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hypersensitivity angiitis 347 hypogammaglobulinemia
Schematic representation of the formation and deposition of immune complexes
in vessel walls in type III hypersensitivity.
hypersensitivity angiitis
Small vessel inflammation most frequently induced by drugs.
hypersensitivity diseases
Disorders medicated at least in part by immune mechanisms
such as autoimmune diseases in which autoantibodies
react with basement membranes such as the kidney,
lung, and skin or in which autoantibodies react against cell
constituents such as DNA as in systemic lupus erythematosus
(SLE). Any of the four mechanisms of hypersensitivity
reaction may participate in the production of a hypersensitivity
disease.
hypersensitivity pneumonitis
Lung inflammation induced by antibodies specific for
substances that have been inhaled. Within hours of inhaling
the causative agent, dyspnea, chills, fever, and coughing
occur. Histopathology of the lung reveals inflammation of
alveoli in the interstitium with obliterating bronchiolitis.
Immunofluorescence examination reveals deposits of C3.
Hyperactivity of the lungs to airborne immunogens or
allergens may ultimately lead to interstitial lung disease. An
example is farmer’s lung, which is characterized by malaise,
coughing, fever, tightness in the chest, and myalgias. Of
the numerous syndromes and associated antigens that may
induce hypersensitivity pneumonitis, humidifier lung (thermophilic
actinomycetes), bagassosis (Thermoactinomyces
vulgaris), and bird fancier’s lung (bird droppings) are well
known. Types of hypersensitivity pneumonitis caused by
Penicillium species include cheese worker’s disease, humidifier
lung, woodman’s disease, and cork worker’s disease.
hypersensitivity reaction
Refer to hypersensitivity.
hypersensitivity vasculitis
An allergic response to drugs, microbial antigens, or antigens
from other sources, leading to an inflammatory reaction
involving small arterioles, venules, and capillaries.
hyperthyroidism
A metabolic disorder attributable to thyroid hyperplasia
with an elevation in thyroid hormone secretion. Also called
Graves’ disease.
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Antigen
determinant
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Light chain
Heavy chain
hypervariable regions
A minimum of four sites of great variability that are present
throughout the heavy and light chain V regions. They
govern the antigen-binding sites of antibody molecules. The
grouping of these hypervariable residues into areas governs
both conformation and specificity of the antigen-binding
sites upon folding of the protein molecules. Hypervariable
residues are also responsible for variations in idiotypes
between immunoglobulins produced by separate cell clones.
Those parts of the variable region that are not hypervariable
are called framework regions (FRs). Hypervariable regions
are also called complementarity-determining regions
(CDRs; refer to hot spot). The term also refers to portions
of T cell receptors (TCRs) that constitute antigen-binding
sites. Each antibody heavy chain and light chain and each
TCR α chain and β chain possesses three hypervariable
loops, also called CDRs. Most of the variability between
different antibodies or TCRs is present within these loops.
hypocomplementemia
Diminished complement in the blood. It can arise from
a number of diseases in which immune complexes fix
complement in vivo, leading to decreases in complement
proteins. Examples include active cases of systemic lupus
erythematosus (SLE), proliferative glomerulonephritis, and
serum sickness. Protein-deficient patients may also have
diminished plasma complement protein levels.
hypocomplementemic glomerulonephritis
Decreased complement in the blood during the course of
chronic progressive glomerulonephritis, in which C3 is deposited
in the glomerular basement membrane of the kidney.
hypocomplementemic vasculitis urticarial syndrome
A type of systemic inflammation with leukocytoclastic vasculitis.
Diminished serum complement levels and urticaria
are present.
hypogammaglobulinemia
Deficient levels of IgG, IgM, and IgA serum immunoglobulins
that may be attributable to decreased synthesis
or increased loss. Hypogammaglobulinemia can be
physiologic in neonates. It may be a manifestation of
congenital or acquired antibody deficiency syndromes.
Several types are described and include Bruton’s
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The structure of the six hypervariable regions of an antibody.
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