Effector T Cells Promote Fibrosis in Corneal Transplantation Failure

PURPOSE. To evaluate whether fibrosis contributes to corneal transplant failure and to determine whether effector CD4+ T cells, the key immune cells in corneal transplant rejection, play a direct role in fibrosis formation. METHODS. Allogeneic corneal transplantation was performed in mice. Graft opacity was evaluated by slit -lamp biomicroscopy, and fibrosis was assessed by in vivo confocal microscopy. Expression of alpha -smooth muscle actin (alpha-SMA) in both accepted and failed grafts was assessed by real-time PCR and immunohistochemistry. Frequencies of graft -infiltrating CD4+ T cells, neutrophils, and macrophages were assessed using flow cytometry. In vitro, MK/T-1 corneal fibroblasts were co -cultured with activated CD4+CD25- effector T cells isolated from corneal transplant recipient mice, and alpha-SMA expression was quantified by real-time PCR and ELISA. Neutralizing antibody was used to evaluate the role of interferon gamma (IFN-gamma) in promoting alpha-SMA expression. RESULTS. The majority of failed grafts demonstrated clinical signs of fibrosis which became most evident at week 6 after corneal transplantation. Failed grafts showed higher expression of alpha-SMA as compared to accepted grafts. Flow cytometry analysis showed a significant increase in CD4+ T cells in failed grafts compared to accepted grafts. Co -culture of activated CD4+CD25- effector T cells with corneal fibroblasts led to an increase in alpha-SMA expression by fibroblasts. Inhibition of IFN-gamma in culture significantly suppressed this increase in alpha-SMA expression as compared to immunoglobulin G control. CONCLUSIONS. Fibrosis contributes to graft opacity in corneal transplant failure and is mediated at least in part by effector CD4+ T cells via IFN-gamma.