MEDizzy - Ten minutes after being stung by a wasp, a 30-year-old man

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General Pathology (II)

Ten minutes after being stung by a wasp, a 30-year-old man develops multiple patches of red, irregular skin lesions over his entire body. These lesions (urticaria) are pruritic, and a new crop of lesions develops the next day. Which one of the following statements correctly describes an important component of the pathomechanism of this immune response?

ExplanationHypersensitivity diseases are caused by immune mechanisms. They are classified into four different categories based on the immune mechanisms involved. Type I hypersensitivity reactions involve IgE (reaginic) antibodies that have been bound to the surface of mast cells and basophils. These IgE antibodies are formed by a T cell-dependent process. An allergen initially binds to antigen-presenting cells, which then stimulate TH2 cells to secrete interleukin 4 (IL-4), IL-5, and IL-6. IL-5 stimulates the production of eosinophils, while IL-4 stimulates B cells to transform into plasma cells and produce IgE. This IgE then attaches to mast cells and basophils, because these cells have cell surface receptors for the Fc portion of IgE. When these “armed” mast cells or basophils are reexposed to the allergen, the antigen bridges two IgE molecules and causes mast cells to release preformed (primary) mediators. This antigen-to-antibody binding also causes these cells to synthesize secondary mediators.