Immunohematology pt 3

Interactions of Immunology in Blood Bank

Overview of Antigens and Antibodies

  • Antigen Definition: An antigen is also known as an immunogen; it is a substance that initiates the immune response.

  • Composition of Antigens:

    • Primarily composed of proteins, which are most effective in generating long-lasting immunity.

    • Composed of carbohydrates, which are less effective and provide short-term immunity.

    • Lipids and nucleic acids are not immunogenic on their own.

  • Function: Antigens initiate the formation of specific antibodies through a "lock and key" interaction.

Testing for Antibodies

  • Indirect Antiglobulin Test: This test identifies antibodies present against blood group antigens in a patient’s plasma.

  • Variability in Immunogenicity: Different blood group antigens exhibit varying immunogenicity dependent on:

    • Structural attributes

    • Molecular weight

    • Accessibility to the immune system

  • Examples of Antigen Types:

    • Highly immunogenic antigens (e.g., Anti-D, Anti-Kl)

    • Antigens that demonstrate dosage effects (e.g., Kidd blood group, Duffy blood group)

Types of Antibodies

  • Complete Antibodies:

    • Typically IgM antibodies

    • React in saline and cause agglutination, producing visible clumps.

  • Incomplete Antibodies:

    • Typically IgG antibodies

    • Bind to red blood cells without causing visible agglutination unless potentiators are used to reduce the zeta potential.

Reporting Antibodies in Blood Bank Testing

  • Naming Convention: Antibodies should be prefixed with "anti-" followed by the blood group (e.g., anti-D) to indicate they are antibodies.

  • IgM Attributes:

    • Comprise about 10% of serum immunoglobulins.

    • First antibodies produced during a humoral immune response, capable of activating complement and promoting phagocytosis.

  • IgG Attributes:

    • Most abundant immunoglobulin in serum.

    • Can activate complement and cross the placenta.

Antigen-Antibody Interaction

  • Location: Antigens reside on red blood cells while antibodies are present in plasma, which is crucial during blood bank testing.

Grading Reactions in Blood Bank Testing

  • Scoring System:

    • 4+ Reaction: Strong clumping, with a solid cell button at the bottom of the tube or a clump at the top of the gel card.

    • 3+ Reaction: Less strong than 4+, noticeable clumps noticeable, but not a solid mass.

    • 2+ and 1+ Reactions: Weaker clumping is observed with smaller clumps, usually seen towards the bottom of gel.

    • Negative Reaction: Appears smooth (no clumps) with a single cell button at the bottom of the tube.

Types of Antibodies in Blood Group Systems

  • Naturally Occurring Antibodies:

    • Produced without prior transfusion or pregnancy.

    • Generally IgM antibodies, they may arise from diseases or non-specific stimulations.

  • Immune Antibodies:

    • Require red blood cell stimulation through transfusion, pregnancy, or transplant.

    • Typically IgG antibodies found in systems like Rh, Kell, Duffy, Kidd, and S.

  • History Importance: Patient history is crucial in evaluating antibody presence and potential reactions.

Types of Agglutination Tests

  • Direct Agglutination: Involves mixing red blood cells with antibodies, leading to visible agglutination. Common examples include ABO and Rh blood typing.

    • Typically performed at room temperature or via immediate spin.

  • Indirect Antiglobulin Test: Designed to detect IgG antibodies or complement components.

    • Incubation: Performed at 37 degrees to sensitize red blood cells before adding reagents.

    • Components: Requires potentiator to reduce zeta potential before washing and adding anti-human globulin (AHG).

Sources of Error in Antiglobulin Testing

  • Washing Errors: Inadequate washing of red cells can lead to false negatives due to unbound antibodies interfering with results.

  • Contamination: Presence of bacteria or improper reagents can produce false positives.

  • Cell Concentration: Too concentrated or diluted red blood cells can obscure a true reaction.

  • Proper Reagent Addition: Forgetting to add AHG reagent results in false negatives due to lack of a reaction medium.

  • Centrifugation: Improper centrifugation may lead to failure in agglutination due to lack of lattice formation.

Blood Bank Reagents

  • Monoclonal Reagents: Produced from inoculating animals, such as rabbits, with human components and collecting specific anti-human antibodies:

    • Benefits: High specificity, no human variability, unlimited production, not subject to cross-reactivity.

  • Polyclonal Reagents: Derived from using human donors with immunization against specific blood cells.

    • Issues: Variability due to different donor responses and potential cross-reactions, leading to discrepancies in ABO typing.

  • Forward Type vs. Reverse Type Reagents:

    • Forward type reagents contain antibodies detecting antigens on red blood cells.

    • Reverse type reagents detect antibodies using known antigens.

  • Potentiators: Substances used in indirect tests to enhance sensitization of antibodies:

    • Examples include: Low Ionic Strength Solution (LIS), Polyethylene Glycol (PEG), and AAP.

  • Enzyme Reagents: Used to enhance or destroy specific antigens, although saline is less preferred as it requires lengthy incubation.

Conclusion

  • These insights conclude the lecture on the interactions of immunology within the blood bank setting, emphasizing the importance of antigen-antibody reactions in transfusion medicine.