IMMUNOLOGICAL TOLERANCE 



Table 4. Effect of immunization on the titre and character of 

 T agglutinin {Fraser, igjj) 



Unabsorbed Abs. with RD cells at 40° 



Titres against RD cells shown. 



Fraser interprets this as indicating that the cells responsible 

 for the normal T agglutinin were responsible also for produc- 

 tion of the immune agglutinin. A physiological change has, 

 however, taken place in virtue of which the non-avid cold 

 agglutinin is no longer produced. With waning of the stimu- 

 lus the cells revert to the former type. 



This system of normal and immune T agglutinin may well 

 prove to be of great importance in testing the clonal selection 

 hypothesis. 



The interpretation on that hypothesis would take the 

 following form. There is no known neuraminidase in the 

 body, at least where it is accessible to the red cell surface, 

 and its action results in the exposure of a set of determinants 

 new to the body. The determinant in question is not the 

 same for each species of red cell but has at least the common 

 quality of being not-self. There may well be one common 

 determinant for all RD cells plus others more species-specific. 

 It is probably significant that the guinea-pig T titres obtained 

 by French and Ada were relatively low and transient com- 

 pared with those obtained by heterologous cells in the rabbit. 



We assume that the normal T agglutinin is a fraction of 

 the gamma globulin population which 'by accident' reacts 

 with the common determinant produced or uncovered by 

 RDE action. It is produced by one or more clones of mesen- 

 chymal cells. In embryonic and neonatal life those clones 

 had no power to produce globulin but could have been 



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