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Experimental bacterial keratitis in neutropenic guinea pigs: polymorphonuclear leukocytes in corneal host defense
Abstract:
Quantitative techniques were used to determine the relative concentrations of viable bacteria and polymorphonuclear leukocytes (PMNs) in the corneas of neutropenic and non-neutropenic guinea pigs with experimental bacterial keratitis induced with three strains of Pseudomonas aeruginosa. Neutropenia was produced by whole-body X-irradiation 1 week before infection. Significantly greater numbers of bacteria were present in the cornea of neutropenic animals 48 h after infection than were present in the corneas of non-neutropenic animals. The same was true 24 and 48 h after infecting animals with Staphylococcus aureus. Examination of histological sections showed that fewer PMNs were present in the corneas of infected neutropenic animals than in the corneas of infected non-neutropenic animals. Radiolabeling of PMNs confirmed a significant reduction in PMN concentration in the corneas of infected neutropenic animals. Tears and the corneal epithelium appear to be the most important elements protecting the cornea against local invasion by bacteria. However, once bacterial keratitis is established, PMNs play a role in limiting bacterial multiplication.
Insights
Neutropenic guinea pigs infected with Pseudomonas aeruginosa showed significantly higher bacterial numbers in their corneas. This highlights the crucial role of neutrophils (PMNs) in controlling bacterial keratitis.
Area of Science:
- Ophthalmology
- Immunology
- Microbiology
Background:
- Bacterial keratitis is an infection of the cornea.
- Neutrophils (PMNs) are key immune cells involved in combating bacterial infections.
- The role of PMNs in experimental bacterial keratitis, particularly in a neutropenic state, requires further elucidation.
Purpose of the Study:
- To investigate the impact of neutropenia on bacterial keratitis progression in guinea pigs.
- To quantify bacterial load and polymorphonuclear leukocyte (PMN) infiltration in the cornea.
- To assess the protective mechanisms of the cornea against bacterial invasion.
Main Methods:
- Induction of experimental bacterial keratitis in neutropenic and non-neutropenic guinea pigs using Pseudomonas aeruginosa and Staphylococcus aureus.
- Quantitative assessment of viable bacteria and PMNs in corneal tissues.
- Histological examination of corneal sections.
- Radiolabeling of PMNs to track their concentration in the cornea.
Main Results:
- Neutropenic animals exhibited significantly higher bacterial concentrations in the cornea at 48 hours post-infection compared to non-neutropenic animals.
- This observation was consistent for both Pseudomonas aeruginosa and Staphylococcus aureus infections.
- Histological and radiolabeling data confirmed a marked reduction in PMN infiltration in the corneas of infected neutropenic guinea pigs.
Conclusions:
- Neutrophils (PMNs) play a critical role in limiting bacterial multiplication during established bacterial keratitis.
- The cornea's natural defenses, including tears and the corneal epithelium, are vital in preventing initial bacterial invasion.
- Impaired PMN function due to neutropenia exacerbates bacterial keratitis severity.