DISCUSSION 343 



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DISCUSSION 



Medawar: I take it, Dr. Nakic, that your theory of tolerance implies 

 that you agree with Dr. Voisin that tolerance of living cellular antigens 

 is a totally different phenomenon from tolerance of "dead" antigens 

 such as soluble protein ? 



Nakic: That is correct. 



Voisin: It might be more accurate to say that tolerance of living cells 

 is a phenomenon different from and more complex than tolerance of 

 chemically defined antigens. In this respect. Dr. Nakic made a very 

 important point, that is, the presence of immunized cells from both host 

 and donor strain in the spleen of tolerant animals. If these results are 

 confirmed, they will have extremely important impHcations. As a 

 matter of fact, they are already confirmed in a sense, for we have 

 obtained the same kind of result as Dr. Nakic with a completely differ- 

 ent experimental set-up (Leonard, L., Kinsky, R. and Voisin, G. 

 American Association for Advancement of Sciences. Biology section. 

 Arizona Academy of Science. April 1961). We started with a weakly 

 incompatible strain combination, BALB/c->DBA/2, injecting homo- 

 logous spleen cells into newborns, and did not produce runt disease 

 with doses of about 7 million cells. The only way to get runt disease is 

 either to inject a very large dose of homologous cells (and this is tech- 

 nically very difficult) or to use preimmunized cells. But, now, if we 

 take spleen cells from a BALB/c mouse tolerant to DBA/2 and inject 

 them into newborn of either BALB/c or DBA/2 strains, then we can 

 observe a certain percentage of runting which is around 10 per cent of 



