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Nazeem Shamsuddin, Jacob Blair, Ashok Kumar; Toll Like Receptor 2 Mediates The Innate Immune Response Of Retinal Muller Glia To Staphylococcus Aureus. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2959.
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© ARVO (1962-2015); The Authors (2016-present)
Muller cells, the principal glia of the retina, play several key roles in normal and disease states. The purpose of this study is to characterize their innate response in Staphylococcus aureus (SA) endophthalmitis and to determine the involvement of Toll-like receptor 2 (TLR2).
Live or heat-killed SA (strain RN 6390) and TLR2 ligand Pam3Cys was used to challenge human retinal muller cell line, MIO-M1. The expression of TLR2 was determined by RT-PCR, Western blot, immunostaining and flow cytometry. The activation of NF-ΚB, and P38 pathways was assessed by Western blotting. RT-PCR was used to detect the mRNA expression of various proinflammatory cytokines/chemokines, whereas ELISA was used to measure their protein levels. The production of antimicrobial peptide human LL-37 was detected by dot blot. To verify the involvement of TLR2 in the process, inhibition studies were performed using siRNA, TLR2 neutralizing antibody, and use of NF-kB and p38 inhibitors.
MIO-M1 cells constitutively expressed TLR 1, 2, and 6 mRNA. The expression of TLR2 at both mRNA and protein levels was up-regulated in muller glia challenged with Pam3Cys or heat-killed bacteria. Both bacteria (live & heat-killed) and Pam3Cys induced time-dependent activation of NF-ΚB, and P38 pathways. Concomitant with their activation, production of IL-6, IL-8, IL-1β and TNF-α was also induced in stimulated MIO-M1 cells. Furthermore, TLR2-activated muller glia markedly produced LL-37. Blocking TLR2 with antibodies or siRNA-mediated knockdown resulted in decreased production of inflammatory mediators. Inhibition studies revealed that NF-ΚB inhibitors completely blocked Pam3Cys- or bacteria-induced production of cytokines and chemokines, while p38 inhibitors blocked partially.
This is the first report to show that retinal muller glia expresses TLR2 and stimulation of this receptor by S. aureus induces inflammatory response and production of antimicrobial peptide LL-37. These findings reveal an active role of muller glia in innate defense against bacterial infection in the retina.
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