CHAPTER 8 



THE ANTIGENIC STRUCTURE OF BACTERIA 



A COMPLETE description of tlie antigenic structure of a bacterial cell would include 

 (a) the number and kind of different antigens present, (b) their relative proportions, 

 and (c) their position in the cell or cell aj^pendages. 



Though in no instance has a complete description of this kind been achieved, 

 yet for certain bacterial species we can construct working models of the antigenic 

 structure, which, though crude, have at least enabled us to solve a number of 

 immunological puzzles ; and it seems certain that further advance along the same 

 lines will enable us to solve many more. 



We may start our discussion by considering the methods that are available for 

 studies of this kind. 



Antigenic Analysis by Selective Qualitative Absorption of Antibodies. 



The fact that a single bacterial cell . contains many antigens was established 

 during the earliest studies on the agglutination reaction. The original observations 

 of Gruber and Durham (1896) showed that the specificity of this reaction was not 

 peculiar to each species of bacterium. For instance, while the colon bacillus was 

 sharply differentiated from the typhoid bacillus and both from certain vibrios, 

 these vibrios were not so clearly differentiated from one another. Durham (1901) 

 as the result of a more detailed study of these group agglutinations enunciated 

 quite clearly the hypothesis of a multiplicity — as he called it, a mosaic — of antigens 

 within a single bacterial cell. Employing small letters to denote the antigenic 

 bacterial components, and capitals to denote the corresponding agglutinins in the 

 antisera, he suggested that the aqtual agglutinins and agglutinogens involved might 

 be represented as follows : 



Agglutinogens. Agglutinins. 



Bacterium 1. a, h, c, d, e. Serum 1. A, B, C, D, E. 



Bacterium 2. c, d, e, f, <j, h. Serum 2. C, D, E, F, G, H. 



Bacterium 3. e, f, g, h, j, k. Serum 3. E, F, G, H, J, K. 



The serum prepared against Bacterium 1 would contain the agglutinins 

 A, B, C, D, E, and in virtue of the presence of each and all of these it would agglutin- 

 ate the corresponding bacterium. It would also agglutinate Bacterium 2 in virtue 

 of agglutinins C, D, and E, and Bacterium 3 in virtue of agglutinin E. 



The method that has been employed in analysing the antigenic structure of a 

 particular bacterial strain — the method of agglutinin absorption — was introduced 

 by Castellani in 1902 ; though a precisely similar method had been previously 

 employed by Ehrlich and his co-workers in demonstrating the multiplicity of 



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