Blood Types:
There are four main blood types; A, B, AB, and O. Each of these consist of two types A+, A-, B+, B-, AB, AB-, and O+, O-. The type of blood a person has tell what type of antigens are in their body. The A blood type has anti-B antibodies. B blood type has anti-A antibodies. AB has neither anti-A or anti-B antibodies. While O has both anti-A and anti-B antibodies. Antigens in your blood trigger an immune system response, and our blood type is determined by which antigens are present of absent from the surface antigens.
That is why when a blood transfusion is made the blood type needs to be known, so that your body doesn't attack it's own blood. Unless the blood given is O-, O- is the universal donor blood.
http://1.bp.blogspot.com/-EdrgrZACs1g/T7NpVFOONbI/AAAAAAAAGZ0/vxhs5-Ep9NQ/s1600/bloodtypes.jpg
That is why when a blood transfusion is made the blood type needs to be known, so that your body doesn't attack it's own blood. Unless the blood given is O-, O- is the universal donor blood.
http://1.bp.blogspot.com/-EdrgrZACs1g/T7NpVFOONbI/AAAAAAAAGZ0/vxhs5-Ep9NQ/s1600/bloodtypes.jpg