R. J. DUBOS 



mune response of the animal host to the whole bacterium and is re- 

 flected in the type and amount of antibody produced. It also condi- 

 tions the reaction of the bacterial cell with a given antibody, since the 

 intact microorganism unites much more readily, if not solely, with the 

 antibodies which are specifically directed against those of its con- 

 stituents exposed at or near the surface. Analysis of antibody pro- 

 duction and of antigen-antibody reaction can therefore help in formu- 

 lating an approximate picture of the arrangement of the different 

 antigens in the architecture of the cell. 



To summarize, the use of immunological procedures for the 

 study of cellular structure involves a number of successive steps: 

 (a) the preparation and separation of antibodies specific for each one 

 of the chemical constituents of the cell; (b) the utilization of these 

 antibodies as specific reagents for the detection and preparation in 

 pure form of the cellular constituents; and finally, (c) the interpreta- 

 tion of antigen-antibody reaction in an attempt to define the relative 

 positions occupied by these chemical constituents in the living cell 

 (7,9,11,14). 



The results obtained by immunochemical analysis have led to 

 the recognition that the different bacterial groups (pneumococci, 

 streptococci, sporulating aerobic bacilli, organisms of the colon- 

 typhoid-dysentery group, etc.) are characterized by a general pattern 

 of antigenic organization which is common to the different members 

 of each group. On the other hand, the various species and immuno- 

 chemical types within any general group differ from each other by 

 virtue of the chemical specificity of the different components of their 

 antigenic mosaic. Thus, all virulent pneumococci possess a capsule 

 which is polysaccharide in nature, but the polysaccharide varies 

 chemically and antigenically from type to type (3) . The virulent forms 

 of human streptococci (group A) can also produce a capsule made up 

 of hyaluronic acid; moreover, they all possess as surface constituents 

 peculiar proteins (the M substances), and other substances of unknown 

 chemical nature (the T antigens), which vary in immunochemical 

 specificity from type to type (13). Several of the aerobic sporulating 

 bacilli have been found to produce a capsule consisting essentially, if 

 not solely, of polypeptides; the polypeptide, in the case of the anthrax 

 bacillus, appears to be made up exclusively of ^/-glutamic acid (6). 

 The virulent coliform bacilli (typhoid, dysentery, etc.) all produce the 



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