Renal transplantation in the unimmunosuppressed pig: an abnormal response.

A series of 82 kidney allografts and autografts in unimmunosuppressed pigs surviving for longer than 5 days has been compared with a previously reported series of 24 unimmunosuppressed pig kidney allografts. In the previous series 40 per cent survived for longer than 20 days. In the present series only 2 per cent of 55 transplants performed in cross-bred pigs obtained from different farms survived for longer than 20 days. The major causes of death were unrelated to rejection, prinicipally gastric ulcer bleeding. In the further 16 transplants between different pure-bred animals (thereby ensuring genetic disparity) the ulcer incidence was lowered by a gastro-enterostomy, and 12 per cent survived for longer than 20 days. Histological assessment of rejection in the latter group revealed 20 per cent with minimal rejection, was considered insufficient to account for the death of the animals. Based on the evaluation of 95 unimmunosuppressed pig kidney allografts in both series, it is concluded that a wide and unpredictable range of survival time occurs. Therefore the pig kidney allograft model is an unsatisfactory model in which to study immunosuppressive régimes. Also the unimmunosuppressed pig appears to show less evidence of kidney allograft rejection than the dog, irrespective of genetic disparity. It is tentatively suggested that this might be a lesser manifestation of the unexplained phenomenon of minimal rejection of liver allografts noted in unimmunosuppressed pigs.