Staphylococcus Aureus Toxins and Asthma: Pathophysiological Mechanisms, Clinical Relevance, and Therapeutic Implications in the Biologics Era.

Staphylococcus aureus frequently colonizes the skin and upper airways and produces a broad repertoire of immunomodulatory molecules. In asthma, the most consistent evidence concerns staphylococcal enterotoxins (SEs), which can act both as superantigens and as allergens, and IgE sensitization to SEs (SE-sIgE). SE-sIgE is associated with severe asthma, type 2 inflammation, chronic rhinosinusitis with nasal polyps (CRSwNP), exacerbations, and, in some longitudinal studies, persistent airflow obstruction. However, this relationship is not necessarily causal: SE-sIgE may reflect exposure, an immune response, or a biologically active endotype, whereas colonization, local toxin production, and systemic sensitization are not equivalent. SEs simultaneously bind class II MHC molecules and Vbeta regions of the T-cell receptor, activating large fractions of T lymphocytes; they also promote IL-4, IL-5, and IL-13 production, polyclonal B-cell activation, local IgE synthesis, mast-cell degranulation, eosinophilia, and IL-8/neutrophil circuits. Alpha-toxin (Hla) and SEB can damage the epithelial barrier, facilitating allergen penetration and alarmin signalling. These observations support an interaction model in which dysbiosis, barrier dysfunction, and type 2 immunity mutually reinforce one another along the nasobronchial axis. Corticosteroids and antibiotics may modify selected nodes in this circuit, but current evidence is insufficient to recommend decolonization or antitoxin therapy in stable asthma. Biologics interrupt downstream pathways potentially fuelled by toxins: omalizumab neutralizes free IgE; mepolizumab and benralizumab reduce the eosinophilic axis; dupilumab blocks IL-4/IL-13 signalling; and tezepelumab acts upstream on TSLP. Nevertheless, randomized trials stratified by SE-sIgE are lacking, and no evidence demonstrates that these treatments eliminate colonization or toxin production. SE-sIgE therefore appears to be a promising biomarker, particularly in severe asthma with CRSwNP, but it is not yet an autonomous criterion for biologic selection. A broader barrier-organ analysis also identifies nasal, cutaneous, and intestinal colonization as distinct ecological states; atopic dermatitis as a complementary model of toxin-amplified type 2 inflammation; and biofilms and extracellular vesicles as candidate mechanisms of persistent toxin delivery. These data increase biological plausibility but remain indirect for asthma.