FAS and rheumatoid arthritis: Specifically, several studies with cultured RASFs showed that synoviocytes from rheumatoid synovium tissue express functional Fas [8,17,18] and that Fas activation induces apoptosis only in a small population of cells, even though the Fas/FasL system seems to be incapable of eliminating cells in proliferative RA synovium [8,18,37,40,41].