Transfusion Medicine — PAGE BY PAGE Notes (HML3043)

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Institution and course context: Higher Colleges of Technology (Khalifa)
- Transfusion Medicine, HML3043. This course provides an in-depth understanding of the principles and practicesessential for safe blood transfusion.
Section aims: Overview of antigen–antibody reactions in blood bank practice, reagents and systems for detecting blood group antigens/antibodies, and the factors that influence typing and testing.
- This section is foundational, setting the stage for understanding the complex interplay between antigens and antibodies both within the body (in-vivo) and in laboratory settings (in-vitro).

Key idea introduced: The material sets up the practical framework for understanding in-vivo and in-vitro antigen–antibody interactions and the laboratory tools used to detect and interpret them, which are crucial for ensuring patient safety in transfusion therapy.

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Week 2 Learning Objective (LO1): Describe antigen–antibody reactions as they apply to Blood Bank practice and the reagents and systems used for detection of blood group antigens and antibodies.
- This objective emphasizes the critical link between theoretical immunology and practical laboratory applications in transfusion medicine.
Subpoints under LO1:
- Describe the in-vivo and in-vitro reactions between antigens and antibodies and the factors that influence the tests used in blood transfusion practice for blood typing.
  - In-vivo reactions refer to those occurring within a living organism, such as a patient experiencing a hemolytic transfusion reaction due to incompatible blood.
  - In-vitro reactions occur in a test tube or laboratory setting, forming the basis of all blood bank tests (e.g., agglutination in a gel card).
  - Factors influencing tests include temperature, pH, ionic strength, incubation time, and the concentration of both antigens and antibodies.
- Describe the systems available for detection of blood group antigens and antibodies, including the use of tiles/slides, tubes, microtitre plates and gel-based systems.
  - These different platforms offer varying degrees of throughput, automation, and sensitivity for detecting blood group antigens and antibodies.

Significance: Grounds testing workflows in both biological phenomena (antigen–antibody interactions) and practical laboratory platforms (tiles/slides, tubes, microplates, gels), ensuring comprehensive understanding from molecular to macroscopic levels.

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Content overview: Preparation of samples, reagents & controls; HEMATEST; various antibody reagents (Anti-A, Anti-B, Anti-A,B) and controls; Anti-D (Rh) reagents; brand references and format notes (IVD, Diagnast, etc.).
- Meticulous preparation is essential to avoid false positive or false negative results.
Practical note: The slide/kit notation indicates availability of diverse reagent panels for ABO and Rh typing, with controls to verify assay validity and ensure reliable results.

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Preparation of samples (section heading only): Focus on how samples are handled prior to testing, including centrifugation, proper labeling, and assessment for hemolysis or lipemia, which can interfere with test results.

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Sample to detect Antibody (indirect antigen–antibody screening):
- Serum from clotted blood is usually used for transfusion work to detect antibodies.
  - Serum is preferred over plasma because it contains active complement, which is crucial for detecting certain clinically significant antibodies (e.g., those causing complement-mediated hemolysis).
- To speed clotting, add 1 drop of thrombin (concentration $\sim100$ IU/mL).
  - Thrombin accelerates the conversion of fibrinogen to fibrin, allowing for faster serum separation, especially when a rapid turnaround time is required.
- Tested serum can be stored at 4°C for 24 hours before use.
  - Short-term storage at refrigeration temperatures helps preserve antibody activity.
- Serum can be stored at $-20$ °C for months.
  - For longer-term storage, freezing is necessary to minimize antibody degradation, though repeated freeze-thaw cycles should be avoided as they can denature antibodies.
Practical implication: Serum is preferred for Ab screening because it contains components (e.g., complement) that are informative for certain Ab–Ag interactions, and the absence of anticoagulants ensures complement activity remains intact.

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Why serum (not plasma) is usually used:
- Detection of activated complement (C) is often important in Ag–Ab reactions.
  - Complement activation is a key mechanism of immune-mediated cell destruction and can be indicative of clinically significant antibodies.
- Complement requires calcium for activation.
  - The classical and alternative complement pathways are calcium-dependent.
- In anticoagulated plasma, calcium is removed by EDTA or citrate, which impedes complement-mediated reactivity.
  - EDTA and citrate are chelating agents that bind to calcium ions, effectively preventing complement activation and thus hindering the detection of complement-binding antibodies.
Routine transfusion testing workflow for samples:
- Blood should clot at room temperature, then be centrifuged to obtain serum, which is used for testing. Complete clot retraction is essential for optimal serum yield and quality.

