Why does any group of blood have anti-body without any strange material going into the body? For example, automatically group A has anti-gain A and anti- body B.

Red blood cells have surface antigens, which allow their identification in blood groups, but not antibody. Antibodies develop when the organism comes into contact with an unknown antigen.

Explanation:

Red blood cells can be classified in groups by the existence of surface antigens on the erythrocyte membrane.

When a person comes into contact with an antigen that does not possess, he can make antibodies to that antigen, so that :

This means that a specific blood type does or does not possess an antigen, but does not include the antibody. The body's defenses are what make the antibody when it comes into contact with the antigen that it does not recognize.