Pseudomonas aeruginosa protease IV: a corneal virulence factor of low immunogenicity.

Purpose: To study antibody production to Pseudomonas aeruginosa protease IV (PIV) for immunoassay development and to assess the possible role of antibody in arresting corneal damage.
Methods: Rabbits were immunized with PIV, urea-soluble recombinant PIV (rPIV), or precipitated rPIV. Antibody was analyzed by ELISA and Western blotting. Antibody-mediated inhibition of PIV activity was tested by colorimetric assay and during keratitis by slit-lamp examination of infected eyes.
Results: Antibody was not produced after PIV immunization but was induced by rPIV. Rabbits immunized first with soluble and then precipitated rPIV produced high titers (log(10)) to rPIV (4.28 +/- 0.09) and significantly higher titers to PIV (3.90 +/- 0.06) compared to the other immunized groups. Antibody to rPIV reacted with PIV, but neither neutralized enzyme activity in vitro nor protected infected rabbits in vivo.
Conclusions: The present study demonstrates that PIV is a virulence factor which can escape a protective immune response.