200 MORTEN SIMONSEN 



by this method, in the 4 strain combinations with C3H. It is 

 evident that they indicate a relative antigenic strength which 

 conforms with the estimates on spleen enlargement (Table II, 

 column 6). 



Discussion 



The present experiments compared with earlier findings 



Other workers have provided evidence that preimmunized 

 donors provoke a stronger graft-versus-host reaction than normal 

 donors (e.g. Billingham and Brent, 1959; Gorer and Boyse, 1959; 

 Howard, 1961). However, their assays do not allow conclusions 

 to be drawn about the relative potency of the two kinds of cells. 

 Nor do they suggest any difference between weaker and stronger 

 antigens in this respect. 



The latter fact, however, is strongly suggested by the studies 

 of Berrian and McKhami (i960) who performed ist- and 2nd-set 

 skin grafts in co-isogenic strains of mice differing either in respect 

 to the H-2 or the H-3 locus. When the antigen was a strong one 

 (H-2), the 2nd-set grafts survived only 3 days less than the ist-set 

 (6 days instead of 9). Whereas, when the antigen was weak (H-3), 

 2nd-set grafts lasted 8 days as contrasted to 20 or 34 days in the 

 two strain combinations tested. 



The skin grafting technique has very severe limitations for this 

 kind of study. The short survival of ist-set grafts in a strong 

 combination sets a very narrow limit to the degree of immunity 

 which can be detected here. Even if the gain in "rejecting power" 

 was equal to, or greater than in a weak system, there would be 

 no way of observing it. With these reservations in mind, there is 

 clearly agreement in quahtative terms between the fmdings of 

 Berrian and McKhami and the present fmdings. 



The present experiments in relation to clonal selection 



There is much in the discussion in my recent review on graft- 

 versus-host reactions (Simonsen 1962, chapter X) that would be 

 relevant here. Repetition, however, cannot be entirely avoided. 



