CLONAL SELECTION THEORY 



If the potential antigen persists long enough in high enough 

 concentration, all clones which can produce this natural 

 antibody will be eliminated. This provides a simple explana- 

 tion for the red cell woagglutinins and could obviously be 

 extended to cover all examples of prenatal tolerance. Self- 

 not-self recognition means simply that all those clones which 

 would recognize (that is, produce antibody against) a self 

 component have been eliminated in embryonic life. All the 

 rest are retained. 



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Fig. 7. To illustrate the clonal selection theory of immunity. Contact 

 of the corresponding antigenic determinant Ag.C with cells of clone c 

 stimulates proliferation to antibody-producing plasma cells cp and non- 

 antibody producing types c. 



To obtain such a result a fairly complex developmental 

 sequence must be postulated. The first point to be considered 

 is how a complete sequence of globulin patterns capable of 

 reacting with all possible determinants could be established. 

 There is a possible clue to be found in the fact that all 

 substances capable of acting as antigens are susceptible to 

 enzymic breakdown. Enzymes are proteins and it is probably 

 a reasonable deduction that proteins have the potentiality of 

 carrying steric patterns complementary to every chemical 



59 



