Clinical and immunological determinants of severe/refractory asthma (SRA): association with Staphylococcal superantigen-specific IgE antibodies.

BACKGROUND: Demographic and immunological determinants of severe refractory asthma (SRA) are not well characterized. Because Staphylococcus aureus enterotoxins with superantigenic activity have been associated with upper and lower airway inflammation, we aimed to evaluate the association of sensitization to Staphylococcal enterotoxins with asthma severity and various asthma phenotypes.

METHODS: The study included 109 patients with SRA diagnosed according to the American Thoracic Society Workshop 2000, and 101 patients with nonsevere asthma, followed for at least 12 months. Specific IgE to Staphylococcus enterotoxins and total IgE and eosinophil cationic protein concentrations were measured in serum with immunoassays.

FINDINGS: A significant risk for severe asthma was associated with female gender [Odds Ratio (OR) = 2.04], history of wheezing in childhood (OR = 2.47), presence of hypersensitivity to aspirin (OR = 1.96) and with body mass index (OR = 3.08). The mean level of enterotoxin-specific IgE was 3-fold higher in patients with severe asthma when compared to patients with nonsevere asthma (P = 0.01). Serum-specific IgE to enterotoxins was significantly associated with low respiratory function parameters (FEV₁, FEV₁/FVC and MEF 25/75) and increased airway reversibility in response to albuterol. The presence of specific IgE to enterotoxin carried a significant risk for patients to have serum total IgE level above 100 kU/l (OR = 7.84).

INTERPRETATION: Specific immunological response to enterotoxins is associated with clinical and immunological parameters of asthma severity, suggesting a role for Staphylococcal enterotoxins in the asthma pathogenesis.