THE FACTS OF IMMUNITY 



not Stimulated when the child is inoculated with foreign red 

 cells of the type which should stimulate their formation in 

 the individual studied. This is at least another hint that 

 normal agglutinins and immune antibodies have much in 

 common. 



6. Lymphocytes and plasma cells as antibody producers 



At the present time there is no serious opinion against the 

 view that the acute production of antibody in, for example, 

 the secondary response to some standard antigen like 

 diphtheria toxoid is a function of plasma cells, especially 

 what Fagraeus (1948) calls immature plasma cells. The 

 study by Coons, Leduc and Connolly (1955) of antibody- 

 producing cells using the fluorescent antibody 'sandwich' 

 technique provided a clinching final support for a variety 

 of less direct earlier approaches. 



This, however, is only part of the story. For an adequate 

 account of the cellular basis of immune responses we need 

 to know: 



(i) What is the origin of plasma cells? In two senses, 

 {a) from what cell types are they descended and 

 {b) what stimulus in the internal environment calls 

 forth their appearance? 

 (ii) What are the origins and degrees of interconverti- 

 bility of macrophages, lymphoid cells and plasma cells? 

 (iii) What is the cellular basis of Types 2 and 3 



responses? 

 (iv) Can antibody be liberated from lymphocytes and, if 



so, under what conditions? 

 (v) Have the spleen and thymus immunological functions 



different in quality from other mesenchymal tissues? 

 It seems necessary to say at once that no complete answer 

 to these questions is available, and the rest of this section will 

 be confined to listing some of the evidence that small 

 lymphocytes are concerned in the immune response, and to 

 offering some opinions from the literature in regard to the 



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