[CD4+CD25+ T cells involved in induction of rat corneal allograft immune tolerance]

To explore the expression of CD4+CD25+ regulatory T cells in corneal graft, in the iris and peripheral blood in the high risk rat corneal transplant tolerance induced by superantigen staphylococcal enterotoxin B (SEB).

A high risk rat penetrating corneal transplantation model was established, whereas SD rat donor corneas were implanted into Wistar rat recipients. The recipient rats were divided into two groups. Group control and group SEB had intraperitoneal injection of normal saline solution or SEB (75 microg/kg), respectively. Orthotopic corneal transplantation was performed 1 day after the injection. The corneal graft survival time was evaluated. The expression of CD4+CD25+ T cells in corneal grafts and the iris was evaluated by immunohistochemical staining. The percentage of CD4+CD25+ regulatory T cells in peripheral blood was determined by flow cytometry.

Corneal graft mean survival time was (11.63+/-2.83) d in group control and (14.13+/-0.99) d in group SEB. The difference of survival time between these two groups was statistically significant (P<0.05). Histopathology showed remarkable inflammatory cells infiltration in the rejected grafts. The intensity of the infiltration was compatible with the severity of rejection reaction. Immunohistochemical staining of grafts showed that the CD4+CD25+ regulatory T cells were expressed in rejected grafts in both groups 20 days after the surgery, but not before the surgery. The iris whole mount staining showed that before the surgery, no expression of CD4+CD25+ regulatory T cells was observed in group control but relatively remarkable expression was observed in group SEB. Twenty days after the transplantation, CD4+CD25+ regulatory T cells were observed in both groups while group SEB had more pronounced expression. Peripheral blood flow cytometry analysis revealed that the mean percentages of CD4+CD25+ regulatory T cells were stable before and after surgery in group control. However, in group SEB, an increase shift appeared and followed by a decrease to normal level 20 d after the surgery.

CD4+CD25+ regulatory T cells take part in immune tolerance in rat immune tolerance induced by superantigen SEB in high risk rat corneal transplantation.