Systemic sclerosis (scleroderma) is characterized by immunologic abnormalities, injury of endothelial cells, and tissue fibrosis. Abnormal oxidative stress has been documented in scleroderma and linked to fibroblast activation. Since platelet-derived growth factor (PDGF) stimulates the production of reactive oxygen species (ROS) and since IgG from patients with scleroderma reacts with human fibroblasts, we tested the hypothesis that patients with scleroderma have serum autoantibodies that stimulate the PDGF receptor (PDGFR), activating collagen-gene expression.

Background Dysbiosis has been recently demonstrated in patients with ankylosing spondylitis (AS) but its implications in the modulation of intestinal immune responses have never been studied. The aim of this study was to investigate the role of ileal bacteria in modulating local and systemic immune responses in AS. Methods Ileal biopsies were obtained from 50 HLA-B27⁺ patients with AS and 20 normal subjects. Silver stain was used to visualise bacteria. Ileal expression of tight and adherens junction proteins was investigated by TaqMan real-time (RT)-PCR and immunohistochemistry. Serum levels of lipopolysaccharide (LPS), LPS-binding protein (LPS-BP), intestinal fatty acid-BP (iFABP) and zonulin were assayed by ELISA. Monocyte immunological functions were studied in in vitro experiments. In addition the effects of antibiotics on tight junctions in human leukocyte antigen (HLA)-B27 transgenic (TG) rats were assessed. Results Adherent and invasive bacteria were observed in the gut of patients with AS with the bacterial scores significantly correlated with gut inflammation. Impairment of the gut vascular barrier (GVB) was also present in AS, accompanied by significant upregulation of zonulin, and associated with high serum levels of LPS, LPS-BP, iFABP and zonulin. In in vitro studies zonulin altered endothelial tight junctions while its epithelial release was modulated by isolated AS ileal bacteria. AS circulating monocytes displayed an anergic phenotype partially restored by ex vivo stimulation with LPS+sCD14 and their stimulation with recombinant zonulin induced a clear M2 phenotype. Antibiotics restored tight junction function in HLA-B27 TG rats. Conclusions Bacterial ileitis, increased zonulin expression and damaged intestinal mucosal barrier and GVB, characterises the gut of patients with AS and are associated with increased blood levels of zonulin, and bacterial products. Bacterial products and zonulin influence monocyte behaviour.

Objective To explore the role of reactive oxygen species (ROS) in the in vitro activation of skin fibroblasts from patients with systemic sclerosis (SSc). Methods Fibroblasts were obtained from involved skin of patients with limited or diffuse SSc. Oxidative activity imaging in living cells was carried out using confocal microscopy. Levels of O₂⁻ and H₂O₂ released from fibroblasts were estimated by the superoxide dismutase (SOD)–inhibitable cytochrome c reduction and homovanilic acid assays, respectively. To verify NADPH oxidase activation, the light membrane of fibroblasts was immunoblotted with an anti‐p47^phox–specific antibody. Fibroblasts were stimulated with various cytokines and growth factors to determine whether any of these factors modulate ROS generation. Cell proliferation was estimated by ³H‐thymidine incorporation. Northern blot analysis was used to study α1 and α2 type I collagen gene expression. Results Unstimulated skin fibroblasts from SSc patients released more O₂⁻ and H₂O₂ in vitro through the NADPH oxidase complex pathway than did normal fibroblasts, since incubation of SSc fibroblasts with diphenylene iodonium, a flavoprotein inhibitor, suppressed the generation of ROS. This suppression was not seen with rotenone, a mitochondrial oxidase inhibitor, or allopurinol, a xanthine oxidase inhibitor. Furthermore, the cytosolic component of NADPH oxidase, p47^phox, was translocated to the plasma membrane of resting SSc fibroblasts. A transient increase in ROS production was induced in normal but not in SSc fibroblasts by interleukin‐1β (IL‐1β), platelet‐derived growth factor type BB (PDGF‐BB), transforming growth factor β1 (TGFβ1), and H₂O₂. Treatment of normal and SSc fibroblasts with tumor necrosis factor α (TNFα), IL‐2, IL‐4, IL‐6, IL‐10, interferon‐α (IFNα), IFNγ, granulocyte–macrophage colony‐stimulating factor (GM‐CSP), G‐CSF, or connective tissue growth factor (CTGF) had no effect on ROS generation. Constitutive ROS production by SSc fibroblasts was not inhibited when these cells were treated with catalase, SOD, IL‐1 receptor antagonist, or antibodies blocking the effect of TGFβ1, PDGF‐BB, and other agonists (IL‐4, IL‐6, TNFα, CTGF). In contrast, treatment of SSc fibroblasts with the membrane‐permeant antioxidant N‐acetyl‐L‐cysteine inhibited ROS production, and this was accompanied by decreased proliferation of these cells and down‐regulation of α1(I) and α2(I) collagen messenger RNA. Conclusion The constitutive intracellular production of ROS by SSc fibroblasts derives from the activation of an NADPH oxidase–like system and is essential to fibroblast proliferation and expression of type I collagen genes in SSc cells. Our results also exclude O₂⁻, H₂O₂, IL‐1β, TGFβ1, PDGF‐BB, IL‐4, IL‐6, TNFα, or CTGF as mediators of a positive, autocrine feedback mechanism of ROS generation.

Extensive chronic graft-versus-host disease (ecGVHD) is characterized by fibrosis similar to that of patients with systemic sclerosis (scleroderma). Since stimulatory autoantibodies against the platelet-derived growth factor (PDGF) receptor (PDGFR) have been found in patients with scleroderma and are responsible for the activation of skin fibroblasts, we tested the hypothesis that these autoantibodies are also present in patients affected by ecGVHD. Serum from 39 patients subjected to allogeneic stem cell transplantation for hematologic malignancies (22 with ecGVHD and 17 without cGVHD) and 20 healthy controls was assayed for the presence of stimulatory autoantibodies to the PDGFR by incubating purified IgG with mouse-embryo fibroblasts lacking PDGFR α or β chains or with the same cells expressing PDGFR α. Stimulatory antibodies to the PDGFR were found selectively in all patients with ecGVHD but in none of the patients without cGVHD. Higher levels were detected in patients with generalized skin involvement and/or lung fibrosis. Antibodies recognized native PDGFR, induced tyrosine phosphorylation, accumulation of reactive oxygen species (ROS), and stimulated type 1 collagen gene expression through the Ha-Ras-ERK1/2-ROS signaling pathway. The biologic activity of these autoantibodies suggests a role in the development of fibrosis and argues for a common pathogenetic trait in ecGVDH and scleroderma phenotypes.

The levels of Ras proteins in human primary fibroblasts are regulated by PDGF (platelet-derived growth factor). PDGF induced post-transcriptionally Ha-Ras by stimulating reactive oxygen species (ROS) and ERK1/2. Activation of ERK1/2 and high ROS levels stabilize Ha-Ras protein, by inhibiting proteasomal degradation. We found a remarkable example in vivo of amplification of this circuitry in fibroblasts derived from systemic sclerosis (scleroderma) lesions, producing vast excess of ROS and undergoing rapid senescence. High ROS, Ha-Ras, and active ERK1/2 stimulated collagen synthesis, DNA damage, and accelerated senescence. Conversely ROS or Ras inhibition interrupted the signaling cascade and restored the normal phenotype. We conclude that in primary fibroblasts stabilization of Ras protein by ROS and ERK1/2 amplifies the response of the cells to growth factors and in systemic sclerosis represents a critical factor in the onset and progression of the disease.