruction program. Here, we show that human immature DCs exposed to IL-1ß promote IL-17 production in human memory CD4+ T cells. IL-1ß-primed DCs express high levels of CD14 that mediate IL-17 production through direct interaction with T cells. Moreover, culturing human CD4+CD45RO+ memory T cells with soluble CD14 is sufficient for the upregulation of retinoic acid-related orphan receptor-γ thymus and IL-17 production. In addition, in a human in situ model using tissue-resident skin DCs, upregulation of CD14 expression induced by IL-1ß on skin residents DCs promotes IL-17 production in memory T cells; strongly suggesting the in vivo relevance of this mechanism. Our findings uncover new roles for IL-1ß and CD14, and may therefore have important consequences for the development of new therapies for Th17-mediated autoimmune diseases and bacterial and fungal pathogenic infections.

Topical rather than intradermal application of the TLR7 ligand imiquimod leads to human dermal dendritic cell maturation and CD8+ T-cell cross-priming.

Toll-like receptor (TLR) ligands are attractive candidate adjuvants for therapeutic cancer vaccines, since TLR signaling stimulates and tunes both humoral and cellular immune responses induced by dendritic cells (DCs). Given that human skin contains a dense network of DCs, which are easily accessible via (intra-)dermal delivery of vaccines, skin is actively explored as an antitumor vaccination site. Here we used a human skin explant model to explore the potential of TLR ligands as adjuvants for DC activation in their complex microenvironment. We show that topical application of Aldara skin cream, 5% of which comprises the TLR7 agonist imiquimod, significantly enhanced DC migration as compared with that resulting from intradermal injection of the TLR7/8 ligand R848 or the soluble form of imiquimod. Moreover, Aldara-treated DCs showed highest levels of the costimulatory molecules CD86, CD83, CD40, and CD70. Topical Aldara induced the highest production of pro-inflammatory cytokines in skin biopsies. When combined with intradermal peptide vaccination, Aldara-stimulated DCs showed enhanced cross-presentation of the melanoma antigen MART-1, which resulted in increased priming and activation of MART-1-specific CD8(+) T cells. These results point to advantageous effects of combining the topical application of Aldara with antitumor peptide vaccination.

CD5 costimulation induces stable Th17 development by promoting IL-23R expression and sustained STAT3 activation.

IL-17-producing CD4(+) T helper (Th17) cells are important for immunity against extracellular pathogens and in autoimmune diseases. The factors that drive Th17 development in human remain a matter of debate. Here we show that, compared with classic CD28 costimulation, alternative costimulation via the CD5 or CD6 lymphocyte receptors forms a superior pathway for human Th17-priming. In the presence of the Th17-promoting cytokines IL-1ß, IL-6, IL-23, and transforming growth factor-ß (TGF-ß), CD5 costimulation induces more Th17 cells that produce higher amounts of IL-17, which is preceded by prolonged activation of signal transducer and activator of transcription 3 (STAT3), a key regulator in Th17 differentiation, and enhanced levels of the IL-17-associated transcription factor retinoid-related orphan receptor-γt (ROR-γt). Strikingly, these Th17-promoting signals critically depend on CD5-induced elevation of IL-23 receptor (IL-23R) expression. The present data favor the novel concept that alternative costimulation via CD5, rather than classic costimulation via CD28, primes naive T cells for stable Th17 development through promoting the expression of IL-23R.

Muramyl dipeptide-induced differential gene expression in NOD2 mutant and wild-type Crohn's disease patient-derived dendritic cells.

BACKGROUND: Mutations in the gene encoding the nucleotide-binding oligomerization domain 2 (NOD2) protein are associated with Crohn's disease (CD), but the mechanism underlying this is not completely understood. To study the mechanism of CD resulting from NOD2 mutations, we analyzed NOD2-dependent whole-genome expression profiles of patient-derived antigen-presenting cells. PATIENTS AND METHODS: Monocyte-derived dendritic cells (DCs) from CD carriers of double-dose NOD2 mutations, wild-type CD patients, and wild-type healthy volunteers were stimulated with the NOD2 ligand muramyl dipeptide. Whole-genome microarrays were used to assess the differential gene expression. The clustering of significantly changed genes was analyzed by online gene ontology mapping software. RESULTS: In the DCs from the wild-type CD patient group, 683 genes were significantly changed, with most of the genes clustering in the pathways of inflammatory response. In addition, a significant number of genes clustered in the apoptosis regulation-related pathway. In the DCs from the healthy volunteer group, only 50 genes were significantly changed, predominantly those belonging to the response to pathogen pathway. Analysis of differentially expressed gene ontology pathways in the DCs from the NOD2 mutant CD patient group showed that the transcription of pathogen response genes was absent. In this group, 298 genes were significantly changed, predominantly clustering in the negative apoptosis regulation and cell organization and biogenesis pathways. CONCLUSIONS: Our results suggest that NOD2 mutations may result in perpetuation of mucosal inflammation through insufficient pathogen elimination. Further, these observations implicate a possible role of defective regulation of dendritic cell apoptosis in CD pathogenesis.

