Background: We explored the effect of rapamycin (RAPA) and interleukin (IL)-2 on regulatory CD4(+)CD25(+)Foxp3(+) T cells (Treg) in recipient mice after allogenic corneal transplantation and analyzed its correlation with graft outcome.
Methods: Allogenic corneal transplantation was performed using C57/BL6 mice as donors and Balb/c mice as recipients. RAPA, IL-2, and RAPA + IL-2 (mixed group) were administered to recipient mice, with three dosages for each therapeutic protocol. The graft status was assessed twice per week. The percentage of CD4(+)CD25(+)Foxp3(+) Treg in the peripheral blood, spleen, and draining lymph nodes was analyzed. The expression of Foxp3 mRNA in grafts was tested, and the concentration of IL-10 and transforming growth factor (TGF)-β1 in serum and aqueous humor was measured.
Results: The lowest scores of graft neovascularization and opacity were mainly found in mixed groups. The percentage of CD4(+)CD25(+)Foxp3(+) Tregs in blood was increased significantly in mice treated with either high-dose RAPA or high-dose IL-2, and a synergistic effect was found in mixed high-dose group. So were the Tregs in either spleen or draining lymph nodes. However, such effects were weakened with decreased dosage. Foxp3 gene expression in grafts was elevated significantly in the recipients treated with median dosage of RAPA, IL-2, and mixed agents. The concentration of IL-10 in serum and aqueous humor was increased significantly in mice with mixed- high-dose treatment. Mixed treatments also enhanced TGF-β1 level in serum and aqueous humor, except those receiving low dosage.
Conclusion: In vivo administration of RAPA prohibited graft rejection after allogenic penetrating keratoplasty through expansion of CD4(+)CD25(+)Foxp3(+) Tregs. Simultaneous treatment of IL-2 enabled further elevation of Tregs. However, the synergistic effect was dosage-dependent, being the most potent at high dosage. The protocol may be beneficial to induce transplantation tolerance.
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