IL-20 promotes epithelial healing of the injured mouse cornea

After corneal epithelial injury, the ensuing inflammatory response is necessary for efficient wound healing. While beneficial healing effects are attributed to recruited neutrophils and platelets, dysregulated inflammation (too little or too much) is associated with impaired wound healing. The purpose of this study was to use an established C57BL/6J mouse model of corneal injury to evaluate the potential modulatory role of interleukin-20 (IL-20) on the inflammatory and healing responses to epithelial wounding. In the uninjured cornea, immunofluorescence staining for IL-20 and its receptor, IL-20RA, was observed on basal epithelial cells at the limbus. After a 2 mm central epithelial abrasion, IL-20 staining was also observed in stromal keratocytes and ELISA studies showed a significant increase (nearly 3-fold) in IL-20 expression. Injured corneas healed more slowly when treated with a topical application of a neutralizing anti-IL-20 antibody. While corneal epithelial cell division and epithelial nerve recovery measured at 24 h post-injury were reduced compared to controls, neutrophil influx into the cornea was increased. In contrast, topical application of recombinant IL-20 (rIL-20) decreased corneal inflammation as evidenced by reductions in limbal vessel dilatation, platelet extravasation, neutrophil recruitment and CXCL1 expression. In wild type mice, topical rIL-20 had a limited effect on corneal wound healing and resulted in only a slight increase in epithelial cell division and epithelial nerve recovery; the rate of wound closure was unaffected. To clarify the effect of IL-20 on corneal wound healing, rIL-20 was topically applied to neutropenic wild type (WT) mice and mutant mice (ɣδ T cell deficient mice and CD11a deficient mice), all of which have well characterized reductions in neutrophil recruitment and delayed wound healing after corneal injury. In each case, rIL-20 restored corneal wound healing to baseline levels while neutrophil recruitment remained low. Thus, it appears that IL-20 plays a beneficial and direct role in corneal wound healing while negatively regulating neutrophil and platelet infiltration.