Clemens Scheinecker

Dickkopf-1 is a master regulator of joint remodeling

Degenerative and inflammatory joint diseases lead to a destruction of the joint architecture. Whereas degenerative osteoarthritis results in the formation of new bone, rheumatoid arthritis leads to bone resorption. The molecular basis of these different patterns of joint disease is unknown. By inhibiting Dickkopf-1 (DKK-1), a regulatory molecule of the Wnt pathway, we were able to reverse the bone-destructive pattern of a mouse model of rheumatoid arthritis to the bone-forming pattern of osteoarthritis. In this way, no overall bone erosion resulted, although bony nodules, so-called osteophytes, did form. We identified tumor necrosis factor-α (TNF) as a key inducer of DKK-1 in the mouse inflammatory arthritis model and in human rheumatoid arthritis. These results suggest that the Wnt pathway is a key regulator of joint remodeling.

TNF-induced structural joint damage is mediated by IL-1

Blocking TNF effectively inhibits inflammation and structural damage in human rheumatoid arthritis (RA). However, so far it is unclear whether the effect of TNF is a direct one or indirect on up-regulation of other mediators. IL-1 may be one of these candidates because it has a central role in animal models of arthritis, and inhibition of IL-1 is used as a therapy of human RA. We removed the effects of IL-1 from a TNF-mediated inflammatory joint disease by crossing IL-1α and β-deficient mice (IL-1−/−) with arthritic human TNF-transgenic (hTNFtg) mice. Development of synovial inflammation was almost unaffected on IL-1 deficiency, but bone erosion and osteoclast formation were significantly reduced in IL-1−/−hTNFtg mice, compared with hTNFtg mice based on an intrinsic differentiation defect of IL-1-deficient monocytes. Most dramatically, however, cartilage damage was absent in IL-1−/−hTNFtg mice. Chimera studies revealed that protection of cartilage is based on the loss of IL-1 on hematopoietic, but not mesenchymal, cells, leading to decreased expression of ADAMTS-5 and MMP-3. These data show that TNF-mediated cartilage damage is completely and TNF-mediated bone damage is partially dependent on IL-1, suggesting that IL-1 is a crucial mediator for inflammatory cartilage and bone degradation.

Activator protein 1 (Fos/Jun) functions in inflammatory bone and skin disease

Activator protein 1 (AP-1) (Fos/Jun) is a transcriptional regulator composed of members of the Fos and Jun families of DNA binding proteins. The functions of AP-1 were initially studied in mouse development as well as in the whole organism through conventional transgenic approaches, but also by gene targeting using knockout strategies. The importance of AP-1 proteins in disease pathways including the inflammatory response became fully apparent through conditional mutagenesis in mice, in particular when employing gene inactivation in a tissue-specific and inducible fashion. Besides the well-documented roles of Fos and Jun proteins in oncogenesis, where these genes can function both as tumor promoters or tumor suppressors, AP-1 proteins are being recognized as regulators of bone and immune cells, a research area termed osteoimmunology. In the present article, we review recent data regarding the functions of AP-1 as a regulator of cytokine expression and an important modulator in inflammatory diseases such as rheumatoid arthritis, psoriasis and psoriatic arthritis. These new data provide a better molecular understanding of disease pathways and should pave the road for the discovery of new targets for therapeutic applications.

Phenotypic and Functional Analysis of CD4+CD25−Foxp3+ T Cells in Patients with Systemic Lupus Erythematosus

CD4+CD25+Foxp3+ regulatory T cells (Treg) that specialize in the suppression of immune responses might be critically involved in the pathogenesis of autoimmune diseases. Recent studies have described increased proportions of CD4+Foxp3+ T cells that lacked expression of CD25 in systemic lupus erythematosus (SLE) patients but the suppressive capacity of these cells has not been analyzed so far. We therefore performed combined phenotypic and functional analyses of CD4+CD25−Foxp3+ T cells in patients with autoimmune diseases and healthy controls (HC). Phenotypic analysis revealed increased proportions of CD4+CD25−Foxp3+ T cells in SLE patients as compared with patients with systemic sclerosis, rheumatoid arthritis, (RA), or HC. In addition, increased proportions of CD4+CD25−Foxp3+ T cells correlated with the clinical disease activity and the daily cortisone dose. According to phenotypic analysis, CD4+CD25−Foxp3+ T cells resembled regulatory T cells rather than activated T cells. For functional analysis, a surrogate surface marker combination to substitute for intracellular Foxp3 was defined: CD4+CD25−CD127− T cells from SLE patients were isolated by FACS sorting and analyzed for their suppressive capacity in vitro. CD4+CD25−CD127− T cells, that contained up to 53% Foxp3+ T cells, were found to suppress T cell proliferation but not IFN-γ production in vitro. In summary, CD4+CD25−Foxp3+ T cells phenotypically and to a certain extent also functionally resemble conventional Treg. Despite increased proportions, however, their selective functional defects might contribute to the failure of Treg to control autoimmune dysregulation in SLE patients.

