Purpose: To clarify the possible involvement of the type 2–initiating cytokines interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin (TSLP) in the pathophysiology of allergic conjunctivitis, we evaluated ragweed (RW)-induced experimental allergic conjunctivitis (EAC) models by using IL-25 knockout (KO), IL-33 KO, and TSLP receptor (TSLPR) KO mice.

Methods: Interleukin-25 KO, IL-33 KO, TSLPR KO, and BALB/c wild-type mice were sensitized twice with RW in alum and then challenged with RW in eye drops. Clinical scores and eosinophil infiltration were evaluated. Expression levels of serum immunoglobulin E (IgE) and cytokines in the conjunctival tissues were quantified and immunohistochemical analysis was carried out.

Results: Significant reductions in clinical scores and numbers of infiltrating eosinophils were observed in the RW-EAC model using IL-33 KO mice. There were no significant differences in clinical scores and numbers of infiltrating eosinophils among IL-25KO, TSLPR KO, and wild-type mice. Serum IgE concentration was upregulated after RW challenges, and there were no differences among the mouse genotypes. Expression levels of of il4, il5, il13, and ccl5 mRNA were diminished in the conjunctivae of the RW-EAC model using IL-33 KO mice compared to those in wild-type mice. Interleukin-33 expression was upregulated as early as 1 hour after RW eye-drop challenge. The number of infiltrating basophils in the conjunctivae of the RW-EAC model using IL-33 KO mice was diminished compared to that in wild-type mice.

Conclusions: Among the type 2–initiating cytokines, IL-33 may play a major role in conjunctival inflammation in an RW-EAC model.