Effects of deep-frozen treatment on the immune response of bone-patellar tendon-bone xenograft rejection

AIM: To investigate the effects of deep-frozen treatment on the immune response of bone-patellar tendon-bone (BPB) xenograft rejection. METHODS: A muscle pocket model was used to study the immune response of rat to deep-frozen treated BPB xenograft from guinea pig, autograft and fresh xenograft served as controls. The expression of T-cell surface activation antigen CD25 in the peripheral blood and the morphological changes of the implants were used to measure the immune response. RESULTS: The expression of CD25 in CD4+, CD8+ cells greatly increased 3 d after fresh BPB xenograft, the obvious difference to that of autograft (P<0.05) was observed. It reached a peak level 14 d after fresh BPB xenograft and didnt decrease 35 d after transplantation. The expression of CD25 in CD4+, CD8+ cells was greatly inhibited in deep-frozen treated BPB xenograft. Its expression was delayed and just had a small increase 14 d after transplantation. The P values were all less than 0.05 compared to those of fresh xenograft at every time-point after transplantation. Histologic examination showed that there were a few lymphocytes surrounding the bone and tendon tissue in deep-frozen treated BPB xenograft, but the lymphocytes hadnt invaded into the tissues. No tissue necrosis, but a clear tendon structure and regular fibrogen arrangement were observed. There were large amount of fragmentary lymphocytes infiltrating into or surrounding the bone and fibrogen tissues after fresh xenograft, the bone was broken into pieces, the tendon structure was unclear and the fibrogen arrangement was irregular, quite a few of inflammatory cells such as acidophilic granulocytes and macropolycytes were found in some slices. CONCLUSION: Deep-frozen treatment markedly reduces BPB xenograft antigenicity and inhibits the immune rejection.