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Sample to detect antigens (RBCs):
- Red cells can be used from EDTA, citrated, or clotted blood samples.
  - While all three types are acceptable, proper washing is critical to remove plasma components that might interfere with antigen detection.
- Cells from the bottom of clotted blood tubes are most often used.
  - This is convenient as it allows for the use of the same patient sample for both serum (for antibody detection) and red cells (for antigen typing).
- Cells should be washed in saline twice before testing.
  - Washing removes unbound antibodies, plasma proteins, and excess anticoagulant that could cause false positive or negative results.
- Red cells are suspended in buffered saline at the appropriate cell concentration before use.
  - Typically, a 2-5% red cell suspension is used, as this concentration provides optimal sensitivity for agglutination reactions without causing prozone or postzone effects.
- They can be stored for 5 hours at 4°C.
  - Short-term storage preserves cell integrity and antigenicity.

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Preparation of reagents (examples of products/labels):
- DiaCall A1, DiaCall A2, DiaCall B, DiaCall 0, CinnaClone II, Anti-B (mouse monoclonal), Antibodies from Anaten Inc. (various dilutions and formats), 10% (likely concentration for reagents), Microplate/Slide/Tube formats, CinnaClone I (Anti-AB).
  - These specific reagent names indicate standardized commercial products designed for reliable blood group typing and antibody detection. Clonal reagents like CinnaClone highlight the use of monoclonal antibodies for improved specificity.
Takeaway: Reagents come in multiple formats (microplate, slide, tube) and are often monoclonal antibodies prepared for specific antigen targets (A, B, AB), with accompanying control reagents. The format choice depends on the volume of testing and desired level of automation.

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Reagents: Cells (reagent red cells) for testing:
- Reagent cells to be used for longer than a few hours should be suspended in a preservative solution containing glucose, adenine & citrate.
  - Glucose provides metabolic energy for red cell survival. Adenine is a precursor for ATP synthesis, maintaining cell viability. Citrate acts as an anticoagulant and helps maintain pH.
- Antibiotics can be added to prevent bacterial contamination.
  - Bacterial growth can alter red cell antigenicity or cause non-specific agglutination.
- Cells preserved in this way can be kept up to 4 weeks at 4°C.
  - This allows for practical shelf-life for routine laboratory use.

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Reagent red cells: practical notes on quality control
- Precise measurement of cell concentrations is not strictly required; many workers estimate by eye.
  - While visual estimation is common for routine screening, quantitative antibody titrations or certain specialized tests may require more precise cell suspensions.
- Reagent red cells are prepared from donors with known antigenic types.
  - This ensures that their antigen profile is well-characterized for detecting specific antibodies in patient samples.
- Whenever possible, reagent cells should be homozygous for the antigen of interest.
  - Homozygous cells express a double dose of the antigen, which can detect weaker antibodies that might be missed if heterozygous cells (single dose) were used due to the phenomenon known as dosage effect.
- Some heterozygous cells do not react as strongly as homozygous cells.

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Reagent Serum – Antiserum (Antibody reagents):
- Most antibody reagent sera are purchased (commercial antisera).
  - Commercial antisera offer standardization, consistent potency, and validated specificity, reducing variability between batches.
- Some rare antisera can be made in the lab from patient samples.
  - This typically involves patients with clinically significant alloantibodies or autoantibodies that react with high-frequency antigens.
- Antibodies used as reagents can be various types and must be used according to manufacturer’s instructions.
  - Adherence to instructions is crucial for optimal performance, ensuring correct antibody concentration, incubation times, and storage conditions.
- Possible serum reagents categories: Polyclonal or Monoclonal; IgG or IgM.

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Antibodies basic concepts (illustrative schematic):
- Antibodies are produced from antigen exposure.
  - When the immune system encounters an antigen, B lymphocytes are activated and differentiate into plasma cells, which produce antibodies specific to that antigen.
- Polyclonal antibodies are a mixture produced by many clones; monoclonal antibodies come from a single clone.
  - Polyclonal: Respond to multiple epitopes on an antigen. Monoclonal: Respond to a single, specific epitope.
- Diagrammatic idea: Antigen interacts with multiple antibody clones vs. a single clone.

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Polyclonal antibodies (Abs):
- Produced by inoculating animals with the antigen of interest.
  - Animals (e.g., rabbits, goats) are immunized, and their immune systems generate a diverse antibody response.
- Serum from the animal is collected and used as the reagent.
  - This serum contains a heterogeneous mixture of antibodies.
- Resulting reagents are a mixture of Abs from many clones, termed polyclonal.
  - While effective, polyclonal reagents can show lot-to-lot variability and may contain unwanted antibodies.

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Monoclonal antibodies (Abs):
- Obtained from cell cultures of genetically engineered plasma cells from animals (usually mice) immunized with purified antigens.
  - This process, often utilizing Hybridoma Technology, involves fusing antibody-producing B cells with myeloma (cancer) cells to create immortal cell lines that continuously produce specific antibodies.
- Cell cultures derived from a single plasma cell produce one type of Ab that can react with a single epitope on the antigen.
  - This ensures high specificity and minimizes non-specific reactions.
- Advantage: provides consistent, specific reactivity; often uses Hybridoma Technology.
  - Monoclonal antibodies offer superior batch-to-batch consistency and can be produced in large quantities, making them ideal for diagnostic reagents.

