TOLERANCE TO ANTIGENS 



{b) Dormant damage inhibiting active response for 

 a prolonged period. 



{c) Rapid liberation of relatively small amounts of 

 preformed antibody as in Stevens' and Pei try's (1957) 

 and Wesslen's (1952) experiments, 

 (ii) Responses essentially relevant to descendants. 



{a) Activation to multiply after lodgment in appro- 

 priate tissue to lymphocytes or plasma cells. Under 

 special circumstances proliferation may occur as 

 epithelioid cells, and perhaps as eosinophils. 

 (b) The switch from primary modification to the 

 secondary type of reactivity. 

 B. The most important factors in determining which of 



these types of response is elicited may be 

 (i) The concentration of antigen or the number of surface 



receptors on the cell stimulated. 

 (ii) The goodness of fit between antigenic determinant and 



surface receptor. 

 (iii) The past immunological history of the cell and of the 



clone to which it belongs. 

 (iv) The physiological age of the individual at the time. 

 (v) The particular internal environment in which a stimu- 

 lated cell happens to lodge. 

 On this background we should ascribe the non-reactivity 

 of young animals largely to their inability to provide an 

 environment in which plasma cells can develop, plus the fact 

 that the existent clones carry only primary type patterns. 



The conditions relevant to tolerance can perhaps best be 

 illustrated by such a family of curves as is shown in Figure 8. 

 This allows a continuously changing pattern of reactivity 

 with the maturation of mesenchymal cells, plus an indication 

 of the influence of antigen concentration. It is probable that 

 the parameter antigen concentration is in part a function of 

 'goodness of fit' between antigenic determinant and reactive 

 site on the cell. The better the fit the higher the equivalent 

 concentration. As has been suggested on other pages the 



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