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Sharon McClellan, Kerry Vistisen, Linda D Hazlett; A role for NLRC4 in resistance of BALB/c mice infected with P. aeruginosa.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):316.
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© 2017 Association for Research in Vision and Ophthalmology.
Inflammasomes are molecular platforms activated upon cellular infection that trigger maturation of IL-1β and IL-18. In C57BL/6 (B6) mice, IL-1β processing during P. aeruginosa keratitis has been shown to be mediated by neutrophil serine proteases, independent of the inflammasome NLRC4 and caspase 1. However, the role of NLRC4 in the resistance response of BALB/c mice to bacterial infection with this pathogen has not been examined and is the purpose of this study.
Eyes of B6 and BALB/c mice were infected with P. aeruginosa ATCC strain 19660 and inflammasomes NLRP3 and NLRC4 were tested by ELISA. BALB/c mice were treated with siRNA for NLRC4 or a scrambled control peptide and clinical scores, photography with a slit lamp, Western blot, ELISA, MPO assay, and viable bacterial plate counts were used to assess the disease response.
Protein levels of NLRC4 were upregulated significantly in BALB/c vs B6 mice at 24 h, with no difference at 5 days p.i. In contrast, NLRP3 protein levels were a 100 fold less, did not differ between groups at 1 day p.i. and were reduced in BALB/c mice at 5 days p.i. NLRC4 and NLRP3 levels were further tested in BALB/c mice and at 6, 12 and 24 h p.i., only NLRC4 levels were significantly increased over normal. Silencing NLRC4 (reduced at 1-5 days p.i.) vs scrambled peptide treatment, exacerbated disease in BALB/c mice, increased pro-IL-1β, but reduced total amounts of IL-1β and IL-18 at 5 days p.i. It also significantly reduced MPO values indicating a reduced neutrophil infiltrate at 5 but not 1 day p.i. Consistent with this, bacterial plate counts were unchanged at 1 day, but significantly elevated at 5 days p.i.
These data provide evidence that the NLRC4 inflammasome contributes to resistance through regulation of both mature IL-1β and IL-18 that modulate the neutrophil infiltrate with subsequent decreased bacterial killing.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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