Elevated levels of soluble Fas in systemic lupus erythematosus: comment on the article by Knipping et al

Soluble Fas mRNA is dominantly expressed in cases with silicosis

Although it is well known that cases with silicosis exhibit various immunological abnormalities, the mechanisms involved in the occurrence of immuno-dysfunction or dysregulation induced by silica compounds have not yet been determined. Fas is a well-known cell surface molecule that is involved in the apoptosis pathway that belongs to the tumour necrosis factor-receptor family. Soluble Fas (sFas) is produced as an alternatively spliced product of the Fas gene and protects cells from apoptosis due to antagonization of the binding between membrane form of the Fas gene (mFas) and the Fas ligand. To determine the role of the Fas/Fas ligand system in silica-induced immunological abnormalities, we investigated Fas and Fas-ligand message expression levels using the multiplex reverse transcription-polymerase chain reaction (RT-PCR) method with peripheral blood mononuclear cells from silicosis cases with no clinical symptoms of autoimmune diseases. Although the relative expression levels of the Fas or Fas-ligand genes were not remarkably altered in these cases, we observed the sFas message was dominantly expressed compared with mFas expression. These results suggest that self-recognizing clones in cases with silicosis survive for decades, escaping the exclusion mechanisms induced by apoptosis. Then they cause the appearance of autoantibodies and the acquisition of autoimmune diseases sequentially.

Serum concentration of soluble Fas in patients with autoimmune thyroid diseases

Fas is an apoptosis-signaling receptor molecule found on the surface of a number of cell types. Malfunction of the Fas system accelerates autoimmune diseases, whereas its exacerbation may cause tissue destruction. Soluble Fas (sFas) molecule lacks the transmembrane domain due to alternative splicing and blocks Fas-mediated apoptosis. This study investigated serum levels of sFas in autoimmune thyroid diseases. Serum levels of sFas were determined by enzyme-linked immunosorbent assay in 46 patients with Graves' disease, 32 patients with Hashimoto's thyroiditis, 14 patients with silent thyroiditis, and 24 normal controls. Compared with normal subjects (1.43+/-0.37 ng/mL), sFas was increased in thyrotoxic patients with Graves' disease (1.89+/-0.47 ng/mL, p < 0.001), and was decreased in patients with Graves' disease in remission (1.02+/-0.41 ng/mL, p < 0.001) and in euthyroid patients with Hashimoto's thyroiditis (0.97+/-0.25 ng/mL, p < 0.0001), but was normal in hypothyroid patients with Hashimoto's thyroiditis and in thyrotoxic patients with silent thyroiditis. Thus, changes in serum levels of sFas could not be explained by changes in serum thyroid hormones, although sFas concentration correlated with free thyroxine (r = 0.692, p < 0.0001). Also, the levels of sFas significantly correlated with the activities of TSH receptor antibody in Graves' disease (r = 0.671, p < 0.0001). Increased sFas in Graves' disease suggests increased expression of alternatively spliced Fas mRNA variant that produces sFas protein and decreased of cell surface expression of Fas, and may induce thyroid cell growth and production of TSH receptor antibody by protecting against apoptosis of thyroid cells and autoreactive B cells. Decreased sFas in Hashimoto's thyroiditis suggests decreased Fas mRNA variant and increased full-length Fas mRNA and membrane Fas, and may induce destruction of thyroid cells by promoting apoptosis of thyroid cells.

Serum levels of soluble form of Fas molecule in patients with congestive heart failure

Compared with soluble Fas molecule (sFas, an inhibitor of Fas-mediated apoptosis) in normal volunteers, the serum level of sFas significantly increased by 41% in New York Heart Association (NYHA) class III (p <0.05) and by 97% in NYHA class IV patients with congestive heart failure (p <0.001). Furthermore, sFas showed correlations with soluble forms of TNF receptor-p55 (RI) and -p75 (RII) (r = 0.68 and r = 0.56) which inhibit activities of TNF alpha.

Detection of the soluble form of the Fas molecule in patients with multiple sclerosis and human T-lymphotropic virus type I-associated myelopathy

We evaluated the presence of soluble Fas molecule (sFas) in the cerebrospinal fluids (CSF) and the sera of patients with multiple sclerosis (MS) or human T-lymphotropic virus type I (HTLV-I) associated myelopathy (HAM) using an enzyme-linked immunosorbent assay (ELISA). Patients with multiple sclerosis in the active phase had higher sFas serum levels than control (p < 0.005). In addition, significantly increased serum levels of sFas were found in patients with HAM (p < 0.005). We found a significantly increased CSF levels of sFas in patients with HAM and patients with MS in the active stage (p < 0.005). These results suggest that serum sFas may be related to clinical activity in patients with MS and that Fas may play an important role in the pathogenesis of HAM.