ANAMNESTIC RESPONSES 



tion that a proportion of sites b' c' and d'^ develop. If we 

 now tabulate: 



Serum (3) absorbed with 

 Serum (i) ah c d ABCD — 



(2) abcc' dd' ABEF c d d^ 



(3) ab y cc' dd'd^ AEGH b c d d' 



we obtain a formal representation of the results in Jensen's 

 experiment as well as an indication of the nature of Daven- 

 port's phenomenon, namely, that the original components 

 a b c and d still dominate the mixture. 



The only visible mechanism is some form of somatic 

 mutation. Any cell of clones corresponding to a, b, c, d or 

 complexes thereof in which a mutation to broader reactivity 

 (allowing reaction with (2) or (3)) has occurred will be 

 preferentially stimulated to proliferation. Equally it is only 

 in clones of the types that have responded to A B C D in the 

 past that the minor mutations needed to fit a new A type 

 virus are likely to have occurred. These experiments of 

 Jensen's appear to provide substantial support for the view 

 that, provided the fit between antigenic determinant and cell 

 receptor is good enough to start a process of selective pro- 

 liferation, this will result in a sufficient scatter of mutations 

 to allow the emergence of a better fitting type of cell receptor 

 (and antibody) with considerable speed. 



A related phenomenon not as yet so intensively studied 

 concerns the broadening of antibody response that is seen 

 after infection with a second serotype of the ARBOR viruses 

 of Casals' group B (Casals, 1957). Here it seems that first 

 infection, say with Dengue I virus, gives a relatively specific 

 response, but if this is then followed by an Ilheus virus in- 

 fection the subsequent serum is likely to neutralize yellow 

 fever and many of the other type B viruses as well. The 

 interpretation here will be that if several types of reactive 

 site can change by mutation and selective survival to fit 

 two modifications of the determinants concerned, then they 

 are likely to show as well an increased reactivity to other 



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