Evolution Toward Chip-Based Arrays in the Laboratory Diagnosis of Human Allergic Disease

Venom Component Allergen IgE Measurement in the Diagnosis and Management of Insect Sting Allergy

Accurate identification of allergy-eliciting stinging insect(s) is essential to ensuring effective management of Hymenoptera venom-allergic individuals with venom-specific immunotherapy. Diagnostic testing using whole-venom extracts with skin tests and serologic-based analyses remains the first level of discrimination for honeybee versus vespid venom sensitization in patients with a positive clinical history. As a second-level evaluation, serologic testing using molecular venom allergens can further discriminate genuine sensitization (honeybee venom: Api m 1, 3, 4, and 10 vs yellow jacket venom/Polistes dominula venom Ves v 1/Pol d 1 and Ves v 5/Pol d 5) from interspecies cross-reactivity (hyaluronidases [Api m 2, Ves v 2, and Pol d 2] and dipeptidyl peptidases IV [Api m 5, Ves v 3, and Pol d 3]). Clinical laboratories use a number of singleplex, oligoplex, and multiplex immunoassays that employ both extracted whole-venom and molecular venom allergens (highlighted earlier) for confirmation of allergic venom sensitization. Established quantitative singleplex autoanalyzers have general governmental regulatory clearance worldwide for venom-allergic patient testing with maximally achievable analytical sensitivity (0.1 kUA/L) and confirmed reproducibility (interassay coefficient of variation <10%). Emerging oligoplex and multiplex (fixed-panel) assays conserve on serum and are more cost-effective, but they need regulatory clearance in some countries and are prone to higher rates of detecting asymptomatic sensitization. Ultimately, the patient's clinical history, combined with proof of sensitization, is the final arbiter in the diagnosis of Hymenoptera venom allergy.

Molecular allergology: a clinical laboratory tool for precision diagnosis, stratification and follow-up of allergic patients

Identification of the molecular culprits of allergic reactions leveraged molecular allergology applications in clinical laboratory medicine. Molecular allergology shifted the focus from complex, heterogeneous allergenic extracts, e.g. pollen, food, or insect venom, towards genetically and immunologically defined proteins available for in vitro diagnosis. Molecular allergology is a precision medicine approach for the diagnosis, stratification, therapeutic management, follow-up and prognostic evaluation of patients within a large range of allergic diseases. Exclusively available for in vitro diagnosis, molecular allergology is nonredundant with any of the current clinical tools for allergy investigation. As an example of a major application, discrimination of genuine sensitization from allergen cross-reactivity at the molecular level allows the proper targeting of the culprit allergen and thus dramatically improves patient management. This review aims at introducing clinical laboratory specialists to molecular allergology, from the biochemical and genetic bases, through immunological concepts, to daily use in the diagnosis and management of allergic diseases.

Screening asthmatics for atopic status using the ALergy EXplorer (ALEX2) macroarray

BACKGROUND

Screening asthma patients for atopy facilitates management. Since 2010, the core biomarker for screening asthma subjects for atopic status has been the qualitative Phadiatop. multi-aeroallergen screen. A more quantitative macroarray, the Allergy Explorer (ALEX2), shows promise as an alternative.

OBJECTIVE

The study's goal was to examine the pros and cons of the use of ALEX2 in the screening of asthma patients for atopic status.

METHODS

We evaluated the atopic (IgE-sensitization) status in asthmatic Amish and Hutterite farm children using the ImmunoCAP and ALEX2 assays in Phadiatop equivocal and positive subjects.

RESULTS

All 42 asthmatic children were analyzed by Phadiatop and total serum IgE. Of these, 22 had a negative Phadiatop (<0.1 kUa/L) and total IgE <100 kU/L which defined them as non-atopic and they were excluded from ALEX2 testing. Of six children with equivocal Phadiatops (0.1-0.2 kUa/L-Group 1) and three children with a negative Phadiatop but total IgE >100 kUa/L (group 3), 44% (n = 4) had detectable IgE antibody by ALEX2 to mite, tree pollen, and other allergens not detected by Phadiatop, but confirmed by allergen-specific ImmunoCAP testing. In 11 Phadiatop positive subjects (>0.2 kUa/L-group 2), all but one were positive by ALEX2. IgE antibody specific for mold and rabbit aeroallergens matched their agricultural and pet exposure history. Three children were positive for IgE antibody to allergens in the profilin, nsLTP, or PR-10 cross-reactive protein families.

CONCLUSION

Judicious use of ALEX2's enhanced specificity data not provided by the Phadiatop can aid in the interpretation of sensitization patterns and planning management of atopic asthmatics, but sensitization relevance must be confirmed by the patient's clinical history.

A human monoclonal antibody based immunoenzymetric assay to measure Fel d 1 concentrations in cat hair and pelt allergenic extracts

In the United States, 19 allergen extracts of different specificities are standardized, which means that their potencies are determined in comparison to a US reference standard. For cat allergen extracts, potency is determined by measuring Fel d 1 content expressed in in Fel d 1 units, and with a unitage that correlates with skin test reactions (bioequivalent allergy units or BAU). Currently, Fel d 1 content is measured with a radial immunodiffusion (RID) assay that uses polyclonal sheep antisera to detect the allergenic protein by producing a white precipitin line in agar gel. However, the RID is considered cumbersome, and the polyclonal sera may qualitatively vary among animals and may recognize epitopes irrelevant to human allergic disease. In this report, we describe a quantitative two-site immunoenzymetric assay (IEMA) for Fel d 1 that uses immobilized capture and soluble biotin-labeled detection Fel d 1-specific human IgE monoclonal antibodies (mAb) that have been class-switched to IgG4. Together, they sandwich Fel d 1 molecules from extracts. Using purified natural Fel d 1 as a calibrator, the historically reported ∼4 micrograms Fel d 1/Fel d 1 unit assignment was directly measured in this mAb-based IEMA at 3.12 ± 0.24 micrograms of Fel d 1 per Fel d 1 unit. This IEMA appears to be equivalent to RID in the measurement of biological potencies of commercial cat hair and cat pelt extracts marketed in the United States.

Understanding the heterogeneity of childhood allergic sensitization and its relationship with asthma

PURPOSE OF REVIEW

To review the current state of knowledge on the relationship between allergic sensitization and asthma; to lay out a roadmap for the development of IgE biomarkers that differentiate, in individual sensitized patients, whether their sensitization is important for current or future asthma symptoms, or has little or no relevance to the disease.

RECENT FINDINGS

The evidence on the relationship between sensitization and asthma suggests that some subtypes of allergic sensitization are not associated with asthma symptoms, whilst others are pathologic. Interaction patterns between IgE antibodies to individual allergenic molecules on component-resolved diagnostics (CRD) multiplex arrays might be hallmarks by which different sensitization subtypes relevant to asthma can be distinguished. These different subtypes of sensitization are associated amongst sensitized individuals at all ages, with different clinical presentations (no disease, asthma as a single disease, and allergic multimorbidity); amongst sensitized preschool children with and without lower airway symptoms, with different risk of subsequent asthma development; and amongst sensitized patients with asthma, with differing levels of asthma severity.

SUMMARY

The use of machine learning-based methodologies on complex CRD data can help us to design better diagnostic tools to help practising physicians differentiate between benign and clinically important sensitization.