The role of CXC chemokine receptor 2 in Staphylococcus aureus keratitis

- CXC receptor 2 gene knock-out mice had more severe keratitis.
- CXC receptor 2 knock-out mice had defects in recruitment of PMNs into the cornea.
- CXC chemokines were significantly upregulated during keratitis in knock-out mice.
- Cmkar −/− mice failed to upregulate mRNA for VCAM-1 or PECAM-1.

Staphylococcus aureus is a leading cause of corneal infection. CXC receptor 2 binding chemokines have been implicated in the pathogenesis of Pseudomonas aeruginosa keratitis. The role of this receptor in immune responses during Staphylococcus keratitis remains to be fully understood. Corneas of CXC receptor 2 knockout and wild-type mice (Cmkar −/− & Cmkar +/+) were scratched and 1 × 108 cfu/ml of strain Staph 38 applied. Twenty-four hours post-infection, mice were sacrificed and eyes harvested for enumeration of bacteria and measurement of myeloperoxidase levels. Production of inflammatory mediators, cellular adhesion molecules and chemokines in response to infection were investigated by ELISA, and PCR. 24 h after challenge with S. aureus, Cmkar −/− mice had developed a more severe response with a 50-fold higher bacterial load than WT mice. PMNs failed to penetrate the corneas of Cmkar −/− mice. However, concentrations of KC, MIP-2, IL-1β and IL-6 were significantly elevated (6-13 fold) in Cmkar−/− mice. The concentration of LTB4 was decreased (2 fold). Cmkar−/− mice failed to upregulate mRNA for VCAM-1 or PECAM-1 in response to infection, but had constitutively higher levels of ICAM-1. A lack of CXC receptor 2 lead to an inability to control bacterial numbers as a result of failure of PMNs to penetrate the cornea to the site of infection, even when chemokines were more highly produced. These results imply that CXCR2-mediated signaling through upregulation of adhesion molecules is essential to margination of PMNs in this infection model.