Atopy Patch Test (APT)--its role in diagnosis of food allergy in atopic dermatitis

Allergy to cow's milk proteins: what contribution does hypersensitivity in skin tests have to this diagnosis?

Food allergy is an immunologically mediated adverse reaction to food protein. Cow's milk protein allergy (CMPA) is the most frequent type and is the one that is most difficult to diagnose. This study had the objective of analyzing the accuracy of hypersensitivity and specific IgE skin tests among children with CMPA and predominantly gastrointestinal clinical manifestations. The participants in this study were 192 children aged one and five (median of 2 yr). Among these, 122 underwent open oral challenge to the suspected food. After evaluating the sensitivity, specificity and positive and negative predictive values (respectively, PPV and NPV) of skin and specific IgE tests in relation to the gold standard (open oral challenge); all the children underwent the skin prick test (SPT), specific IgE test and atopy patch test (APT) for cow's milk, eggs, wheat and peanuts and the open oral challenge for the food to which the child was sensitive or had suspected sensitivity. Presence of food allergy was confirmed for 50 children (40.9%). Among these cases, 44/50 (88%) were of allergy to cow's milk protein. Children who presented a positive response to an oral challenge to cow's milk protein were considered to be cases, while the controls were children with negative response. Twenty-two of the 44 cases (50.0%) presented symptoms within the first 4 h after the challenge. The SPT presented 31.8% sensitivity, 90.3% specificity, 66.7% PPV and 68.4% NPV. The APT presented 25.0% sensitivity, 81.9% specificity, 45.8% PPV and 64.1% NPV. The specific IgE test presented, respectively, 20.5%, 88.9%, 52.9% and 64.6%. Despite the operational difficulty and the possible exposure risk, oral challenge is the best method for diagnosing CMPA, because of the low sensitivity and PPV of skin and specific IgE tests.

The diagnostic value of atopy patch testing and prick testing in atopic dermatitis: facts and controversies

We conducted a systematic Medline search of the literature (1998-2008) on the criteria for performing the skin prick test and atopy patch testing (APT) to determine their utility in atopic dermatitis (AD). The skin prick, scratch, and skin patch tests are performed to identify which allergen is causing eczematous skin symptoms in patients with AD, or sneezing, nasal congestion, itchy eyes, wheezing, skin rash, and swelling. Many allergens in foods, drugs, and environmental substances (eg, ragweed and fungus), as well as contact allergens, can elicit eczematous skin reactions after epicutaneous application. Because no gold standard exists for aeroallergen provocation in AD, the APT is currently used to evaluate allergen without comparison with another accurate and reliable method. The APT is presumed to reflect delayed-phase clinical reactions. Even with delayed onset of symptoms (more than 2 hours after food ingestion), APT findings were not consistent among AD children. The APT could be used in children with gastrointestinal reactions to foods as well as AD. After standardization, the APT may provide further diagnostic information in addition to the skin prick test and serum immunoglobulin E values and may be able to evaluate the actual clinical relevance of immunoglobulin E-mediated sensitizations for eczematous lesions. The European APT model used with standardization of allergen concentration and vehicle may provide an important diagnostic tool to select patients for avoidance and for procedures of allergen-specific immunotherapy, but the clinical relevance of positive APT reactions awaits standardized provocation and avoidance testing.

Food allergy: review, classification and diagnosis

Food allergies, defined as an immune response to food proteins, affect as many as 8% of young children and 2% of adults in westernized countries, and their prevalence appears to be rising like all allergic diseases. In addition to well-recognized urticaria and anaphylaxis triggered by IgE antibody-mediated immune responses, there is an increasing recognition of cell-mediated disorders such as eosinophilic esophagitis and food protein-induced enterocolitis. New knowledge is being developed on the pathogenesis of both IgE and non-IgE mediated disease. Currently, management of food allergies consists of educating the patient to avoid ingesting the responsible allergen and initiating therapy if ingestion occurs. However, novel strategies are being studied, including sublingual/oral immunotherapy and others with a hope for future.

Skin localization of cow's milk proteins delivered by a new ready-to-use atopy patch test

PURPOSE

Atopy patch tests (APTs) allow the detection of delayed allergies at the skin level. The localization of beta-lactoglobulin delivered into the skin by an innovative ready-to-use APT (E-patch was investigated and the efficacy and safety of this device were assessed.

METHODS

The E-patch containing beta-lactoglobulin was placed for 24 h in contact with hairless rat skin mounted in a Franz diffusion cell. Transdermal passage was monitored by measurement of beta-lactoglobulin A-[methyl-(14)C] or by two-site enzyme immunoassay. An iterative skin stripping allowed measurement of the beta-lactoglobulin penetrating the first external skin layers.

RESULTS

After 24 h, 92% of beta-lactoglobulin remained on the skin. The iterative skin strippings showed a 135-fold higher concentration of beta-lactoglobulin in the stratum corneum than that found in the epidermis-dermis. Analysis of the solution in the receiver compartment by radioactivity assays or immunoassays indicates that intact protein did not cross the skin.

CONCLUSIONS

The E-patch system allows native beta-lactoglobulin to concentrate in the stratum corneum, in the vicinity of immunological cells, but does not lead to its systemic delivery. Therefore, it is suggested that this delivery system creates ideal conditions for promoting a positive topical response with reduced risk of systemic anaphylactic reactions caused by the native form of the beta-lactoglobulin A.

