Serum levels of soluble Fas ligand in patients with silicosis

Certain patients with silicosis have been reported to exhibit immunological abnormalities such as the appearance of antinuclear antibodies and the occ urrence of autoimmune diseases. Fas ligand (FasL) is a type II membrane pro tein which induces apoptosis by binding to its membrane receptor, Fas. FasL is converted to a soluble form by a metalloproteinase-like enzyme. We have already found serum soluble Fas (sFas) levels in silicosis patients as wel l as in patients with systemic lupus erythematosus (SLE) to be significantl y higher than those in healthy volunteers. To examine further the role of t he Fas/FasL system in silica-induced immunological abnormalities, we invest igated serum soluble FasL (sFasL) levels in silicosis patients with no clin ical symptoms of autoimmune diseases, using ELISA for sFasL. Although the s erum sFasL levels in patients with SLE were significantly higher than those in healthy volunteers and showed a slight positive correlation with serum sFas levels, those in silicosis patients exhibited no significant differenc e from those in healthy volunteers, and there was no correlation with serum sFas levels. However, sFasL levels were elevated in silicosis patients wit h slight dyspnoea or normal PCO2 among various clinical parameters of silic osis. It may be speculated that the immunological disturbances presented by the abnormalities of apoptosis-related molecules in silicosis patients do not occur with a similar degree of respiratory involvement. Further studies are required to clarify which kinds of factors are involved in silicosis p atients who exhibit immunological abnormalities.