CHAPTER LIX 

 THE FUNCTIONAL ROLE OF AGGLUTININS 



G. HOWARD BAILEY 



School of Hygiene and Public Health, Johns Hopkins University 



Although several other investigators had previously observed agglutination with 

 a variety of bacteria and immune sera, Gruber and Durham,' in i8g6, were the first 

 to make an intensive study of the phenomenon during the course of work with the 

 colon bacillus and the cholera vibrio. They pointed out the specificity of the reaction 

 and the fact that it differed in certain essentials from previously studied serum reac- 

 tions. It was soon noted, however, that there is not absolute specificity, that group 

 reactions occur, and also that blood-cells and other body cells could be agglutinated 

 by specific sera. It was found that agglutinins of various kinds exist normally in cer- 

 tain sera and that these antibodies may be produced artificially by immunization. It 

 was observed also that the property of specifically agglutinating bacteria is developed 

 in man and animals in the course of infectious disease, and this led, a short time after 

 Gruber and Durham's publication, to the discovery of the now widely used Widal 

 test for typhoid fever. Agglutination reactions have been employed for the identifi- 

 cation of bacteria and various other diagnostic and clinical purposes, and the study of 

 this reaction in vitro has brought out many facts of both practical and theoretical 

 significance. 



A more important consideration, however, is the question of the functional role 

 of agglutinins in infectious disease, that is, the part agglutination as such plays as a 

 factor in protecting the body against infection. What is the relation between the pres- 

 ence or production of specific agglutinating and precipitating substances and natural 

 or acquired immunity? For a long time there was much speculation as to the biological 

 significance of this phenomenon, and much difference of opinion has been expressed 

 concerning the influence exerted by agglutinins in the infected organism in warding 

 off a bacterial invasion or in restraining the growth of bacteria after they have once 

 become established. 



. The agglutinative property is met with in the body fluids of many species of normal 

 and immune animals and is exercised upon many bacteria. It may be demonstrated 

 not only in blood serum but also in transudates and exudates and in certain secretions 

 such as milk, tears, saliva, and urine. The presence of agglutinins in the sera or body 

 fluids of infected individuals has long been considered an index at least of the existence 

 of a greater or lesser degree of immunity. That there should be some relation be- 

 tween agglutinins and immunity would appear certain, if only from the fact that bac- 

 teria become immobilized under the influence of the corresponding agglutinins. Yet 

 among the factors to which bacterial immunity is usually ascribed, agglutination has 

 been considered by most immunologists to occupy a subordinate place; for, however 



' Gruber, M., and Durham, H. E.: Miinchen. med. Wchnschr., 43, 285. 1896. 



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