Scarlet Fever — Sandpaper Rash + Strawberry Tongue

A 7-year-old boy presents with a 2-day history of fever (39.2°C), sore throat, and a finely papular erythematous rash that started on his neck and spread downward. On examination, he has a beefy red oropharynx with tonsillar exudate, circumoral pallor, and a characteristic "sandpaper" texture to the rash. His tongue initially showed a white coating with prominent red papillae. The structure marked **D** in the diagram is responsible for the clinical manifestations of this condition. Which of the following best describes the pathogenic mechanism of this exotoxin?

A 7-year-old girl presents with 2 days of high-grade fever (39.4°C), sore throat, and headache, followed by a diffuse rash on the neck and chest. On examination, she has a flushed face with circumoral pallor, bright-red enlarged tonsils with white exudate, and a fine erythematous sandpaper rash on the trunk and flexures. The structure marked **A** in the diagram shows the characteristic finding of a bright-red, beefy tongue with prominent papillae after the white coat has peeled. Which of the following best explains the pathophysiology of this clinical presentation?