IMMUNOLOGICAL TOLERANCE 



irradiation with an appropriate dose of X-rays. The most 

 conspicuous effect histologically is a striking disappearance 

 of small lymphocytes — a variety of other mesenchymal types 

 persist. For a short period after irradiation there is virtually 

 no power to give an antibody response. X-radiation can also 

 prevent the development of tuberculin sensitivity in rabbits 

 (Lennox, Dempster and Boag, 1952). These processes are 

 undoubtedly complex. For one thing whole-body irradiation 

 provokes a stress reaction with cortisone, producing a circu- 

 latory lymphopenia and atrophy of lymphoid tissue. 



In respect to the influence of X-radiation on antibody 

 production as such, most of the work has been done with 

 rabbits and it is convenient to follow Taliaferro and his 

 colleagues in their studies of the response to sheep red cells 

 as antigen given intravenously. The most striking finding 

 is that there seems to be only a very limited phase of the 

 antibody-producing process that is susceptible to inhibition 

 by non-lethal irradiation. If a maximal effect is to be pro- 

 duced, the radiation should be given 24 to 48 hours before 

 the immunizing injection. If given after, or even simul- 

 taneously with, the antigen there is very little influence. 

 When the spleen is shielded, there is a variable reduction in 

 the effect of whole-body irradiation. According to Sussdorf 

 and Draper (1956), shielding the appendix provides 100% 

 protection, although irradiation of the appendix alone has 

 no power to reduce antibody production. In fact, there is 

 slight evidence of an additive effect. With very heavy irradia- 

 tion of the rabbit spleen, the rest of the animal being shielded, 

 Taliaferro found a highly significant increase in antibody 

 production. 



There is some controversy as to the effect of X-rays on the 

 secondary antibody response, but Talmage, Freter and 

 Thomson (1956) conclude that there is no clear difference 

 in the effect on primary and secondary responses. 



The standard effects — namely that {a) radiation must be 

 given 24 hours before the antigen to produce a maximal 



100 



