IMPLICATIONS OF CLONAL SELECTION 



of antibody precipitable by both antigens than is found with 

 any monovalent serum. Instead of at most 15%, the pro- 

 portion of doubly reacting antibody is always higher and 

 often over 50 %. 



To account for such results, one could represent the two 

 antigens as each having three types of determinant B S A and 

 H S' A' in the sense that ►S' and S' are sufficiently similar that 

 a commonly occurring mutation may change S- to ►S'-pro- 

 ducing cells and vice versa. A and A' have an equivalent 

 relation, B and H are quite distinct. 



On any clonal selection hypothesis BSA will produce cells 

 conditioned to produce b, s and a, but with a large prolifera- 

 tion of these clones a significant proportion of a' and s' cells 

 will also appear. This will allow the possibility that either 

 HSA or BSA will be able to evoke a secondary type response. 

 The fact, however, that HSA provokes an increase in specific 

 BSA antibody must indicate that clones of cells exist which, 

 when stimulated by one antigen, can produce another. If we 

 use lower-case letters to represent the antibody types corres- 

 ponding to each antigenic determinant, it must be assumed 

 that clones of the type ab, aa\ a'b, a's, as\ sb, bsa' are in 

 existence at the time of the second stimulus and that 

 when a cell of clone a'b is stimulated by A' (of HSA) in 

 addition to a' globulin molecules b will also be liberated. 

 As long as we keep within the framework of a clonal selec- 

 tion hypothesis, no other type of explanation seems to be 

 available. 



A similar conclusion that a single cell can produce two 

 types of antibody molecule, both being liberated by stimula- 

 tion with either antigenic determinant, can be drawn from 

 the virological work. 



The first group of observations can be conveniently 

 brought together under the name of Davenport's pheno- 

 menon or, if preferred, under Davenport's own description 

 of it as the 'doctrine of original immunologic sin'. When 

 someone has an attack of influenza A or is given an immuniz- 



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