Richard Huijbens

The dendritic cell-specific CC-chemokine DC-CK1 is expressed by germinal center dendritic cells and attracts CD38-negative mantle zone B lymphocytes

DC-CK1 (CCL18) is a dendritic cell (DC)-specific chemokine expressed in both T and B cell areas of secondary lymphoid organs that preferentially attracts CD45RA+ T cells. In this study, we further explored the nature of DC-CK1 expressing cells in germinal centers (GCs) of secondary lymphoid organs using a newly developed anti-DC-CK1 mAb. Immunohistochemical analysis demonstrated a remarkable difference in the number of DC-CK1 expressing cells in adjacent GCs within one tonsil, implicating that the expression of DC-CK1 in GCs depends on the activation and/or progression stage of the GC reaction. Using immunohistology and RNA analysis, we demonstrated that GCDC are the source of DC-CK1 production in the GCs. Considering the recently described function of GCDC in (naive) B cell proliferation, isotype switching and Ab production, we investigated the ability of DC-CK1 to attract B lymphocytes. Here we demonstrate that DC-CK1 is a pertussis toxin-dependent chemoattractant for B lymphocytes with a preference in attracting mantle zone (CD38−) B cells. The findings that GCDC produce DC-CK1 and attract mantle zone B cells support a key role for GCDC in the development of GCs and memory B cell formation.

TLR2 promotes Th2/Th17 responses via TLR4 and TLR7/8 by abrogating the Type I IFN amplification loop

TLR2 plays an important role in the removal of Gram-positive bacteria; contrastingly, it also appears to have important protective effects against unrestrained inflammation and subsequent organ injury during infection and autoimmunity. We hypothesized that TLR2 tunes the phenotype of dendritic cells (DCs) activated through other TLRs, thereby fulfilling a crucial role in the modulation of the immune response. TLR2 potently inhibited TLR4- and TLR7/8-induced cytokine production by human DCs. The inhibitory effect of TLR2 on the release of TNF-α but not of IL-12p70 was mediated by PI3K. TLR2 inhibits the production of IL-12p70 by dampening the type 1 IFN amplification loop. When DCs were triggered with the potent synergistic combination of LPS (TLR4) and R848 (TLR7/8) in conjunction with a TLR2 ligand, a clear shift to more Th2- and Th17-prone responses in the naive and memory T cell subpopulations was observed. This shift in T cell responses was inherent to the inability of TLR2-stimulated DCs to produce IL-12p70 and was dependent on the production of IL-1 and IL-6.

The inhibitory Fc gamma IIb receptor dampens TLR4-mediated immune responses and is selectively up-regulated on dendritic cells from rheumatoid arthritis patients with quiescent disease.

Rheumatoid arthritis (RA) is a common autoimmune disease leading to profound disability and premature death. Although a role for FcγRs and TLRs is accepted, their precise involvement remains to be elucidated. FcγRIIb is an inhibitory FcR important in the maintenance of tolerance. We hypothesized that the inhibitory FcγRIIb inhibits TLR responses on monocyte-derived dendritic cells (DC) and serves as a counterregulatory mechanism to dampen inflammation, and we surmised that this mechanism might be defective in RA. The expression of the inhibitory FcγRIIb was found to be significantly higher on DCs from RA patients having low RA disease activity in the absence of treatment with antirheumatic drugs. The expression of activating FcγRs was similarly distributed among all RA patients and healthy controls. Intriguingly, only DCs with a high expression of FcγRIIb were able to inhibit TLR4-mediated secretion of proinflammatory cytokines when stimulated with immune complexes. In addition, when these DCs were coincubated with the combination of a TLR4 agonist and immune complexes, a markedly inhibited T cell proliferation was apparent, regulatory T cell development was promoted, and T cells were primed to produce high levels of IL-13 compared with stimulation of the DCs with the TLR4 agonist alone. Blocking FcγRIIb with specific Abs fully abrogated these effects demonstrating the full dependence on the inhibitory FcγRIIb in the induction of these phenomena. This TLR4-FcγRIIb interaction was shown to dependent on the PI3K and Akt pathway.

