Blood transfusion

Blood transfusion
Blood transfusion is a kind of transplant in which whole blood or blood cells are transferred intravenously into the host circulation. Transfusions allow the replacement of blood loss due to hemorrhages and help to correct the secondary defects of insufficient production of blood cells associated with different diseases.

The main obstacle to a successful blood transfusion is the immune response to cell surface molecules which are different among subjects. The most important system of alloantigen for blood transfusion is ABO. ABO antigens are expressed in all cells, including erythrocytes. People who do not have a specific blood-group antigen synthesize naturals IgM antibodies against this antigen. When these people receive blood cells that express the antigen that they do not have, presynthesized antibodies will join the transfused cells, the complement system will be activated and it will produce the lysis of cells. The lysis of the foreign erythrocytes results in a transfusion reaction, which could be potentially lethal.

The choice of donor’s blood for a particular receptor must take into account the antigens of the blood groups. Most people express the H antigen therefore they do not synthesize anti-H antibodies. People who express A or B antigens do not synthesize anti-A or anti-B antibodies, respectively. However, OO and AO people produce anti-B IgM while OO and BO people synthesize anti-A IgM. The consequence is that AB patients can tolerate transfusions from all possible donors, therefore they are called universal receptors; at the same time, OO patients can only tolerate OO donors` transfusions, but they can provide blood to all receptors, therefore they are called universal donors.

The Rhesus antigen (Rh) is another important antigen of erythrocytes which could cause a transfusion reaction. Although there do not exist natural antibodies against Rh antigens, people who do not express the Rhesus D antigen (Rh) (about 15% of the population) could be sensitized against this antigen and they could produce anti-Rh antibodies when they receive blood transfusions from donors who express RhD. Transfusion reactions will take place after the second Rh-positive blood transfusion.