DISCUSSION 37 



Brent: To come back to the modest prolongation of survival of skin 

 grafts produced by gastric phenol extracts: this is probably due to a 

 general, non-specific suppression of the immune response of the animals. 

 There are quite a few reports in the literature indicating that animals 

 can be made very much more susceptible to bacterial infection by 

 gastric extracts of this kind. 



Albert: Dr. Lejeune suggested the same explanation of the prolonged 

 survival of the skin homografts induced by his "mucoid extracts'*; 

 that is, a general depression of the immunological reactions. 



As far as the soluble extracts are concerned, Dr. Lejeune and Dr. 

 Castermans are studying comparatively the various fractions of their 

 extracts from the point of view of the transplantation immunity in- 

 duced /// vivo and the haemagglutination inhibition in vitro. So far, any 

 fraction which induces transplantation immunity also inhibits the 

 haemagglutination reaction. 



Brent: Does Dr. Lejeune have any idea why epidermal cells should be 

 so very much more potent antigenically than lymphoid cells ? 



Albert: I don't think he has any formal explanation; so far it has just 

 been an observation. The difference of potency is even more impressive 

 when epidermal and spleen cell extracts are used. 



Medawar: Is it not possible that epidermal cells don't contain the 

 enzymes, certainly present in spleen cell extracts, which degrade these 

 antigens ? One of the difficulties with the type of preparation we use is 

 that it is exceedingly unstable to incubation ; but it is possible with these 

 epidermal cell extracts, and also with ascitic fluid preparations of the 

 kind that Dr. Davies has used, that these enzymes are simply not present, 

 so that one doesn't have this constant nuisance of a progressive loss of 

 potency in the course of preparation. Has Dr. Lejeune tested the stabiHty 

 of his epidermal cell extracts to incubation? Does the haemagglutina- 

 tion inhibition potency of an epidermal cell extract decline very 

 rapidly, as that of a splenic cell extract would do ? 



Albert: Dr. Lejeune tested the stability of his epidermal cell extracts at 

 various temperatures : At 4° the potency of the extracts remains stable 

 for 48 hours, after which it decreases rapidly. At 20° the potency de- 

 clines very quickly and the extract loses nearly all its activity after 24 

 hours. At 37° the extract loses the major part of its activity after only 

 one hour of incubation. The stability of the epidermal cell extracts 



