ST2 Is Required for Th2 Responsiveness and Resistance to Pseudomonas Aeruginosa Keratitis

Abstract

Purpose:: To elucidate the role of ST2, a member of the TLR/IL-1R (TIR) superfamily, in resistance to Pseudomonas aeruginosa (P. aeruginosa) keratitis in BALB/c mice.

Methods:: ST2 mRNA and protein levels were tested using real-time PCR and western-blot in C57BL/6 (B6, susceptible) vs. BALB/c (resistant) mice before and after P. aeruginosa (5 µl of 10⁶ CFU/µl, ATCC strain 19660) challenge. Infected BALB/c mice also were tested after subconjunctival injection with rmST2/Fc fusion protein or PBS. Disease was monitored by PCR, clinical score, slit lamp, bacterial plate count, myeloperoxidase (MPO) assay to measure PMN infiltrate, and ELISA assays.

Results:: ST2 mRNA and protein were constitutively expressed in the uninfected, normal cornea of both mouse groups. ST2 levels in the cornea of BALB/c over B6 mice were elevated significantly at 1-3 days p.i., peaked at 3 and decreased at 5 days p.i. BALB/c mice treated with rmST2/Fc (a decoy to block ST2 signaling) over PBS controls showed increased corneal opacity and perforation (at 5 days p.i.). These mice also exhibited increased bacterial load, PMN infiltrate and higher corneal mRNA levels for IL-1ß, MIP-2, IL-1R1 and the Th1 type cytokine, IFN-γ. Protein levels for IL-1ß and MIP-2 were significantly upregulated in rmST2 over PBS controls. In contrast, Th2 cytokines IL-5 (mRNA) and IL-10 (mRNA and protein) were significantly reduced.

Conclusions:: ST2 is critical in resistance to P. aeruginosa keratitis, functioning to reduce corneal infection and inflammation by negatively regulating proinflammatory cytokines, inhibiting type-1 immunity, and upregulating type-2 cytokine production, particularly IL-10.

Keywords: keratitis • inflammation • Pseudomonas