12 January - 20 June 2016

Basophil activation test reflects the severity and threshold of allergic reactions to peanut

28 January 2015

Basophil reactivity is associated with the severity and basophil sensitivity is associated with the threshold of allergic reactions to peanut, according to research published in the Journal of Allergy and Clinical Immunology. The research focused on patients who participated in a study about the use of the basophil activation test (BAT) in the diagnosis of peanut allergy or in the Peanut Allergy and Sensitization study with a positive oral peanut challenge result.  

All the children underwent clinical evaluation, skin prick tests (SPT’s) using commercially available peanut extract and blood collection for specific IgE determination and BAT’s. Six verum doses and 3 placebo doses were randomly interspersed with verum doses up to a cumulative dose of 9.35 g of peanut protein. Children 1 to 3 years of age were given 5 verum doses and 1 placebo dose up to a cumulative dose of 4.35g of peanut protein. High risk patients (those with high risk of peanut allergy, history of life-threatening food induced anaphylaxis of a SPT response ≥7 mm) received an additional lower starting active dose of 0.033 g of protein. Double-blind, placebo-controlled peanut challenge (DBPCPC) was performed in 93% of cases.

Allergic reactions to peanut during challenges were attributed a symptom score varying between 1 and 5, and the severity was classified into mild, moderate or severe categories. Patients were dichotomized depending on whether their reaction was mild-moderate or severe and were grouped according to the cumulative threshold dose at the time of reaction into low (≤0.1 g of peanut protein) versus high (>0.1 g of peanut protein)

One hundred and twenty four patients were submitted to oral peanut challenges. Fifty-two (42%) of patients had a positive challenge result to peanut. Symptoms during the challenge ranged from mild oral symptoms to anaphylaxis. Twenty (41%) patients had severe reactions, nine (18%) patients required the administration of intramuscular epinephrine and 10 (77%) required the administration of intravenous fluid boluses. One patient had a biphasic reaction about 5 hours after the allergic systems that occurred during the challenge. 

The results showed that severe reactors had comparable SPT responses (P=.102) and higher levels of specific IgE to peanut (P=.010), Ara h 1 (P=0.021), and Ara h 2 (P=.003) compared with patients who had mild-to-moderate reactions. Having greater number of peanut major allergens reactions was associated with severe reactions. Patients with severe reactions to peanut during OFCs showed a higher proportion of CD63 basophils at concentrations of PR ranging from 1 to 100,000 ng/mL compared with patients with PA with mild-to-moderate reactions.  The dose response for peanut-induced basophil activation of patients with lower cumulative peanut threshold doses on OFCs was shifted to the left compared with the dose response of patients with a higher cumulative threshold dose.  After multivariable analyses, only the basophil activation markers were retained for severity and threshold meaning that the BAT alone was more discriminative in predicting the severity and threshold of allergic reactions. 
Further to this, the symptom score and threshold were not correlated though the basophil markers and severity and threshold were strongly correlated.

It would appear that the BAT can be used to identify patients who are at risk of reacting to small amounts of the allergen and of having severe symptoms that require special attention. 

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