Lenny van Bon

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.

Soluble immune complexes shift the TLR-induced cytokine production of distinct polarized human macrophage subsets towards IL-10.

Background Costimulation of murine macrophages with immune complexes (ICs) and TLR ligands leads to alternative activation. Studies on human myeloid cells, however, indicate that ICs induce an increased pro-inflammatory cytokine production. This study aimed to clarify the effect of ICs on the pro- versus anti-inflammatory profile of human polarized macrophages. Materials and Methods Monocytes isolated from peripheral blood of healthy donors were polarized for four days with IFN-γ, IL-4, IL-10, GM-CSF, M-CSF, or LPS, in the presence or absence of heat aggregated gamma-globulins (HAGGs). Phenotypic polarization markers were measured by flow cytometry. Polarized macrophages were stimulated with HAGGs or immobilized IgG alone or in combination with TLR ligands. TNF, IL-6, IL-10, IL-12, and IL-23 were measured by Luminex and/or RT-qPCR. Results HAGGs did not modulate the phenotypic polarization and the cytokine production of macrophages. However, HAGGs significantly altered the TLR-induced cytokine production of all polarized macrophage subsets, with the exception of MΦIL-4. In particular, HAGGs consistently enhanced the TLR-induced IL-10 production in both classically and alternatively polarized macrophages (M1 and M2). The effect of HAGGs on TNF and IL-6 production was less pronounced and depended on the polarization status, while IL-23p19 and IL-12p35 expression was not affected. In contrast with HAGGs, immobilized IgG induced a strong upregulation of not only IL-10, but also TNF and IL-6. Conclusion HAGGs alone do not alter the phenotype and cytokine production of in vitro polarized human macrophages. In combination with TLR-ligands, however, HAGGs but not immobilized IgG shift the cytokine production of distinct macrophage subsets toward IL-10.

A rare polymorphism in Toll Like Receptor 2 is associated with systemic sclerosis phenotype and increases production of inflammatory mediators

T.R. was sponsored by the Dutch association of Research (NWO). J.M. was sponsored by grants SAF2009-1110, cts-4977 T.R. and J.M. were sponsored by the Orphan Disease program grant from the European League Againts Rheumatism (EULAR)

MicroRNAs underlie plasmacytoid dentritic cell dysfunction in systemic sclerosis

Background Systemic sclerosis (SSc) is an autoimmune disease characterized by fibrosis of the skin and internal organs that carries a high burden of morbidity and mortality. Immune system dysfunction has been undisputedly demonstrated to underlie SSc pathogenesis. In particular, pDCs not only circulate in very high number in SSc patients but also secrete high concentrations of specific chemokines that directly drive various features of SSc, including endothelial dysfunction and fibroblast activation.

Macrophage dysfunction in Psoriatic Arthritis

The pathogenesis of Psoriatic Arthritis (PsA) remains poorly understood. The underlying chronic inflammatory immune response is thought to be triggered by unknown environmental factors and might arise due to an impaired (innate) immune function by Dendritic Cells (DCs) [1]. Anti-inflammatory CD163+ type 2 macrophages (mf-2) are thought to have important functions in restoring immune homeostasis during an inflammatory response. Mf-2 are present in PsA synovium at high numbers. Why the immune response in PsA goes awry, despite the presence of these mf-2, is still largely undetermined.

Impaired dendritic cell proinflammatory cytokine production in psoriatic arthritis

Objective: The pathogenesis of psoriatic arthritis (PsA) remains poorly understood. The underlying chronic inflammatory immune response is thought to be triggered by unknown environmental factors potentially arising from a defective immune function. We undertook this study to determine whether an impaired acute inflammatory response by dendritic cells (DCs) might compromise the clearance of bacteria and predispose to chronic inflammation. Methods: We determined cytokine production by DCs from healthy controls and from patients with rheumatoid arthritis, PsA, and psoriasis in response to Mycobacterium tuberculosis, Mycobacterium avium paratuberculosis, and a range of other bacteria and Toll-like receptor (TLR) ligands. Phenotypic differences involved in cellular responses against (myco) bacteria were determined by quantitative polymerase chain reaction and flow cytometry. Results: The secretion of proinflammatory cytokines by PsA DCs was impaired upon in vitro challenge with mycobacteria and TLR-2 ligands. This impairment was associated with elevated serum levels of C-reactive protein. The expression of TLR-2 and other receptors known to mediate mycobacterial recognition was unaltered. In contrast, the intracellular TLR inhibitors suppressor of cytokine signaling 3 and A20 were more highly expressed in DCs from PsA patients. PsA DCs further demonstrated up-regulated levels of ATG16L1, NADPH oxidase 2, and LL37, which are molecules implicated in the immune response against intracellular bacteria. Conclusion: Our findings indicate that DCs from PsA patients have a disordered immune response toward some species of (myco) bacteria. This might predispose to impaired immune responses to, and in turn impaired clearance of, these bacteria, setting the stage for the chronic inflammation of joints, entheses, skin, and the gut.

CD4+CD45RA+ T-cells from early diffuse systemic sclerosis patients produce high levels of interleukin-17

Background In Systemic Sclerosis (SSc) the detrimental role of the immune system is a topic of great interest. In recent genetic association studies most genes identified to date are immunity related genes. A contribution of T-cells as important cytokine producing cells is shown and the skewing of this population can be an important player in the maintenance and progression of inflammation and fibrosis.

Antigen-Presenting Cells and their Fcγ and Toll-Like Receptors: Leading Suspects in Autoimmunity

Antigen-presenting cells (APCs) play an important role in the development of autoimmune diseases. These cells recognize pathogen associated molecular patterns but also endogenously produced ligands through toll-like receptors (TLRs). Aberrant activation of these receptors and the following intracellular signaling pathways can induce the deleteri- ous production of pro-inflammatory cytokines. In genetically predisposed individuals this might lead to a breach in toler- ance and eventually autoimmunity. IgG and IgG immune complexes (ICs), which are abundantly present in autoimmune diseases like systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and systemic sclerosis (SSc) are recognized by APCs via Fc gamma receptors (Fc Rs) and can also modulate their activation state. Upon their uptake specific antigens present in ICs are capable of stimulating APCs via their intracellular TLRs, increasing their capability to induce (autoreac- tive) T and B cell responses. This underscores their likely role in the generation and maintenance of autoimmunity. By fo- cusing on three autoimmune diseases, SLE, RA and SSc, we will illustrate the importance of TLRs and Fc Rs in the pathogenesis of autoimmune diseases.