| Introduction:Xenotransplantation is the best way to solve the problem of donor absence, but its development is barreled by the xenograft rejection. This study was designed to investigate the effect of T cells on the delayed xenograft rejection by B7-mAb blockading B7/CD28 interaction-the most important stimulatory molecules of T lymphocyte , and to investigate the possibility of inducing the immune tolerance to heart xenografts by the way of T cells. Materials and methods:In this experiment, guinea-pig and SD rat were, respectively, selected as donor and recipient. A model of rat heterotopic heart allograft was established by using Ono's technique. Experimental animals were randomly divided into three groups: 1. the blank group(group A):rec;pients didn't accept any pretreatments but heart Xenotransplantation; 2.the control group(group B):recipients were treated with CVF by intraperitoneal injection at the dose of 0.4mg/kg on 20-24 hours before transplantation.3. the B7-mAb group(group C):recipients were treated with B7-mAb by intraperitoneal injection at the dose of 100ug before transplanting operation, the other pretreatments were the same as group B. In order to observe the survival time of cardiac xenografts, the heart beating was palmed in rat's abdomen. The mixed lymphocyte reaction with [3H] thymidine of 24 hours was used to inspect the B7-mAb blockading costimulatory molecules in vitro, the CPM(counts per minute)were measured .The changes of subgroup of lymphocytes were detected with the flow cytometry, surveying the change of the CD4+, CD8+, CD4+/CD8+, CD3+CD25+, CD3+, CD25+CD3+/CD3+ of the PBMCs(peripheral blood mononuclear cells) before andafter transplantation. Results:1 . In heart xenotransplantation group: Mean survival time of donor heart in group B(17.2 1.9h),group C(24.5 l.lh) were significantly longer than group A(0.4 0.1h) (p<0.01); group C was longer than group B(p<0.05). the graft survival time was significantly prolonged by BVmAb blocking B7/CD28 interaction.(pO.Ol)2. The results of MLR (mixed lymphocyte reaction) showed that the stimulative effect in group C(2556+220) were less active than that in group A(3532+469) and group B(3553+386) (pO.Ol).but there were no evident difference between group A and group B (p>0.05). the three group A,B,C were stronger than group O.3. The CD4+ cells in group B (47.3 2.3%) was significantly higher than that in group A (41.0+2.1%) and group 0(42.4+2.3%) after transplantation (p<0.05); there were no evident difference in group A (41.3+3.16%), B (40.8+1.7%), C (41.5+2.6%) before transplantation (p>0.05). The CD8+ cells in group B (24.4+1.2%) was significantly higher than group A (20.0+2.3%) and group C (22.3+1. 4%)after transplantation (p<0.05); there were no evident difference in group A (20.0+2.2%), B (20.3+1.2%), C (21.7+2.1%) before transplantation (p>0.05). But the ratio of CD4+/CD8+ was no evident difference before and after transplantation.4. The CD25+CD3+ double positive cells in group B (20.3+3.6%) and group C (11.5+1.8%) were significantly higher than group A(2.2+0.3%) after transplantation (p<0.05);That in group C were significantly lower than that in group B. there were no evident difference in group A(2.4 0.4%),group B(2.6 0.2%),group C(2. 8+0.2%) before transplantation(p>0.05). The CD3+ cells were no change s between before and after transplantation. The ratio of CD3+CD25+/CD3+ in group B and group C were higher than that in group A after transplantation ,but that in group C was lower than that in group B. Conclusions:1 . CVF is beneficial to overcome the hyperacute rejection.2. B7-mAb can partly inhibited the activating of T lymphocytes in vitro.3. The blockade B7-CD28 interaction can prolong the survival of the donor heart. . It may provide a new way to treat immune rejection after xenotransplantation.4. The proliferation of CD4+ T-lymphocyte subsets and CD8+ T-lymphocyte subsets were significantly inhibited by B7-mAb as compared with the control group. The ratio of CD4+/CD8+ was not changed.
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