Differential expression of corneal and limbal cytokines and chemokines throughout the clinical course of sulfur mustard induced ocular injury in the rabbit model

Abstract

Purpose: The sight threatening sulfur mustard (SM) induced ocular injury presents specific symptoms for each clinical stage. The acute injury develops in all of the exposed eyes and is characterized by erosions and severe inflammation. The irreversible late pathology develops only in part of the eyes, and is clinically expressed by chronic inflammation and corneal neovascularization (NV). The mechanisms underlying this injury are still in research and treatment is insufficient. Aiming to shed light on pathological mechanisms and improve the therapeutic measures, we studied the expression pattern of various cytokines and chemokines at different clinical stages of the ocular injury.

Methods: Rabbit right eye was exposed to SM vapor and a clinical follow-up was carried out up to 4 weeks. Corneal and limbal tissues were collected at 48 h, 1w and 4w post exposure and IL-1α, IL-1β, IL-6, TNFα, macrophage chemotactic protein (MCP)-1 and IL-8 levels were measured by commercial ELISA kits.

Results: SM exposed eyes presented an acute injury that was partially resolved within a week in all of the exposed eyes, and was followed by an irreversible late pathology in 50%-80% of the eyes, beginning at 2w. A significant elevation was seen in levels of the studied factors, however each factor presented a unique expression pattern. At the peak of the acute injury, at 48 h, significantly higher levels of corneal IL-1α, IL-8, and TNFα and limbal IL-1α and MCP-1 were found compared to naïve eyes. At 1w, corneal IL-1β, IL-6, IL-8 and TNFα and limbal IL-8 and MCP-1 levels were significantly higher compared to naïve eyes. During the late pathology, at 4w, elevated levels of corneal IL-1β, IL-6 and MCP-1 and limbal MCP-1 and IL-8 were found only in eyes presenting NV.

Conclusions: The levels of the studied factors changed throughout the dynamic course of the ocular injury. The prolonged increased levels of limbal MCP-1 and IL-8 may contribute to the continuous recruitment of inflammatory cells, characterizing the symptoms of the late pathology. The significantly elevated IL-1β and IL-6 at 1w, after the resolution of the acute injury but before the clinical manifestation of the late pathology suggests a therapeutic window for intervention with prevention therapy. Mapping the expression pattern of these cytokines and chemokines points out towards stage-specific therapeutic options.

Keywords: Chemokines; Cytokines; Inflammation; Ocular surface; Sulfur mustard.