62 IMMUNO-CATALYSIS 



antibody is formed and the rate at which it is metabolized, antibody ^ 

 amino acids ^ normal proteins, will condition the maintenance or 

 decline of the peak of humoral concentration of antibody. The rate of 

 antibody formation will be governed by three principal factors: 



(a) The ability of antigen to resist the host's catabolic activities. 



(b) The rate at which antibody accumulates and thereby shifts 

 the equilibrium from left to right in the following complex reaction 

 mechanism : cell-antigen-antibody ^ cell-antigen -j- antibody. Because 

 of the strong specific affinity between antigen and antibody, antigen- 

 antibody complex formation, in the presence of an accumulated amount 

 of antibody, may predominate, blocking the activity of antigen (see 

 p. 137) to direct the formation of new antibody."^ However, this con- 

 dition cannot last long for the obvious reason that the amount of anti- 

 body will soon diminish by participating in the protein metabolism of 

 the host, or by some special mechanism for eliminating antibody from 

 the antibody forming cells, and, therefore, the reaction will resume 

 its forward trend once again. 



(c) The magnitude of the dissociation constants derivable from the 

 reaction equilibria. The rates of the backward and forward reactions 

 in the establishment of the states of equilibria are governed also by 

 the magnitude of the dissociation constants of various reactions. The 

 following may be cited to illustrate the possible reaction equilibria: 



CO Antigen-cell ^ cell -|- antigen 



(2) Cell-antigen-antibody ^ cell -|- antigen -f- antibody 



(3) Antigen-cell-antibody ^ antigen -(- cell -|- antibody 



(4) Antigen-antibody ^ antigen -|- antibody 



From the standpoint of continued antibody formation, the most 

 critical of the above relationships would appear to be a very small 

 degree of dissociation of the cell-antigen complex,! supplemented with 



*In the presence of an excess of antigen Csevere infection) small amounts of anti- 

 body formed could not be demonstrated because of antigen-antibody complex forma- 

 tion and elimination. 



tin connection with the above relationships it may be pointed out that the inter- 

 action between antigens, antibodies, and the susceptible tissue cells could be expected 

 to exercise marked effects on the above reaction equilibria. It has been pointed out by 

 Friedmann (1947), for example, that the avidity of tetanus toxin for the tissue cells 

 will result in slower rate and degree of reaction between the toxin and the antitoxin. 

 The combination between the tetanus toxin and tissue was stated to undergo a gradual 

 increase in firmness and that, consequently, it became increasingly difficult for the 

 antitoxin to dislodge the toxin from the tissue. The resistance of toxin to antitoxin 

 under conditions as they prevail in the natural disease is explained by the high avidity 



