Figure 4 Immune complex-mediated hypersensitivity.

Figure 5 The development of an allergy (allergic contact dennatitis) to catechols from the poison ivy plant. Pentadecacatechol is a mixture of catechols, which are oils secreted by the plant thatdissolve easily in skin oils and penetrate the skin. In theskin, the catechols function as haptens - that is, theycombine with skin proteins to become antigenic andprovoke an immune response. The first contact withpoison ivy sensitizes the susceptible person, andsubsequent exposure results in contact dermatitis.

Figure 1c. A schematic view of cellular reactions during the type I allergic response. (a)Sensitization (initial contact with sensitizing dose). (b)Provocation (later contacts with provocative dose).

Figure 1d. The spectrum of reactions to inflammatory cytokines and the common symptoms they elicit in target tissues and organs.Note the extensive overlapping effects.

Figure 1e Immunotherapy for IgE Allergies (a)Repeated injections of very small amounts of antigenare given over several months. (b)This regimen leads tothe formation of specific IgG antibodies. The IgG reactswith antigen before it can bind to IgE, and therefore itblocks the IgE reaction.