IMPLICATIONS OF CLONAL SELECTION 



antibody-type globulin of a single pattern or at most of 

 a uniform small range of patterns. 



It could be disproved by showing that cells of a pure clone 

 could, by appropriate manipulations, be induced to produce 

 any one of a variety of antibodies. 



Until such methods of handling pure clones in vitro are 

 available, choice between the current hypotheses can only be 

 on the basis of their convenience in co-ordinating phenomena 

 and their heuristic value in stimulating new experimental 

 approaches. It will therefore be essentially from these two 

 points of view that the topics in this chapter will be treated. 



I . The secondary response and cognate phenomena 

 One of the first objections which might be raised against the 

 clonal selection hypothesis is its failure to give due weight 

 to the difference between primary and secondary responses. 

 On the simplest form of the hypothesis, all responses could be 

 said to be secondary in type, the only difference being a 

 quantitative one. The primary stimulus finds only a few 

 examples of the appropriate clones; by the time of the 

 secondary stimulus many more individuals of the selected 

 clones are accessible. In fact, however, there appears to be 

 an additional qualitative factor. Coons' studies on the intra- 

 cellular demonstration of antibody by the ' sandwich ' tech- 

 nique of fluorescent staining (Coons, Leduc and Connolly, 

 1955) led him to differentiate very sharply between primary 

 and secondary response. In his view, the secondary ' stimulus 

 acts as a trigger mechanism which detonates a remarkable 

 biological event engaging many cells in the area ' in contrast 

 to 'the paucity of cells engaged in antibody synthesis during 

 the primary response'. Coons holds that antibody response is 

 a function of the plasma cell family, a cell type which does 

 not exist except for this function and which conceivably may 

 be called into existence only by a secondary antigenic 

 stimulus. In the previous chapter we have described the 

 behaviour of staphylococcal toxoid as an antigen and cited 



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