Knut Schäkel

The CD16+ (FcγRIII+) Subset of Human Monocytes Preferentially Becomes Migratory Dendritic Cells in a Model Tissue Setting

Much remains to be learned about the physiologic events that promote monocytes to become lymph-homing dendritic cells (DCs). In a model of transendothelial trafficking, some monocytes become DCs in response to endogenous signals. These DCs migrate across endothelium in the ablumenal-to-lumenal direction (reverse transmigration), reminiscent of the migration into lymphatic vessels. Here we show that the subpopulation of monocytes that expresses CD16 (Fcγ receptor III) is predisposed to become migratory DCs. The vast majority of cells derived from CD16+ monocytes reverse transmigrated, and their presence was associated with migratory cells expressing high levels of CD86 and human histocompatibility leukocyte antigen (HLA)-DR, and robust capacity to induce allogeneic T cell proliferation. A minority of CD16− monocytes reverse transmigrated, and these cells stimulated T cell proliferation less efficiently. CD16 was not functionally required for reverse transmigration, but promoted cell survival when yeast particles (zymosan) were present as a maturation stimulus in the subendothelial matrix. The cell surface phenotype and migratory characteristics of CD16+ monocytes were inducible in CD16− monocytes by preincubation with TGFβ1. We propose that CD16+ monocytes may contribute significantly to precursors for DCs that transiently survey tissues and migrate to lymph nodes via afferent lymphatic vessels.

Low-Dose Irradiation Programs Macrophage Differentiation to an iNOS+/M1 Phenotype that Orchestrates Effective T Cell Immunotherapy

Inefficient T cell migration is a major limitation of cancer immunotherapy. Targeted activation of the tumor microenvironment may overcome this barrier. We demonstrate that neoadjuvant local low-dose gamma irradiation (LDI) causes normalization of aberrant vasculature and efficient recruitment of tumor-specific T cells in human pancreatic carcinomas and T-cell-mediated tumor rejection and prolonged survival in otherwise immune refractory spontaneous and xenotransplant mouse tumor models. LDI (local or pre-adoptive-transfer) programs the differentiation of iNOS⁺ M1 macrophages that orchestrate CTL recruitment into and killing within solid tumors through iNOS by inducing endothelial activation and the expression of TH1 chemokines and by suppressing the production of angiogenic, immunosuppressive, and tumor growth factors.

6-Sulfo LacNAc, a Novel Carbohydrate Modification of PSGL-1, Defines an Inflammatory Type of Human Dendritic Cells

The monoclonal antibody M-DC8 defines a major subset of human blood dendritic cells (DCs). Here we identify the M-DC8 structure as 6-sulfo LacNAc, a novel carbohydrate modification of the P selectin glycoprotein ligand 1 (PSGL-1). In contrast to previously described blood DCs, M-DC8+ DCs lack the cutaneous lymphocyte antigen (CLA) on PSGL-1 and fail to bind P and E selectin. Yet they express anaphylatoxin receptors (C5aR and C3aR) and the Fcgamma receptor III (CD16), which recruit cells to inflammatory sites. While sharing with DC1 the expression of myeloid markers and a potent capacity to prime T cells in vitro, M-DC8+ DCs produce far more TNF-alpha in response to the bacterial endotoxin lipopolysaccharide (LPS). Thus, 6-sulfo LacNAc-expressing DCs appear as a novel proinflammatory DC subset.

A novel dendritic cell population in human blood: one-step immunomagnetic isolation by a specific mAb (M-DC8) and in vitro priming of cytotoxic T lymphocytes

Originating from a common progenitor cell, dendritic cells (DC) appear to develop along early branched pathways into various yet ill‐defined subpopulations residing at various sites throughout the body where they capture and present antigen in the most professional fashion. Here we give evidence for a unique subpopulation of human DC circulating in blood that account for 0.5 – 1 % of blood leukocytes only, their most specific characteristic being the expression of a cell surface protein recognized by a novel monoclonal antibody (M‐DC8) which enables their isolation by a one‐step immunomagnetic procedure. The isolated cells (> 97 % pure) present morphologically as typical dendritic cells. They express the FcγRIII (CD16), sofar not found on DC, and avidly phagocytose latex beads as well as opsonized erythrocytes. These cells not only present antigens efficiently to naive T cells but also induce purified CD8+ T cells to become alloantigen‐specific cytotoxic cells. Furthermore, when loaded with a tyrosinase‐derived peptide they stimulate T cells from normal donors and melanoma patients to exhibit MHC‐restricted specific cytotoxicity against melanoma cells.

