Production of LIX, the Neutrophil CXC Chemoattractant– Lipopolysaccharide–Induced Chemokine, in a Model of LPS Keratitis

Abstract

Abstract: : Purpose: Neutrophils are the predominant inflammatory cell type in keratitis induced by bacteria and bacterial products such as LPS. LIX is a recently described novel ELR+ CXC chemokine in which in situ processing enhances its chemotactic activity. The purpose of this study was to examine production of LIX in comparison to the other two known ELR+ CXC chemokines KC and MIP–2 by corneal epithelial cells, stromal cells (primarily keratocytes), and neutrophils in a mouse model of LPS–induced keratitis. Methods: C57BL/6 corneas were treated by intrastromal injection or epithelial abrasion with LPS. LIX, KC, and MIP–2 production by corneal epithelial cells, stromal cells, and neutrophils was examined by ELISA. Synthetic LIX was also injected into the corneal stroma and neutrophil infiltration was determined. Results: Intrastromal injection of LPS stimulated increased production of LIX (357 + 44.37 pg/ml) in stromal cells after 18h compared with cells from trauma and naive controls (<15pg/ml). Epithelial cells examined after either intrastromal or epithelial exposure to LPS produced <15pg/ml LIX (compared with 209.7 + 26.52 pg/ml KC). Similarly, neutrophils stimulated with LPS produced <15 pg/ml LIX (compared with 1043 + 243.7 pg/ml MIP–2). Intrastromal injection of synthetic LIX induced a pronounced neutrophil infiltrate. Conclusions: LIX seems to be produced exclusively by stromal cells, which are primarily keratocytes, in contrast to KC produced by both epithelial and stromal cells, and infiltrating neutrophils serving as the predominant source of MIP–2. These results identify LIX as an additional ELR+ CXC chemokine produced during corneal inflammation as well as demonstrates a distinct pattern of CXC chemokine production which could reflect their contribution to the inflammatory process. Together with the potent activity of synthetic LIX, this CXC chemokine may therefore have an important role in early neutrophil recruitment to the corneal stroma in bacterial keratitis.

Keywords: cytokines/chemokines • keratitis • cornea: stroma and keratocytes