Antigens and antibodies
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Red cell antibodies are produced in response to an antigenic stimulus |
Safe and effective red cell transfusions are based on your knowledge of red cell antigens and antibodies.
This knowledge also forms your understanding about the aetiology of haemolytic disease of the newborn and its clinical management.
Antigens
These are either carbohydrate or protein substances that trigger our immune system to produce antibodies.
Antigens are found on the surface of red cells, white cells and platelets but are also found on surfaces of bacteria and viruses.
Antigenic cellular blood elements and plasma proteins can result in alloimmunisation or the production of antibodies, specifically called alloantibodies, which are directed against the blood group antigens of another individual.
The immune system's response to some of these antigens range from clinically benign to massive and complicated immune reactions, possibly resulting in death.
Antibodies
These substances are produced by our body's immune system in response to an antigenic stimulus.
Antibodies or immunoglobulins (Ig) are made of gammaglobulins, consisting of five main types: IgG, IgM, IgA, IgD and IgE. Each type performs a different role. Almost all antibodies to red cells are IgG or IgM, and a minority have an IgA component.
Most naturally occurring antibodies are non-reactive at 37 ºC, thus, are of little clinical significance. These are usually IgM, which are found in individuals who have never been transfused with red cells or pregnant with a fetus carrying the relevant red cell antigen.
Naturally occurring antibodies may result from 'natural' exposure to substances within the environment or diet that have a similar structure to the corresponding red cell antigen.
Of critical clinical importance are naturally occurring antibodies that are reactive at body temperature (37 ºC) because they are capable of mediating destruction or sequestration of transfused allogeneic red cells at this temperature.
For example, IgG atypical antibodies formed upon exposure to foreign red cell antigens during transfusion or pregnancy may cause haemolytic transfusion reactions or haemolytic disease of the fetus and newborn.
