The Immune Effect And Mechanism Of The Delayed Xenograft Rejection In The Discordant Heart Xenotransplantation Produced By Intrathymic Inoculation And Whole Body Irradiation

Introduction: Xenotransplantation is the best way to solve the problem of donor absence, but its development is barrelled by the xenograft rejection. This study was designed to investigate the effect of T cells on the delayed xenograft rejection by intrathymic injection of xenogeneic antigen in the discordant cardiac Xenotransplantation, and to investigate the possibility of inducing the tolerance to cardiac xenografts by restraining of T cell activity. Materials and methods: In this experiment, pig and monkey were, respectively, selected as donor and recipient. Experimental animals were divided randomly into four groups. The blank group(group A): recipients didn't accept any pretreatments but heart Xenotransplantation; Whole body irradiation(WBI) group(group B): recipients only received 2.5 Gy(60Co) WBI in 30 days(d-30) before transplantation; Intrathymic injection(IT) group(group C): recipients were only pretreated by the intrathymic injection of pig spleen cells(5 X 107) in 23days(d-23) before transplantation; Irradiation and intrathymic injection group(group D): recipients were pretreated by WBIat the time just as at the group B and the intrathymic injection of pig spleen cells at the time just as at the group C. In each group, monkeys were performed heterotopic heart xenotransplantation in abdomen and the survival time of cardiac xenografts were observed in every day.And the changes of peripheral lymphocytes were detected continuously in the 1st day. the 3rd day. the 7th day. the 15th day and the 30th day after irradiation in the monkey. The changes of subgroup of lymphocytes were detected with the flow cytometry.The mixed lymphocyte reaction with H3 thymidine was used to inspect the change of lymphocytes function on the transplanting day in all groups.Results: (1) The survival time of cardiac xenografts in group B(65.6 6.5h) group C(64.4 14.9h) and group D(91.1 22.8h) was significantly longer than that in group A(36.6 5.8h)(P<0.05).The survival time of cardiac xenografts in group B and group C was longer than group A (P<0.05), but there was no significant difference between group B and group C(P>0.05). (2)The number of lymphocytes and its subgroup CD4+ and CD8+ T cell were significantly decreased after irradiation, especially CD8+ T cell. There was no significant difference in CD4+ and CD8+ T cell of peripheral blood between group A and group C before transplantation(P>0.05). (3) The results of MLR showed that T cell function was more significant reduction in group D than that in group A (P<0.01).But that in group A was more stronger than that in group C and B (P<0.05). (4) The level of IL-2 of recipients was much higher in the rejection of xenografts than that before transplantation in all groups (P<0.01). The level of IL-10 in group D was increased on the 5th day after transplantation . (5)The histological changes of delayed xenograft rejection were discovered in all groups.conclusions: (1) Pretreatment with IT and WBI .could prolong survival time of the donor heart.. (2) Pretreatment with IT and WBI could induce T cells immune suppression and intrathymic inoculation could't influence the percent of CD4+ and CD8+ T cells in peripheral blood. (3) The chang of serum level of IL-2 is closely correlated with the development of xenograft rejection or it may be an important index to inspect the rejection. (4) WBI at dose 2.5Gy could clean most of the lymphocytes in the peripheral blood and its injury was limit.