TRANSPLANTATION TOLERANCE AND AGE 



141 



The higher dose levels of irradiation and of donor-type spleen 

 cells yielded a crop of graft-bearing animals of long duration for 

 further analysis. As a first check on specificity one of them was 

 grafted with C57BL skin. This was rejected within two weeks 

 with no apparent effect upon the resident (A x CBA)Fi graft. 



Analysis of chimerism in graft-bearing A mice 



The next step was to test for the continued presence and func- 

 tional activity of the host's own lymphoid cells. The discriminant 



A- strain mouse 



bearing (Ax CBA)Fi skin graft ( AxCBA)Fi Normal A- strain mouse 



10^/ml. suspension 10®/ml. suspension 10^/ml. suspension 



1 i 1 



1ml. 0-1ml. 01ml. 1ml. 



1ml. 



I I I I I 



(AxC57BlTf. 'S^^S^^S^^ 

 hybrids ^ 



^E^ 



Killed and spleen weighed 9 days later 



Fig. I. Design of discriminant assays estimating anti-C57BL 

 activity in the spleen cells of A tolerant (Ax CBA) mice ("test") 

 relative to that of normal A mice ("standard"). T=test; S = 

 standard; B = blank. An uninjected control is included to check 

 that theB-suspension has little or no effect. All injections were i.p. 



