IMMUNOLOGICAL TOLERANCE 



producers of a,nti-A which can ' recognize ' and react with A 

 by undergoing either destruction or inactivation. Those 

 which are potential producers of anti-5, in the absence of ^, 

 survive, and with or without multipHcation give rise to cells 

 capable at the proper time of secreting anti-^. At a later 

 stage the introduction of B substance provides a stimulus to 

 the production of a rising titre of anti-^. 



These points are stressed to show the possibility that clones 

 of a given character may or may not be in a state in which 

 they produce soluble antibody and may differ greatly in the 

 character of their response to the specific antigenic stimulus. 

 It is not necessary that we should be able to demonstrate 

 minute amounts of all possible antibodies in the plasma to 

 make the clonal selection theory tenable. 



4. T agglutinin as a model of a natural antibody 



Our own laboratory has had a minor continuing interest in 

 T agglutinin and T antigens on red cells treated with viral 

 neuraminidase or the receptor-destroying enzyme RDE of 

 Vibrio cholerae. Normal human serum does not agglutinate 

 erythrocytes. If the red cells, however, are treated with 

 RDE or a myxovirus, they become agglutinable to a serum 

 dilution of about 100. This phenomenon is seen almost 

 equally well with chicken or guinea-pig cells, and all adult 

 vertebrate sera seem to contain T agglutinin. 



At birth, human cord blood contains no T agglutinin, the 

 first appearing about six months and reaching to about 

 a quarter of the final adult titre at the age of two years. In 

 our experience the only pathological condition showing a 

 sharp rise in T agglutinin is atypical pneumonia. In those 

 sera from cases of this disease which showed cold agglutinins 

 in significant titre, very high titres (average 850) of T ag- 

 glutinin were found (Lind and McArthur, 1947). 



Experimentally, T agglutinin titres can be raised by giving 

 guinea-pigs large enough doses of purified RDE to modify all 

 the circulating erythrocytes. In French and Ada's experi- 



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