Purpose: Alterations in immune system function associated with aging may contribute to increased morbidity in this population of individuals. The current studies were performed to determine aging-related changes in polymorphonuclear neutrophil (PMN) function after corneal infection with Pseudomonas aeruginosa.

Methods: Total PMN number, macrophage inflammatory protein (MIP)-2 mRNA and protein expression, and ocular bacterial load were determined in 8-week- and 12-month-old inbred BALB/c mice at various times after infection with P. aeruginosa. In addition, 12-month-old mice were treated systemically with the MIP-2 polyclonal antibody (pAb) to determine the effects of MIP-2 neutralization on ocular disease and PMN recruitment.

Results: Histologically, PMN infiltration into the cornea of 12-month-old mice was delayed initially and was associated with an inability to reduce bacterial load at later postinfection (PI) times. In addition, a significantly greater number of PMNs were found in the cornea of 12-month-old mice at later PI times. The increase in PMN number in 12-month-old mice correlated with a persistence of MIP-2 expression in cornea at these later times. Systemic treatment of 12-month-old mice with neutralizing MIP-2 pAb versus normal rabbit serum (NRS) resulted in reduced corneal PMN number and ocular disease.

Conclusions: These data provide evidence that persistence of PMN in the cornea of 12-month-old mice contributes to corneal tissue destruction after P. aeruginosa challenge. Further evidence also is provided that the chemoattractant MIP-2 contributes to the altered PMN response in these animals.