Difference in Host Immune response to Methicillin-Resistant and Methicillin Sensitive Staphylococcus aureus (MRSA and MSSA) Endophthalmitis

Purpose The study aimed to understand the differential immune response of methicillin susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains in in vitro models of endophthalmitis. Methods Retinal pigment epithelium (RPE) and microglia cells (CHME-3) were exposed to MRSA and MSSA strains and analyzed for expression of inflammatory mediators by real-time quantitative PCR and validated by ELISA or immunofluorescence assay. Heatmap and STRING analysis was used to assess the differential immune expression. Results Both microglia and RPE expressed TLR-2, TLR-1, TLR-6, and TLR -9 after challenge with MRSA and MSSA strains though the expression varied. MRSA-infected cells induced higher expression of IL-1 beta, IL-8, 1 L-10, IL-6, and GM-CSF, while TNF-alpha and IFN-gamma were downregulated in comparison to MSSA-infected cells. We also demonstrate that MRSA infection leads to increased activation of MMP-9 and MMP-2 in RPE cells, while microglia expressed only MMP-9 in MRSA-infected cells. Conclusions MRSA strain can induce an exacerbated immune response in retinal cells. Giving clues for potential targets in immunomodulatory therapies.