ANAMNESTIC RESPONSES 



(ii) whether more than one type of specific site can exist 



on a single antibody molecule, 



(iii) how many types of antibody can be produced by a 



single cell, and if more than one what the mechanism is 



by which the cell is stimulated to produce them. For 



example, if a cell can produce two distinct antibodies, 



a and ^, will stimulation of the cell by A result in the 



liberation of ^ and b or only of a? 



In order to simplify discussion, we shall assume that 



antigenic determinants are relatively small and that the 



specificity of a serum depends largely on the constitution of 



the antibody population, not on the existence of a single type 



of antibody molecule. An antigen ABCD will provoke an 



antibody population which may be represented abed. These 



in turn may be derived from separate clones of cells for a, and 



for b, c and d, or from a clone, each cell of which can produce 



fl, b, c and d antibody molecules. 



The evidence on these points comes largely from studies 

 of immunity to virus disease in which the antigens involved 

 are admittedly poorly defined. Such virological studies can, 

 however, give striking and reproducible results and they will 

 be discussed in some detail. Before doing so, however, it is 

 desirable to examine experimental work in which Dixon and 

 Maurer studied the type of response to a number of purified 

 antigens given in different sequence. 



In general, they found that unrelated antigens — for 

 example, tgg albumin and human serum albumin — showed 

 no mutual influence when used as antigens one after the 

 other. If, however, bovine serum albumin (BSA) and human 

 serum albumin (HSA) were used, the response to the second 

 antigen was strongly modified. With BSA given first, injection 

 of HSA intravenously [a) results in a moderate increase of 

 anti-BSA, some of which is specific in the sense that it cannot 

 be absorbed by HSA, {b) produces anti-HSA, including 

 specific antibody, more rapidly than would be the case with 

 a primary response, and (c) gives a much higher proportion 



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