Hypersensitive Reactions CHAPTER 16 365 TABLE 16-2 Identification of IgE based on reactivity of atopic serum in P-K test Treatment Allergen added P-K reaction at skin site A None antiserum to human atopic serum Rabbit antiserum to human igM, igG, IgA, and IgD Serum from an atopic individual was injected into rabbits to produce antiserum against human atopic serum. When this antiserum was reacted with human atopic serum, it neutralized the p-k reaction. SOURCE: Based on K Ishizaka and T Ishizaka, 1967, J Immunol. 99: 1187. granulocytes that circulate in the blood of most vertebrates; mm. Electron micrographs of mast cells reveal numerous in humans, they account for 0.5%-1.0% of the circulating membrane-bounded granules distributed throughout the white blood cells. Their granulated cytoplasm stains with cytoplasm, which, like those in basophils, contain pharmaco- basic dyes, hence the name basophil. Electron microscopy re- logically active mediators(Figure 16-3). After activation, these veals a multilobed nucleus, few mitochondria, numerous mediators are released from the granules, resulting in the clin- glycogen granules, and electron-dense membrane-bound ical manifestations of the type I hypersensitive reaction. granules scattered throughout the cytoplasm that contain Mast cell populations in different anatomic sites differ sig pharmacologically active mediators(see Figure 2-10c) nificantly in the types and amounts of allergic mediators they Mast-cell precursors are formed in the bone marrow dur- contain and in their sensitivity to activating sti ing hematopoiesis and are carried to virtually all vascularized cytokines. Mast cells also secrete a large variety of cytokine peripheral tissues, where they differentiate into mature cells. that affect a broad spectrum of physiologic, immunologic, Mast cells are found throughout connective tissue, particu- and pathologic processes(see Table 12-1) larly near blood and lymphatic vessels. Some tissues, includ- ing the skin and mucous membrane surfaces of the respira- IgE-BINDING FC RECEPTORS tory and gastrointestinal tracts, contain high concentrations The reaginic activity of igE depends on its ability to bind to a of mast cells; skin, for example, contains 10,000 mast cells receptor specific for the Fc region of the e heavy chain. Two FIGURE 16-3(a)Electron micrograph of a typical mast cell reveals membrane of a mast cell. (c)Granule releasing its contents(towards numerous electron-dense membrane- bounded granules prior to top left) during degranulation. / From S. Burwen and B. Satir, 1977, degranulation. (b) Close-up of intact granule underlying the plasma J Cell Biol. 73: 662. 1granulocytes that circulate in the blood of most vertebrates; in humans, they account for 0.5%–1.0% of the circulating white blood cells. Their granulated cytoplasm stains with basic dyes, hence the name basophil. Electron microscopy re￾veals a multilobed nucleus, few mitochondria, numerous glycogen granules, and electron-dense membrane-bound granules scattered throughout the cytoplasm that contain pharmacologically active mediators (see Figure 2-10c). Mast-cell precursors are formed in the bone marrow dur￾ing hematopoiesis and are carried to virtually all vascularized peripheral tissues, where they differentiate into mature cells. Mast cells are found throughout connective tissue, particu￾larly near blood and lymphatic vessels. Some tissues, includ￾ing the skin and mucous membrane surfaces of the respira￾tory and gastrointestinal tracts, contain high concentrations of mast cells; skin, for example, contains 10,000 mast cells per mm3 . Electron micrographs of mast cells reveal numerous membrane-bounded granules distributed throughout the cytoplasm, which, like those in basophils, contain pharmaco￾logically active mediators (Figure 16-3). After activation, these mediators are released from the granules, resulting in the clin￾ical manifestations of the type I hypersensitive reaction. Mast cell populations in different anatomic sites differ sig￾nificantly in the types and amounts of allergic mediators they contain and in their sensitivity to activating stimuli and cytokines. Mast cells also secrete a large variety of cytokines that affect a broad spectrum of physiologic, immunologic, and pathologic processes (see Table 12-1). IgE-BINDING Fc RECEPTORS The reaginic activity of IgE depends on its ability to bind to a receptor specific for the Fc region of the  heavy chain. Two Hypersensitive Reactions CHAPTER 16 365 TABLE 16-2 Identification of IgE based on reactivity of atopic serum in P-K test Serum Treatment Allergen added P-K reaction at skin site Atopic None – – Atopic None + + Nonatopic None + – Atopic Rabbit antiserum to human atopic serum* + – Atopic Rabbit antiserum to human IgM, IgG, IgA, and IgD† + + *Serum from an atopic individual was injected into rabbits to produce antiserum against human atopic serum. When this antiserum was reacted with human atopic serum, it neutralized the P-K reaction. † Serum from an atopic individual was reacted with rabbit antiserum to the known classes of human antibody (IgM, IgA, IgG, and IgD) to remove these isotypes from the atopic serum. The treated atopic serum continued to give a positive P-K reaction, indicating that a new immunoglobulin isotype was responsible for this reactivity. SOURCE: Based on K. Ishizaka and T. Ishizaka, 1967, J. Immunol. 99:1187. (a) (b) (c) FIGURE 16-3 (a) Electron micrograph of a typical mast cell reveals numerous electron-dense membrane-bounded granules prior to degranulation. (b) Close-up of intact granule underlying the plasma membrane of a mast cell. (c) Granule releasing its contents (towards top left) during degranulation. [From S. Burwen and B. Satir, 1977, J. Cell Biol. 73:662.]