Abstract
Purpose :
To test the hypothesis that absence of innate immune pathways and modulators alters Staphylococcus aureus persistence in the mouse cornea.
Methods :
Male and female C57BL/6J mice and mice deficient in innate immune pathways (TLR2/4) or proinflammatory mediators (CXCL1, CXCL2, CXCL10, CCL2, CCL3, or TNFα) were used in these studies (9-11 weeks old, N=6-12 corneas/group). After anesthesia, corneas were scarified (18g needle) and Staphylococcus aureus strain SH1000 (~108 colony forming units [CFU]/10 μl) was topically instilled into each eye. On days 1, 2, and 3, mice were euthanized and eyes harvested for CFU and myeloperoxidase (MPO) quantitation and histology to assess the extent of ocular infection and inflammation.
Results :
Comparisons of CFU and MPO in the corneas of male and female mice of each strain on each day revealed few statistically significant differences. In comparisons of combined male and female CFU data, CFU in eyes of C57BL/6J mice were lower than CFU in eyes of mice absent in TLR2/4, TNFα, CCL2, or CCL3 over 3 days. Statistical significance was reached on at least one day in these comparisons. In C57BL6/J eyes, CFU decreased from ~2 x 103 on day 1 to ~3 x 102 by day 3. CFU exceeded 104/eye on day 1 in eyes of mice absent in CXCL1, TLR2/4 or TNFα, but decreased thereafter to 103/eye by day 3 in these groups. ~103 CFU were recovered from eyes of mice absent in CXCL2 or CXCL10 on day 1, which remained constant by day 3. ~5 x 103 were recovered from eyes of mice absent in CCL2 or CCL3 on day 1, which remained constant by day 3. Combined male and female MPO data and representative histology data were generally consistent with decreased inflammation on days 2 and 3, regardless of CFU burden. In strain groups with significant CFU and MPO burdens, histology showed influx of neutrophils and pockets of staphylococci in the cornea, but very few epithelial defects were observed.
Conclusions :
Wild type mice were able to control, but not eliminate this toxin-producing S. aureus strain from the eye. S. aureus persisted in the corneas of mice absent in innate immune pathways or individual modulators to a greater degree than that of wild type mice. These data suggest that the burden and persistence of S. aureus in the cornea depends on functioning innate immunity. Maintenance of anti-staphylococcal immunity in the eye is likely due to redundant mechanisms.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.