Massive infiltration of eosinophils is the typical histopathologic feature of severe forms of allergic conjunctival diseases (ACDs) such as vernal keratoconjunctivitis. Although ACD is an antigen (Ag)-specific disease, eosinophils lack Ag-specific receptors. Therefore, my group studied the likely roles of immunocompetent cells bearing Ag-specific receptors in inducing conjunctival eosinophil infiltration in ACDs. To induce experimental conjunctivitis (EC), Brown Norway rats and C57BL/6 and Balb/c mice were passively immunized by the transfer of Ag-specific or primed IgE, splenocytes, or purified T-cells and then challenged with Ag in eyedrops. The transfer of Ag-primed splenocytes or T-cells, but not of Ag-specific IgE, induced conjunctival eosinophil infiltration. We also showed that soon after EC induction by T-cell transfer, activated Ag-specific T-cells infiltrated the conjunctiva. Moreover, when EC-developing animals were topically treated with the T-cell-specific immunosuppressants cyclosporin A and FK506, conjunctival eosinophil infiltration was abrogated. In addition, only the transfer of Ag-specific type 2 helper T-cells (TH2 cells), but not of type 1 helper T-cells or CD8+ T-cells, could induce conjunctival eosinophil infiltration. Our data show that Ag-specific TH2 cells play a crucial role in inducing conjunctival eosinophil infiltration during the development of EC. It is necessary to elucidate the roles that conjunctival residential cells and immunocompetent cells other than T-cells play in the conjunctival eosinophil infiltration of EC.