THEORIES OF ANTIBODY PRODUCTION 



embryo spleen and produce antibody against the new 

 host. 



(v) Several immunologists, including Jerne himself, have 

 suggested that the self-marker theory is semi-mystical 

 in character and generally unattractive. 



For these reasons a sketch of what appeared to be necessary 

 modifications in Jerne's theory was prepared (Burnet, 

 1957 a) and found to have some interesting potentialities, 

 particularly in relation to the pathology of immune reactions 

 in man. As in every such theoretical elaboration, a number 

 of ad hoc assumptions had to be made, but it is felt that all of 

 these are in line with the basic concept. This may be stated 

 from a more generalized viewpoint as follows : 



The antibody-producing cells of the body make up a 

 mobile population of mesenchymal cells constantly under- 

 going physiological and mutational change. It is composed 

 of large numbers of clones from which subclones are con- 

 stantly arising as a result of somatic mutation. 



Individual clones prosper or dwindle in accord with their 

 experience of contact with the corresponding antigenic 

 determinants. The result of such contact will depend on 

 a variety of physiological considerations of which the most 

 important is probably the age of the individual concerned. 

 The fate of these clones can legitimately be regarded as a 

 study in the population genetics of mesenchymal cells in the 

 internal environment of the whole organism. 



[a) Developmental considerations 



The development of the starting population of mesen- 

 chymal cells present at birth or hatching is part of the general 

 problem of differentiation and requires a number of addi- 

 tional ad hoc assumptions which, however, are of the same 

 general quality as are needed for the provisional interpreta- 

 tion of any phase of embryonic differentiation. 



Perhaps the clearest way to present the processes that must 

 be postulated during embryonic development is to consider 



56 



