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.

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, Enteroccocus 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.

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.

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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 crosspresentation 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.Keywords: Adjuvants r Aldara r Cross-presentation r DCs r Human skin r T-cell priming Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionVaccination is used to generate strong and specific immune responses against target antigens with minimal side effects. In particular, cancer vaccines aim to generate an efficient immune Correspondence: Prof. Yvette van Kooyk e-mail: y.vankooyk@vumc.nl response against tumor-associated antigens (TAAs), which will depend on the instruction of CD8 + T cells that can effectively eradicate the tumor [1]. However, cancer vaccines often show poor immunogenicity, making them dependent on adjuvants to induce an immune response and to avoid the generation of tolerance.Adjuvants consist of compounds that boost the potency, quality, or longevity of specific immune responses to antigens, but should cause minimal toxicity on their own [2]. They accomplish C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 2416 Cynthia M. Fehres et al. Eur. J. Immunol. 2014. 44: 2415-2424 these effects via the generation of antigen depots, attraction of an immune infiltrate, enhancement of antigen presentation through the activation of antigen-presenting cells (APCs) including the induction of appropriate costimulatory molecules and cytokines [3]. Toll-like receptor (TLR) ligands have been extensively studied as the latest generation of adjuvants [4]. These receptors are widely expressed by both immune cells such as dendritic cells (DCs), and nonimmune cells such as keratinocytes and fibroblasts [5]. TLRs represent a receptor family that recognizes a broad spectrum of conserved m...

IL-17-producing CD4 IntroductionIL-17 producing CD4 ϩ T helper (Th17) cells are important in immunity against extracellular pathogens, in particular at the mucosa, and are implicated in a variety of immune-mediated inflammatory disorders. Similar to other effector T cell types, Th17 cells develop from naive CD4 ϩ T cells in response to antigen presenting cell (APC)-derived signals. Whereas the cytokines IL-1␤, IL-6, IL-23, and TGF-␤ have been identified to support Th17 differentiation in both mice and human, there is less consensus on the costimulatory signals that drive the development of human Th17 cells. [1][2][3][4] A basic principle of T-cell activation is that proper stimulation of naive T cells requires costimulation via CD28 for survival and expansion, which licenses their subsequent development into distinct effector Th subsets driven by appropriate signal 3 factors. Surprisingly, 2 recent studies reported that Th17 development is selectively inhibited by CD28 costimulation. 5,6 One of these studies suggested that human Th17 development is alternatively mediated via ligation of the inducible costimulator (ICOS). 6 Among the other molecules that may alternatively costimulate CD4 ϩ T cells are the lymphocyte receptor CD5 and CD6. 7,8 CD5 and CD6 are both group B members of the Scavenger Receptor Cystein-Rich domains superfamily (SRCR-SF). CD5 and CD6 share important structural and functional properties, and have probably arisen from a common ancestral gene. During interaction between the APC and T cell, CD5 and CD6 form part of the immunologic synapse. 9,10 This localization makes them well positioned to modulate the signals that follow antigen-specific T-cell receptor (TCR) ligation. For CD5, this concept has been most clearly demonstrated. CD5 plays a role in the late events of synapse-mediated signal transduction, whereby the large cytoplasmatic domain of CD5 can recruit both positive and negative regulators of T-cell signaling. Consequently, CD5 is a modulator of T-cell responses with both stimulatory and inhibitory activities. 8,11 In the thymus, CD5 plays a role in regulating TCR-mediated expansion and survival during T-cell ontogeny. 7,8,12 In peripheral resting CD4 ϩ T cells, CD5 costimulation results in proliferation levels as high as obtained with classic CD28-mediated costimulation. A possible role of CD5-mediated costimulation of T cells in Th17 cell development is favored by the finding that mice deficient in signaling between CD5 and CK-2, a prosurvival serine/threonine kinase that associates with CD5, show diminished populations of IL-17-expressing T cells in the central nervous system, in a model of experimental autoimmune encephalomyelitis. 13 In the present study, we show that costimulation via CD5 or CD6 is superior to classic CD28 costimulation in driving Th17 cell development from human naive CD4 ϩ T cells. CD5 induces high and consistent levels of IL-17, indicating the induction of stable terminal differentiation. Indeed, CD5 promotes elevated expression of various intracellular fact...

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.

In Alzheimer’s disease, neuritic amyloid-β plaques along with surrounding activated microglia and astrocytes are thought to play an important role in the inflammatory events leading to neurodegeneration. Studies have indicated that amyloid-β can be directly neurotoxic by activating these glial cells to produce oxygen radicals and proinflammatory cytokines. This report shows that, using primary human monocyte-derived macrophages as model cells for microglia, amyloid-β1–42 stimulate these macrophages to the production of superoxide anions and TNF-α. In contrast, astrocytes do not produce both inflammatory mediators when stimulated with amyloid-β1–42. In cocultures with astrocytes and amyloid-β1–42-stimulated macrophages, decreased levels of both superoxide anion and TNF-α were detected. These decreased levels of potential neurotoxins were due to binding of amyloid-β1–42 to astrocytes since FACScan analysis demonstrated binding of FITC-labeled amyloid-β1–42 to astrocytoma cells and pretreatment of astrocytes with amyloid-β1–16 prevented the decrease of superoxide anion in cocultures of human astrocytes and amyloid-β1–42-stimulated macrophages. To elucidate an intracellular pathway involved in TNF-α secretion, the activation state of NF-κB was investigated in macrophages and astrocytoma cells after amyloid-β1–42 treatment. Interestingly, although activation of NF-κB could not be detected in amyloid-β-stimulated macrophages, it was readily detected in astrocytoma cells. These results not only demonstrate that amyloid-β stimulation of astrocytes and macrophages result in different intracellular pathway activation but also indicate that astrocytes attenuate the immune response of macrophages to amyloid-β1–42 by interfering with amyloid-β1–42 binding to macrophages.