IMMUNOLOGICAL COMPETENCE OF SMALL LYMPHOCYTES 253 



from transplantation disease. Since death of all or none of the test 

 cells was not obtainable, it is possible that a very low proportion 

 of donor type cells might have been present, but not detected. 



Tolerance without disease mediated by foetal liver cells 



The fmding that A/Jax survivors of runt disease were neither 

 tolerant of C57BL/6 cells nor chimeras with respect to such cells 

 indicates that the originally inoculated lymphocytes failed to 

 leave descendants. Before these results could be further evaluated, 

 it was necessary to establish whether A/Jax newborns could be 

 made tolerant of C57BL/6 tissue under any circumstances. 



Several htters of A/Jax mice less than 24 hours old were injected 

 via the heart with foetal C57BL/6 liver cells. Each animal received 

 I • 3 miUion viable nucleated cells. As expected, none of these 

 mice subsequently showed any signs of graft-versus-host reactions. 

 At eight weeks of age, 12 of these animals were test-grafted with 

 adult female C57BL/6 skin. All recipients were found to be 

 tolerant and most were highly tolerant with homografts surviving 

 in excellent condition for 60 days or more. Thus the failure of 

 adult lymphocytes to induce tolerance must be attributed to the 

 characteristics of these cells, rather than to the nature of the host 

 or the antigenic disparity in this strain combination. 



Transplantation disease in F^ (C57BL/6 x A/Jax) hybrids 



Early in the course of this investigation, reciprocal intrastrain 

 skin grafts were exchanged between 12 mice of like sexes in both 

 our A/Jax and C57BL/6 colonies. All intrastrain grafts were 

 successful and remained in perfect condition indefmitely. This 

 fmding confirmed the supposition that each colony was highly 

 inbred and essentially isogenic with respect to histocompatibihty 

 antigens. From a theoretical standpoint, Fj hybrids from any 

 two such highly inbred parental lines should be more favourable 

 hosts for evaluation of the potentiahties of adult parent-line grafts, 

 since incompatibility is possible in only one direction. This 



