DISCUSSION 379 



sensitive than the spleen assay system to detect the residual reactivity of 

 the grafted cells against the host. 



Medawar: I think it would be valuable in this connexion to ventilate 

 a point which I have discussed privately with Dr. Simonsen, namely 

 the technical validity of the serial passage of spleen cells in studying the 

 propagation of runt disease or splenomegaly. Suppose one injects 

 adult lymphoid cells into newborn animals to cause splenomegaly and 

 runting : if the lymphoid cells which actually react against the host 

 undergo the kind of transformation that Dr. Gow?ns has described, 

 they may turn into cells which are perhaps stickier and less easy to get 

 out of the spleen when one wants to make a cell suspension, or into cells 

 which, with a lot of cytoplasm, are more vulnerable to handling. So 

 that I don't think one can tease or squeeze the cells out of enlarged 

 spleens and assume they are necessarily a fair sample of the reactive 

 population. This seems to me to be, perhaps an illusory difficulty, but 

 anyhow a difficulty of principle in using serial passage of cells to estimate 

 the immunological potencies of cells taken from enlarged spleen. 



Simonsen: I don't think there is much difficulty in getting the cells out 

 of the spleen. Perhaps more would disintegrate, in this process, in 

 enlarged spleens than in normal spleens, but I think your objection 

 would not apply to the spleen removed at one day after injection which 

 is not yet an enlarged spleen at all. 



Medawar: These transformations described by Gowans occur with 

 incredible rapidity. Still, we don't really know enough about this to 

 discuss it. I'm merely raising it as a theoretical point. 



Billingham: I was interested to hear of Dr. Russell's difficulty in 

 transmitting runt disease from one runt to another potential host. 

 We've tried to "passage" this disease in rats and have had only sporadic 

 successes. Buffy-coat leucocytes pooled with suspensions of spleen and 

 node cells were transferred from runts. Sometimes the disease appeared 

 consistently in every member of the host litter but we never managed 

 to get beyond the first passage. 



Dr. Russell, have you compared the runt-causing effects of lymph 

 node cells with those of spleen in your very sensitive system ? 



Russell: We have done just a Httle work along these lines. We 

 believe that lymph node cells are more effective than spleen cells in 

 equal numbers. 



