Effector mechanisms of protection against Pseudomonas aeruginosa keratitisin immunized rats

Pseudomonas aeruginosa is an opportunistic pathogen which causes sight-thre atening corneal infections in humans. The purpose of this study was to eval uate various immunization routes that may provide protection against Pseudo monas keratitis and to define the molecular mechanisms involved in the prot ection. Sprague-Dawley rats (10 to 12 weeks old) were immunized using paraf ormaldehyde-killed P. aeruginosa (strain 6206) via oral, nasal, and intra-P eyer's patch (IPP) routes followed by an ocular topical booster dose. Scrat ched corneas were challenged with an infective dose of P, aeruginosa. Follo wing clinical examination, eyes were enucleated for histology, polymorphonu clear leukocyte (PMN) quantitation bacterial count, enzyme-linked immunosor bent assay, and RNase protection assay. PMN infiltration was higher early ( 4 h) during the infection in immunized rats than in nonimmunized rats, Late r during the infection, the number of PMNs diminished in immunized rats whi le in nonimmunized animals the number of PMNs continued to increase. Bacter ia were cleared much faster from immunized groups than from the nonimmunize d group, and the nasally immunized group had the most efficacious response among the immunized groups. Nasal and IPP immunization groups had increased cytokine expression of interleukin-2 (IL-2) and IL-5 and differed from eac h other for IL-6. All three immunized groups had significantly reduced IL-1 beta levels when compared with the nonimmunized rats and a significantly a ltered profile for CINC-1 expression. This study has shown that the route o f immunization modulates the inflammatory response to ocular P. aeruginosa infection, thus affecting the severity of keratitis and adverse pathology, with nasal immunization being the most effective.