Exploring SplA-Specific IgE as a Biomarker in Late-Onset Asthma Patients

<bold>Introduction:</bold> Staphylococcus aureus (SA) can secrete staphylococcal enterotoxins (SEs) or serine protease-like proteins (Spls), which may drive allergic inflammation. Previous studies have shown that SE-IgE sensitization is associated with severe eosinophilic asthma phenotypes. However, the significance of Spl-IgE sensitization in clinical outcomes remains unclear. This study aims to explore the relationships between Spl-IgE levels and clinical parameters in late-onset asthmatics. <bold>Methods:</bold> A total of 113 late-onset asthmatics (onset age≥40 years) were prospectively recruited. Patient assessments included demographics, onset age, recent acute exacerbation history, inflammatory markers, and lung function tests. Serum total IgE and SE-IgE levels were measured using ImmunoCAP assays, while SplA-IgE levels were determined through enzyme-linked immunosorbent assays. Nasal swabs were utilized to assess for the colonization of SA. <bold>Results:</bold> The serum level of SplA-IgE was significantly associated with male sex and smoking history. However, the relationship with nasal SA colonization was not significant (p=0.056). In Spearman's correlation, moderate correlations were observed between SplA-IgE levels and both total IgE (r = 0.50, p < 0.001) and SE-IgE (r = 0.43, p < 0.001); however, the correlation with blood eosinophils was weak (r = 0.21, p = 0.034). The associations of SplA-IgE levels with blood eosinophils and IgE levels remained significant in multivariate regression analyses. Nonetheless, there was no significant relationship between SplA-IgE levels and the severity of asthma or history of exacerbations. <bold>Conclusion:</bold> SplA-IgE could serve as a biomarker for a distinct Type 2 phenotype in late-onset asthmatics.