344
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).
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
Disorders of
the Immune
Response
16
C h a p t e r
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
