350 IMMUNOLOGICAL STUDIES 



Topley and Wilson, 1946). Even natural antibodies, such as the 

 isoagglutinins of the human blood groups do not appear in the 

 serum until some time after birth ( see Wiener, 1943 ) . Antibodies 

 that are found in the newborn can be attributed to transfer from 

 the mother through the placenta, in the case of manmials, or to 

 the egg in the case of birds. The discovery by Levine et al. ( 1939, 

 1941 ) of isoimmunization of the mother by fetal cells demon- 

 strated at the same time, dramatically, the transfer of maternal 

 antibodies to the fetus. Experiments on immunization of the fetus 

 in mammals would be complicated by uncertainties as to whether 

 or not the antigen reached the maternal circulation and antibod- 

 ies produced there passed back into the fetus. However, even the 

 newborn mammal evidently lacks antibody-forming capacity as 

 shown, for example, in experiments by Freund ( 1930 ) on rabbits. 

 In chickens various experiments (cited by Tyler, 1955b) have 

 shown no antibody formation before the fifteenth day of incuba- 

 tion and very weak if any activity at the time of hatching (cf. 

 Wolfe and Dilks, 1948). 



Correlated with this apparent lack of antibody-forming capac- 

 ity is the ability of foreign tissue grafts to establish themselves 

 in the embryo whereas they consistently fail in the adult. Lack 

 of antibody-forming capacity has also been assumed to account 

 for the ready growth of various viruses on membranes and tissues 

 of chick and mammalian embiyos. 



It has been previously suggested (Tyler, 1955b) that the vari- 

 ous experiments need not be interpreted as indicating inability 

 of cells of the developing embryo to manufacture antibodies. 

 Quite possibly the embryonic cells do produce antibodies, in re- 

 sponse to foreign antigens, without releasing them into the fluids 

 that are customarily tested. Since the embryo, fetus, and new- 

 born are in a process of rapid gi'owth it is quite conceivable that 

 such antibodies as they might produce would remain a part of 

 the structural proteins of the cell. Thus they would not appear 

 in serum, or even be available for tissue-incompatibility reac- 

 tions. This is consistent with experiments on cells grown in tissue 

 culture where, for example, it has been shown that rat and mouse 

 tissues exhibit no incompatibility in mixed cultures (Harris, 



