Blood Typing and Agglutination

• Blood transfusions involve taking blood from a donor and giving it to a recipient, a common medical treatment.
• The discovery of surface markers or antigens on biological molecules led to safer transfusion practices.
• The immune system recognizes and tries to remove foreign antigens, and this response was the cause of early transfusion fatalities.
• Antigens on erythrocytes, specifically genetically determined carbohydrate chains, give rise to different blood groups.
• The ABO and Rh blood groups are two groups of 30 different antigens on erythrocytes and are particularly useful for clinical use.

Blood Typing

• The ABO blood group includes A and B antigens, giving rise to four ABO types.
• Type A erythrocytes have only A antigens present.
• Type B erythrocytes have only B antigens present.
• Type AB erythrocytes have both A and B antigens present.
• Type O erythrocytes have neither A nor B antigens; absence of A and B antigens is denoted by "O".
• The Rh blood group contains the Rh antigen first discovered in rhesus monkeys.
• Individuals with the Rh antigen (D antigen) on their erythrocytes are Rh-positive (Rh+).
• Individuals without the D antigen are Rh-negative (Rh-).
• The combination of ABO and Rh blood groups results in eight common blood types.
• Type O+ is the most common blood type in US populations.
• Type AB- is the least common.

Blood Typing in the Lab

• Blood typing uses antibodies that bind to individual antigens on erythrocytes.
• Antibodies, known as agglutinins, bind to surface-bound antigens, causing them to clump together, or agglutinate.
• Agglutination ultimately leads to erythrocyte destruction, called hemolysis.
• A blood sample is treated with three different antibodies.
• Agglutination indicates the presence of an antigen on erythrocytes, while no agglutination indicates its absence.
• Anti-A antibodies bind and agglutinate A antigens.
• Anti-B antibodies bind and agglutinate B antigens.
• Anti-Rh (Anti-D) antibodies bind and agglutinate Rh antigens.

Blood Transfusions

• The immune system recognizes antigens on erythrocytes as "self" antigens; therefore, it does not produce antibodies to them.
• The immune system produces antibodies to foreign antigens, meaning that antibodies are present in plasma only when antigens are absent from erythrocytes.
• Anti-A and anti-B antibodies are pre-formed, present in plasma regardless of prior exposure to those antigens.
• Anti-Rh antibodies are produced only after exposure to blood containing Rh antigens.
• Rh- individuals generally do not have anti-Rh antibodies unless sensitized to Rh+ erythrocytes.
• Blood matching is based on antigens and antibodies, where donor blood is screened for compatibility before administration to the recipient.
• Patients cannot receive blood containing antigens that their immune system would recognize as foreign.
• A match occurs when the donor blood type is compatible with the recipient's blood type.
• A transfusion reaction occurs when recipient antibodies bind to donor antigens, causing agglutination, which destroys donor erythrocytes and can lead to kidney failure and death.

Universal Blood Types

• The universal donor blood type is O-.
• Erythrocytes do not have A, B, or Rh surface antigens.
• It can be given to any other blood type in an emergency when blood matching is not an option.
• The universal recipient blood type is AB+.
• They do not make antibodies to A, B, or Rh antigens.
• Can generally receive blood from any blood type donor.
• Matching remains the safest practice.

Donor's antibodies

• Donor antibodies can bind to recipient's antigens.
• Unless blood types are exactly matched, some donor antibodies may destroy a few of the recipient's erythrocytes.
• Usually only a few recipient's erythrocytes are harmed.

Hemolytic Disease

• Erythroblastosis fetalis, occurs when an Rh- mother gives birth to an Rh+ fetus.
• Fetal RBCs enter the mother's blood during birth, stimulating her immune system to produce anti-Rh antibodies.
• The first pregnancy is typically not at risk.
• Subsequent pregnancies are at risk.
• Maternal anti-Rh antibodies can cross the placenta and hemolyze Rh+ fetal RBCs.
• Disease is prevented with blood type screening.
• If the woman is Rh-, she can be given Rh (D) immune globulin.
• Immune globulin contains anti-Rh antibodies that bind fetal cells in maternal circulation, preventing maternal production of anti-Rh antibodies.