Q. An 18-year-old male was referred to your clinic for evaluation of a skin rash that started after he went on a camping trip. He reports coming into contact with a plant that he believed to be poison ivy. The patient has never had any previous history of poison ivy exposure. On physical examination, the patient is found to have multiple, erythematous, pruritic papules and vesicles over his arms, legs, and torso (see image). The lesions are distributed in a linear pattern, consistent with contact dermatitis secondary to poison ivy exposure. You diagnose him with poison ivy dermatitis and advised him to wash the affected areas with soap and water to remove any residual urushiol oil. You also give him a topical corticosteroid cream to apply to the affected areas to reduce inflammation and itching. The patient is instructed to return to the clinic if there is any worsening of his symptoms, or if new symptoms develop. Over the next few days, the patient's symptoms improve with treatment, and he is eventually able to return to his normal activities without any further complications. Which of the following molecular mechanisms is responsible for this patient’s symptoms?