T cells and B cells in the pathogenesis of systemic sclerosis: recent insights and therapeutic opportunities

Epigenetics and pathogenesis of systemic sclerosis; the ins and outs

The pathogenesis of many diseases is influenced by environmental factors which can affect human genome and be inherited from generation to generation. Adverse environmental stimuli are recognized through the epigenetic regulatory complex, leading to gene expression alteration, which in turn culminates in disease outcomes. Three epigenetic regulatory mechanisms modulate the manifestation of a gene, namely DNA methylation, histone changes, and microRNAs. Both epigenetics and genetics have been implicated in the pathogenesis of systemic sclerosis (SSc) disease. Genetic inheritance rate of SSc is low and the concordance rate in both monozygotic (MZ) and dizygotic (DZ) twins is little, implying other possible pathways in SSc pathogenesis scenario. Here, we provide an extensive overview of the studies regarding different epigenetic events which may offer insights into the pathology of SSc. Furthermore, epigenetic-based interventions to treat SSc patients were discussed.

Potential role of human-specific genes, human-specific microRNAs and human-specific non-coding regulatory RNAs in the pathogenesis of systemic sclerosis and Sjögren's syndrome

The etiology and pathogenesis of human autoimmune diseases remain unknown despite intensive investigations. Although remarkable progress has been accomplished through genome wide association studies in the identification of genetic factors that may predispose to their occurrence or modify their clinical presentation to date no specific gene abnormalities have been conclusively demonstrated to be responsible for these diseases. The completion of the human and chimpanzee genome sequencing has opened up novel opportunities to examine the possible contribution of human specific genes and other regulatory elements unique to the human genome, such as microRNAs and non-coding RNAs, towards the pathogenesis of a variety of human disorders. Thus, it is likely that these human specific genes and non-coding regulatory elements may be involved in the development or the pathogenesis of various disorders that do not occur in non-human primates including certain autoimmune diseases such as Systemic Sclerosis and Primary Sjögren's Syndrome. Here, we discuss recent evidence supporting the notion that human specific genes or human specific microRNA and other non-coding RNA regulatory elements unique to the human genome may participate in the development or in the pathogenesis of Systemic Sclerosis and Primary Sjögren's Syndrome.

B cell block: is rituximab a new possible treatment for systemic sclerosis?

There is no treatment for fibrotic diseases, including the autoimmune disease systemic sclerosis (sclerderma, SSc). Although broad spectrum immune suppressants have little to no effect on the fibrosis in SSc, agents targeting specific proinflammatory agents are currently being considered as possible therapeutic approaches to combating SSc. B cells are lymphocytes that proliferate and secrete antibody molecules which drive the autoimmune response. CD20 is a B cell marker; the agent rituximab is an antibody against CD20. In a recent report by Bosello and colleagues (Arthritis Res. Ther. 12(2): R54, 2010), rituximab was tolerated in SSc patients and appeared to result in an improvement of the skin score and of clinical symptoms of SSc. This report is one of a series of recent studies suggesting that rituximab may be a possible treatment for SSc. This commentary summarizes these observations.

Early recovery of CD4 T cell receptor diversity after "lymphoablative" conditioning and autologous CD34 cell transplantation

T cell diversity posttransplantation is thought to be severely restricted, based on T cell receptor beta-chain immunophenotyping or spectratyping. Using beta-chain sequencing, we studied CD4 T cell diversity in 2 adult patients undergoing "lymphoablative" conditioning with cyclophosphamide (Cy), total body irradiation (TBI), and antithymocyte globulin (ATG) and autologous transplantation of hematopoietic cells depleted of T cells by enrichment for CD34 cells. The indication for the transplantation was systemic sclerosis (SSc) or multiple sclerosis (MS). Pretransplantation, the estimated number of distinct beta chains (the minimum number of CD4 T cell clones) in the 2 patients was 600,000 to 700,000, similar to the number in a healthy control. This number was 200,000 to 500,000 at 1 month posttransplantation and 400,000 to 1,600,000 at 12 months posttransplantation. In conclusion, the number of T cells early after lymphoablative conditioning and autologous CD34 cell transplantation may be more diverse than previously appreciated, possibly because many T cell clones survive the conditioning or are reinfused with the graft. Thus, the therapy may not be completely T cell lymphoablative.

T cells expressing allograft inflammatory factor 1 display increased chemotaxis and induce a profibrotic phenotype in normal fibroblasts in vitro

OBJECTIVE

Allograft inflammatory factor 1 (AIF-1) was first identified in rat cardiac allografts undergoing chronic rejection. The vasculopathy of chronic allograft rejection is strikingly similar to that seen in patients with systemic sclerosis (SSc). We previously demonstrated AIF-1 expression in inflammatory cells infiltrating skin and lungs from SSc patients, but its role in SSc pathogenesis is unknown. The present study was undertaken to investigate the effects of AIF-1 on T cell migration and production of cytokines capable of modulating normal dermal fibroblast functions.

METHODS

Stably transfected Jurkat T cells expressing 2 AIF-1 splicing variants were prepared, and their migration toward fibroblast monolayers assayed in Transwell cultures. Cytokine production was assessed by real-time polymerase chain reaction (PCR) and multiplex enzyme-linked immunosorbent assay. Fibroblast gene expression was quantified by real-time PCR, and collagen production by Western blot analysis of culture media.

RESULTS

AIF-1 significantly increased Jurkat T cell migration toward fibroblast monolayers. Expression of AIF-1 isoform 2 in Jurkat T cells up-regulated their production of interleukin-4 (IL-4) and IL-17. Conditioned media from AIF-1-expressing clones stimulated synthesis of types I and III collagen and expression of IL-6, transforming growth factor beta, endothelin receptor, and alpha-smooth muscle actin by normal dermal fibroblasts.

CONCLUSION

These results suggest that AIF-1 may participate in the early pathogenesis of SSc by promoting tissue T cell infiltration and production of cytokines capable of inducing the expression of a fibrotic phenotype in normal fibroblasts.

[Etiopathogenesis. New concepts]

Systemic sclerosis is a complex, progressive autoimmune disease. The origin is, so far, unknown and it is characterized by immunological and endothelial damage followed by fibrosis. Interaction between the host genetic backgrounds with environmental factors is thought to turn out an abnormal immune response characterized by clonal expansion of Th2 repertoire, upregulation of pro-fibrotic cytokines and dysregulated B cells. Specific autoantibodies profiles are associated with clinical subtypes of the diseases. Endothelial activation is an early feature with damage of the vasocontrictive and vasodilation response. Finally, persistent tissue ischemia and abnormal immune response produce myofibroblast proliferation andoverproduction of extracellular matrix proteins and fibrosis.