Pierer M et al. (2007) The TNF superfamily member LIGHT contributes to survival and activation of synovial fibroblasts in rheumatoid arthritis. Rheumatology (Oxford) 46: 1063–1070

Activated T-cells are involved in the pathogenesis of rheumatoid arthritis (RA). LIGHT (also known as tumor necrosis factor ligand superfamily member 14) is produced by various immune cells, including activated T-cells. Pierer et al., therefore, analyzed the expression and function of LIGHT and its receptors in synovial samples from patients with RA.

Synovial fluid was obtained from patients with RA (n = 6, with cells; n = 42, without cells) and osteoarthritis (OA; n = 25, without cells). Synovial tissue obtained from individual patients undergoing knee replacement surgery was used for isolation of cultured synovial fibroblasts (SFs).

LIGHT was expressed by CD4+ T cells, but not CD68+ macrophages, in synovial samples obtained from patients with RA. LIGHT was not detected in synovial samples from patients with OA; however, activated T cells were virtually absent in these samples. SFs cultured from patients with RA or OA expressed receptors for LIGHT. The authors, therefore, suggest that it might be the availability of LIGHT, rather than increased expression of its receptors, that is required for development of RA. LIGHT stimulation of SFs enhanced the expression and/or activity of various molecules involved in immune cell activation, and significantly decreased FasL (Fas ligand; also known as tumor necrosis factor ligand superfamily member 6)-induced cell death of SFs, but not their rates of spontaneous apoptosis or proliferation.

Pierer et al. conclude that LIGHT is upregulated in the joints of patients with RA, but not OA, and suggest that it might lead to T-cell co-stimulation, enhanced infiltration of lymphocytes and synovial hyperplasia.