SECONDARY RADIATION DISEASE FOLLOWING HETEROGRAFTING 



between 3-2 and 4-2x10^ each of less than fiftccn-hours-old baby rat spleen 

 cells. Nine irradiated control mice were all dead within thirteen days. 



Twenty C57 mice received 900 rad ''"Co lethal wholc-b()d\- y irradiation. 

 A DBA mouse which had littered not more than nineteen hours previously 

 was the source of the donor material. Six mice received 1 -2 x 10*^ each of 

 adult bone-marrow cells, whilst five received 1 • 1 x 10** each of less than 



30 day Onset of secondary disease- s 



survival 

 Figure 1. Length of survival of mice after irradiation and grafting 



nineteen-hours-old DBA baby spleen cells. Nine inadiated control mice 

 were all dead \vithin 14 days. The results are represented graphically in 

 Figure 1. 



DISCUSSION OF RESULTS 



The University College Hospital Group=^ has described a state of actively 

 acquired tolerance which follows intravenous injection of spleen cells of one 

 strain into newborn or foetal mice of another strain. The host and donor 

 cells continue to live harmoniously together in favourable combinations and 

 skin can be grafted from mice of the donor strain to the chimaera. The 

 abrogation of host immune mechanisms by lethal whole-body irradiation 

 results in 'radiation tolerance' for an haemopoietic graft comparable to 

 the use of a newborn host by Billingham and Brent^. In one the immune 

 mechanism has not developed and in the other it is suppressed so tliat for 

 a time at least a graft may be acceptable. But because the mechanism of 

 secondary radiation disease is believed to be a chronic antigen-antibody 

 reaction of donor cells at a later date against the host, which is characterized 

 by wasting, diarrhoea and specific time of onset, the use of immunologically 

 'null' donor material (itself of foetal origin) might result in a non-reactive 

 situation. In practice it is seen that intravenous injection of foetal 

 haemopoietic homografts into lethalh- irradiated hosts results in their 



74 



