254 HILDEMANN, LINSCOTT AND MORLINO 



immunogenetic design has, of course, been employed to advan- 

 tage in a number of recent studies. 



We sought to ascertain whether purified preparations of adult 

 C57BL/6 small lymphocytes would produce runt disease in 

 neonatal Fi (C57BL/6 x A/Jax) hybrids similar to that observed 

 in A/Jax newborns. A total of 12 Fj hybrid litters was injected 

 with C57BL/6 blood lymphocytes in doses ranging from 1*25- 

 1*86 miUion viable cells per recipient. The procedures employed 

 were the same as in previous experiments. The inoculated mice 

 ranged in age from less than 18 hours to four days of age. Three 

 entire litters of mice injected with the same preparation, as well as 

 control httermates, died nine to ten days later with an acute 

 enteric infection, possibly transmitted by a blood donor. Systemic 

 manifestations of disease in these animals at the time of death were 

 so profound that the occurrence of runt disease per se could not be 

 estabhshed. No special problems were encountered with the 

 remaining htters. In this group there were 48 experimental 

 survivors initially; these animals were regularly observed and 

 weighed beginning seven days after injection. 



Much to our surprise, only four mice subsequently died of 

 runt disease. Eight additional animals showed definite evidence of 

 transplantation disease with shght runting within 32 days after 

 injection. Thus 36 of 48 injected Fj hybrids revealed no symptoms 

 of graft-versus-host reactions. It is noteworthy that severe reactions 

 occurred only in Fj hybrids that were less than 48 hours old at the 

 time of injection with C57BL/6 lymphocytes. A clue to the 

 apparent resistance of the Fj animals was their hybrid vigour; 

 normal Fj controls as well as many experimental animals showed 

 weight gains substantially greater than normal A/Jax mice of the 

 same age from seven days on. 



Discussion 



Although Russell (i960) and others have found that as few as 

 50.000 adult spleen cells may regularly cause fatal runt disease 



