ANTIBODIES II 17 



To inhibit completely the reaction of an anti-hapten antibody with 

 the conjugated hapten-antigen generally requires a good deal more of 

 the inhibiting hapten, in dissolved form, than that contained in the 

 conjugated antigen. From this we might deduce that the binding force 

 of the hapten alone with the antibody is less than the force which 

 unites the antibody and the conjugated antigen. The hapten does 

 combine with the antibody, however, for unrelated haptens have no 

 inhibitory effect, and a given hapten does not inhibit unrelated anti- 

 body-antigen reactions. In other words, inhibition is specific. In 

 Fig. 2-5 the inhibition is completely specific, that is, each hapten pre- 

 vents precipitation only of the homologous antibody and antigen. That 

 haptens combine with their specific antibody can be demonstrated by 

 the power of antibody to prevent a diffusible hapten from dialyzing 

 through a membrane otherwise permeable to it. 



If closely related haptens are tested against the same antibody- 



Amount of precipitate given by antisera 

 for corresponding antigen, in presence of 



Antiserui 

 for 



H2N 



AsOsHz H2N 



H2N 



COOH 



SO3H 



H2N 



+ + + 



+ + + 



+ + + 



+ + + 



+ + 



+ + + 



COOH 



Fig. 2-5. Inhibition of precipitin reaction with homologous and heterologous 

 haptens. 



