Tumour necrosis factor alpha (TNF-alpha) interferes with Fas-mediated apoptotic cell death on rheumatoid arthritis (RA) synovial cells: A possible mechanism of rheumatoid synovial hyperplasia and a clinical benefit of anti-TNF-alpha therapy for RA

To investigate the mechanism of rheumatoid synovial hyperplasia (RASH), the influence of tumour necrosis factor alpha (TNF-alpha) on Fas-mediated apop totic cell death (Fas-ACD) was examined on cultured rheumatoid synovial cel ls (RASCs), RASCs were obtained from the synovial tissues of eight patients with rheumatoid arthritis (RA) and SCs from eight patients with osteoarthr itis (OA) were used as a control. To examine the influence of TNF-alpha on Fas-ACD, SCs were cultured with anti-Fas antibody (CH11) for 16 h in the ab sence or presence of different doses of recombinant TNF-alpha. ACD was dete rmined by electron microscopic analysis and the percentage of apoptotic cel ls was calculated by trypan blue staining. In addition, the expression of F as and Bcl-2 on RASCs was examined by flow cytometry, As a result, RASCs we re more susceptible to Fas-ACD in vitro than OASCs, TNF-alpha interfered wi th Fas-ACD on RASCs in a dose-dependent manner. Moreover, removal of TNF-al pha activity by a neutralizing anti-TNF-alpha antibody (cA2) restored Fas-A CD. Flow cytometric analysis showed no significant changes in either Fas or Bcl-2 expression on RASCs after the culture with TNF alpha. These results suggest the following: (1) Fas-ACD might be diminished in viv o by local excessive TNF-alpha and this might contribute in part to RASH, ( 2) The inhibition of Fas-ACD on RASCs by TNF-alpha might not be associated with changes in the expression of Fas or Bcl-2, (3) In addition, considerin g a magnetic resonance imaging (MRI) finding of marked reduction in the RAS H after cA2 treatment, blockade of TNF-alpha activity could restore Fas-ACD in RA synovium, implicating a clinical benefit of anti-TNF-alpha therapy f or RA. (C) 2000 Academic Press.