Interleukin-17 in inflammatory skin disorders.

PURPOSE OF REVIEW: Recently, a novel and unique subset of interleukin (IL)-17-producing CD4+ T helper (Th17) cells, distinct from Th1 and Th2 cells, was discovered. The question is addressed as to what extent inflammatory skin diseases are associated with the actions of this newly discovered Th17 cell subset. RECENT FINDINGS: Th17 cells are involved in protection against bacterial pathogens. In addition, it is now clear that Th17 cells may also be crucial in the pathogenesis of various chronic inflammatory diseases that were formerly categorized as Th1-mediated disorders. SUMMARY: In this review, we summarize the current knowledge of IL-17 and Th17 cells and discuss the possible role of IL-17 in the pathology of psoriasis, contact hypersensitivity and atopic dermatitis. Whereas IL-17 may play an important role in the pathogenesis of psoriasis and contact hypersensitivity, its role in atopic dermatitis is still unclear.

In situ Delivery of Antigen to DC-SIGN(+)CD14(+) Dermal Dendritic Cells Results in Enhanced CD8(+) T-Cell Responses.

CD14(+) dendritic cells (DCs) present in the dermis of human skin represent a large subset of dermal DCs (dDCs) that are considered macrophage-like cells with poor antigen (cross)-presenting capacity and limited migratory potential to the lymph nodes. CD14(+) dDC highly express DC-specific ICAM-3-grabbing non-integrin (DC-SIGN), a receptor containing potent endocytic capacity, facilitating intracellular routing of antigens to major histocompatibility complex I and II (MHC-I andII) loading compartments for the presentation to antigen-specific CD8(+) and CD4(+) T cells. Here we show using a human skin explant model that the in situ targeting of antigens to DC-SIGN using glycan-modified liposomes enhances the antigen-presenting capacity of CD14(+) dDCs. Intradermal vaccination of liposomes modified with the DC-SIGN-targeting glycan Lewis(X), containing melanoma antigens (MART-1 or Gp100), accumulated in CD14(+) dDCs and resulted in enhanced Gp100- or MART-1-specific CD8(+) T-cell responses. Simultaneous intradermal injection of the cytokines GM-CSF and IL-4 as adjuvant enhanced the migration of the skin DCs and increased the expression of DC-SIGN on the CD14(+) and CD1a(+) dDCs. These data demonstrate that human CD14(+) dDCs exhibit potent cross-presenting capacity when targeted in situ through DC-SIGN.

Viral dsRNA-activated human dendritic cells produce IL-27, which selectively promotes cytotoxicity in naive CD8+ T cells.

Viral recognition programs DCs to express Signal 3 molecules that promote the differentiation of effector CD8(+) T cells. Besides IL-12, another DC-derived IL-12 family member, IL-27, has been reported to contribute herein, but its specific role is not well understood. Here, we show that whereas IL-12 potently induces inflammatory cytokines (i.e., IFN-γ and TNF-α, but not IL-2), IL-27 excels in inducing proliferation and a cytotoxic profile (GrB, cytotoxicity of target cells) in human naïve CD8(+) T cells. Compared with bacterial cell-wall peptidoglycan, viral dsRNA-mimic poly (I:C) is superior in priming human BDCA1(+) peripheral blood DCs to produce IL-12 and IL-27, which promote inflammatory cytokines and a cytotoxic profile in differentiating CD8(+) T cells, respectively. These data support the concept that viral dsRNA-activated human DCs produce IL-27 to act as a specialized procytotoxic, antiviral cytokine in the development of effector CD8(+) T cells.

Glycan-modified liposomes boost CD4+ and CD8+ T-cell responses by targeting DC-SIGN on dendritic cells.

