Immunology: Basic Principles and Applications in the Blood Bank

These flashcards cover the basic principles of immunology in transfusion medicine, including antigen and antibody characteristics, immune responses, complement pathways, and agglutination testing.

Antigens

Molecules that bind to antibodies or T-cell receptors.

Allogeneic antigens

Nonself antigens.

Autologous antigens

Self antigens.

Haptens

Partial antigens that require a carrier molecule to elicit an immune response (e.g., medications).

Antigenic determinants (epitopes)

Specific parts of an antigen that can elicit different types of antibodies.

Plasma cells

B lymphocytes that produce the majority of antibodies.

Memory B cells

B cells that respond rapidly to next exposure and transform into plasma cells; they do not require T-cell activation on subsequent exposure.

Antibodies

Glycoproteins made of $4$ polypeptide chains (2 heavy and 2 light chains) joined by disulfide bonds.

Variable region

The region of an antibody made of light and heavy chains that binds the antigen.

Constant region

The heavy chains of an antibody that determine the antibody class (IgG, IgA, IgM, IgD, or IgE).

IgG

An antibody with Gamma ($\text{y}$) heavy chains, a molecular weight of $150,000\text{ D}$, and a valence of $2$; it crosses the placenta and is typically clinically significant.

IgM

A pentameric antibody with Mu ($\text{p}$) heavy chains, a molecular weight of $900,000\text{ D}$, and a valence of $10$; it includes a J-chain and is very efficient at activating the classical complement pathway.

Primary Immune Response

The response elicited on first exposure to an antigen with a lag phase of $5$ to $10$ days; IgM is produced first, followed by IgG.

Secondary Immune Response

The response elicited on second exposure to the same antigen occurring within $1$ to $3$ days; it produces mostly IgG with higher antibody affinity.

Immune complex

The structure formed when an antigen and antibody combine, held together by noncovalent forces.

Binding affinity

The strength of the interaction between the antigen's epitope and the antibody at a singular binding site.

Avidity

The total antibody-binding strength at every binding site, determined by affinity, valency, and structure.

Membrane attack complex (C5b-C9)

The final phase of complement activation that causes cell lysis.

Classical pathway

A complement activation pathway triggered by antibodies.

Alternative pathway

A complement activation pathway triggered by foreign cell surface constituents like bacteria.

Opsonization

An immunological by-product of complement that enhances phagocytosis.

Sensitization

The first step of agglutination where antibody binds to an antigen, but no visible agglutination occurs.

Lattice formation

The second step of agglutination where antibody-coated cells cross-link with the help of AHG to form visible agglutination.

Prozone

A state of antibody excess that produces small complexes and causes false negative agglutination reactions.

Postzone

A state of antigen excess that produces small complexes and causes false negative agglutination reactions.

Zone of Equivalence

The concentration range where Ag and Ab form large complexes capable of causing agglutination; requires a cell suspension between $2\%$ to $$5\%Initial exposure to an antigen is slower and elicits the formation of IgM, followed by IgG antibodies and memory B cells. The lag time is longer, and antibody affinity is lower. The second response to the same antigen is more robust and causes much greater production of IgG antibodies and less IgM antibody secretion. The lag time is shorter, and antibody affinity is higher.

Hemolysis

An indicator of an Ag-Ab reaction caused by complement activation, characterized by a pink to red supernatant and a missing or smaller RBC button.

Reagent RBCs

Commercially prepared red blood cells used as a known source of antigen in routine testing.

Reagent antisera

Commercially prepared solutions used as a known source of antibody in routine testing.

Clinically Significant Antibodies

Antibodies capable of decreasing red cell survival, leading to transfusion reactions or Hemolytic disease of the fetus and newborn (HDFN).