Human slan (6-sulfo LacNAc) dendritic cells are inflammatory dermal dendritic cells in psoriasis and drive strong Th17/Th1 T-cell responses

BACKGROUND Psoriasis is a chronic inflammatory skin disease that is considered to result from activated T cells stimulated by a population of inflammatory dermal dendritic cells (DCs). The origin and identity of these inflammatory dermal DCs are largely unknown. OBJECTIVE We previously identified slanDCs (6-sulfo LacNAc) DCs as a rich source of TNF-α and as the early major source of IL-12. Here we studied the relevance of slanDCs as inflammatory dermal DCs in psoriasis. METHODS Psoriasis skin samples were stained for the presence of activated slanDCs. Functional studies were carried out to determine the cytokine production of slanDCs, their T(h)17/T(h)1 T-cell programming, and their migration behavior. RESULTS Large numbers of IL-23, TNF-α, and inducible nitric oxide synthase expressing slanDCs were found in psoriatic skin samples, which can be recruited by C5a, CX3CL1, and CXCL12. SlanDCs isolated from blood produced high levels of IL-1ß, IL-23, IL-12, and IL-6. Compared with classic CD1c(+) DCs, slanDCs were far more powerful in programming T(h)17/T(h)1 T cells that secrete IL-17, IL-22, TNF-α, and IFN-γ, yet CD1c(+) DCs induced a higher IL-10 production of T cells. Self-nucleic acids complexed to cathelicidin LL37 trigger endosomal Toll-like receptor (TLR) signaling (TLR7, TLR8, TLR9) and are key factors for the activation of DCs in psoriasis. We show that slanDCs respond particularly well to complexes formed of self-RNA and LL37. Similarly, slanDCs stimulated with a synthetic TLR7/8 ligand produced high levels of proinflammatory cytokines. CONCLUSION Our study defines slanDCs as inflammatory dermal DCs in psoriasis and identifies their strong capacity to induce T(h)17/T(h)1 responses.

Systemic treatment of severe atopic eczema: a systematic review.

Systemic immunosuppressive agents are recommended for patients with atopic eczema in whom disease activity cannot be controlled adequately with topical treatments. Guidelines do not give clear advice which agents to prefer. We systematically reviewed clinical trials on systemic treatment for severe atopic eczema to provide evidence-based treatment recommendations. Standardized literature search, independent standardized assessment of eligibility and data abstraction was performed by 2 reviewers. Twenty-seven studies totalling 979 patients were included. Eleven studies consistently showed effectiveness of cyclosporine. Cyclosporine is recommended as first option for patients with atopic eczema refractory to conventional treatment. Evidence from randomized controlled trials also exists for interferon-? and azathioprine. Although frequently used in clinical practice, systemic glucocorticosteroids have not been assessed adequately in studies. Mycophenolate mofetile showed effectiveness in 2 small uncontrolled studies. Intravenous immunoglobulins and infliximab are not recommended based on published data.

Tumoricidal Potential of Native Blood Dendritic Cells: Direct Tumor Cell Killing and Activation of NK Cell-Mediated Cytotoxicity

Dendritic cells (DCs) are characterized by their unique capacity for primary T cell activation, providing the opportunity for DC-based cancer vaccination protocols. Novel findings reveal that besides their role as potent inducers of tumor-specific T cells, human DCs display additional antitumor effects. Most of these data were obtained with monocyte-derived DCs, whereas studies investigating native blood DCs are limited. In the present study, we analyze the tumoricidal capacity of M-DC8+ DCs, which represent a major subpopulation of human blood DCs. We demonstrate that IFN-γ-stimulated M-DC8+ DCs lyse different tumor cell lines but not normal cells. In addition, we show that tumor cells markedly enhance the production of TNF-α by M-DC8+ DCs via cell-to-cell contact and that this molecule essentially contributes to the killing activity of M-DC8+ DCs. Furthermore, we illustrate the ability of M-DC8+ DCs to promote proliferation, IFN-γ production, and tumor-directed cytotoxicity of NK cells. The M-DC8+ DC-mediated enhancement of the tumoricidal potential of NK cells is mainly dependent on cell-to-cell contact. These results reveal that, in addition to their crucial role in activating tumor-specific T cells, blood DCs exhibit direct tumor cell killing and enhance the tumoricidal activity of NK cells. These findings point to the pivotal role of DCs in triggering innate and adaptive immune responses against tumors.

