A 30-year-old man is known for his large appetite. At a luncheon meeting, he notices that all the cookies contain nuts, which the other diners have ordered knowing that he would not eat them because he would develop blotchy, erythematous, slightly edematous, pruritic plaques on his skin. These plaques would form and then fade within 2 hours. If the man eats the cookies, which of the following sensitized cells would release a mediator that produces these skin lesions?