EOSINOPHIL FUNCTION 



suggest that the lymphocyte is specially adapted to move to 

 areas where mesenchymal activity is required and there take 

 on the appropriate functional activity. It is the obvious and, 

 in fact, only possible candidate for the role of the responsive 

 cell type in the clonal selection theory. 



The alternative view is that there persists a line of stem 

 cells, primitive reticular cells presumably, which retain all 

 the potentialities of the embryonic mesenchyme, giving rise 

 to granulocyte, erythrocyte, lymphocyte, plasma cell or 

 macrophage, as occasion requires. On this view there will 

 also be a place for the replication of intermediate forms, 

 myelocytes, erythroblasts, etc.,butwithanyurgentcallfor new 

 cells the stem cells are presumed to be brought into activity. 



As Marshall points out, there is no present way of deter- 

 mining whether a primitive-appearing cell has been already 

 conditioned to produce one line of descendants only or still 

 retains potentiality to produce any line when appropriately 

 stimulated. To this we could add that it is equally impossible 

 to be sure that the primitive cell is not a derivative of a line 

 which had included developed lymphocytes or macrophages 

 in its sequence. If the facts of immunology demand such an 

 interpretation, there seems to be nothing in the histological 

 picture which renders it untenable. 



There is one special reason for stressing the probability 

 that the primitive reticulum cell is not descended from a line 

 of primitive cells which have never been exposed to functional 

 experience. If this were the case, there would be no place 

 for the store of ' memories ' which allow the various types of 

 secondary and anamnestic responses discussed in chapter v. 

 Whatever hypothesis of antibody production is adopted, the 

 mesenchymal cells of the adult need to carry a relatively 

 enormous amount of information based on past immuno- 

 logical experience. This demands either that cells which have 

 been functionally selected as successful give rise to descendants 

 directly or that they transfer to stem cells the relevant genetic 

 information gained as a cause or result of that success. The 



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