140 HOWARD, MICHIE AND WOODRUFF 



sufficient to bring their host down two or three weeks later with 

 signs of severe graft-versus-host disease. Our acceptance of 

 Simonsen's interpretation has therefore been tempered by a desire 

 to seek independent confirmation in the more orthodox host- 

 versus-graft situation, and to analyse an induced specific unrespon- 

 siveness of the host to the graft in the light of criteria of tolerance 

 so framed as to exclude, as Simonsen has done, all the variant 

 possibilities previously enumerated. 



Induction of unresponsiveness in adult A mice 



Adult A-strain mice were given 350 r. or 500 r. X-irradiation, 

 followed during the next two, or three, days by the injection of 

 from 500 milHon to 1,200 million spleen cells respectively taken 

 from (A X CBA)Fi donors. Two treatments were administered 

 per day, inocula being divided between the intravenous and intra- 

 peritoneal routes. Fi hybrids were used as donors in order to 

 obviate graft-versus-host disease, wliich had been found in a 

 preliminary test to constitute a frequently fatal hazard when pure- 

 strain CBA spleen cells were used. Three or more weeks later the 

 treated animals were grafted with (A x CBA)Fi skin. Table I 

 summarizes the results, a fuller account of which will appear else- 

 where (Michie and Woodruff, 1962). 



Table I 

 Long-term acceptance of (A x CBA)Fi skin grafts by adult A-strain 



MICE following VARIOUS TREATMENTS 



(Data from Michie and Woodruff, 1962) 



{A X CByl)Fi Interval before Proportion of grafts 



Irradiation spleen cells skin grafting (days) surviving > 2 months 



500 r. Nil 21-35 0/19 



500 r. 5-6 X 10® 21-55 0/3* 



500 r. 7-8 X 10^ 18-46 5/7 



500 r. 12 X 10® 21 8/8 



350 r. 8x iqS 17-37 0/3 



* One graft survived 38 days. 



