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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 (>0.1kU/L and >0.35kU/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 >0.35kU/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.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare, small vessel, necrotizing vasculitis. The disease is mainly characterized by hypereosinophilia and asthma with frequent sinonasal involvement, although multiple organs can be affected, including the heart, lungs, skin, gastrointestinal tract, kidneys, and nervous system. IL-5 production is pathogenetically central for the development of the disease by promoting proliferation, transvascular migration and functional activation of eosinophils. The degree of blood and tissue eosinophilia appears to be associated with disease pathogenesis and eosinophil depletion represents a promising treatment approach for EGPA. We prospectively evaluated the efficacy and safety of a low dose (100 mg q4w), 12-month course of mepolizumab, an anti-IL-5 monoclonal antibody, in eight patients with severe asthma and active EGPA. Patients were recruited by the tertiary care center of Clinical Immunology and Allergy, University of Naples Federico II. The following outcomes were assessed before (T0), and after 6 (T6) and 12 months (T12) of mepolizumab treatment: Birmingham Vasculitis Activity Score (BVAS), prednisone intake, Sino-Nasal Outcome Test (SNOT-22), Total Endoscopic Polyp Score (TENPS), Asthma Control Test (ACT), Forced Expiratory Volume one second (FEV1)%, blood eosinophilia. BVAS score significantly decreased showing a sharp reduction in disease activity score. Clinical improvements in terms of sinonasal scores and asthma symptoms were observed, in parallel with a drastic drop in eosinophil blood count. Prednisone intake was significantly reduced. In two patients, asthma exacerbations led to discontinuation in mepolizumab therapy after 6 and 12 months despite BVAS reduction. Mepolizumab treatment was well tolerated, and no severe adverse drug effects were registered. In conclusion, our 12-month real-life study suggests that mepolizumab may be beneficial and safe in active EGPA patients by improving disease activity score, sinonasal and asthma outcomes while reducing the burden of prednisone intake.