Objective  To investigate the effect of infusion of spleen lymphocytes treated by extracorporeal photochemotherapy on the regulatory T cell (Treg) and survival time of skin allograft in mice.

  Methods  The skin allograft model in mice was established with C57BL/6 mice as donors and BALB/c mice as recipients. The spleen lymphocytes (CSP, BSP) in mice C57BL/6 and BALB/c were isolated, and the mice spleen lymphocytes (PUVA-SP) treated with 8-methoxypsoralen plus ultraviolet (PUVA) were prepared. The experimental animals were randomly divided into 5 groups according to the compositions infused into the recipients through vein: PUVA-BSP, PUVA-CSP, BSP, CSP and phosphate buffer solution (PBS) control groups (n=12 in each group). All recipients of each group were injected with PUVA-BSP, PUVA-CSP, BSP, CSP or PBS on day 7 before the operation, on the operation day and day 7 after the operation through the tail vein, respectively. The survival time of graft in the recipients was observed, and the expression of CD4⁺CD25⁺Foxp3⁺Treg in peripheral blood was detected.

  Results  After skin allograft, the rate of CD4⁺CD25⁺Foxp3⁺Treg in peripheral blood of the recipients in PUVA-BSP group and PUVA-CSP group was significantly higher than those of BSP, CSP and PBS control groups. The rate of CD4⁺CD25⁺Foxp3⁺Treg in PUVA-CSP group was higher than that of PUVA-BSP group, while BSP and CSP groups were lower than that of PBS control group. The survival time of skin graft in the recipients in PUVA-BSP group and PUVA-CSP group was significantly longer than that of BSP, CSP and PBS control groups (all P < 0.05).

  Conclusions  Sufficient infusion of PUVA-SP can induce more CD4⁺CD25⁺Foxp3⁺Treg in the recipients and prolong survival time of skin graft significantly.