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IgG vs IgM antibody reagents:
- IgG reagents: do not agglutinate cells by themselves; described as sensitizing or incomplete Abs; usually do not react at room temperature.
  - IgG antibodies are smaller (monomeric) and typically require assistance (e.g., antiglobulin reagents or enhancement media) to bridge the distance between red cells, which is impeded by the zeta potential.
- IgM reagents: can agglutinate cells by themselves; do not require additional reagents; typically react at room temperature; described as saline agglutinating or complete Abs.
  - IgM antibodies are large pentameric structures, allowing them to effectively bridge red cells over the zeta potential, leading to direct agglutination.

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Reagent Serum / Antiserum handling for IgG reagents:
- Because IgG by itself does not cause visible agglutination, enhancing strategies are used:
  - These strategies aim to overcome the electrostatic repulsion between red cells and facilitate antibody binding and subsequent lattice formation.
- Addition of high-molecular-weight substances: Albumin, polybrene, or PEG (polyethylene glycol).
  - These substances increase the positive charge interactions and reduce the zeta potential, bringing cells closer to enable agglutination.
  - Zeta potential refers to the electrostatic repulsion between red cells caused by negatively charged sialic acid residues on their surface. High-molecular-weight substances reduce the effective charge and hydration shell around the cells.

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Alternative methods to enhance agglutination: disulfide bond modification
- Removal of disulfide bonds at the hinge region of the antibody can increase the span (distance between two antigen-binding sites) of the Ab, allowing agglutination to occur more readily.
  - This enzymatic modification essentially makes the IgG molecule more flexible and extended, improving its ability to cross-link antigens on adjacent red cells.
- This is achieved using specific enzymes.
- Visual cues in notes show a span of about $15$ nm to $25$ nm (illustrative measurement referring to Ab fragment flexibility).

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Blood grouping reagents (major categories): 1) High molecular weight polymers (antibody potentiators)
- These enhance agglutination by modifying the environment around red cells.
  2) Low ionic strength solutions (LISS)
- These increase antibody uptake by red cells.
  3) Proteolytic enzymes
- These alter the red cell membrane, making antigens more accessible or reducing repulsion.
  4) Antiglobulin reagents – Coombs reagents
- These are antibodies that react with human antibodies or complement components.
  5) Lectins
- These are plant-derived proteins that bind specifically to certain carbohydrate antigens.

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High molecular weight polymers (Ab potentiators):
- Common reagents: 22% bovine albumin, Polyvinylpyrrolidone (PVP), Dextran.
- Function: added to IgG antibody reagents to induce visible agglutination and strengthen Ab–Ag reactions.
  - They effectively concentrate antibodies near the red cell surface and promote cell-to-cell contact.
- Mechanism: reduce zeta potential by facilitating interactions between cells and providing temporary bridges; may cause rouleaux if used at high concentrations.
  - Rouleaux is a non-specific aggregation of red cells that resemble stacks of coins and can be mistaken for true agglutination. It's important to distinguish rouleaux from agglutination by microscopic examination or saline replacement techniques.

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Proteolytic enzymes and LISS (Low Ionic Strength Solutions):
- Proteolytic enzymes turn on or enhance IgG-mediated agglutination by removing negative charges and exposing hidden antigens.
  - Enzymes achieve this by cleaving specific glycoproteins and glycopeptides (e.g., sialic acid residues) from the red cell membrane, which reduces the zeta potential and makes some antigens more accessible.
- Enzymes discussed: papain (from Carica papaya), trypsin (from pig stomach), bromelin (pineapple), ficin (fig).
- How LISS works: increases the uptake of IgG by cells; particularly useful for detecting Rh antibodies.
  - By reducing the concentration of sodium chloride (ions) in the reaction mixture, LISS decreases the shielding effect of positive ions around red cells, allowing more IgG molecules to bind to antigens.

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Details on enzymes and practical use:
- Papain: common, cheap, effective, safe; derived from papaya.
  - Widely used due to its broad activity and cost-effectiveness.
- Trypsin: animal source (often pig); not routinely used in practice.
  - Less stable and can be harsher on red cells compared to papain or bromelin.
- Bromelin (bromelain): from pineapple; frequently used in automated systems.
  - Its consistent activity makes it suitable for standardized automated platforms.
- Ficin: from figs; not commonly used due to irritant properties (eye/skin).
  - Its handling requires more precautions due to its potent irritant nature.

