Experimental Pseudomonas aeruginosa keratitis in interleukin-10 gene knockout mice

Abstract

Pseudomonas aeruginosa keratitis is one of the most destructive diseases of the cornea. The host response to this infection is critical to the outcome. The cytokine interleukin-10 (IL-10) is thought to play an important role in modulating excessive inflammation and antimicrobial defenses. We have found that in IL-10(-/-) mice there is a significant decrease in bacterial load in corneas at 7 days postchallenge with P. aeruginosa. This decrease was accompanied by a reduction in neutrophil numbers in the cornea and changes in cytokine levels compared to those of wild-type mice. A characteristic increase in neovascularization in the cornea was found in the IL-10(-/-) mice. This increased angiogenesis correlated with an increased expression of KC, whereas the kinetics of macrophage inflammatory peptide 2 expression correlated with neutrophil numbers. This finding suggests that KC may play a role in corneal angiogenesis. The source of IL-10 in mouse corneas was identified as a subpopulation of infiltrating cells and keratocytes. This study demonstrates that IL-10 plays an important role in regulating the balance of inflammatory mediators during P. aeruginosa infection of the cornea.

Figures

FIG. 1.

Histological and clinical examination of mouse corneas infected with P. aeruginosa. Histological sections are stained with hematoxylin and eosin. The magnification of all sections is ×200, except for the inset in panel D, which is at ×400. (A) Wild-type mouse at 24 h postchallenge; (B) IL-10−/− mouse at 24 h postchallenge; (C) wild-type mouse at 7 days postchallenge; (D) IL-10−/− mouse at 7 days postchallenge (the arrow indicates the area shown at higher magnification in the inset); (E) wild-type mouse at 7 days postchallenge; (F) IL-10−/− mouse at 7 days postchallenge showing increased vascularization.

FIG. 2.

(A) Average numbers of viable P. aeruginosa cells in corneal tissue at 1 and 7 days postchallenge as determined by direct plate counting. The mean number of CFU (± the standard deviation) is expressed as a log10 value. At 7 days postchallenge, the bacterial loads in corneas of IL-10−/− mice were significantly reduced (P = 0.004) compared to those of wild-type mice. (B) Relative myeloperoxidase (MPO) activity per cornea at 1 and 7 days postchallenge with P. aeruginosa. Black bars indicate data for wild-type mice. White bars indicate data for IL-10−/− mice. *, P < 0.05.

FIG. 3.

Concentrations of cytokines in wild-type and IL-10−/− corneas during infection with P. aeruginosa as determined by ELISA. (A to D) Concentrations of IL-10 (A), MIP-2 (B), TNF-α (C), and IFN-γ (D) in wild-type mouse corneas 7 days after challenge with P. aeruginosa strain 6294 or 6206. Black bars indicate data for wild-type mice. White bars indicate data for IL-10−/− mice. *, P < 0.05.

FIG. 4.

Concentrations of cytokines in wild-type and IL-10−/− corneas during infection with P. aeruginosa as determined by ELISA. (A to C) Concentrations of KC (A), IL-6 (B), and VEGF (C) in mouse corneas after challenge with P. aeruginosa. Black bars indicate data for wild-type mice. White bars indicate data for IL-10−/− mice. *, P < 0.05.