530 IMMUNOLOGY 



and a similar substance present in the tuberculous lesion; Selter 

 regards tuberculin as a specific irritant for tuberculin-sensitive 

 cells and assumes that its action is catalytic in that it promotes 

 but does not participate in the reaction. The antigen-antibody 

 theory was suggested by von Pirquet and Schick in 1903 and is 

 tentatively accepted by Zinsser, Enders, and Fothergill (1939). 

 If antibodies do not participate in the reaction, then to us the most 

 plausible alternative would be to accept the hypothesis tliat the 

 tissues acquire the property of reacting directly with tuberculhi 

 without the participation of antibod.y. 



The differences in the severity of tissue reactions (pointed out 

 by Aronson and others) in tuberculin allergy and protein ana- 

 phylaxis, respectively, do not, in our opinion, invalidate the concept 

 that the tuberculin reaction is mediated by an antigen-antibody 

 mechanism. These results might be interpreted as indicating one 

 or more of the following : 



a. A qualitative or quantitative difference in antibodies which 

 leads to a greater degree of sensitization in tuberculin allergy 

 than in protein anaphylaxis. Under such conditions the meeting 

 of the antigen (tuberculin) and its antibody might produce either 

 a more profound physical change than in protein anaphylaxis or 

 liberate more histamine or perhaps some substance with greater 

 toxicity than is liberated in protein anaphylaxis. 



b. The site of the reaction in tuberculin allergy may be intra- 

 cellular, while in protein anaphylaxis it may occur at the cell 

 surface. Such a difference in the field of operation might ex- 

 plain the difference in toxicity. 



7. According to Seibert a tuberculin preparation (SOTT) was 

 able to inhibit the precipitin reaction when tubercle protein and its 

 homologous antiserum Avere brought together. The tuberculin 

 (SOTT) had a molecular weight of 3,800. It apparently acted 

 as a hapten. 



Questions Raised by Antigen-Antibody Concepts. — For the 

 present we are accepting the theory that the reaction of antigen 

 and antibody is an important factor in tuberculin hypersensitive- 

 ness. When one takes this stand he is confronted immediately with 

 questions relating to the nature of the sensitizing and reacting 

 substance, the site of antibody formation, the principal tissues in- 



