MECHANISM OF ANTIBODY FORMATION 53 



ditions, they can exercise no antigenic stimuli. The readiness with 

 which these proteins are dispensed with is most Hkely due to an absence 

 of structural difference among the proteins of the individuals of a given 

 species. In contrast, the parenteral injection of a protein, derived from 

 a species different from the species of the recipient host, being struc- 

 turally different will resist greatly the action of the host enzymes. Due 

 to this resistance, the life of the whole protein, or its structurally 

 specific part, will be prolonged. Transferred by phagocytes to a center 

 of protein metabolism, not only will it resist complete degradation but 

 would seem also to influence the course of the synthesis and certain 

 details in the pattern of the normal globulin, yielding immune anti- 

 body globulin. In this manner, the foreign protein, or antigenic unit, 

 exercises the role of specific catalytic modifier, or superimposes a new 

 catalytic role of its own on the enzymes which synthesize globulins. 

 This role continues so long as the antigenic unit remains intact. Any 

 process whereby the life of the antigen in the host is prolonged might 

 result in a degree of antibody response. 



The difference between a species specific substance and that which 

 is foreign to the host rests on the distinctive differences in the specifici- 

 ties of host enzymes (or the genes which are assumed to be responsible 

 for the origin of enzymes). The ready digestibility and utilization of a 

 species protein by the species specific host enzyme system is understand- 

 able, for the specialized enzyme system is capable not only of digesting 

 such a protein when parenterally introduced but also is capable of 

 synthesizing it in an identical pattern. This may be presented in the 

 following manner: 



species enzyme 

 Species protein v amino acids 



On the other hand, a host can either eliminate a foreign protein 

 (or substance) by excretion, or digestion by virtue of the inherent 

 abilities of proteolytic enzymes to split peptide linkages common to all 

 proteins. Because of the basic structural (or architectural) difference 

 of the molecular species, there is no doubt that the elimination of the 

 foreign protein when parenterally introduced, will proceed at a very 

 different rate than the digestion of the species specific protein. In con- 

 trast to this ability of the host enzymes to eliminate a foreign substance, 

 they totally lack the ability to resynthesize or regenerate the foreign- 



