Page 655 - Clinical Immunology_ Principles and Practice ( PDFDrive )

CHaPTEr 45 Food Allergy 629

The oral food challenge (OFC) remains the gold standard for beta-blocker medications; there is increased mortality in teen
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the diagnosis of food allergy. OFCs can be conducted in an open and young adult age groups. Intramuscular autoinjectable
manner; with a placebo control, where the patient is blinded to epinephrine must be readily available to patients with IgE-
the product being given; or in a double-blinded manner, with mediated food allergies and is the first-line treatment for a
both the physician and patient blinded to the food being given food-induced allergic reaction. Patients with food allergies are
to the patient. An open OFC is most commonly performed in encouraged to have a written emergency action plan that lists
clinical practice, while the double-blind, placebo-controlled food the signs and symptoms of an allergic reaction and details treat-
challenge is considered the diagnostic standard typically reserved ment of those symptoms.
for research studies. During the OFC, a standard serving size
of the allergen is divided into 4–7 servings and administered PREVENTION OF FOOD ALLERGY
over 60–90 minutes, with each dose being given 15–20 minutes
apart. The initial amount fed to the patient is typically a very Exposure to antigen early in life is likely very important for
small proportion of the total serving, and each successive shaping the appropriate immune response to foods. Primary
dose administers a larger amount of protein. At the first sign exposure through the oral route is believed to predispose to the
of an objective reaction, the OFC is stopped and appropriate development of a tolerogenic response, whereas primary exposure
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treatment administered. In cases where anxiety or subjective through skin may result in sensitization. Support for the theory
symptoms may affect the interpretability of the OFC, a single- of prevention through primary oral exposure has been strongly
blind or double-blind placebo-controlled food challenge may be supported through epidemiological studies showing that some
preferred. cultural groups that introduce peanuts to their children in the
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first year of life have a lower incidence of peanut allergy. This
MANAGEMENT theory has been strengthened through recent evidence demon-
strating that children identified as being at high risk of developing
The patient with a food allergy must maintain strict avoidance peanut allergy (severe atopic dermatitis and/or egg allergy) are
of the food allergen to prevent an allergic reaction. Avoidance substantially protected against the development of peanut allergy
requires constant vigilance. Accidental ingestion is common, with if they regularly ingest peanut, from between 4 and 11 months
reports showing that as many as 50% of children with a peanut of age through 60 months of age, compared with matched controls
allergy may experience an adverse reaction in a 2-year period who avoid peanut. 23
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and up to 75% over 10 years. Individuals with food allergies Evidence in favor of a compromised skin barrier as the primary
and their caregivers must read ingredient labels closely, prevent site of sensitization was shown in the Avon Longitudinal Study
cross-contact, communicate with restaurant staff when eating of Parents and Children birth cohort study, which reported that
outside of the home, and be prepared to treat a reaction, when infants who had peanut allergy were more likely to have had
necessary. severe AD in the first 6 months of life and also to have been
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Food allergy labeling laws in the United States require that treated with application of peanut oil to the skin. In children
the presence of the most common allergens (milk, egg, peanut, with AD, the outermost layer of skin (stratum corneum) con-
tree nuts, wheat, soy, fish, and crustacean shellfish) must be tributes to skin barrier function. Patients with AD have increased
declared in simple English on the ingredient labels of all packaged transepidermal water loss (TEWL). Increased TEWL not only
foods. Individuals allergic to foods other than the eight most allows water loss through skin but also facilitates allergen penetra-
common allergens may have more difficulty with interpretation tion and resultant sensitization. Further work is required to
of ingredient labels. Ingredient labels may report “spices” or understand whether emollient use may reduce the risk of AD
“natural flavors,” which could include a multitude of foods or development and possibly reduce the risk of developing food
food products not covered by food allergy labeling laws. State- allergy.
ments such as “may contain [allergen]” and “manufactured on The role of the microbiome is an intense area of study with
shared equipment with [allergen]” are voluntary and not regulated. regard to food allergy development. Microbial products in the
Allergen content in such products is unknown, and it is typically gut flora interact with innate immune receptors, such as Toll-like
recommended that individuals with allergies avoid products with receptors (TLRs) and relay signals implicated in the activation
“may contain” labeling. of regulatory T cells (Tregs), which are important in the promo-
Children with milk allergy or with two or more food allergies tion of tolerance. Activation of a specific TLR using nonpathogenic
have been shown to be at particular risk of growth deficiency. bacteria (probiotics) could conceivably prevent allergic disease.
Nutritional counseling with a registered dietitian is encouraged Unfortunately, studies investigating the role of probiotics in
for these patients. A registered dietitian will help educate the preventing allergic disease have not shown promise, probably
patient and his or her family on avoidance of food allergens, in because of the difficulty in identifying which specific strains of
addition to providing guidance on nutrient supplementation to gut bacteria are beneficial. Encouragingly, new techniques, such
avoid potential dietary deficiencies. as deep-sequencing technologies, are allowing better characteriza-
tion of the gut flora. As techniques improve and our understanding
TREATMENT OF A REACTION deepens, there is hope that new therapeutic targets will emerge
for food allergy prevention.
An acute reaction must be recognized and treated expeditiously.
Food-induced fatalities are most commonly reported from EXPERIMENTAL INTERVENTIONAL THERAPIES
ingestion of peanut and tree nuts, but any food allergen can
induce a severe reaction. Fatalities have been associated with The standard of care for IgE-mediated food allergy is avoidance
delay in administration of autoinjectable epinephrine, preexisting of the potentially triggering allergen, treatment of a reaction
and/or poorly controlled asthma, and concomitant use of with autoinjectable epinephrine, and dietary supplementation