414 Microbes and You 



cells was soon complicated by the discovery of a number of sub- 

 groups, since the Rh antigen is not a single, homogeneous sub- 

 stance. But Rh-positiveness has come to mean that at least one 

 particular antigen is present in the cells. 



Expanded investigations have disclosed that the incidence of 

 the major Rh antigen in Caucasians is close to 85%, with as low as 

 65% in the Basques of Argentine, and as high as 99% Rh-positives 

 in American Indians, Chinese, and Japanese. Such studies on Rh 

 distribution have added information to that being gathered by 

 anthropologists interested in mass migrations of various peoples. 



MULTIPLE TRANSFUSIONS 

 Rh-positive blood cells are antigenic for Rh-negative individuals, 

 even though their type with respect to the "A" and "B" systems of 

 blood groups may be identical. Introduction of such antigenic 

 cells into an Rh-negative person will stimulate the production of 

 antibodies which will agglutinate and hemolyze Rh-positive cells. 

 It becomes apparent, therefore, that Rh-negative individuals must 

 be transfused only with Rh-negative cells of the correct blood 

 type, or subsequent transfusions with Rh-positive blood may work 

 to the disadvantage of the recipient. 



Rh AND PREGNANCY 



Rh factors have considerable significance in certain pregnancies. 

 If a woman possesses Rh-negative blood and her husband is Rh- 

 positive, there is a strong possibility that the fetus will inherit the 

 father's dominant Rh-positive factor. Should anv of the blood 

 from such a fetus gain entrance to the mother's blood circulation, 

 the Rh-positive cells will serve as an antigen, and the mother will 

 respond by producing antibodies for these Rh-positive cells. It 

 should be remembered that even though the cellular portions of 

 the blood of the fetus are separated from the mother's circulation 

 by the placental barrier, antibodies can pass between mother and 

 fetus. It is by this means that newborn babies are endowed with 

 passive immunity to certain diseases. 



It is not well understood how the cells of a fetus find their way 