Prednisolone vs. ciclosporin for severe adult eczema. An investigator-initiated double-blind placebo-controlled multicentre trial.

Background  Patients with severe eczema frequently receive systemic glucocorticosteroids. The efficacy of prednisolone and other steroids, however, has never been evaluated appropriately. A meta‐analysis indicated that ciclosporin is the best evaluated systemic treatment for eczema.

Human neutrophils interact with both 6-sulfo LacNAc + DC and NK cells to amplify NK-derived IFNγ: role of CD18, ICAM-1, and ICAM-3

The role of neutrophils as key players in the regulation of innate and adaptive immune responses is increasingly being recognized. We report that human neutrophils establish a network with both natural killer (NK) cells and 6-sulfo LacNAc(+) dendritic cells (slanDCs), which ultimately serves to up-regulate NK-derived interferonγ (IFNγ). This network involves direct reciprocal interactions and positive amplification loops mediated by cell-derived cytokines. Accordingly, we show that after lipopolysaccharide + interleukin-2 (IL-2) or IL-15/IL-18 stimulation, neutrophils directly interact with and potentiate the activity of both slanDCs and NK cells. On the one hand, neutrophils augment the release of IL-12p70 by slanDCs via a CD18/ intercellular adhesion molecule-1 (ICAM-1) interaction that stimulates activated NK cells to produce IFNγ. IFNγ further potentiates the interaction between neutrophils and slanDCs and the release of slanDC-derived IL-12p70, thus creating a positive feedback loop. On the other hand, neutrophils directly co-stimulate NK cells via CD18/ICAM-3, leading to the production of IFNγ. Colocalization of neutrophils, NK cells, and slanDCs, as well as of IL-12p70 and IFNγ, in inflamed tissues of Crohn disease and psoriasis provides strong evidence for a novel cellular and cytokine cooperation within the innate immune system in which neutrophils act as amplifiers of NK cell/slanDC-mediated responses.

IL-4 abrogates T(H)17 cell-mediated inflammation by selective silencing of IL-23 in antigen-presenting cells.

Significance Interleukin 4 (IL-4) has been shown to be highly protective against delayed type hypersensitivity and organ-specific autoimmune and autoinflammatory reactions in mice and humans, but its mode of action has remained controversial and has failed to be explained solely by redirection of TH1/TH17 toward a TH2-type immune response. Here we uncovered that IL-4 selectively suppresses IL-23 transcription and secretion by cells of the innate immune system. We further describe a previously unidentified therapeutic mode of action of IL-4 in TH17-mediated inflammation, and a physiologically highly relevant approach to selectively target IL-23/TH17-dependent inflammation while sparing IL-12 and TH1 immune responses. Interleukin 4 (IL-4) can suppress delayed-type hypersensitivity reactions (DTHRs), including organ-specific autoimmune diseases in mice and humans. Despite the broadly documented antiinflammatory effect of IL-4, the underlying mode of action remains incompletely understood, as IL-4 also promotes IL-12 production by dendritic cells (DCs) and IFN-γ–producing TH1 cells in vivo. Studying the impact of IL-4 on the polarization of human and mouse DCs, we found that IL-4 exerts opposing effects on the production of either IL-12 or IL-23. While promoting IL-12–producing capacity of DCs, IL-4 completely abrogates IL-23. Bone marrow chimeras proved that IL-4–mediated suppression of DTHRs relies on the signal transducer and activator of transcription 6 (STAT6)-dependent abrogation of IL-23 in antigen-presenting cells. Moreover, IL-4 therapy attenuated DTHRs by STAT6- and activating transcription factor 3 (ATF3)-dependent suppression of the IL-23/TH17 responses despite simultaneous enhancement of IL-12/TH1 responses. As IL-4 therapy also improves psoriasis in humans and suppresses IL-23/TH17 responses without blocking IL-12/TH1, selective IL-4–mediated IL-23/TH17 silencing is promising as treatment against harmful inflammation, while sparing the IL-12–dependent TH1 responses.