Abstract
Purpose: :
The purpose of this study was to determine whether active immunization with a recombinant form of pneumolysin (PLY) could lower the severity of pathogenesis observed in pneumococcal endophthalmitis.
Methods: :
Specific pathogen free New Zealand white rabbits were actively immunized with recombinant heat-inactivated PLY (experimental group) or PBS (mock group) with Complete Freund’s Adjuvant (initial immunization) or Incomplete Freund’s Adjuvant (subsequent immunizations). A clinical pneumococcal endophthalmitis strain was grown in media and diluted such that each vitreous (n = 6 eyes for each group) was injected with 102 colony-forming units (CFU) in 10 µl. Severity of endophthalmitis infection was graded by two observers using slit lamp examination (SLE) at 24 and 48 hours post-infection (PI). Vitreous was removed from rabbits, serially diluted, and plated on blood agar for bacterial CFU quantitation. Histological sections of whole eyes were stained with hematoxylin and eosin.
Results: :
IgG titers were > 51,600 for the actively immunized rabbits and < 800 for the mock immunized rabbits. There was not a significant difference in average SLE scores between actively immunized and mock immunized rabbits at 24 hours PI (10.17 ± 2.22 and 16.35 ± 2.55 respectively; P = 0.0968). However, at 48 hours PI the mock immunized rabbits had a significantly higher average SLE score than the actively immunized rabbits (29.02 ± 0.80 and 21.00 ± 2.15 respectively; P = 0.0058). Average log10 CFU recovered from the vitreous of both groups at 24 and 48 hours PI was ≥ 9.48. Eyes of mock immunized rabbits showed a more severe endophthalmitis infection as observed by histology than eyes of PLY immunized rabbits. The pathology of mock immunized rabbits was evident throughout the entire eye (retina, vitreous, aqueous, cornea, and conjunctiva), whereas the pathology of PLY immunized rabbits was maintained in the vitreous and most posterior portion of the retina.
Conclusions: :
Active immunization with recombinant PLY aids in lowering the severity of pneumococcal infection.
Keywords: endophthalmitis • vitreous • bacterial disease