Trong thời gian mang thai, các tế bào lá nuôi phôi thai của lời nói dối (Chương 19) nhau thai tiếp xúc trực tiếp với các tế bào miễn dịch mẹ. Kể từ khi một nửa của các gen thai nội, tất cả các protein được mã hóa của các gen này được nước ngoài cho người mẹ. Tại sao hệ thống miễn dịch của người mẹ không tấn công | Vander et al. Human Physiology The Mechanism of Body Function Eighth Edition III. Coordinated Body Functions 20. Defense Mechanisms of the Body The McGraw-Hill Companies 2001 Defense Mechanisms of the Body CHAPTER TWENTY 717 TABLE 20-8 Human ABO Blood Groups Blood Group Percent Antigen on RBC Genetic Possibilities Antibody in Blood Homozygous Heterozygous A 42 A AA AO Anti-B B 10 B BB BO Anti-A AB 3 A and B AB Neither anti-A nor anti-B O 45 Neither A nor B OO Both anti-A and anti-B In the United States. The Fetus as a Graft During pregnancy the fetal trophoblast cells of the placenta Chapter 19 lie in direct contact with maternal immune cells. Since half of the fetal genes are paternal all proteins coded for by these genes are foreign to the mother. Why does the mother s immune system not attack the trophoblast cells which express such proteins and reject the placenta This problem is far from solved but one critical mechanism there are certainly others is as follows Trophoblast cells unlike virtually all other nucleated cells do not express the usual MHC class I proteins instead they express a unique MHC class I protein that maternal immune cells do not recognize as foreign. Transfusion Reactions Transfusion reactions the illness caused when erythrocytes are destroyed during blood transfusion are a special example of tissue rejection one that illustrates the fact that antibodies rather than cytotoxic T cells can sometimes be the major factor in rejection. Erythrocytes do not have MHC proteins but they do have plasma-membrane proteins and carbohydrates the latter linked to the membrane by lipids that can function as antigens when exposed to another person s blood. There are more than 400 erythrocyte antigens but the ABO system of carbohydrates is the most important for transfusion reactions. Some people have the gene that results in synthesis of the A antigen some have the gene for the B antigen some have both genes and some have neither gene. Genes cannot code for