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Problems with enzyme use:
- Enzymes can enhance some antigen–antibody reactions (notably Rh systems) but may yield false positives.
  - False positives can arise from enhancing cold autoantibodies or non-specific reactions.
- Some red cell antigens are destroyed by enzymes, leading to false negatives:
  - Duffy antigens: Fya, Fyb (e.g., Anti-Fya detection would require non-enzyme-treated cells).
  - MN antigens
  - Kell antigens: K, k (while Kell is primarily resistant to most enzymes, prolonged exposure or certain enzymes can affect it).
  - Awareness of these antigen destructions is critical for accurate antibody identification.

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Antiglobulin reagents (Coombs reagents):
- Function: Link sensitized red cells by reacting with IgG heavy chains and/or complement (C) attached to cells, enabling agglutination.
  - This step is essential because many clinically significant antibodies (e.g., most Rh antibodies) are IgG and do not directly agglutiante red cells. The antiglobulin reagent acts as a bridge.
- Reagents types:
  - Polyspecific Coombs reagents: anti-IgG (gamma chain) plus anti-C3 (complement).
  - Used for initial screening in both Direct Antiglobulin Test (DAT) and Indirect Antiglobulin Test (IAT).
  - Monospecific Coombs reagents: anti-IgG or anti-C (used for specialized testing).
  - Employed to determine if red cell sensitization is due to IgG, complement, or both, which helps in diagnosing specific immune conditions or transfusion reactions.

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Lectins (seed extracts that bind to certain red cell antigens):
- Not antibodies themselves but can cause agglutination by cross-linking relevant antigens.
  - Lectins are plant-derived proteins that have specific binding sites for carbohydrate structures on red cell surfaces.
- Examples and roles:
  - Dolichos biflorus: Lectin anti-A1; very strong and specific for A1 antigen; used to distinguish A1 vs A2 subgroups.
  - A1 red cells possess an $\alpha$ -N-acetylgalactosaminyltransferase that adds N-acetylgalactosamine to H antigen, while A2 cells have a less efficient enzyme. Dolichos biflorus specifically binds to the A1-specific carbohydrate structure.

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Additional lectins and their uses:
- Vicia faba (Vlex europaeus): Lectin anti-H; strongly agglutinates O cells, moderately with A2 cells, little to none with A, AB, or B.
  - This lectin binds to the H antigen, which is the precursor for A and B antigens. O cells have abundant H antigen, while A and B cells have converted most of their H antigen.
- Purpose: verify the presence of H antigen and distinguish blood types, notably identifying Bombay (Oh) phenotype vs normal O.
  - The Bombay (Oh) phenotype is a rare blood group where individuals lack the H antigen due to a genetic mutation, and therefore cannot form A or B antigens, despite having the genes for them. Their red cells are not agglutinated by anti-H lectin.
- Other lectins routinely used: Lectin anti-M and anti-N to verify M and N antigens on red cells.

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Gel Technology (gel-based testing) overview:
- A modern, user-friendly method in blood bank labs offering increased standardization and objectivity compared to traditional tube methods.
- Applicable tests: ABO and Rh typing, antibody screens, antibody identification (ID/panel tests), and Direct Antiglobulin Test (DAT).
  - Gel technology integrates multiple testing phases (e.g., incubation, centrifugation, reading) into a single, compact system.

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Gel Technology principle:
- Uses small plastic cards containing microtubes; each microtube contains gel particles with a reagent.
  - The gel often contains an antiglobulin reagent (e.g., anti-IgG) or specific anti-A, anti-B, etc., depending on the test.
- Procedure: patient sample added to each tube, incubated, centrifuged, and read for agglutination.
  - During centrifugation, non-agglutinated red cells pass through the gel to the bottom, while agglutinated red cells are trapped within or on top of the gel, forming distinct patterns.
- Reading interpretation:
  - No agglutination: red cells settle to the bottom of the tube ( $0$ reaction).
  - Strong agglutination: red cells remain at the top of the gel ( $4+$ reaction), forming a tight band.
  - Intermediate agglutination shows red cells dispersed throughout the gel ( $1+$ to $3+$ reactions), with the degree of dispersion indicating the strength of the reaction.

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References (selected):
- Harmening, D.M. (2018). Modern Blood Banking & Transfusion Practices (7th ed.).
- Overfield, Dowson, Hamer (2007). Transfusion Science (2nd Revised ed.).
- Dacie & Lewis. Practical Haematology (9th ed.).
- Bryant, N. Introduction to immunohaematology (3rd ed.).
- Normansell, D. Principles and Practice of Diagnostic Immunology.

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Contact and administrative footer:
- Higher Colleges of Technology, Abu Dhabi, UAE.
- 800 MyHCT (800 69428) • communication@hct.ac.ae • www.hct.ac.ae
- Thank you note and social/branding markers.