Basophil activation test for Staphylococcus aureus enterotoxins in severe asthmatic patients

Background: Several studies have shown an association between severe asthma and serum immunoglobulins E (IgE) against Staphylococcus aureus enterotoxins (SEs). SEs—the prototypes being types A (SEA), B (SEB) and toxic shock syndrome toxin 1 (TSST-1)—can induce both polyclonal and specific IgE responses. Objective: The aim of the study was to evaluate the ability of SEs to induce basophil activation in severe asthmatic patients using the basophil activation test (BAT). Methods: 57 severe asthmatic patients were enrolled. BAT in response to SEA, SEB and TSST-1 was performed in all patients, while serum IgE to SEA, SEB and SEC was available in 49 patients. BAT was considered positive when CD203c+ basophils to SEs were ≥5%, and the stimulation index (SI, ratio between % of CD203c+ basophils to SEs and to negative control) was >2. Two threshold values (>0.1 kU/L and >0.35 kU/L, respectively) were used to assess serum SEsIgE. Results: 36.8% of severe asthmatic patients had a BAT positive for at least one SE (BAT SEs+). Serum SEsIgE >0.35 kU/L (SEs IgE+) was associated with BAT SEs positivity. Among patients with negative skin prick test, 35% were BAT SEs+, 30% SEs IgE+, 55% BAT or IgE− SEs+. A negative correlation between SI of BAT to SEs and both clinical (ACT score) and functional parameters was observed, together with a positive correlation of BAT with asthma exacerbations. Conclusions: The positivity of BAT for SEs in a subgroup of severe asthmatic patients further supports the pathogenic role of Staphylococcus aureus in severe asthma.