The role of soluble programmed death protein-1 (sPD-1) and soluble programmed death ligand-1 (sPD-L1) in rat corneal transplantation rejection.

Background. Immunological rejection is one of the problems in corneal transplantation. Recently, some research found out that soluble programmed death protein-1 (sPD-1) and soluble programmed death ligand protein-1 (sPD-L1) play a significant role in immunologic suppression. Objectives. To explore expression of sPD-1 and sPD-L1 in a penetrative corneal transplantation model and its relationship with transplant rejection. Material and methods. Autologous corneal transplantation rat models and allogeneic corneal transplantation rat models were used as the control group and the experimental group, respectively. Changes of the transplanted grafts were observed under a slit-lamp microscope. Hematoxylin-eosin (H&E) staining was applied to examine the histopathological features of the corneal grafts. Flow cytometry was used to analyze CD4⁺CD25⁺Treg in the serum and spleen. The sPD-1, sPD-L1, interleukin-10 (IL-10) and interleukin-4 (IL-4) levels in serum and the aqueous humor of the rats were detected using enzyme-linked immunosorbent assay (ELISA). Results. After the operation, no transplant rejection occurred in the control group. Flow cytometry results showed that expressions of CD4⁺CD25⁺Treg in serum in the experimental group were lower than those in the control group (p < 0.05). The ELISA results showed that after the operation, sPD-1 and sPD-L1 expression levels in serum in the experimental group were higher than in the control group (all p < 0.05). After the operation, lL-10 and IL-4 content in serum in the experimental group was lower than in the control group (all p < 0.05). The sPD-1/sPD-L1 ratio in the experimental group was higher than in the control group. Conclusions. Increases of sPD-1 content and decreases of CD4⁺CD25⁺Treg, IL-10 and IL-4 levels may be involved in corneal allograft rejection. Dynamic detection of the content of sPD-1 and sPD-L1 in serum and aqueous humor after the operation would help in understanding the local immune response in a clinical setting and predicting the occurrence of corneal graft rejection. [ABSTRACT FROM AUTHOR]