In your case, there would be a bad reaction. There are antigens in A, B, and AB blood (A = A antigens, B = B antigens, AB = both A and B antigens); there are no antigens in O type blood. If you have type A blood, you can only receive types A and O blood because those people with type A blood will create antibodies to fight, and destroy, type B antigens. It is the same with type B blood. If a person has type B blood and gets a transfusion with type A blood, there will be the same reaction. The type B blood will fight to destroy the type A blood. This is called a transfusion reaction.
A transfusion reaction causes antibodies to attach to the antigens in red blood cells. This causes the cells to coagulate and will plus up your blood vessels. Eventually these clumps of cells are usually destroyed but in the process (called hemolysis) hemoglobin is released. When hemoglobin gets broken down, it becomes bilirubin. Most people know that a lot of bilirubin in the system causes jaundice (like in some newborn babies). Vitamin D can help rid the body of bilirubin.
A hemolytic reaction can cause fever and chills, pain in the back or chest areas, and a shortness of breath. This reaction can also cause even worse symptoms such as damage to the kidney, and either a raise in heart rate or blood pressure can drop significantly.
The good news: a transfusion mix up generally does not occur. Doctors take extra precautions, making sure the blood types will work together instead of destroying each other. They will know your blood type and do a cross match test. This test places your blood with the potential donor’s blood together. They view the two bloods to make sure they work together instead of trying to destroy each other.