Final answer:
TNF-alpha is the substance that could mediate the fever, shock, and tissue injury observed in patients with STSS.
Step-by-step explanation:
The substance that could mediate the fever, shock, and tissue injury observed in patients with STSS is TNF-alpha (Tumor Necrosis Factor-alpha). TNF-alpha is a pro-inflammatory cytokine that is released by immune system cells. It stimulates excessive activation of immune system cells and release of cytokines, resulting in life-threatening fever, inflammation, and shock. In the context of STSS, TNF-alpha plays a significant role in the pathophysiology of the condition.