3l8 GUY A. VOISIN AND RADSLAV KINSKY 



alterations are compatible with the view that at least as early as 

 day 5, and continuing thereafter, runting is counteracted by some 

 mechanism which will have to be explained. 



B. What is the basic mechanism by which immune sera 

 exert protection against runting ? 



Immune anti-newborn sera do possess a definite (sometimes 

 strikingly strong) protective activity toward newborns of the 

 same strain injected at birth with homologous adult spleen cells. 

 This activity cannot be ascribed to mechanisms such as anti- 

 bacterial activity for instance, for obvious quantitative reasons; 

 furthermore, if it was the case, it would mean that runting is a 

 bacterial disease, which does not seem reasonable. On the other 

 hand, this protective activity is confmed to sera having special 

 immunological properties: utilized at "high doses" they are 

 immunotoxic for the corresponding homologous newborns, 

 while they are innocuous to isologous newborns. Furthermore 

 these sera possess a specific haemagglutinating power towards red 

 cells of the same strain as the newborns. When they do not 

 possess this activity, there are reasons (see results on haemagglu- 

 tination) to think that they possess an immunological activity of a 

 comparable order. These different properties of the sera utilized 

 in these experiments — namely protective or preventive activity 

 against a reaction analogous to homotransplantation reaction, 

 immunotoxicity at higher doses and haemagglutinating power — 

 are precisely the properties characteristic of sera able to produce 

 passive immunological enhancement (or faciHtation) of trans- 

 planted homologous tumours (Kahss, 1957^; Gorer, 1958). For all 

 the preceding reasons it is reasonable to assume that the basic 

 mechanism by which these sera protect the corresponding new- 

 boms against runting is the same as the one by which enhancing 

 sera protect the corresponding tumours against rejection reaction. 

 This was indeed the working hypothesis which led us to perform 

 the reported experiments (Voisin, 1958, i960). 



