Porth's Essentials of Pathophysiology, 4e

he immune system is a multifaceted defense network that has evolved to protect against invading micro- organisms, prevent the proliferation of cancer cells, and mediate the healing of damaged tissue. Under normal conditions, the immune response deters or prevents disease. Occasionally, however, the inadequate, inap- propriate, or misdirected activation of the immune sys- tem can lead to debilitating or life-threatening illnesses, typified by allergic or hypersensitivity reactions, trans- plantation rejection, autoimmune disorders, and immu- nodeficiency states. Hypersensitivity Disorders Although activation of the immune system normally leads to production of antibodies and T-cell responses that protect the body against attack by microorganisms, it is also capable of causing tissue injury and disease. Disorders caused by immune responses are collectively referred to as hypersensitivity reactions, a term that arose from the observation that someone exposed to a particular antigen exhibited a detectable reaction or was “hypersensitive” to subsequent encounters with the same antigen. 1 Hypersensitivity disorders are commonly classi- fied into four groups according to the type of immune response causing the injury and the nature and location of the antigen that is the target of the response: type I, immediate hypersensitivity disorders; type II, antibody- mediated disorders; type III, immune complex–mediated disorders; and type IV, T-cell–mediated disorders 1–3 (Table 16-1). Disorders of the Immune Response 16 C h a p t e r Type I, Immediate Hypersensitivity Disorders Type I hypersensitivity reactions are IgE-mediated reac- tions that begin rapidly, often within minutes of an antigen challenge. Often, they are referred to as allergic reactions and the antigens are called allergens. Typical T

Hypersensitivity Disorders Type I, Immediate Hypersensitivity Disorders Systemic (Anaphylactic) Reactions Local (Atopic) Reactions Type II, Antibody-Mediated Disorders Complement- and Antibody-Mediated Cell Destruction Complement- and Antibody-Mediated Inflammation Antibody-Mediated Cellular Dysfunction Type III, Immune Complex–Mediated Disorders Systemic Immune Complex Disorders Local Immune Complex Reactions Type IV, Cell-Mediated Hypersensitivity Disorders Direct Cell-Mediated Cytotoxicity Delayed-Type Hypersensitivity Disorders Transplantation Immunopathology Immune Recognition of Allografts Patterns and Mechanisms of Solid Organ Graft Rejection Hyperacute Rejection Acute Rejection Chronic Rejection Transplantation of Hematopoietic Cells Graft-Versus-Host Disease Autoimmune Disease Immunologic Tolerance B-Cell Tolerance T-Cell Tolerance Mechanisms of Autoimmune Disease Genetic Susceptibility Role of Infections Release of Sequestered Antigens Diagnosis and Treatment of Autoimmune Disease Immunodeficiency Disorders Primary Immunodeficiency Disorders Humoral (B-Cell) Immunodeficiency Disorders Cellular (T-Cell) Immunodeficiency Disorders Severe Combined Immunodeficiency Disorders Immune Deficiency with Thrombocytopenia and Eczema Acquired Immunodeficiency Syndrome Transmission of HIV Infection Molecular and Biologic Features of HIV Infection Classification and Stages of HIV Infection Opportunistic Infections Malignancies Wasting Syndrome and Metabolic Disorders Diagnosis and Treatment HIV Infection in Pregnancy and in Infants and Children

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