IMPLICATIONS OF CLONAL SELECTION 



abc, etc. When appropriately stimulated these will give 

 globulins a b c and d. Extension of the argument to the 

 serum after triple immunization, however, meets serious 

 difficulties. Since ABCD absorbs the antibody completely, 

 all antibody molecules must have a b c or d quality. Yet the 

 facts are that new reactivities have been added to the globulin 

 population by the immunizations with (2) and (3). It is 

 clear that no explanation with globulin molecules indicated 

 as simple units will suffice. 



Unabsorbed 



1 and 2 1 and 2 and 3 



Absorbed 1 



Absorbed 2 



Absorbed 3 



D 



1 2 3 



2 3 



Fig. 9. Successive immunization of ferrets by three influenza strains 

 (i), (2), (3) (after Jensen). Bars indicate anti-haemagglutinin titres 

 against influenza virus strains (i), (2) and (3), using sera unabsorbed 

 and absorbed as shown. 



If we switch Jensen's own explanation into terms of the 

 present theoretical approach, it is that the same clones re- 

 sponsible for antibody to ( i ) are concerned in responding to 

 (2) and (3). If fl b c and d are sites corresponding to virus (i) 

 [ABCD) then the change to fit virus (2) must involve the 

 modification of some of sites c and d to modified forms c' and 

 d'. These are sites which can now fit determinants E and 

 F respectively of the new strain as well as C and D of the old. 

 Similarly, to react with the third strain, AEGH, we have to 

 assume such a further modification of the antibody popula- 



76 



