Stimulation indices of dose-dependent induction of (a) prostaglandin E2 (PGE2), (b) matrix metalloproteinase-1(MMP-1) and (c) IL-8 by human TNF-like weak inducer of apoptosis (hTWEAK) in combination with tumour necrosis factor (TNF) or IL-1β in dermal fibroblasts. Cells were incubated for 72 hours in the presence of hTWEAK at the indicated doses, together with TNF (1 ng/ml) or IL-1β (0.1 ng/ml). Supernatants were analyzed by ELISA for the different products. Stimulation indices represent TNF plus hTWEAK over control medium (in grey); IL-1β plus hTWEAK over control medium (in black). Similar results were obtained in nine independent experiments on dermal fibroblasts (P < 0.07 for 50 ng/ml hTWEAK compared to control).