An experimental study of the effect of total lymphoid irradiation on the survival of skin allografts

The study was undertaken to detemine the effect of fractionated high-dose total lymphoid irradiation (TLI) onthe servival of skin allograft despite major histocompatibility difference. Total lymphoid irraditation is arelatively safe form of radiotherapy, has been used extensively to treat lymphoid malignancies in humans with fewside effects. A total of 90 rats, Sprague-Dawley rat as recipient and Wistar rat as donor, were used for theexperiment, of which 10 rats were used to determine mixed lymphocyte response (MLR) for antigenic difference andskin allografts was performed in 30 rats given total lymphoid irradiation to assess the immunosuppressive effectof total lymphoid irradiation despite major histocompatibility difference. In addition, the peripheral white bloodcell counts and the proportion of lymphocytes was studied in 10 rats given total lymphoid irradiation but no skingraft to determine the effects of bone marrow suppression. The results obtained are summerized as follows. 1. Theoptimum dose of total lymphoid irradiation was between 1800 rads to 2400 rads. 2. The survival of skin graft onrats given total lymphoid irradiation (23.2±6.0days) was prolonged about three folds as compared to unirradiated-control (8.7±1.3 days). 3. Total lymphoid irradiation resulted in a severe leukopneia with marked lymphopenia,but the count was normal by the end of 3rd week. 4. The study suggests that total lymphoid irradiation is anonlethal procedure that could be used successfully in animals to transplant allograft across major-histocompatibility barriers.