Thymic inoculation does not result in development of tolerance to allogeneic thyroid grafts in the outbred rabbit
Torchia, Mark G.
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The focus of our study was to determine whether allogeneic thyroid graft tolerance could be achieved in outbred rabbits. In the experimental group (n = 5), recipient rabbits (NZW) received an intrathymic injection of donor (California) lymphocytes $(5\times 10\sp7)$ and a single treatment of 165 g of antilymphocyte serum (ALS). Controls (n = 5) received intrathymic cell culture medium and ALS treatment. Donor-recipient allogenicity was monitored with mixed lymphocyte culture (MLC) before and at one, seven, and eighteen weeks following intrathymic injection. Donor thyroid tissue was placed into recipient gluteal muscle fibres one week following the last MLC measurement. A third group of rabbits (n = 4) received thyroid autografts without any other treatment. Biopsies of the thyroid grafts were taken one and six weeks following graft placement. One experimental group donor-recipient pair was lost due to late death of the recipient (respiratory complication). There were no differences in MLC stimulation indices between the control and experimental group. MLC did not change within groups over the eighteen week monitoring period. All thyroid autografts survived over a two week monitoring period and demonstrated normal thyroid follicles on histologic examination. All thyroid allografts resulted in severe acute rejection reactions noted on the one week biopsy, with rare intact follicles visible. No intact follicles were seen in any allograft recipient at six weeks following grafting. The reason for the failure to induce tolerance in the outbred rabbit model is unknown. (Abstract shortened by UMI.)