Cancer immunotherapy requires potent tumor-specific CD8(+) and CD4(+) T-cell responses, initiated by dendritic cells (DCs). Tumor antigens can be specifically targeted to DCs in vivo by exploiting their expression of C-type lectin receptors (CLR), which bind carbohydrate structures on antigens, resulting in internalization and antigen presentation to T-cells. We explored the potential of glycan-modified liposomes to target antigens to DCs to boost murine and human T-cell responses. Since DC-SIGN is a CLR expressed on DCs, liposomes were modified with DC-SIGN-binding glycans Lewis (Le)(B) or Le(X). Glycan modification of liposomes resulted in increased binding and internalization by BMDCs expressing human DC-SIGN. In the presence of LPS, this led to 100-fold more efficient presentation of the encapsulated antigens to CD4(+) and CD8(+) T-cells compared to unmodified liposomes or soluble antigen. Similarly, incubation of human moDC with melanoma antigen MART-1-encapsulated liposomes coated with Le(X) in the presence of LPS led to enhanced antigen-presentation to MART-1-specific CD8(+) T-cell clones. Moreover, this formulation drove primary CD8(+) T-cells to differentiate into high numbers of tetramer-specific, IFN-γ-producing effector T-cells. Together, our data demonstrate the potency of a glycoliposome-based vaccine targeting DC-SIGN for CD4(+) and CD8(+) effector T-cell activation. This approach may offer improved options for treatment of cancer patients and opens the way to in situ DC-targeted vaccination.

DC-SIGN mediated antigen-targeting using glycan-modified liposomes: formulation considerations.

Dendritic cells (DCs) are key antigen presenting cells that have the unique ability to present antigens on MHC molecules, which can lead to either priming or suppression of T cell mediated immune responses. C-type lectin receptors expressed by DCs are involved in antigen uptake and presentation through recognition of carbohydrate structures on antigens. Here we have explored the feasibility of modification of liposomes with glycans for targeting purposes to boost immune responses. The potential of targeting glycoliposomal constructs to the C-type lectin DC-SIGN on DCs was studied using either PEGylated or non-PEGylated liposomes. Our data demonstrate that formulation of the glycoliposomes as PEGylated negatively affected their potential to target to DCs.

Stimulation of the intracellular bacterial sensor NOD2 programs dendritic cells to promote interleukin-17 production in human memory T cells.

How the development of antibacterial T helper 17 (Th17) cells is selectively promoted by antigen-presenting dendritic cells (DCs) is unclear. We showed that bacteria, but not viruses, primed human DCs to promote IL-17 production in memory Th cells through the nucleotide oligomerization domain 2 (NOD2)-ligand muramyldipeptide (MDP), a derivative of bacterial peptidoglycan. MDP enhanced obligate bacterial Toll-like receptor (TLR) agonist induction of IL-23 and IL-1, which promoted IL-17 expression in T cells. The role of NOD2 in this IL-23-IL-1-IL-17 axis could be confirmed in NOD2-deficient DCs, such as DCs from selected Crohn's disease patients. Thus, antibacterial Th17-mediated immunity in humans is orchestrated by DCs upon sensing bacterial NOD2-ligand MDP.

Commensal Gram-negative bacteria prime human dendritic cells for enhanced IL-23 and IL-27 expression and enhanced Th1 development.

Dendritic cells (DC) are the main orchestrators of specific immune responses. Depending on microbial information they encounter in peripheral tissues, they promote the development of Th1, Th2 or unpolarized Th cell responses. In this study we have investigated the immunomodulatory effect of non-pathogenic intestinal Gram-negative (Escherichia coli, Bacteroides vulgatus,Veillonella parvula, Pseudomonas aeruginosa) and Gram-positive (Bifidobacterium adolescentis, Enterococcus faecalis, Lactobacillus plantarum and Staphylococcus aureus) bacteria on human monocyte-derived DC (moDC). None of the Gram-positive bacteria (GpB) primed for Th1 or Th2 development. In contrast, despite the low levels of IL-12 they induce, all Gram-negative bacteria (GnB) primed moDC for enhanced Th1 cell development, which was dependent on IL-12 and an additional unidentified cofactor. Strikingly, GnB-matured moDC expressed elevated levels of p19 and p28 mRNA, the critical subunits of IL-23 and IL-27, respectively, suggesting that the IL-12 family members may jointly be responsible for their Th1-driving capacity. Purified major cell wall components of either GnB or GpB did not yield Th cell profiles identical to those obtained with whole bacteria, and could not explain the induction of the IL-12 family members nor Th1 priming by GnB. Importantly, this study gives indications that the expression of the different IL-12 family members is dictated by different priming conditions of immature DC.