Introduction to Immunohematology

Blood group system

Group of antigens determined by a single gene or two closely linked genes

Phenotype vs genotype (define + testing style)

Phenotype: physical expression → determined by serological testing (heme-agglutination)

Genotype: genetic makeup → DNA/molecular testing

Clinically significant vs clinically insignificant RBC antibodies

• Clinically significant: abs that cause immune destruction of transfused RBCs

  • React at 37 °C; mostly IgG

• Clinically insignificant: abs that usually do not destroy transfused RBCs

  • React at 4 °C; mostly IgM

            **except ABO abs

Allogeneic

Autologous

Allogeneic: transplants that are genetically different 

Autologous: transplants originate from self

In Vivo

• alloantibody production + re-exposure

• Extravascular vs intravascular RBC destruction

• Alloantibody production - exposure to foreign (allo)antigens

  • Transfusion

  • Transplantation

  • Pregnancy

• Re-exposure leads to hemolysis

  • Complement 

  • Ab/Ag complex clearance

Extravascular

• IgG

• Phagocytes in liver and spleen destroy RBCs

Intravascular

• IgM

• Activation of complement in vessels destroys RBCs

In Vitro

• testing principles

• Agglutination (hemagglutination)

  • Sensitization + lattice formation

• Hemolysis

Dosage effect

Antithetical

Dosage effect: phenomenon where Ab reacts with RBC carrying double dose (homozygous) of ag over RBC carrying single dose (heterozygous)

Antithetical: antigens that are products of allelic genes 

IgG vs IgM

Hemolysis, FAB sites, reaction temp, crosses placenta?, stimulation, serum half-life

Aggluation factors

• zeta potential:

  • significance?

• pH

  • best for testing?

  • hemolyzed plasma pH?

• length of incubation

  • why?

• agglutination

  • methods

Zeta potential: what is it?

• Reduce electrical repulsion to get RBC together for agglutination via enhancement media/potentiators (usually IgG in IAT) 

pH 

• Best for testing: 6.5 to 7.0

• Hemolyzed plasma has pH 7.4

• Some abs react better at lower pH 

Centrifugation

• Facilitates lattice formation

Length of incubation

• Time for ab-ag complex formation

Agglutination

1. Tube (common)

2. Column agglutination (gel)

3. Solid phase