Prophylactic and therapeutic efficacy of immunoglobulin G antibodies to Pseudomonas aeruginosa lipopolysaccharide against murine experimental corneal infection

Abstract

Purpose: To evaluate the efficacy of lipopolysaccharide (LPS)-specific antibodies administered prophylactically or therapeutically to protect against corneal challenge with Pseudomonas aeruginosa.

Methods: The prophylactic efficacy of active immunization with purified P. aeruginosa LPS was evaluated in a murine corneal-scratch model of P. aeruginosa keratitis. The same model was used to evaluate both the prophylactic and the therapeutic efficacy of systemic passive transfer of variable region-identical, isotype-switched, LPS-specific, murine immunoglobulin M (IgM) and immunoglobulin G (IgG) monoclonal antibodies (mAbs). The mAbs were injected intraperitoneally at various times either before or after corneal challenge and the corneal response was monitored macroscopically. In addition, immune rabbit sera were used to evaluate the efficacy of treatment.

Results: Active immunization with homologous, but not heterologous, LPS before challenge reduced the severity of corneal disease and protected challenged mice against permanent corneal damage. Passive transfer of the LPS-specific IgM mAb 1F6 before challenge did not prevent corneal damage at any dose tested and had no effect on the course of disease. However, results of dose-response studies of the passive transfer of a variable region-identical IgG2b mAb, 2H3, before challenge indicated a 50% protective dose of 11.8 micrograms. When mAb 2H3 was administered at a dose of 50 micrograms before challenge and the challenge inoculum was increased, all mice were protected from corneal damage up to a challenge inoculum of 2.2 x 10(8) CFU/eye. When given 2 or 4 hours after corneal challenge with P. aeruginosa strain 6294 (which invades corneal epithelial cells during infection) but not when given at 8 or 24 hours, 50 micrograms of mAb 2H3 conferred significant protection (P < 0.05). The maximal interval after challenge during which this antibody could be administered and still protect 50% of mice was calculated by probit analysis to be 9.4 hours. Administration of homologous LPS-specific rabbit antiserum to mice at various times after challenge with P. aeruginosa strain 6206 (which is cytotoxic to corneal epithelial cells and does not remain in these cells during infection) resulted in significant protection when administered 4 or 8 hours after infection. Although probit analysis could not be performed with the available data, 50% of mice were completely protected when the antiserum was given up to 24 hours after challenge.

Conclusions: In an experimental model of P. aeruginosa keratitis, systematically delivered IgG antibodies directed against the O-side-chain antigens of P. aeruginosa, LPS conferred protection against severe corneal damage when administered both prophylactically and therapeutically.