• Th17-associated immune responses are required for resolution of Staphylococcus aureus nasal carriage

      Archer, Nate; Shirtliff, Mark (2013)
      The anterior nares of humans are the major reservoir for Staphylococcus aureus colonization. Approximately 20% of the healthy human population is persistently and 80% intermittently colonized with S. aureus in the nasal cavity. Previous studies have shown a strong causal connection between S. aureus carriage and increased risk of nosocomial infection, as well as increased carriage due to immune dysfunction. However, the immune responses that permit persistence or mediate clearance are undefined. We developed a carriage model in C57BL/6J mice and showed that clearance begins 14 days post-inoculation. In contrast, SCID mice that have a deficient adaptive immune response are unable to eliminate S. aureus even after 28 days post-inoculation. Furthermore, decolonization was found to be T-cell mediated, but B-cell independent by evaluating carriage clearance in TCR-beta/delta KO and IgH-mu KO mice, respectively. Up-regulation of IL-1beta, KC, IL-17A and IL-17F occurred following inoculation with intra-nasal S. aureus. IL-17A production was crucial for clearance since IL-17A-deficient mice were unable to eliminate S. aureus carriage. In addition, inoculation of IL-17A/F KO mice displayed a significant inability to control S. aureus growth in the nares. Subsequently, cell differential counts were evaluated from nasal lavage fluid obtained from wild type and IL-17A-deficient colonized mice. These counts displayed IL-17A-dependent neutrophil migration. Antibody-mediated depletion of neutrophils in colonized mice caused reduced clearance compared to isotype treated controls. Th17-associated responses are reported to induce antimicrobial peptide production at epithelial surfaces. Therefore, we utilized RT-PCR to determine nasal tissue expression following inoculation with S. aureus of three antimicrobial peptides with anti-staphylococcal activity, mouse CRAMP, beta-defensin-3 (mBD-3), and beta-defensin-14 (mBD-14). We elucidated an IL-17A-dependent up-regulation of antimicrobial peptides post-S. aureus inoculation, and enhanced nasal tissue expression of mouse beta-defensin-3 upon IL-17A stimulation. Additionally, we discovered that ex-vivo nasal tissue supernatants have anti-staphylococcal activity that is solute-dependent and heat-sensitive. Our data suggest that the Th17-associated immune response is required for nasal decolonization. This response is T-cell dependent, mediated via IL-17F and IL-17A production, neutrophil influx, and potentially antimicrobial peptide induction. Th17-associated immune responses may be targeted for strategies to mitigate distal infections originating from persistent S. aureus carriage in humans.