ABO system of blood groups in people and their resistance to certain infectious diseases (prognosis).

Natural resistance to many infectious disease which to certain extent depends on the blood group of a person is inherent in people. As is known, human erythrocytes possess the surface antigens A, B, AB that determine the groups of blood. Blood group O erythrocytes do not possess these antigens but blood serum of such people have antibodies to A and B antigens. In people with blood group A there are antibodies to antigen B and vice versa. Human blood of AB group does not contain antibodies to erythrocyte antigens of other blood groups. This determines natural resistance of people to many infectious diseases whose agents have antigens on the surface of their cells that are similar to antigens of one or another group of blood. Thus antigens similar to those of blood group A erythrocytes are localized on the agents' cells, such agents are neutralized by natural antibodies of blood groups O and B. When antigens similar to those of blood group B erythrocytes are localized on the agents' cells, that is the obstacle for them when affecting people with blood group A and B whose serum includes a lot of antibodies to these antigens. Only people with blood group AB are most sensitive to infectious diseases which agents carry antigens A, B or both A and B on their cells, since blood of such people does not contain the corresponding natural antibodies. To illustrate the above said the author gives a prognosis of possible affection of people by most pathogenic mycoplasmas whose cells possess antigens similar to those of erythrocytes of one or another blood group.