A 24-year-old woman presents with sudden onset high fever (40.5°C), hypotension (BP 88/54 mmHg), diffuse erythematous rash, and acute renal dysfunction. She had inserted a high-absorbency tampon 3 days ago. Blood cultures are negative, but Gram-positive cocci in clusters are isolated from vaginal swabs. The structure marked **C** in the diagram is suspected to be the primary virulence factor driving her clinical presentation. Which of the following best explains the mechanism by which this toxin causes such rapid, severe systemic inflammation?