Allergic Reactions to Serine Protease-Like Proteins of Staphylococcus aureus

Abstract

In cystic fibrosis (CF) infectious and allergic airway inflammation cause pulmonary exacerbations that destroy the lungs. Staphylococcus aureus is a common long-term colonizer and cause of recurrent airway infections in CF. The pathogen is also associated with respiratory allergy; especially the staphylococcal serine protease-like proteins (Spls) can induce type 2 immune responses in humans and mice. We measured the serum IgE levels specific to 7 proteases of S. aureus by ELISA, targeting 5 Spls (76 CF patients and 46 controls) and the staphopains A and B (16 CF patients and 46 controls). Then we compared cytokine release and phenotype of T cells that had been stimulated with Spls between 5 CF patients and 5 controls. CF patients had strongly increased serum IgE binding to all Spls but not to the staphopains. Compared to healthy controls, their Spl-stimulated T cells released more type 2 cytokines (IL-4, IL-5, IL-13) and more IL-6 with no difference in the secretion of type 1- or type 3 cytokines (IFNγ, IL-17A, IL-17F). IL-10 production was low in CF T cells. The phenotype of the Spl-exposed T cells shifted towards a Th2 or Th17 profile in CF but to a Th1 profile in controls. Sensitization to S. aureus Spls is common in CF. This discovery could explain episodes of allergic inflammation of hitherto unknown causation in CF and extend the diagnostic and therapeutic portfolio.

Keywords: IgE; Staphylococcus aureus; Th2 cells; allergy; cystic fibrosis; type 2 immune response.

Figure 1

S. aureus protease-specific IgE in sera of CF patients and healthy adults. Specific serum antibody binding was determined by ELISA. Each data point represents the mean of two technical replicates. Spl-specific serum IgE levels were significantly higher in CF patients (n = 76) than in healthy controls (n = 46) (A), whereas no significant differences were seen in the staphopain A and staphopain B specific IgE levels (CF: n = 14; controls: n = 46) (B). Medians (grey bars) with interquartile ranges are shown. ****P < 0.0001; Mann Whitney U test. CF, cystic fibrosis, ns, not significant, OD, optical density.

Figure 2

Cytokine production by Spl-stimulated T cells. T cells were isolated from whole blood of CF patients (n = 5) and healthy volunteers (n = 5) and stimulated with a mixture of recombinant SplA, SplB, SplD, SplE and SplF (5 µg/mL each) in the presence of CD14+ antigen-presenting cells. Supernatants were taken at day 9 and cytokine concentrations measured by a cytometric bead array. Concentrations were normalized to 1 million T cells. Production of Th2 cytokines (IL 4, IL 5, IL 13) and IL 6 was significantly higher in CF patients compared to healthy controls, IL 10 release in tendency lower, while there were no significant differences in the concentrations of IFNγ, IL 17A, or IL 17F. Medians (grey bars) with interquartile ranges are indicated; *P < 0.05; **P < 0.01; Mann Whitney U test. CF, cystic fibrosis.

Figure 3

T cell differentiation following Spl stimulation. From the same cell cultures described in Figure 2, T cells were harvested at day 9 and the proportion of each T cell subtype was determined by FACS. Fold changes between unstimulated and Spl-stimulated cells are shown. Compared to healthy controls, the changes in Th2 and Th17 cells were significantly higher and those in Th1 cells significantly lower in Spl-stimulated T cells from CF patients. *P < 0.05; Mann Whitney U test. CF, cystic fibrosis.