Quantitative and qualitative deficiencies of regulatory T cells in patients with systemic lupus erythematosus (SLE)

The objective of the study was that the regulatory T cells (Treg) that specialize in the suppression of immune responses might be critically involved in the pathogenesis of autoimmune disease. As for systemic lupus erythematosus (SLE), however, published data concerning Treg phenotype and function are partly conflicting. We therefore performed quantitative and qualitative analyses of naturally occurring CD4(+)CD25(+) Treg from SLE patients as compared with healthy controls (HC) in order to further elucidate the role of Treg in this systemic autoimmune disease. The phenotype of peripheral blood CD4(+)CD25(+) Treg was determined by flow cytometry (FACS) in SLE patients and HC. Treg were isolated from SLE patients and HC and their functional capacity was analyzed in suppression assays. Phenotypic and functional data were correlated with clinical data. Decreased proportions of CD4(+) Treg with high-level expression of CD25 (CD4(+)CD25(hi)) were observed in active and inactive SLE patients (0.96 +/- 0.08 and 1.17 +/- 0.08%, respectively) as compared with HC (2 +/- 0.1%). In contrast to HC, Treg from SLE patients displayed an activated phenotype as determined by the expression of CD69, CD71 and HLA-DR. The suppressive capacity of isolated Treg from SLE patients, however, was significantly reduced as compared with HC. Proportions of CD4(+)CD25(hi) T cells and the suppressive capacity of Treg were inversely correlated with the clinical disease activity in SLE patients. Our data describe quantitative and qualitative defects of Treg in SLE patients. These deficiencies might contribute to the breakdown of self-tolerance and the development of the autoimmune response in SLE patients.

Pathogenetic aspects of systemic lupus erythematosus with an emphasis on regulatory T cells.

The development of autoimmune diseases is characterized by the breakdown of mechanism(s) that are responsible for maintaining immunological tolerance against self-structures in the periphery. Several aberrations of immune cells have been described so far. Most recently quantitative and/or qualitative defects of T cells with the capacity to suppress or regulate the proliferation of effector T cells in vitro - subsequently termed regulatory T cells (Treg) - have been suggested to substantially contribute to the imbalance of peripheral tolerance and trigger the outbreak of autoimmune reactions. The aim of this article is to summarize current knowledge about pathomechanisms that are involved in the development of autoimmunity with a special emphasis on the role of Treg in patients with systemic lupus erythematosus (SLE).

Foxp3 expression in CD4+ T cells of patients with systemic lupus erythematosus: a comparative phenotypic analysis

Objectives: The forkhead family transcription factor Foxp3 currently represents the most specific marker molecule for CD4+CD25+ T cells with suppressive/regulatory capacity (Treg) in the mouse. Recent studies in the human system, however, indicate that the expression of Foxp3 can be T cell activation dependent. This tempted us to evaluate the significance of Foxp3 expression under autoimmune conditions with chronic T cell activation in patients with systemic lupus erythematosus (SLE) as compared with healthy controls (HCs). Methods: Proportions of peripheral blood CD4+Foxp3+ T cells and CD4+CD25high T cells were determined in patients with active and inactive SLE as compared with HC by flow cytometry. Comparative analysis of the percentage of CD4+Foxp3+ T cells and of percentage of CD4+CD25high T cells with clinical disease activity and T cell activation marker molecule expression were performed. Finally, the induction of Foxp3 expression was analysed upon T cell activation in vitro. Results: Proportions of CD4+Foxp3+ T cells were significantly increased in patients with SLE as compared with HC and a significant correlation was observed between clinical disease activity and proportions of CD4+Foxp3+ T cells. On the other hand, proportions of CD4+CD25high were decreased in SLE and no correlation with a T cell activation marker expression of was observed. In addition, in vitro activation of T cells induced Foxp3 expression. Conclusions: Our data suggest that the expression of Foxp3 on CD4+ T cells in patients with SLE, at least to some extent, reflects the activation of CD4+ T cells due to underlying disease activity and does not necessarily indicate a functional regulatory T cell capacity.

