Clearance of Pseudomonas aeruginosa from a Healthy Ocular Surface Involves Surfactant Protein D and Is Compromised by Bacterial Elastase in a Murine Null-Infection Model

School of Optometry, University of California, Berkeley, CA 94720-2020, USA.
Infection and immunity (Impact Factor: 3.73). 04/2009; 77(6):2392-8. DOI: 10.1128/IAI.00173-09
Source: PubMed


Our previous studies showed that surfactant protein D (SP-D) is present in human tear fluid and that it can protect corneal
epithelial cells against bacterial invasion. Here we developed a novel null-infection model to test the hypothesis that SP-D
contributes to the clearance of viable Pseudomonas aeruginosa from the healthy ocular surface in vivo. Healthy corneas of Black Swiss mice were inoculated with 107 or 109 CFU of invasive (PAO1) or cytotoxic (6206) P. aeruginosa. Viable counts were performed on tear fluid collected at time points ranging from 3 to 14 h postinoculation. Healthy ocular
surfaces cleared both P. aeruginosa strains efficiently, even when 109 CFU was used: e.g., <0.01% of the original inoculum was recoverable after 3 h. Preexposure of eyes to bacteria did not enhance
clearance. Clearance of strain 6206 (low protease producer), but not strain PAO1 (high protease producer), was delayed in
SP-D gene-targeted (SP-D−/−) knockout mice. A protease mutant of PAO1 (PAO1 lasA lasB aprA) was cleared more efficiently than wild-type PAO1, but this difference was negligible in SP-D−/− mice, which were less able to clear the protease mutant. Experiments to study mechanisms for these differences revealed that
purified elastase could degrade tear fluid SP-D in vivo. Together, these data show that SP-D can contribute to the clearance
of P. aeruginosa from the healthy ocular surface and that proteases can compromise that clearance. The data also suggest that SP-D degradation
in vivo is a mechanism by which P. aeruginosa proteases could contribute to virulence.

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    • "We have previously shown that SP-D, a member of the collectin family of innate defense molecules, is present in tear fluid and the corneal epithelium and plays a role in ocular defense against P. aeruginosa [34], [36]. Thus, SP-D levels were assessed in EDE mice and controls after 5 days of EDE induction, and before and after (6 h) inoculation with 109 cfu PAO1. "
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