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Chapter 16 : Immune-Mediated Skin Diseases
This chapter on immune mechanisms in skin diseases illustrates, in an organ system, the effects of various immune effector mechanisms. The skin is the largest organ of the body and the most common site for manifestations of immune reactions. Cytotoxic effects of antibodies to epithelial cell or basement membrane antigens could also produce separation and destruction of the cells or destruction of the basement membrane. The diseases listed in this chapter have complex features and most likely are due to an interplay of additional pathogenic mechanisms. Cytotoxic reactions produce blistering diseases, immune complex reactions, vascular lesions, anaphylactic reactions, whealing lesions, cell-mediated reactions, chronic infiltrative diseases, granulomatous reactions, and destructive mass lesions of the skin. Immune complex reactions are responsible for a variety of vascular reactions in the skin. Most lesions are secondary to deposition of immune complexes in dermal vessels. Wheal-and-flare reactions and urticarial skin eruptions are common occurrences, not only on contact with allergens but also during the course of infectious diseases or drug treatment. Skin reactions mediated by sensitized cells can be divided into those primarily due to T-cytotoxic (TCTL) cells and those mediated by T-delayed-type hypersensitivity (TDTH) cells. Granulomatous lesions in the skin result from the accumulation of macrophages and reactive fibrosis to poorly degradable phagocytosed debris. The reactions may be initiated by antibody to T cells reacting with antigen or to foreign bodies that are not immunogenic. A common manifestation of lesions of small vessels in the skin is purpura.