Date Published: January 20, 2012
Publisher: BioMed Central
Author(s): Faisal M Khan, Aito Ueno-Yamanouchi, Bazir Serushago, Tom Bowen, Andrew W Lyon, Cathy Lu, Jan Storek.
Skin prick test (SPT) and fluorescence enzyme immunoassay (FEIA) are widely used for the diagnosis of Immunoglobulin-E (IgE)-mediated allergic disease. Basophil activation test (BAT) could obviate disadvantages of SPT and FEIA. However, it is not known whether BAT gives similar results as SPT or FEIA for aeroallergens.
In this study, we compared the results of SPT, BAT and FEIA for different aeroallergens.
We performed BAT, SPT and FEIA in 41 atopic subjects (symptomatic and with positive SPT for at least 1 of 9 common aeroallergens) and 31 non-atopic subjects (asymptomatic and with negative SPT).
Correlations between SPT and BAT, SPT and FEIA, and BAT and FEIA results were statistically significant but imperfect. Using SPT as the “gold standard”, BAT and FEIA were similar in sensitivity. However, BAT had lower specificity than FEIA. False positive (BATposSPTneg) results were frequent in those atopic subjects who were allergic by SPT to a different allergen and rare in non-atopic subjects. The false positivity in atopic subjects was due in part to high levels of serum Total-IgE (T-IgE) levels in atopic individuals that lead to basophil activation upon staining with fluorochrome-labeled anti-IgE.
As an alternative to SPT in persons allergic to aeroallergens, BAT in its present form is useful for distinguishing atopic from non-atopic persons. However, BAT in its present form is less specific than FEIA when determining the allergen which a patient is allergic to. This is due to IgE staining-induced activation of atopic person’s basophils and/or nonspecific hyperreactivity of atopic person’s basophils.
Allergen-specific IgE-mediated inflammation is thought to play a major role in the pathogenesis of allergic diseases including extrinsic asthma, rhinitis or eczema. Fc receptors of IgE bind to basophils and mast cells. Crosslinking of the bound IgE by allergens induces the release of inflammatory mediators. Skin prick testing (SPT) is an indirect measure of specific IgE bound to skin mast cells . It has been widely used for the diagnosis of allergic disease because the results are available quickly. However, the utility of SPT is limited in patients with rash or dermographism or those taking antihistamines [2,3]. An alternative to SPT is the determination of serum concentration of specific IgE using the radioallergosorbent test (RAST) or the fluorescent enzymoimmunoassay (FEIA) . A theoretical disadvantage of RAST or FEIA is that it measures both functional IgE (capable of binding to Fcε receptor I [FcεRI] on mast cells or basophils and activating them) and nonfunctional IgE. Another disadvantage of RAST or FEIA is that results are not available as quickly as with SPT.
Of the 72 subjects (41 atopic and 31 non-atopic subjects), 67 (93%) were evaluable for BAT (39 atopic and 28 non-atopic). The remaining 5 subjects (2 atopic and 3 non-atopic) were not evaluable because of unresponsive basophils (less than 15% basophils expressing CD63 above background upon stimulation with anti-FcεRI [positive control]). The subjects with unresponsive basophils were eliminated from data analysis. Of the 39 evaluable atopic subjects, 11 (28%) had asthma, rhinitis and eczema, 13 (33%) had asthma and rhinitis, 3 (8%) had rhinitis and eczema, 9 (23%) had rhinitis only, 2 (5%) had asthma only, and 1 (3%) had eczema only. By SPT, 19 (49%) of the 39 evaluable atopic subjects were allergic to cat, 14 (36%) to dog, 11 (28%) to Dermatophagoides(D) pteronyssinus, 8 (20%) to Derpmatophagoides(D) farinae, 2 (5%) to Alternaria, 2 (5%) to Hormodendrum, 26 (67%) to Timothy grass, 21 (54%) to birch tree and 10 (26%) to short ragweed. Median number of positive skin prick tests per atopic subject was 2. Given the small number of subjects atopic to D.farinae, Alternaria, Hormodendrum and short ragweed, only analyses pertinent to cat, dog, D.pteronyssimus, Timothy grass and birch tree are presented here.
Our results suggest that BAT is as good as SPT or FEIA for distinguishing atopic from non-atopic persons. However, in identifying the allergen to which an atopic person is allergic, BAT in its present form appears to be inferior to SPT or FEIA. When SPT is considered as the “gold standard” and when the cutoffs are set so that BAT and FEIA have similar sensitivities, BAT has lower specificity than FEIA. The BATposSPTneg (false positive) results are frequent in atopic but rare in non-atopic individuals. This suggests that basophils from atopic subjects are hyperresponsive to a nonspecific stimulus. The results did not changed when we included the additional 5 subjects (2 atopic and 3 non-atopic) which were not included in the primary analysis as they have unresponsive basophils (less than 15% basophils expressing CD63 above background upon stimulation with anti- FcεRI (data not shown).
The authors declare that they have no competing interests.
FMK and AU-Y performed experiments. AU-Y performed analysis and generated the initial draft of the manuscript, FMK performed experiments, carried out final analyses and wrote later drafts of the manuscript, BS and TB recruited atopic subjects and performed skin prick tests, AL was involved in the experiments and analysis related to FEIA and T-IgE measurement, CL was involved in performing laboratory experiments assay, JS designed the study, edited the drafts and the final version of the manuscript. All authors have read and approved the final manuscript.