Abstract
Purpose:
Staphylococcus aureus (S. aureus) is a leading cause of destructive endophthalmitis associated with severe inflammation and loss of retinal function. Innate immunity is the first line of defense against pathogens and we demonstrated previously that Toll-like receptor 2 (TLR2) was required for bacterial clearance. Surprisingly, increased susceptibility to infection in TLR2-KO mice did not coincide with a delay in neutrophil (PMN) infiltration. Recent studies demonstrate that IL-1 is among the most rapidly induced cytokines in multiple animal models of S.aureus infection. The current experiments examine the function of TLR2 and IL-1R in PMN recruitment and activation during S. aureus induced endophthalmitis.
Methods:
IL-1R-KO, TLR2-KO, and C57BL/6 WT mice received intravitreal injections of 500 CFU S. aureus (RN6390). Clinical examinations and bacterial quantification were performed at 24, 48, and 72 hours post injection. H&E retinal sections were used to assess retinal damage. PMN infiltration was assessed quantitatively by flow cytometry and DNA staining of tissue sections was performed to visualize neutrophil extracellular trap (NETs) formation
Results:
C57BL/6 WT mice injected with 500 CFU S. aureus successfully cleared the infection as demonstrated by (i) clinical scores, (ii) bacterial quantification, and (iii) histology. Both IL-1R-KO and TLR2-KO mice were unable to clear an identical inoculation resulting in extensive retinal damage. Flow cytometry analysis revealed no significant delay or decrease in the numbers of PMNs infiltrating the eyes of TLR2-KO mice as compared to WT mice. By contrast, a significant delay in PMN recruitment was observed in the eyes of IL-1R-KO mice as compared to both WT and TLR2-KO mice. Interestingly, despite recruiting normal numbers of PMNs to the infection site, H&E and DAPI staining revealed a reduction in NET formation in TLR2-KO eyes at 24 and 48 hours post infection as compared to WT mice.
Conclusions:
Together these data demonstrate that both TLR2 and IL-1R activation are essential in host defense against S. aureus induced endophthalmitis. However, PMN recruitment is dependent upon IL-1R while TLR2 activation is essential for PMN activation and killing of S. aureus.
Keywords: 513 endophthalmitis •
555 immunomodulation/immunoregulation •
594 microbial pathogenesis: experimental studies