DISCUSSION 43 



tested for it. I am fully aware of this. All I say is that I haven't found 

 it. 



Nakic: I remember some experiments performed by Howard and 

 Michie who attempted to induce tolerance by repeated injections of 

 irradiated spleen cells followed by normal non-irradiated spleen cells 

 and, as far as I know, they obtained no tolerance in newborn animals. 

 That is a point in which I am very much interested. 



Michie: We have subsequently tested the immunizing power of 

 these irradiated preparations, and, although our estimates are still rather 

 vague, it looks as though there is a weakening of immunizing power 

 by a factor of more than ten and less than a thousand. 



Silvers: Was this in C57-CBA? 



Michie: We used two combinations in studying tolerance: A with 

 CBA, and CBA with C57. 



Silvers: Since CBA and C57 is a very difficult combination, I wonder 

 if a similar experiment with CBA and C3H might be worth while. 



Russell: I think a point that Billingham has made in this regard is that 

 if you inject a living, self-replicating inoculum composed of cells which 

 can respond to the foreign antigens that surround them, then you have 

 an increasing dose of antigen since antigenic stimulation will lead to cell 

 multiplication, which may have some bearing on this. 



Michie: That could fully explain it. 



Hildemann: It seems that there is a controversial point in the findings 

 of Lejeune-Ledant and Medawar. If I understood Lejeune-Ledant's 

 presentation correctly, he was able to get immunity with soluble extracts 

 by the intravenous route, and was also able to obtain transplantation 

 immunity without the production of haemagglutinins. However, 

 when large amounts of any of these antigenic preparations were in- 

 jected serum antibodies were also detected. Perhaps this apparent dis- 

 parity between the results of Lejeune-Ledant and Medawar is attribut- 

 able to subtle differences in the antigenicity or chemical composition of 

 the preparations injected. I wonder, though, whether too high a degree 

 of specificity is attributed to the haemagglutinins relative to the anti- 

 genic character of the soluble extracts. In the earHer work that Prof. 

 Medawar and I did together — admittedly with crude preparations — we 

 were able to get transplantation immunity in the absence of detectable 

 serum antibodies. We wondered at that time if other methods might 



