DISCUSSION 265 



form of a cell; it has to turn into something different before it engages 

 in immunological responses. As Miller indicated, it settles down and 

 acquires a pyroninophilic cytoplasm, and that is the business or operative 

 form of the lymphocyte. I don't think this in any way affects any of 

 your conclusions. 



Hildemann: I am still concerned about the complete absence of 

 tolerance and chimerism in the survivors and in addition the threshold 

 dose of small lymphocytes required to produce runt disease, if in fact 

 the majority of these cells proliferate in their hostc. Our results are 

 perhaps consistent with the assumption that some small lymphocytes 

 localize in certain tissues outside the blood and there proliferate for a 

 limited time. 



Medawar: Dr. Hildemann, your test of chimerism was cytotoxic 

 assay. This would cease to be vaUd if the cells you are trying to identify 

 didn't turn up in cell suspensions : if for example they turned into rather 

 sticky or fragile cells that just didn't come out into a cell suspension. 



Hildemann: These were lymph-node cell suspensions. 



Medawar: Maybe these transformed lymphocytes simply don't tease 

 out and don't become isolated cells which you can identify. The failure 

 to produce tolerance surely follows : if these animals have recovered 

 from runt disease, doesn't it follow that they are not tolerant — that it 

 was the ones which died that were tolerant ? 



Loutit: I go along with Dr. Hildemann most of the way — I can con- 

 cede that these small lymphocytes do not persist indefinitely — but I 

 would follow Gowans and Trowell and say that they can transform 

 and go through a number of cycles which would be enough to produce 

 the graft-versus-host reaction or the runting syndrome. Then, as you 

 say, either death occurs or the cells run out of their potential for division. 

 The whole thing is quite compatible with several views, but it needs 

 further experimental work. 



Eichwald: Should we not also consider that the addition of phyto- 

 haemagglutinin to peripheral blood stimulates mitotic division — but 

 mitotic division of which cells ? Certainly not of neutrophilic leuco- 

 cytes. Therefore they would be most probably lymphocytes, would 

 they not ? 



Russell: Gorer and Boyse (1959. Immunology, 2, 182), in their mor- 

 phological studies of the transfer of parental cells to adult Fj hybrids, 



