Purpose: To define factors that protect the eye from Staphylococcus aureus keratitis and limit tissue damage once keratitis occurs.
Methods: Rabbit tears were analyzed for bactericidal and phospholipase A(2) (PLA(2)) activities on S. aureus. Inhibition by spermidine of PLA(2) anti-staphylococcal activity in tears was tested in vitro and in vivo. Rabbits immunized with heat-inactivated alpha-toxin were challenged with intrastromal injection of S. aureus.
Results: Arachidonic acid was cleaved from S. aureus by purified PLA( 2) or rabbit tears. Spermidine inhibited these reactions in vitro and facilitated keratitis in vivo. PLA(2) activity decreased with advanced age and shortly following sleep, but increased with keratitis. Antibody to alpha-toxin significantly reduced corneal damage and epithelial cell sloughing during keratitis.
Conclusions: PLA(2) is a major host-defense component of rabbit tears. Alpha-toxin is a major mediator of corneal damage, and antibody to alpha-toxin reduces pathologic changes during keratitis.