An in vitro model for the allergen-IgE-FcARI interaction

Accuracy of IgE antibody laboratory results

BACKGROUND

Studies have demonstrated that the magnitude of sensitization as evidenced by specific IgE (sIgE) levels provides significant information as to whether a sensitized individual is likely to be truly reactive. However, it is not clear that quantitative sIgE results provided by different laboratories using different technologies are comparable.

OBJECTIVE

To investigate whether similar results were obtained from Clinical Laboratory Improvement Act-certified laboratories that used 3 common systems for sIgE antibody determination with serum samples and mouse-human IgE chimeric antibodies with known specificity and quantity.

METHODS

Sixty samples for peanut and 20 for soy were submitted for sIgE determination on 3 different systems: ImmunoCAP, Immulite, and Turbo radioallergosorbent test (RAST). Mouse-human chimeric IgE antibodies specific for the major birch allergen Bet v 1 and for the dust mite allergen Der p 2 were also included.

RESULTS

A qualitative evaluation using a cutoff of 0.35 kUA/L showed some differences in the ability to detect sIgE sensitization, with the Turbo RAST being most variable. However, considerable differences were found with quantitative evaluation, with Immulite overestimating and Turbo RAST underestimating sIgE compared with ImmunoCAP. Similar discrepancies were seen with the mouse-human chimeric IgE antibody samples.

CONCLUSION

These findings have potentially serious clinical implications, since each of these systems is widely used. It is therefore important that all laboratories clarify which system they are using. Just because 2 systems present their results in the same units does not mean that the results are necessarily correct or interchangeable.

The immunoglobulin-like modules Cepsilon3 and alpha2 are the minimal units necessary for human IgE-FcepsilonRI interaction

Atopic allergy is a genetically determined immunodisorder that affects almost 20% of the population worldwide. Immediate symptoms of type I allergy are caused by the release of biologic mediators from effector cells induced by IgE-allergen complexes that cross-link the high-affinity receptor for IgE (FcepsilonRI). Chronic disease manifestations result from allergen-specific T-cell activation, a process that is enhanced when allergens are presented via FcepsilonRI-bound IgE. We report the baculovirus expression, as soluble recombinant proteins, of the minimal units required for human IgE and FcepsilonRI interaction: Cepsilon3 represents the third constant domain of the IgE heavy chain, and alpha2 is the membrane-proximal Ig-like module from FcepsilonRIalpha. Native overlay experiments showed binding of human FcepsilonRIalpha to recombinant Cepsilon3 and of natural or recombinant human IgE to recombinant alpha2. Moreover, recombinant Cepsilon3 inhibited binding of natural IgE antibodies to alpha2, and preincubation of human IgE with alpha2 inhibited anti-IgE-triggered histamine release from human basophils. Isolated Cepsilon3 and alpha2 can now be used for the molecular and structural analysis of the IgE-FcepsilonRI interaction, as well as for diagnostic and therapeutic applications.