FAS and systemic sclerosis: It is possible that the generated substances counteract with the increase of cell number and regulate the silica-induced effects through the induction of apoptosis.[36] It was demonstrated that high level of serum-soluble Fas (sFas) is found in patients with silicosis, systemic sclerosis (SSC) and systemic lupus erythematosus (SLE) without any clinical symptoms of autoimmune disease in peripheral blood mononuclear cells (PBMC).[46, 47] Reduced expression of inhibitory genes for Fas-mediated apoptosis in PBMC derived from silicosis patients.