DISCUSSION 235 



of transplantation immunity, or (2) a direct effect of the antibodies on 

 enhancing the tumour's growth, thus increasing its resistance to trans- 

 plantation immunity. It is very hard to distinguish, at this time, be- 

 tween these two possibilities. Dr. A. Globerson and I have attempted, 

 however, to see whether one can distinguish between these possibilities 

 by inducing enhancement in isologous systems. We have tried to 

 enhance tumours with hetero-immune serum in a completely isologous 

 system, and clear indications were obtained that such tumours are 

 enhanced. However, the difficulty is that one can never be sure whether 

 even in these isologous systems there are no immunogenetic differences 

 between the tumour and the host. 



Medawar: I don't quite understand this point. Dr. Feldman, about 

 enhancement in completely isologous systems. What exactly do you 

 do? 



Feldman: We took a tumour of strain C57BL, grafted it on mice of 

 the same strain, and then injected antiserum. And the question was will 

 this tumour grow in an enhanced form ? 



Brent: Prof. Medawar and I no longer beheve in the idea that en- 

 hancement is due to the coating of the target cells with antibody, so 

 preventing the sensitized cells from reaching the target. 



Billingham: I should just like to make one point that may have some 

 bearing on our thinking in this area. Some time ago Dr. Silvers and I 

 undertook a reinvestigation of adoptive transfer of immunity with cells, 

 using A-s train mice tolerant of CBA skin and transferring either 

 "activated" node cells or buffy-coat leucocytes from A-strain mice 

 immunized by means of CBA skin homografts. Eleven days after 

 active immunization of the A-strain mice, 5 million buffy-coat leuco- 

 cytes obtained from their blood were found to be just as effective in 

 abrogating tolerance as 5 million regional node cells. Even i million 

 buffy-coat cells had a demonstrable effect. We wonder whether the 

 cells present in the blood, and which are responsible for transferring 

 immunity, continue to form antibody after transfer. 



Mitchison: We can be pretty sure that the peripheral lymphocytes do 

 make antibodies, because Gowans has shown that thoracic duct lym- 

 phocytes can transfer the capacity to produce antibody. 



Medawar: These are isoantibodies ? 



Mitchison: They are hetero-agglutinins, I believe. 



