ANTIGENIC SPECIFICITtS^ ''^z 



v: 



Bernard N. Jaroslow and Henry Quastu 



Division of Biological and Medical Research, 



Argonne National Laboratory, Lemont, Illinois 



and 



Department of Biology, Brookhaven National Laboratory, 



Upton, New York 



Abstract — The production of a specific antibody involves a transfer of information, and so 

 does the specific reaction between antibody and antigen. This paper deals with the 'vocabulary' 

 of this communication process. An antigenic determinant is considered as a 'word' of a 

 certain number of 'letters', subject to certain constraints. It is shown that the number of 

 'words', the number of 'letters', and the degree of constraint can be estimated by methodical 

 random sampling. Experimental methods suitable for this purpose are discussed. Preliminary 

 results are given. 



I. INTRODUCTION 



The question, 'How many different antigens are there?' is one that has not 

 been explored up to now, but which arises naturally if information theory 

 is applied. Information theory interprets the process of antibody formation 

 as the transmission of information from the antigen to the antibody-forming 

 mechanism, with the information then utilized and again transmitted when the 

 antibody reacts selectively with the appropriate antigen. It is then natural 

 to ask how much information is transmitted from antigen to antibody and 

 vice versa. More explicitly, one will ask certain questions about the kind of 

 information traffic between antigen and antibody — the 'vocabulary' in which 

 this information traffic is coded, the 'alphabet' that is used to make up the 

 words of the vocabulary. Now, information theory is not concerned with 

 specific features of 'alphabet' and 'vocabulary' but with general properties 

 of both, such as their sizes. The problem, 'how large is the vocabulary of 

 information transmission between antigen and antibody,' is closely related to 

 the question posed above. A preliminary estimate by one of us (1) has led to 

 a rough estimate of some 125 to 500 different protein antigenic determinants, 

 and a smaller number of different carbohydrate determinants. No attempt 

 was made, at that time, to estimate the number of antigens of other chemical 

 constitutions. Although these figures appear very small in the light of the 

 specificity of immunity to the multitude of infectious agents, the antigen com- 

 plexes of the organisms represent an array of many different determinants 

 and their over-all specificity can be much larger than that of a single antigen. 

 The present investigation is an attempt to measure antigenic specificity. 

 The general plan of the experiment is based on information theory; the specific 

 methods are based on agar diffusion precipitin tests developed by Oudin (2). 



* Work performed under the auspices of the U.S. Atomic Energy Commission. 



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