Activation of the interferon‐γ signaling pathway in systemic lupus erythematosus peripheral blood mononuclear cells

OBJECTIVE To investigate interferon-gamma (IFNgamma) signaling in peripheral blood mononuclear cells (PBMCs) from patients with systemic lupus erythematosus (SLE) by analyzing IFNgamma receptor (IFNgammaR) expression, STAT-1 expression and phosphorylation, and the regulation of IFNgamma-inducible genes. METHODS Fluorocytometry was used to investigate expression of STAT-1, pSTAT-1, CD95, HLA-DR, class I major histocompatibility complex (MHC), IFNgamma-inducible 10-kd protein (IP-10), monokine induced by IFNgamma (Mig), and IFNgammaR in PBMCs from SLE patients and healthy individuals. STAT-1 phosphorylation was determined by fluorocytometry and Western blotting after stimulation with IFNalpha or IFNgamma. Quantitative polymerase chain reaction was used to assess messenger RNA (mRNA) expression of the IFNgamma-inducible genes IP-10 and Mig shortly after preparation or after stimulation with IFNgamma in monocytes. RESULTS STAT-1 expression was increased in PBMCs from SLE patients and correlated significantly with disease activity and with the IFN-inducible expression of CD95 and HLA-DR. STAT-1 expression also showed a trend toward association with class I MHC expression. In addition, the expression of other IFNgamma-inducible genes, such as IP-10 or Mig, was increased in SLE monocytes. While STAT-1 phosphorylation in SLE PBMCs and PBMCs from healthy individuals was similar after IFNalpha stimulation, incubation with IFNgamma induced STAT-1 phosphorylation only in SLE lymphocytes. Moreover, SLE monocytes showed a considerably higher increase in pSTAT-1 expression upon IFNgamma stimulation than monocytes from healthy individuals. Increased responsiveness of SLE monocytes to IFNgamma was also confirmed on the mRNA level, where expression of the IFN-inducible, STAT-1-dependent genes IP-10 and Mig was more efficiently increased in SLE cells. However, IFNgammaR was similarly expressed on SLE lymphocytes and monocytes and those from healthy individuals. CONCLUSION In addition to supporting the role of IFNs in SLE immunopathogenesis in general, the findings of the present study support a role of IFNgamma in this disease.

Cytokines as Therapeutic Targets: Advances and Limitations

Biological therapies targeting cytokines, T cells, or B cells have improved outcomes of inflammatory diseases. However, many issues remain open: What is the best target? How well can response be predicted? How can cure be achieved?

Characterization of Autoreactive T Cells to the Autoantigens Heterogeneous Nuclear Ribonucleoprotein A2 (RA33) and Filaggrin in Patients with Rheumatoid Arthritis

The role of autoimmune reactions in the pathogenesis of rheumatoid arthritis (RA) is poorly understood. To address this issue we have investigated the spontaneous T cell response to two well-characterized humoral autoantigens in RA patients and controls: 1) the heterogeneous nuclear ribonucleoprotein A2, i.e., the RA33 Ag (A2/RA33), and 2) filaggrin in unmodified and citrullinated forms. In stimulation assays A2/RA33 induced proliferative responses in PBMC of almost 60% of the RA patients but in only 20% of the controls (patients with osteoarthritis or psoriatic arthritis and healthy individuals), with substantially stronger responses in RA patients (p < 0.00002). Furthermore, synovial T cells of seven RA patients investigated were also clearly responsive. In contrast, responses to filaggrin were rarely observed and did not differ between RA patients and controls. Analysis of A2/RA33-induced cytokine secretion revealed high IFN-γ and low IL-4 production in both RA and control PBMC, whereas IL-2 production was mainly observed in RA PBMC (p < 0.03). Moreover, A2/RA33-specific T cell clones from RA patients showed a strong Th1 phenotype and secreted higher amounts of IFN-γ than Th1 clones from controls (p < 0.04). Inhibition experiments performed with mAbs against MHC class II molecules showed A2/RA33-induced T cell responses to be largely HLA-DR restricted. Finally, immunohistochemical analyses revealed pronounced overexpression of A2/RA33 in synovial tissue of RA patients. Taken together, the presence of autoreactive Th1-like cells in RA patients in conjunction with synovial overexpression of A2/RA33 may indicate potential involvement of this autoantigen in the pathogenesis of RA.