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E. W. Norcross, S. N. Dixon, M. E. Sanders, Q. C. Moore, III, L. S. McDaniel, M. E. Marquart; Active Immunization Against Pneumolysin Protects the Cornea During Streptococcus pneumoniae Keratitis Infection. Invest. Ophthalmol. Vis. Sci. 2009;50(13):853.
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The purpose of this study was to determine if active immunization against pneumolysin (PLY) can protect against the corneal damage associated with a pneumococcal keratitis infection.
Antiserum was produced in New Zealand white rabbits by three monthly subcutaneous injections of recombinant mutant pneumolysin (ψPLY), which retained 1% of its cytolytic capability. Freund’s complete adjuvant was mixed with 0.1 mg ψPLY in a 1:1 (vol/vol) ratio for primary immunization and injected subcutaneously at four locations along the dorsal side of each rabbit. Subsequent immunizations consisted of a mixture of 0.05 mg ψPLY and Freund’s incomplete adjuvant in a 1:1 (vol/vol) ratio administered in the same manner as primary immunizations. Control rabbits were injected with a mixture of Freund’s complete adjuvant and PBS or Freund’s incomplete adjuvant and PBS. Blood was collected from the rabbits prior to the first immunization and one week after each subsequent immunization. An ELISA was performed on the isolated serum to determine IgG titers against PLY. The corneas of the rabbits were injected with 105 colony-forming units (CFU) of S. pneumoniae strain WU2. Severity of keratitis was determined by slit lamp examination (SLE) at 24 and 48 hours post-infection. Following the final examination, rabbits were sacrificed and their corneas were excised, homogenized, serially diluted and plated on blood agar to determine the log CFU per cornea.
ψPLY immunized rabbits had anti-PLY IgG titers above 51600 whereas mock immunized rabbits had no significant anti-PLY IgG titers. SLE scores of rabbit corneas (n = 11) immunized with ψPLY (3.088 ± 0.311) were significantly lower than the scores of corneas (n = 14) of rabbits that were mock immunized (4.411 ± 0.496) at 24 hours post-infection (P = 0.0007). This difference increased at 48 hours post-infection such that the SLE scores of infected corneas from immunized rabbits were 9.955 ± 1.136, significantly lower than the corneas from mock immunized rabbits at 13.435 ± 0.627 (P = 0.0094). Log CFU recovered from corneas at 48 hours post-infection were not significantly different between the immunized (4.666 ± 0.703) and mock immunized (2.899 ± 0.745) groups (P = 0.109).
Active immunization against PLY can significantly reduce the corneal damage associated with pneumococcal keratitis.
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