Cytokine and Chemokine Production by Human Pancreatic Islets Upon Enterovirus Infection

Enteroviruses of the human enterovirus B species (HEV-Bs) (e.g., coxsackie B viruses [CVBs] and echoviruses) have been implicated as environmental factors that trigger/accelerate type 1 diabetes, but the underlying mechanism remains elusive. The aim of this study was to gain insight into the cytokines and chemokines that are produced by human pancreatic islets upon infection with CVBs. To this end, we studied the response of human islets of Langerhans upon mock or CVB3 infection. Using quantitative PCR, we showed that upon CVB3 infection, transcription of interferon (IFN), IFN-stimulated genes, and inflammatory genes was induced. Analysis of secreted cytokines and chemokines by Luminex technology confirmed production and secretion of proinflammatory cytokines (e.g., interleukin [IL]-6 and tumor necrosis factor-α) as well as various chemotactic proteins, such as IFN-γ–induced protein 10, macrophage inflammatory protein (MIP)-1α, MIP-1β, and IL-8. Infection with other HEV-Bs induced similar responses, yet their extent depended on replication efficiency. Ultra violet–inactivated CVB3 did not induce any response, suggesting that virus replication is a prerequisite for antiviral responses. Our data represent the first comprehensive overview of inflammatory mediators that are secreted by human islets of Langerhans upon CVB infection and may shed light on the role of enteroviruses in type 1 diabetes pathogenesis.

Distinct evolution of TLR-mediated dendritic cell cytokine secretion in patients with limited and diffuse cutaneous systemic sclerosis

Background Systemic sclerosis (SSc) is an autoimmune disease and accumulating evidence suggests a role for Toll-like receptor (TLR)-mediated activation of dendritic cells (DCs). Objective To map TLR-mediated cytokine responses of DCs from patients with SSc. Methods 45 patients with SSc were included. Patients were stratified as having diffuse cutaneous SSc (dSSc) or limited cutaneous SSc (lSSc) according to the extent of skin involvement, and further divided into those with late (>3 years) or early disease (<2 years). DCs were stimulated with ligands for TLR2, TLR3, TLR4, TLR7/8 or combinations. Plasma samples were collected from patients with SSc (n=167) and measured for interleukin 6 (IL-6), tumour necrosis factor α (TNFα), IL-12, IL-10 and interferon γ. Results Stimulation of DC subsets from patients with early lSSc and dSSc with ligands for TLR2, TLR3 or TLR4 resulted in higher secretion of IL-6 and TNFα compared with those having late disease or healthy controls. Remarkably, the production of IL-12 was lower upon stimulation with TLR ligands in most patients with SSc, whereas the secretion of IL-10 was very high in patients with the dSSc phenotype, particularly in those having early dSSc. The combination of various TLR ligands led to reduced cytokine secretion in all patients with SSc. Circulating levels of these cytokines further underscored the presence of differences between various SSc phenotypes. Discussion The altered TLR-mediated activation of DCs may be responsible for Th2 skewed T-cell activation in SSc that may be orchestrated by fibrogenic T-cell cytokines, such as IL-4 and IL-13. DC targeting could thus offer new avenues for therapeutic intervention.

β2 integrins control the proinflammatory phenotype of type 1 macrophages and dendritic cells

The authors hypothesised that the accumulation of macrophages at a site of inflammation induces a shift from an initially proinflammatory macrophage phenotype to a phenotype aimed at suppressing the initiated immune response when sufficient numbers of macrophages have been recruited. To investigate this, the authors cultured monocytes with granulocyte-macrophage colony forming units or macrophage colony forming units into proinflammatory type …

Modulating TLR responses in systemic sclerosis via heme oxygenase-1

Systemic sclerosis (SSc) is an autoimmune disease characterised by fibrosis of the skin and the internal organs. The aetiology is still unknown, but prominent features are vascular injury and chronic inflammation resulting in fibrosis. Accumulating evidence suggests a role for Toll-like receptor (TLR)-mediated activation of dendritic cells (DC). Heme oxygenase-1 (HO-1) is a known cytoprotective enzyme induced in response to stress factors like oxygen radicals or inflammation, both of which …