Evaluation of the utility of atopy patch testing, skin prick testing, and total and specific IgE assays in the diagnosis of cow's milk allergy

BACKGROUND

Information on the utility of atopy patch testing (APT) in the diagnosis of food allergy is derived from studies of children with atopic dermatitis.

OBJECTIVE

To evaluate the usefulness of APT in the diagnosis of cow's milk allergy (CMA) and to determine interleukin 4 and interferon-gamma production by peripheral blood mononuclear cells.

METHODS

Thirty-seven children (median age, 11 months) with suspected CMA who had a variety of symptoms that involved many organ systems were evaluated using double-blind placebo-controlled food challenges (DBPCFCs), and the performances of milk specific IgE, skin prick testing (SPT), and APT were determined. To search for a possible relationship between the diagnostic tests and the TH1/TH2 immune response, we measured interferon-gamma and interleukin 4 levels in the supernatants of peripheral blood mononuclear cell cultures.

RESULTS

Seventeen children with positive DBPCFC results and 6 with a history of anaphylaxis were diagnosed as having CMA. The combined use of APT and SPT had a sensitivity of 100% and a negative predictive value of 100% but a specificity of 50% and a positive predictive value of 76%. The addition of milk specific IgE assays to APT and SPT did not improve these values. Pattern of cytokine secretion was not associated with APT positivity or a specific response to DBPCFC.

CONCLUSIONS

Atopy patch testing may be a useful adjunct to SPT in excluding CMA in children who have allergic manifestations other than atopic dermatitis. However, DBPCFCs are still necessary in the presence of positive test results.

Rice-induced enterocolitis in an infant: TH1/TH2 cellular hypersensitivity and absent IgE reactivity

BACKGROUND

Although food allergy is common in children, rice allergy is unusual in Western cultures.

OBJECTIVE

To report a case of T-cell-mediated rice intolerance in an 11-month-old girl.

METHODS

To evaluate the intolerance to rice in this patient, a graded rice food challenge was performed. To examine the immunologic reactivity to rice, in vitro lymphoproliferative responses and cytokine synthesis of rice-stimulated peripheral blood lymphocytes (PBLs) was performed. Subsequently, skin patch testing to rice and other foods was performed.

RESULTS

Allergy skin prick test results were negative for rice and positive for egg, milk, and soy. Specific IgE antibodies to rice, egg, peanut, wheat, walnut, codfish, milk, soybean, corn, shrimp, scallops, and clams were undetectable. Results of a single-blind rice food challenge were positive, manifested by emesis that persisted for more than an hour and required intravenous hydration. In vitro lymphoproliferation by the patient's PBLs to rice stimulation was positive. In addition, cytokine synthesis of interferon-gamma, interleukin 10 (IL-10), tumor necrosis factor a, and IL-5 by the patient's rice-stimulated PBLs was elevated, indicating a TH1/TH2 cell response to rice. Endoscopy revealed normal esophageal, gastric, and duodenal mucosa; a biopsy specimen revealed mild esophagitis. Duodenal explant T cells were initially established by stimulation with rice and IL-2. After a 2-day rest, the lymphocytes were restimulated with rice for 7 days and revealed increased interferon-gamma and IL-5 synthesis. Twenty billion colony forming units of Lactobacillus GG were added to the patient's diet twice daily. After 6 weeks, rice rechallenge resulted in emesis within 1 hour. Results of patch testing were positive to rice, wheat, and barley but negative to soy, which the patient tolerated on food challenge.

CONCLUSIONS

Although this patient did not demonstrate IgE antibody to rice, TH1/TH2 cell-mediated responses to rice were detected, and the patient experienced significant morbidity. Patch testing for gastrointestinal food allergies may be useful when the food specific IgE antibody is negative. Probiotic therapy in this patient did not ameliorate her sensitivity to rice, and food elimination remains the only reliable treatment for TH1/TH2-mediated food hypersensitivity.

IgE and non-IgE food allergy

BACKGROUND

Food allergy (FA) is characterized by an abnormal immunologic reactivity to food proteins. The gastro-intestinal tract serves not only a nutritive function but also is a major immunologic organ. Although previously thought to be triggered primarily by an IgE-mediated mechanism of injury, considerable evidence now suggests that non-IgE mechanisms may also be involved in the pathogenesis of FA.

OBJECTIVE

To review the immunologic disturbances that occur in FA and to correlate these with the clinical manifestations expressed in affected target organs based upon a classification of IgE and non-IgE mechanisms.

METHODS

Data collected from a computerized MEDLINE search were used for the analysis of the following topics: immediate GI hypersensitivity, oral allergy syndrome, acute urticaria and angioedema, acute bronchospasm, celiac disease, cow's milk enteropathy, dietary protein enterocolitis, breast milk colitis, proctolitis, proctitis, dermatitis herpetiformis, Heiner syndrome, eosinophilic gastroenteritis, atopic dermatitis, asthma, attention-deficit-hyperactivity disorder and behavioral disorders, as well as systems affected by mucosal associated lymphoid tissue-mediated injury of associated lymphoid tissues and the immunologic deviation to Th1 or Th2 mechanisms of FA.

CONCLUSIONS

The results of this review allow the construction of a central, unifying hypothesis for a new classification of FA as follows: the clinical manifestations of FA, expressed in affected target organs, may be the result of immunologic injury mediated by interaction of food antigens with contiguous elements of mucosal associated lymphoid tissue. These appear to be modulated by relative imbalances of the Th1/Th2 paradigm, which may be the ultimate determinant governing the expression of FA as IgE-mediated, non--IgE-mediated, or mixed forms of IgE/non-IgE mechanisms of FA.