While crawling through the underbrush, Gary may have been exposed to poison oak, causing a contact dermatitis. Since this is a delayed hypersensitivity response mediated by T cells, antihistamines would not have alleviated the symptoms. Cortisone helped, however, due to its immunosuppressive effect. The first bee sting did not have much of an effect, but it served to sensitize Gary (through the development of B cell clones) to the second bee sting. The second sting resulted in an immediate hypersensitivity response (mediated by IgE), which caused the release of histamine. This allergic reaction could thus be treated effectively with antihis-tamines. The previous tetanus vaccine that Gary had received had provided him with active immunity against tetanus.
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