Stimulation index of dose-dependent induction of IL-8, IL-6, matrix metalloproteinase-1 (MMP-1) and prostaglandin E2 (PGE2) by hTWEAK in 10 experiments on dermal fibroblasts and four experiments on synoviocytes. Polymyxin B-treated cells (2 × 104/well) were incubated for 72 hours in the presence of human TNF-like weak inducer of apoptosis (hTWEAK) at the indicated doses. Supernatants from dermal fibroblasts or synoviocytes were tested by ELISA for the different products. Values are shown as mean ± SEM. Except for PGE2, Mann–Whitney P values at 50 ng/ml and at 100 ng/ml versus control were significant (P < 0.02).