TNFα plays a crucial role in rheumatoid arthritis (RA) by stimulating fibroblast-like synoviocytes (FLS). Lymphotoxin α (LTα) is a pro-inflammatory cytokine with significant homology to TNFα. We compared the effects of both cytokines on cultured RA FLS.
Receptor expression on RA FLS was analyzed by FACS. Cells were stimulated with LTα or TNFα and proliferation was measured by [3H]thymidine incorporation and secretion of inflammatory cytokines and metalloproteinase 3 by ELISA. Activation of MAP kinases and Akt was analyzed by Western blotting. Nuclear translocation of NFκB was visualized by immunofluorescence.
60-80% and 30-50% of the RA FLS tested expressed TNF receptors I and II, respectively, and 70-75% expressed HVEM. LTα induced RA FLS proliferation at the same level of TNFα, which was blocked by etanercept. Both LTα and TNFα induced activation of MAP kinases ERK1/2 and p38 as well as Akt. 95-98% of FLS showed nuclear translocation of NFκB after stimulation with either cytokines. LTα and TNFα were potent to induce secretion of IL-6, IL-8 and metalloproteinase 3 in FLS.
LTα is as effective as TNFα in stimulating RA FLS. Blocking both cytokines might allow a better control of inflammation and synovial proliferation in RA.