Topical Application of Low-Concentration IL-2 Enhances Treg’s Function and Plays Anti-Inflammatory Roles in Experimental Dry Eye Disease

Purpose To investigate the therapeutic effect of topical low-concentration IL-2 in dry eye disease (DED) and elucidate its underlying mechanisms. Methods During DED induction, mice received topical low-concentration IL-2 (0.1 ng/mL) or PBS. Corneal fluorescein staining (CFS) and tear secretion were evaluated. Tear cytokines were measured using a cytometric bead array, and the cornea underwent RNA-Seq. Immune cells in cervical lymph nodes (CLN), conjunctiva and lacrimal glands were analyzed by flow cytometry. The suppressive function of regulatory T cells (Treg) was assessed by an in vitro Treg suppression assay. CD25 + T cell-depleted mice were generated by intraperitoneal injection of CD25 mAb to determine whether the effect of low-concentration IL-2 was Treg-dependent. Results Topical low-concentration IL-2 significantly improved CFS scores and tear secretion, and decreased tear IL-6 levels. Corneal RNA-Seq revealed IL-17A pathway down-regulation. Low-concentration IL-2 treatment restored the Th17/Treg balance and reduced γδT17 infiltration in CLN, conjunctiva and lacrimal glands. Treg from low-concentration IL-2-treated mice exhibited enhanced suppressive capacity. RNA-Seq of the Treg suppression assay indicated down-regulation of Th17 signaling pathway and up-regulation of Treg signaling pathway. In CD25 + T cell-depleted mice, differences in CFS scores and CLN Th17 proportion between low-concentration IL-2 and PBS groups were abolished; however, corneal Mmp9 expression and the proportions of Th17 and γδT17 in the conjunctiva remained reduced. Conclusions In DED, topical application of low-concentration IL-2 exerts anti-inflammatory effects by enhancing the immunosuppressive function of Treg, which provides a potential therapeutic approach for DED. Treg-independent mechanisms may also contribute to its anti-inflammatory roles.