C h a p t e r 1 6
Disorders of the Immune Response
347
such as the presence of residual amounts of peanut that
remain on equipment used for preparing foods con-
taining peanuts, can be sufficient to cause anaphylaxis
in an extremely sensitive person. Within minutes after
exposure, itching, hives, and skin erythema develop,
followed shortly by bronchospasm and respiratory
distress. Vomiting, abdominal cramps, diarrhea, and
laryngeal edema and obstruction follow, and the per-
son may go into shock and die unless effective treat-
ment is instituted.
The initial management of anaphylaxis focuses
on the establishment of a stable airway and intrave-
nous access, and the administration of epinephrine.
7,8
Epinephrine produces relaxation of bronchial smooth
muscle and inhibits the immediate life-threatening car-
diovascular effects of anaphylaxis. Persons with a his-
tory of anaphylaxis should be provided with preloaded
epinephrine syringes and instructed in their use. They
should also be instructed to seek immediate professional
help regardless of the initial response to self-treatment.
Family members and caregivers of young children
should be trained to inject epinephrine. Prevention of
exposure to potential triggers that cause anaphylaxis is
particularly important. Finally, all persons with poten-
tial for anaphylaxis should be advised to wear or carry
a medical alert bracelet, necklace, or other identifica-
tion to inform emergency personnel of the possibility
of anaphylaxis.
Local (Atopic) Reactions
Local or atopic reactions usually occur when the anti-
gen is confined to a particular site by virtue of expo-
sure. The term
atopic
refers to a genetically determined
hypersensitivity to common environmental allergens
mediated by an IgE–mast cell reaction. Persons with
atopic disorders commonly are allergic to more than
one (often many) environmental allergens. The most
common atopic disorders are urticaria (hives), allergic
rhinitis (hay fever), atopic dermatitis, food allergies,
and some forms of asthma. The discussion in this sec-
tion focuses on allergic rhinitis and food allergy. Allergic
asthma is discussed in Chapter 23 and atopic dermatitis
in Chapter 46.
The susceptibility to immediate hypersensitivity
disorders tends to be inherited.
2
The genetic basis of
atopy is unclear; however, linkage studies suggest an
association with cytokine genes on chromosome 5q
that regulate the expression of circulating IgE.
1
Persons
with atopic allergic conditions tend to have high serum
levels of IgE and increased numbers of basophils and
mast cells. Although the IgE-triggered response is likely
a key factor in the pathophysiology of atopic allergic
disorders, it is not the only factor and may not be solely
responsible for conditions such as atopic dermatitis and
certain forms of asthma.
Allergic Rhinitis.
Allergic rhinitis is characterized
by symptoms of sneezing, itching, and watery dis-
charge from the nose and eyes (rhinoconjunctivitis).
Allergic rhinitis not only produces nasal symptoms
but frequently is associated with other chronic airway
disorders, such as sinusitis and bronchial asthma.
9,10
Severe attacks may be accompanied by malaise (gen-
eral discomfort), fatigue, and muscle soreness from
sneezing. Fever is absent. Sinus obstruction may cause
headache. Typical allergens include pollens from rag-
weed, grasses, trees, and weeds; fungal spores; house
dust mites; animal dander; and feathers. Allergic rhi-
nitis can be divided into perennial and seasonal aller-
gic rhinitis depending on the chronology of symptoms.
Persons with the perennial type of allergic rhinitis
experience symptoms throughout the year, whereas
those with seasonal allergic rhinitis (e.g., hay fever)
are plagued with intense symptoms in conjunction
with periods of high allergen (e.g., pollens, fungal
spores) exposure. Symptoms that become worse at
night suggest a household allergen, and symptoms
that improve or disappear on weekends suggest occu-
pational exposure.
Diagnosis depends on a careful history and physi-
cal examination, microscopic identification of an
increased number of eosinophils on a nasal smear,
and skin or serum testing to identify the offending
allergens. When possible, avoidance of the offending
allergen is recommended. Treatment is symptomatic in
most cases and includes the use of oral antihistamines
and oral or topical decongestants. Intranasal cortico-
steroids often are effective when used appropriately.
Intranasal cromolyn, a drug that stabilizes mast cells
and prevents their degranulation, may be useful, espe-
cially when administered before expected contact with
an offending allergen. A program of specific immu-
notherapy (“allergy shots”) may be used when symp-
toms are particularly bothersome.
9,10
Desensitization
involves frequent (often weekly) injections of the
offending antigens. The antigens, which are given in
increasing doses, stimulate production of high levels of
IgG, which acts as a blocking antibody by combining
with the antigen before it can combine with the cell-
bound IgE antibodies.
Food Allergies.
Virtually any food can produce atopic
or nonatopic allergies. The primary target of food
allergy may be the skin, the gastrointestinal tract, the
respiratory system, or a combination thereof.
11,12
The
foods most commonly causing these reactions are milk,
eggs, peanuts, tree nuts, fish, and shellfish (i.e., crusta-
ceans and mollusks). The allergenicity of a food may
be changed by heating or cooking. A person may be
allergic to drinking milk but may not have symptoms
when milk is included in cooked foods. Both acute
reactions (hives and anaphylaxis) and chronic reac-
tions (asthma, atopic dermatitis, and gastrointestinal
disorders) can occur. Anaphylaxis occurs as a multior-
gan response associated with IgE-mediated hypersensi-
tivity. The foods most responsible for anaphylaxis are
peanuts,
13
tree nuts (e.g., walnuts, almonds, pecans,
cashews, hazelnuts), and shellfish. One form of food-
associated anaphylaxis occurs with exercise. It may
occur when exercise follows ingestion of a particular
food to which IgE sensitivity has been demonstrated,
