THE FACTS OF IMMUNITY 



At the time, we ascribed the clarity of the difference as 

 seen with staphylococcal toxoid to the fact that we were 

 using a soluble antigen given intravenously, so that the 

 stimulus to antibody-producing cells would be simultaneous 

 and the antigen would in all probability then be removed 

 from the system within a few hours. Both primary and 

 secondary stimuli could therefore be pictured as acting on 

 the cells concerned only over a brief period. On the other 

 hand, when any antigen, particulate or soluble, is placed in 

 the tissues as a depot, antigenic material will leak into the 

 body fluids over a period which may be of considerable 

 duration. If the possibility of secondary type reaction 

 appears within this period, antigen from the primary in- 

 jection may be responsible for both types of effect with 

 a corresponding difficulty in the interpretation of results. 



As an example of response to a small particulate antigen, 

 it is convenient to present some unpublished results of my 

 own from mice immunized with a highly antigenic bacterio- 

 phage. Using tenfold dilutions the primary response is 

 shown in the first half of the graph and the secondary 

 response to a uniform small dose in the lower half 



This provides a fairly clear picture, the most striking 

 feature of which concerns the mice given lo® particles as 

 a primary inoculum. Three of these gave no detectable anti- 

 body and one other an insignificant trace. When re-inocu- 

 lated with a dose provoking no antibody in controls, three 

 of the four gave high to very high antibody titres. Only one 

 high secondary response was obtained from mice given the lo' 

 primary inoculum. 



These results point strongly to the conclusion that has 

 frequently been reached in the past, namely, that a first con- 

 tact with antigen sets some sort of a tooling-up process in 

 train, while secondary contact is needed to evoke actual 

 antibody liberation into the circulation. With the largest 

 inoculum, sufficient antigen can be assumed to persist long 

 enough to act as a secondary stimulus on primarily modified 



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