410 GENERAL DISCUSSION 



a circulating serum-borne antibody response at the expense of the 

 cellular homograft response. I don't know whether Dr. Voisin 

 would agree that his interpretation of his own experiments and 

 those of Dr. Nakic demands that the "cellular" and the "serum" 

 responses can occur side by side. 



Voisin: I see your point, Dr. Brent. Yes, in the classical immuno- 

 logical reaction to a single chemically defined antigen, delayed 

 hypersensitivity comes first and circulating antibodies come after- 

 wards at a time when delayed hypersensitivity disappears, a 

 sequence of events which does not support my tentative inter- 

 pretation of tolerance to living cells by a mechanism of enhance- 

 ment. As a matter of fact, in order to make this interpretation 

 likely, one has to believe that a sufficient level of enhancing anti- 

 bodies must be present early enough in comparison to the 

 "rejection reaction" (which is, in your mind, bound to delayed 

 hypersensitivity). This might be attained by at least two ways in 

 the tolerant animals : either the phase of delayed hypersensitivity 

 is extremely transitory, displaced by antibody production, or 

 delayed hypersensitivity and antibody production are dealt with 

 by two different groups of lymphoid tissue cells competing with 

 each other. Whatever the fmal answer may be, it seems that this 

 problem is part of the question of the interrelations between 

 humoral antibodies and sensitized cells, a question with a fascinat- 

 ing future. 



Hasek: May we return to Dr. Brent's question about the im- 

 portance of the delayed and immediate types of immunity, and 

 their possible interactions. I think that the results with induction 

 of tolerance may throw some light on this question as well as on 

 the development of these two reaction pathways. Using tolerance 

 of protein antigen in guinea pigs, J. L. Turk and J. H. Humphrey 

 (1961. Immunology, 4, 310) could not dissociate the delayed and 

 immediate types of antibody formation to a single antigen from 

 each other. 



Dissociation is known to occur between tolerance to erythro- 



