The Diagnosis of Allergy to Lipid Transfer Proteins

PURPOSE OF REVIEW

To provide an update on the diagnosis of non-specific Lipid Transfer Protein (nsLTP) allergy.

RECENT FINDINGS

More publications report the presence of nsLTP allergy in Northern European countries and nsLTP sensitisation in children. Individuals are more likely to have severe reactions if there is recognition of increasing numbers of LTP components. Diagnosis is problematic; not all those with nsLTP allergy will have a positive test to a peach extract containing Pru p 3, the peach nsLTP. Sensitisation to nsLTP is being reported in more countries, including to the nsLTP in Cannabis Sativa in North America. Meals containing multiple nsLTP foods are more likely to be involved in co-factor reactions. Component-resolved diagnostics are superior to skin prick tests, to determine sensitisation to the individual nsLTP allergens causing symptoms and, in the future, the Basophil Activation test may best discriminate between sensitization and clinical allergy.

The diagnosis and management of allergic reactions in patients sensitized to non-specific lipid transfer proteins

Sensitization to one or more non-specific lipid transfer proteins (nsLTPs), initially thought to exist mainly in southern Europe, is becoming accepted as a cause of allergic reactions to plant foods across Europe and beyond. The peach nsLTP allergen Pru p 3 is a dominant sensitizing allergen and peaches a common food trigger, although multiple foods can be involved. A frequent feature of reactions is the requirement for a cofactor (exercise, alcohol, non-steroidal anti-inflammatory drugs, Cannabis sativa) to be present for a food to elicit a reaction. The variability in the food and cofactor triggers makes it essential to include an allergy-focused diet and clinical history in the diagnostic workup. Testing on suspected food triggers should also establish whether sensitization to nsLTP is present, using purified or recombinant nsLTP allergens such as Pru p 3. The avoidance of known trigger foods and advice on cofactors is currently the main management for this condition. Studies on immunotherapy are promising, but it is unknown whether such treatments will be useful in populations where Pru p 3 is not the primary sensitizing allergen. Future research should focus on the mechanisms of cofactors, improving diagnostic accuracy and establishing the efficacy of immunotherapy.

Clinical utility of the basophil activation test in the diagnosis of sweat allergy

BACKGROUND

Many patients with atopic dermatitis and cholinergic urticaria display an immediate-type allergy to autologous sweat. Although the histamine release test (HRT) using semi-purified sweat antigen (QR) was available for the detection of immediate sweat allergy, the existence of HRT low responders could not be disregarded. Furthermore, it has not been established whether the results of the HRT are consistent with the autologous sweat skin test (ASwST). We aimed to compare the HRT and basophil activation test (BAT) for the diagnosis of immediate sweat allergy.

METHODS

The HRT and BAT were performed on 47 subjects (35 ASwST positive, 12 negative) whose symptoms had worsened on sweating. For the BAT, blood was incubated with QR or crude sweat and CD203c upregulation was assessed. A commercial HRT was performed and histamine release induced by QR was quantified.

RESULTS

When excluding non-responders for anti-IgE antibody, the BAT using QR and the HRT had a sensitivity of 100% and 44% and specificity of 75% and 100%, respectively. The BAT and HRT had a positive predictive value of 91.3% and 100% and negative predictive value of 100% and 30%, respectively. The BAT detected 0% non-responders, whereas the HRT identified 22.5%. When using crude sweat for the BAT, the false-positives observed when using QR were not detected.

CONCLUSIONS

The BAT using QR displayed a higher sensitivity and negative predictive value and a lower number of non-responders compared with the HRT. Furthermore, the BAT using crude sweat can also be an alternative tool for the ASwST.

Allergy tests do not predict food triggers in adult patients with eosinophilic oesophagitis. A comprehensive prospective study using five modalities

BACKGROUND

The use of allergy tests to guide dietary treatment for eosinophilic oesophagitis (EoE) is controversial and data are limited. Aeroallergen sensitisation patterns and food triggers have been defined in Northern Hemisphere cohorts only.

AIMS

To determine if allergy tests that are routinely available can predict food triggers in adult patients with EoE. To define the food triggers and aeroallergen sensitisation patterns in a novel Southern Hemisphere (Australian) cohort of patients.

METHODS

Consecutive patients with EoE who elected to undergo dietary therapy were prospectively assessed, demographic details and atopic characteristics recorded, and allergy tests, comprising skin-prick and skin-patch tests, serum allergen-specific IgE, basophil activation test and serum food-specific IgG, were performed. Patients underwent a six-food elimination diet with a structured algorithm that included endoscopic and histological examination of the oesophagus a minimum of 2 weeks after each challenge. Response was defined as <15 eosinophils per HPF. Foods defined as triggers were considered as gold standard and were compared with those identified by allergy testing.

