120 M. HASEK ET AL. 



leucocytes in the intervillous spaces. Fragments of the syncytio- 

 trophoblast are actually often released and pass into the mother's 

 blood and lungs (Bardawill and Toy, 1959; Boyd, 1959; Park, 

 1959). The question is, therefore, why is an immune reaction not 

 induced by syncytiotrophoblast and why is the transplantation 

 reaction of the mother not directed against it ? In our laboratory 

 we have investigated whether the placenta, a part of which is of 

 foetal origin, is capable of inducing transplantation immunity to 

 male-specific antigens. 



Mature female mice of inbred strain A mated with males of 

 CBA strain were used. Under sterile conditions, A x CBA Fj 

 hybrid placentas were deprived of the remnants of foetal 

 membranes (blood was partially removed by washing in 

 physiological saline), weighed, cut into fragments and injected 

 subcutaneously into normal adult (2- to 7-month-old) recipients 

 of the male or female parent strains. The age of placentas, doses 

 and routes of administration are given in Tables I and II. The 

 dosage corresponded to about 2-3 placentas per recipient. Three 

 to six days after application, skin from the back of 2-4-month-old 

 A X CBA Fi hybrid or CBA strain mice was grafted on the 

 recipient, following the technique of Billingham and co-workers 

 (1954). Seven days after transplantation, grafts were fixed in 10 

 per cent formol, embedded and histologically examined. Trans- 

 plantation immunity of the recipient was evaluated according to 

 the state of the epithelium of the test graft. Seven days after 

 transplantation, optimal proliferation of the epithelium was 

 found in previously non-immunized animals: in immunized 

 animals, the epithehum was destroyed. Parallel skin trans- 

 plantations of the recipients receiving other embryonic tissues 

 under the same conditions were positive controls and grafts 

 placed on non-treated animals were negative controls. 



After transfer of 100-200 mg. of the placentas into recipients of 

 the female strain, the recipients did not display immunity 

 (Table I) ; the survival of the epithelium of the test graft was 



