Medicines often are implicated in triggering undesired
immunologic reactions. True drug allergy represents
6 –10% of all adverse drug reactions and is
overreported by individuals. Most drugs are too small
(1000 Da) to incite allergic sensitization alone. To
cause an allergic reaction, a reactive metabolite of the
drug must bind to a macromolecular carrier for antigen processing. The drug metabolite in the carrier molecule
complex is known as a hapten. This makes skin testing
difficult for diagnostic accuracy. Large molecular
weight drugs (heterologous antisera, insulin, streptokinase,
and l-asparaginase), which are 4000 Da, and
medicines that have enough distance between determinants
to be bivalent (quaternary ammonium muscle
relaxants and aminoglycosides), may provoke an allergic
response without forming a hapten–protein complex.
LATEX
Natural rubber latex is a product of the rubber tree
Hevea brasilensis. Sensitization is present in 75% of patients
with spina bifida and 6.5% of the general population.
Health care providers and patients with urological
problems requiring catherization are also at increased
risk. Clinical manifestations of IgE-mediated disease include
allergic rhinitis, asthma, contact urticaria, and anaphylaxis.
The incidence of IgE-mediated reactions to latex
has declined mostly because of the development of powder-free,
low-protein gloves.
INGESTED ALLERGENS
Food allergy is common and appears to be increasing; it can be divided into class 1 and class 2. Class 1 food
allergy is considered “traditional” and occurs in the gastrointestinal
tract. Class 2 food allergy is caused by allergic
sensitization to inhalant allergens that cross-react with
food allergens. Class 1 allergens are 10 –70 kDa and are
heat, acid, and protease stable. Common class 1 allergens
are cow’s milk, chicken egg, peanut, soybean, fish, and
shrimp. Thirty-five percent of children with moderate to
severe atopic dermatitis have an associated food allergy,15
and 6% of asthmatic children have associated
food allergy. Peanut is the most common food allergy in
individuals 4 years old. There has been a dramatic
increase in the number of children with peanut allergy
with one study noting peanut allergy prevalence of 1.4%
in 2008 versus 0.8% in 2002 in the United States. Studies
are currently looking at environmental factors that may
result in this increased prevalence.
Cross-reactivity between members of a food allergen
group varies. Cross-reactivity between peanuts and other
legumes is 5%, between tree nuts 35%, between different
fish 50%, and 75% between members of the shellfish
family. Cross-reactivity also occurs between aeroallergens
and certain food allergy resulting in class 2 food
allergies. This is known as pollen–food syndrome (previously
oral allergy syndrome) and manifests as pruritus
with or without angioedema of the lips, tongue, palate,
and posterior oropharynx. Shared allergen sensitivities
have been reported between ragweed and the gourd
family (watermelon, cantaloupe, zucchini, and cucumbers)
and bananas. Birch pollen shares allergen sensitivities with apples, carrots, parsnips, celery, hazelnuts,
potatoes, celery, and kiwi. Tree and grass pollen share
allergens with apples, tree nuts, peaches, oranges, pears,
cherries, fennel, tomatoes, and carrots. Often, cooking
or peeling these foods reduces symptoms of pollen–food
syndrome.
Reviewing the properties of common allergens reinforces
the foundation of controlling clinical allergy
symptoms, which is avoidance of allergen exposure.
Their properties also form the basis for developing
diagnostic and therapeutic opportunities.
IMMUNOLOGY
• An allergen is typically a protein or glycoprotein
that can induce an IgE-mediated immune response
with an associated clinical reaction.
• Size of pollen determines clinical manifestation of
allergy. Particles between 20 and 60 m in diameter
can be carried in the wind and cause nasal and
ocular symptoms. Particles 7 m can deposit in the
airways and cause symptoms of asthma.
• True drug allergy represents 6 –10% of all adverse
drug reactions. Skin testing is difficult because most
drug allergens are small metabolites of the implicated
drug and they must haptenize a carrier protein
to induce an immune response.
CLINICAL PEARLS
• Most tree pollens do not have significant cross-reactivity
and are released in the spring in the United
States. In the upper midwestern United States, tree
pollination occurs in mid to late March until May.
• Grass pollen comes from the Poaceae family, has
significant cross-reactivity, and is typically released
in the late spring and early summer in the United
States. In the upper midwestern United States, this
time is from mid-May to the end of July.
• Weed pollens are released mostly in the autumn in
the United States with ragweed being the major
allergen from August 15 to October 1 in the upper
midwestern United States.
• Global warming has shifted the floristic zones in
North America to higher latitudes. Ragweed has
increased in size and pollen production because of
increased CO2 and temperature.
• Fungal spores and mycelial elements are released
preferentially in warm, humid environments. The
first hard frost of late autumn decreases outdoor
mold spores.
• Dust mites thrive in warm, humid conditions and
provide allergen through their fecal particles, enhanced
by intrinsic enzymic activity.
• Cat allergen may last in a home for up to 6 months
after the source is removed. It can be isolated from
saliva, urine, dander, and from sebaceous glands.
• The most common class I food allergens are cow’s
milk, chicken egg, peanut, soybean, fish, and
shrimp. There has been an increase in the prevalence
of peanut allergy in children.
• Pollen–food syndrome occurs because of cross-reactivity
between aeroallergens and certain food proteins.
