Antigens and organ transplant
Antigens are chemical markers found in all cells. It is different in every species. The antigens are used by the immunity system to recognize the cells of its own body and the cells from the outside environment such as the cells of a bacteria or virus. The antigens on the blood cells helps in identifying the blood type of a person. The most common known type of blood groups are A and B, which can combine to form new groups such as A, B, AB and O etc. However this can also come at a disadvantage when it comes to organ transplant. In case of blood transfusion, heart transplant, kidney transplant or any other kind of transplant, the immunity system recognizes the antigens on the cells of the organs as a foreign cell and produces antibodies against these organs and destroy the organ, this is called organ rejection.
To prevent organ rejection doctors take a specific organ from another person which has the same blood type. Normally the organ donor is chosen from the family of the patient which has the same blood type. If the family members are unable to provide their organ, such as kidney, then the doctors search for another organ donor with the same blood type as the patient. If such donor is found then immune-suppressant drugs are used to suppress the immunity system to prevent organ rejection. If the transplant is successful then the person would live for five or six more years (or even more).