INFLUENCE OF IONIZING RADIATION 



effect, {b) that if a major source of lymphocytes, the appen- 

 dix, is shielded the response is undiminished and {c) that 

 a variety of cell extracts, etc. given with the antigen will 

 allow response — can be fitted well into the picture of the 

 clonal selection theory. 



X-ray has a destructive effect upon lymphocytes and 

 24 hours later there are few normal lymphocytes which can 

 respond to contact with antigenic determinant in normal 

 fashion. Of the lymphocytes not lethally damaged, the loss 

 of responsivity to antibody takes some hours to develop and 

 contact with antigen in the latent period reverses the damage. 



Any lymphocytes which have been activated to primitive 

 types, or started on development to plasma cells, are relatively 

 resistant. Hence the failure of X-rays to modify the reaction 

 to antigen given before the radiation. 



There is an interesting paradox that while splenectomy 

 diminishes the antibody-producing capacity of the rabbit to 

 a very marked extent, appendicectomy does not modify it. 

 Yet whole-body irradiation with the appendix shielded gives 

 1 00 % protection of antibody production ; with the spleen 

 shielded production is reduced by 82 % (Sussdorf and 

 Draper, 1956). 



The explanation on the clonal selection hypothesis is 

 simply that the appendix is a greater source of mobile 

 lymphocytes than the spleen but the red pulp of the spleen 

 is the place par excellence where lymphocytes stimulated by 

 antigen can settle to produce clones of antibody-forming 

 plasma cells. It is hard to see how any other theory of anti- 

 body production could offer any explanation whatever of 

 the interrelations. 



6. The special qualities of bacterial antigens and endotoxins 



The most soundly based objections to a clonal selection theory 

 of immunity will probably be derived from two sets of facts: 

 (i) It has proved almost impossible to produce tolerance 

 against bacterial antigens, 



lOI 



