THE FACTOR OF IMMUNIZATION: CLONAL 



SELECTION THEORY INVESTIGATED BY SPLEEN 



ASSAYS OF GRAFT-VERSUS-HOST REACTION 



Morten Simonsen 



Mclndoe Memorial Research Unit, Blond Laboratories, Queen Victoria Hospital, 

 East Gr instead, Sussex 



Some two years ago, when the Ciba Foundation held its 

 Symposium in Royaumont on Cellular Aspects of Immunity, a 

 meeting generally influenced by the new theories on clonal 

 selection, I closed my own contribution (Simonsen, 1960^) with 

 the slightly nebulous prophecy that assays of graft-versus-host 

 reactions (thinking particularly of spleen assays) would in the 

 future help us to discriminate between the conflicting and highly 

 speculative theories of antibody formation. 



The attraction of graft-versus-host (GVH) reactions in this 

 context is that some of them, at least, can be used as a means for 

 quantitative estimation of immunologically competent cells. 

 Hence they seem particularly fit for following the dynamics 

 of cell populations of lymphoid organs during the course of 

 immunization. 



The past two years have in fact been witness of considerable 

 interest in the use of GVH reaction for the study of clonal selection. 

 Sir Macfarlane Burnet and his collaborators have made use of their 

 chorioallantoic membrane (CAM) assay of GVH reaction. Their 

 work, so far, has not provided unambiguous evidence in support 

 of clonal selection. Indeed, one of their observations points 

 rather strongly against it. This is the fmding (Burnet and Burnet, 

 i960) that a grafted cell population, derived from a donor which 



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