RESULTS

No allergy test could accurately predict actual food triggers. Concordance among skin-prick and serum allergen-specific IgE was high for aeroallergens only. Among seasonal aeroallergens, rye-grass sensitisation was predominant. Food triggers were commonly wheat, milk and egg, alone or in combination.

CONCLUSIONS

None of the currently-available allergy tests predicts food triggers for EoE. Exclusion-rechallenge methodology with oesophageal histological assessment remains the only effective investigation. The same food triggers were identified in this southern hemisphere cohort as previously described.

Use of a basophil activation test as a complementary diagnostic tool in the diagnosis of severe peanut allergy in adults

Background

Diagnosis of severe peanut allergy is difficult and delays in making an accurate diagnosis may place the patient at risk. Adults with a history of anaphylaxis must strictly avoid any contact with peanuts or products that may contain traces of peanuts. For these persons, conventional evaluations with skin prick testing (SPT) and IgE tests may not be sufficient to assess the risk of anaphylaxis. Therefore, we investigated whether the basophil activation test (BAT) could be used for the diagnosis of severe peanut allergy in adults. We compared the non-invasive BAT with conventional laboratory diagnostic tests, including SPT and specific IgE to allergen extracts and components, for the diagnosis of severe peanut allergy.

Methods

Forty-seven persons with severe allergy to peanuts and a clinical diagnosis of anaphylaxis (PA-group), 22 subjects with peanut sensitization (PS-group) and 22 control (C-group) subjects, all in the age range of 18–60 years, were recruited retrospectively and prospectively into the study. Thirty-four patients with peanut allergy and 11 peanut-sensitized patients were sensitized to soy, while 36 patients in the PA-group and 20 patients in the PS-group were sensitized to birch pollen. All the patients and control subjects were investigated with BAT and SPT for responses to peanut, soy and birch extracts and their serum samples were assayed for the presence of specific IgE to peanut, soy and birch extracts, as well as IgE to allergen components (ISAC).

Results

In a multivariate factor analysis, severe peanut allergy (PA) was positively associated with SPT to peanut, IgE to peanut, BAT to peanut and IgE to rAra h 1, 2, 3 and 6 peanut components, as well as to soy components (nGly m 5 and nGly m 6). In contrast, peanut sensitization was positively associated with increased levels of IgE to rAra h 8, birch and birch-related components. BAT-detected reactivity to peanut was significantly higher in patients who had a history of severe allergy to peanuts, as compared with patients who were sensitized to peanuts (p < 0.001), and the receiver operating curve (ROC) analysis showed that BAT had high sensitivity and specificity for predicting severe peanut allergy, with a ROC area under the curve of 0.862. However, in the PA-group, the BAT results for peanut correlated only weakly with the levels of IgE to rAra h 1, 2 and 3 and nAra h 6. Study limitations: oral provocation in the patients with a history of severe peanut allergy could not be performed to compare clinical reactivity with the BAT result due to ethical constraints. Neither was it possible to perform BAT with peanut recombinant allergens which were not available at the time the study commenced

Conclusions

BAT is useful in determining the severity of peanut allergy and may be used as a complementary diagnostic tool to ensure accurate diagnosis of severe peanut allergy in adults. Thus, it may reduce the need to subject these patients to further tests, including an open challenge with peanuts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13601-015-0064-9) contains supplementary material, which is available to authorized users.

[Cellular in-vitro assays. Applicability in daily routine]

Cellular in-vitro assays are able to detect antigen-dependent cellular processes without any risk for the patient. After antigen stimulation, both the cellular antigen stimulation test assessing sulfidoleukotriene production in leukocyte suspension, and flow cytometric basophil activation assays determining surface activation markers (CD63, CD203c), represent accepted models for in-vivo mast cell stimulation particularly in IgE-dependent reactions of immediate type. The value of these assays should be estimated considering the type of antigen and further diagnostic options. Most studies can not be compared due to different allergen concentrations, conditions of stimulation, methods, and defined cut-offs. Therefore, it is difficult to evaluate published evidence. Because of the logistic effort, cellular assays are often available only in specialized laboratories. However, in daily routine they are important in cases with clear-cut history but negative conventional allergy diagnostic procedures, in case of rare allergens (drugs, exotic food), as well as contraindications for skin and/or provocation test (hymenoptera venom allergy, anaphylaxis).