2. Basic Principles of Immunology in Transfusion Science

Flashcards covering basic principles of immunology, antigen-antibody binding factors, agglutination stages, potentiators, gel/microplate/solid-phase methods, and clinical hemolysis in transfusion science.

What are the two main stages of red blood cell agglutination?

The two stages are Sensitization (the physical attachment of antibody to the antigen on the red cell membrane without visible agglutination) and Lattice Formation (the formation of cross-linkages between adjacent antibody-coated red cells resulting in visible aggregates).

How do temperature requirements differ for IgM and IgG antibodies during the sensitization stage?

IgM antibodies (cold antibodies) react and agglutinate optimally at room temperature or colder ($\le 22\,^{\circ}\text{C}$), whereas IgG antibodies (warm antibodies) require incubation at $37\,^{\circ}\text{C}$.

What is the optimal pH for antigen-antibody binding in immunohematology?

The optimal pH is approximately $7.0$, which falls within the physiologic pH range of $7.35\text{ to }7.45$. Reactions do not occur outside the pH range of $6.5\text{ to }7.5$.

What is Zeta Potential, and what causes it?

Zeta potential refers to the difference in electrostatic charges between the surface of red blood cells and the cations ($\text{Na}^+$) in the surrounding saline medium. It is caused by sialic acid on the red cell membrane creating a net negative charge, which attracts a cationic cloud that repels other red cells.

What is illustrated by this precipitation curve diagram in antigen-antibody testing?

The diagram illustrates the three concentration zones: Prozone (antibody excess, leading to false negatives), Zone of Equivalence (optimal antigen and antibody ratio producing maximum agglutination), and Postzone (antigen excess, leading to false negatives).

What red cell suspension concentration is recommended for standard tube testing versus gel methodology?

Standard tube testing requires a $3\%\text{ to }5\%$ red cell suspension in saline, whereas gel methodology requires a $0.8\%$ red cell suspension.

What are the three classes of Major Histocompatibility Complex (MHC) antigens and their cellular distribution?

Class I antigens are found on platelets, leukocytes, and most nucleated cells; Class II antigens are found on antigen-presenting cells (macrophages, B cells, and dendritic cells); Class III antigens consist of complement proteins.

What is Graft vs Host Disease (GVHD)?

GVHD is a condition occurring in bone marrow transplant patients where the transplanted donor tissue/cells (the graft) recognize the recipient (the host) as foreign and mount an immune attack against the host.

What causes platelet refractoriness in patients receiving multiple platelet transfusions?

Platelet refractoriness occurs when patients develop antibodies directed against Human Leukocyte Antigens (HLA) or platelet-specific antigens due to multiple transfusions, resulting in a failure of their platelet count to rise.

What key applications of HLA testing are listed in clinical practice?

Applications include paternity testing, organ/tissue transplantation, bone marrow transplantation, progenitor cell transplantation, platelet matching, and establishing disease associations.

What four non-covalent attractive forces hold antigen-antibody complexes together?

The four forces are electrostatic forces, hydrogen bonding, hydrophobic bonding, and Van der Waals forces. Covalent bonding does NOT influence antigen-antibody binding.

What is the difference between antibody affinity and avidity?

Affinity refers to the binding strength between a single antibody-binding site and a single epitope of an antigen. Avidity refers to the overall total strength of reactions between multiple epitopes and antibodies.

How does Low Ionic Strength Solution (LISS) function as an antibody potentiator?

LISS reduces the ionic environment ($\text{Na}^+$ and $\text{Cl}^-$ ions) surrounding red cells, decreasing charge interference. This increases antibody uptake during sensitization and reduces incubation time to $5\text{ to }15\,\text{minutes}$ (commonly $10\,\text{minutes}$).

What is the minimum ionic strength limit for LISS solutions and why?

The ionic strength of LISS must be no less than $30\,\text{mmol/L}$ (or $0.03\,\text{mol/L}$) because complement can bind non-specifically to red blood cells in solutions with lower ionic strength.

What are the specific operational requirements and restrictions when using Polyethylene Glycol (PEG)?

PEG concentrates antibodies by removing water molecules. It can only be used in Indirect Antiglobulin Test (IAT) methods, requires a monospecific anti-IgG reagent, and tubes must NOT be centrifuged or read microscopically prior to washing.

Which four proteolytic enzymes are commonly used as potentiators in blood banking?

The four proteolytic enzymes are Papain, Trypsin, Ficin, and Bromelin. They function by destroying protein structures and releasing sialic acid from the red cell surface to reduce negative charge.

What red cell antigen system is best detected using enzyme testing methods?

IgG antibodies in the Rh system are best detected by enzyme methods.

Why is bovine 22% albumin considered a poor enhancement method compared to others?

Albumin is relatively insensitive for both IgG and IgM antibodies, adds cost to testing, enhances clinically insignificant cold antibodies, and generally only reacts well with Rh antibodies rather than Duffy or Kidd antibodies.

What specimen tube is preferred for blood bank testing using gel methodology?

$K_2\text{EDTA}$ anticoagulated plasma collected in a pink-stoppered tube is the preferred specimen choice.

What range of reaction grades is demonstrated in this gel technology card?

The card shows reaction strengths graded as $0$ (negative, unagglutinated button at the bottom), $1+$, $2+$, $3+$, $4+$ (strong positive, band of agglutinates at the top), and MF (mixed field agglutination).

How are positive and negative reactions defined in microplate testing?

A positive reaction is characterized by a concentrated button of red blood cells at the bottom of the well. A negative reaction forms a smooth suspension of red blood cells or a streaming pattern when the plate is held at an angle.

What are the three classifications used for grading hemolysis in serologic testing?

Strong Hemolysis ($\text{Hs}$: clear, red supernatant with few or no intact RBCs), Moderate Hemolysis ($\text{H}$: clear, pink supernatant with some intact RBCs), and Trace Hemolysis ($\text{Hw}$: clear, pink-tinged supernatant with many intact RBCs).

How are positive and negative results interpreted in Solid Phase Red Cell Adherence (SPRCA) testing?

A negative result forms a tight red blood cell button on the bottom of the microplate well. A positive result shows attachment and adherence of indicator red blood cells across the sides and bottom of the well.

What clinical signs and laboratory findings indicate acute intravascular hemolysis?

Signs include a sudden drop in blood pressure (due to anaphylatoxins $C5a$ and $C3a$), hemoglobinuria, hemoglobinemia, decreased haptoglobin levels, and a lack of rise in hematocrit following blood transfusion.

How does Zeta Potential affect the bridging capability of IgG versus IgM antibodies?

IgG molecules measure $14\,\text{nm}$ and cannot bridge the $25\,\text{nm}\text{ to }35\,\text{nm}$ distance created by Zeta Potential between red cells in saline. Pentameric IgM molecules are large enough to span this distance and produce direct agglutination without potentiators.