If clinically incompatible red cells are infused into a person, will the immune system destroy those cells?
This occurs in either an Immediate Transfusion Reaction or a Delayed type, depending on the type of antibody involved and, importantly, the transfusion history of the person.
Naturally occurring red cell antibodies are ones that have been present from birth and occur in most people's plasma and are directed against A and B antigens.
Anti-A occurs in both group O and group B people and anti-B in both group O and group A people. There is no natural O antibody.
Thus, people who have blood group AB have no natural anti-A or anti-B antibodies in their plasma. Group O people have both the anti-A and anti-B antibodies.
These antibodies always illicit an Immediate Transfusion Reaction by activating an enzyme cascade system called 'Complement'. This rapidly destroys incompatible cells by drilling a hole in their surface membrane.
The clinical consequences are immediately life threatening if a large volume of ABO incompatible red cells is infused.
Alternatively, if Rh positive cells are infused into someone who is Rh negative (and hasn't previously been transfused with incompatible Rh positive cells), the immune system will be activated to produce specific antibodies to the Rh antigen group. The foreign antibody coated foreign cells are then cleared from the blood stream by macrophages. The complement cascade system usually is not activated in this Delayed Transfusion Reaction process.
If, however, the patient's immune system has been sensitised to the Rh antigen by a previous transfusion, donor cell clearance is much more rapid.
The wrong blood should not be infused into an individual. Constant vigilance and checking procedures are always undertaken by hospital blood bank scientists to ensure this never occurs.
People who are group O negative are considered to be universal blood donors but this rule is not absolute. Blood from these people is highly valued for extreme emergency situations.
Some patients, however, require constant transfusions just to survive (e.g. people with Sickle Cell disease, some cancer patients and people with resistant auto-immune haemolytic anaemia). A subset of these folk will gradually start developing more and more clinically significant antibodies directed against lesser blood groups on donor cells, thus shortening their survival in the circulation.
Extended phenotyping (i.e. matching their red cell antigens to the donor's antigen array) is done where possible to minimise this problem.
This highly specialised service is something the Australian Lifeblood Service helps hospital blood banks with.
Do become a blood donor if you can. Only 3 per cent of people donate blood annually and they are special people.
The Fuzzy Logic Science Show is 11am Sundays on 2xx 98.3FM.
Send your questions to AskFuzzy@Zoho.com Twitter @FuzzyLogicSci Podcast FuzzyLogicOn2xx.Podbean.com
