Thrombin and IL-1 synergistically induce IL-6 production of SMC. SMC were incubated in 24-well plates until they reached confluency, washed and stimulated separately (A) with IL-1α (1, 10 or 100 pg/mL) or thrombin (Thr; 0.1, 1, 10 U/mL), or with combinations (B) of IL-1α and thrombin. IL-6 activities detected in supernatants of SMC costimulated with combinations of IL-1α and thrombin are shown in (B). For estimation of the synergistic effect IL-6 activities in supernatants of SMC stimulated separately with IL-1α or thrombin are added up and presented in (A). IL-6 activity in supernatants was measured in 7TD1-assay. Four independent experiments showed similar results. The asterisks indicate costimulation cocultures expressing a synergistic effect.