DISCUSSION 233 



national Symp. Immunopathology, ed. P. Grabar and P. Miescher. 

 Basle: Schwabe) has recently found that in the development of allergic 

 encephalomyelitis (AE) for example, those animals which have re- 

 recovered from " AE " and are producing high titre of circulating serum 

 antibody usually do not come down again, upon challenge with spinal 

 cord, with the disease compared with other animals that produce little 

 or no antibody. To confirm the role of serum antibody as a protective 

 agent in this situation, he finds upon transferring high-titre serum anti- 

 body to rats actively sensitized to nervous tissue, allergic encephalo- 

 myelitis is suppressed or prevented entirely. 



Batchelor: I beheve it has been reported that patients with agamma- 

 globulinaemia are particularly susceptible to rheumatoid arthritis, and 

 it seems quite possible that this is all connected with the protective or 

 blocking effect of humoral antibody upon delayed hypersensitivity 

 reactions. 



Mitchison: Dr. Lawrence, you said that human recipients of trans- 

 ferred delayed allergy made no antibodies. What are your limits of 

 detection ? 



Lawrence: When one says that no antibodies were found it is under- 

 stood "within the limits of detection currently available". The ex- 

 periments that I had in mind were those where Pappenheimer and I 

 transferred delayed allergy to diphtheria toxoid with leucocyte extracts. 

 Here the method for detection of antitoxin employs one of the most 

 sensitive biological systems available, that is neutralization of toxin in 

 rabbit skin. This biological test detects antitoxin quantitatively, even 

 when present in low concentration (i.e. <o-oi [ig. per ml. detectable). 



Brent: One observation which we made recently seems to be in 

 conflict with some of the interesting experiments which Dr. Batchelor 

 has told us about. In a non-sensitized animal the sensitizing action of a 

 cell-free antigenic extract can be prevented or counteracted in some 

 way by the injection of antisera. However, if the animal has been 

 presensitized by a relatively small number of allogeneic cells, this 

 counteraction can no longer be brought about. In your experiments 

 you are dealing with an effect of antiserum on presensitized cells, and 

 you are getting exactly the opposite result. 



Batchelor: I am not trying to suggest that the results of Snell et al. 

 (i960, loc. cit) are not genuine, and I am sure that if you put in a lot 



