Background: Staphylococcus aureus is a major human pathogen that is carried in the nose by 30% of healthy adults at any given time. Carriers are more prone to infection than non-carriers, but are more likely to survive the infection. The immune system presumably plays a role in determining carriage patterns. Since the cytokine IL-17 is involved in clearance of extracellular bacteria, we studied IL-17 responses to S. aureus among carriers and non-carriers.
Methods: We determined S. aureus carriage patterns of four healthy adult volunteers by multiple screenings. S. aureus whole cell antigens were prepared from strains isolated from the two carrier volunteers and from a well-documented, virulent MRSA strain (USA300). PBMCs were separated from blood of each volunteer, and stimulated with either OKT3, or one of the three S. aureus whole cell antigens. RNA was extracted from cell culture after 48 hours of incubation, and real-time PCR was done to determine IL-17 gene expression.
Results: Of the four volunteers, two were carriers and two were non-carriers. We observed that PBMCs from the carriers had ~20 fold lower IL-17 responses to stimulation with their own S. aureus strains compared to stimulation with either USA300 or the other carrier strain. Furthermore, the IL-17 response to a particular strain was ~20 fold higher in non-carrier individuals, compared to the response of the carrier of that strain.
Conclusion: We showed a suppressed IL-17 response to a carrier's own strain, which may play a role in determining the S. aureus carriage pattern.
