Immunohematology: Immunology and Blood Banking

Vocabulary flashcards for MLT 2525 Immunohematology Unit II Part II covering fundamental immunology concepts, immune cell types, antibodies, antigen-antibody reactions, complement system, and routine blood bank testing procedures.

Immunity

The process by which a host organism protects itself from attacks by both external and internal agents.

Natural Immunity

A non-specific defense mechanism, also known as innate immunity, consisting of cells like neutrophils, tissue basophils, and macrophages, along with soluble substances such as complement, lysozyme, and interferon.

Interferon

A family of proteins which can block the replication of viruses in cells.

Acquired Immunity

A specific immune mechanism seen only in vertebrates that supplements innate immunity, is acquired by contact with a specific foreign substance, and possesses memory that improves response with each successive exposure.

Humoral Immunity

A branch of the immune system that relies upon the production of antibodies by B cells and plasma cells.

Cell Mediated Immunity

A branch of the immune system involving interactions of helper and cytotoxic T cells with target cells, functioning in delayed hypersensitivity, graft-v-host reactions, and allograft rejection.

B Lymphocytes

Immune cells that mature in the bone marrow and function primarily to produce immunoglobulins.

Plasma Cells

Non-motile, mature end-stage forms of B cells that each produce only one type of immunoglobulin.

Cytokines

Soluble substances produced by a subpopulation of T cells that function in growth promotion, differentiation, chemotaxis, and cell stimulation.

Helper T Cells

A subpopulation of T cells carrying the CD4 membrane marker that help in antibody formation.

Regulatory T Cells

A subpopulation of T cells carrying the CD4 membrane marker that inhibit the immune response (formerly called suppressor T cells).

Cytotoxic T Cells

A subpopulation of T cells carrying the CD8 membrane marker that destroy virus-infected cells and tumor cells.

Natural Killer (NK) Cells

Lymphocytes that provide protection against viruses and abnormal cells by producing perforins to cause lysis, without needing prior stimulation or recognition.

Antigen Presenting Cells (APC)

Professional immune cells (macrophages, dendritic cells, and B cells) that sample extracellular and intracellular environments to process and present antigens to T cells.

Allogeneic Antigens

Nonself antigens.

Autologous Antigens

Self antigens.

Haptens

Partial antigens that require a carrier molecule to elicit an immune response.

Epitope

The part of a complex antigen with which an antibody reacts specifically, also known as an antigenic determinant.

Antibodies

Glycoproteins made of 4 polypeptide chains (2 heavy chains and 2 light chains) joined by disulfide bonds, featuring a constant region determining class and a variable region binding antigen.

IgM Molecule Structure

A pentameric immunoglobulin structure containing a J chain (joining chain), 10 antigen-binding sites, and heavy chains composed of mu ($\mu$) chains with a high molecular weight of 900,000 D.

Primary Response

The immune response elicited on first exposure to an antigen, characterized by a lag phase of 5 to 10 days, initial production of IgM followed by IgG, and lower overall antibody levels.

Secondary Response

The immune response elicited on second exposure to the same antigen, occurring within 1 to 3 days, producing mostly IgG antibodies with high and sustained levels.

Alloantibodies

Antibodies produced after exposure to genetically different or non-self antigens of the same species.

Naturally Occurring Antibodies

RBC antibodies present without prior red cell exposure or pregnancy, mostly IgM cold agglutinins that react best at room temperature or lower.

Immune Antibodies

RBC antibodies found in the serum of transfused or previously pregnant individuals, mostly IgG, reacting best at 37\,\text{^\circ C} and Coombs (AHG) phases.

Autoantibodies

Antibodies produced in response to self antigens.

Affinity

The strength of a single antigen-antibody bond produced by the sum of attractive and repulsive forces.

Avidity

The functional ability of serum antibody to bind to antigen.

Specificity

An important characteristic of an antiserum or antibody related to its relative avidity for antigen.

Complement System

A group of proteins that enhance immunologic processes and form a membrane attack complex (MAC) to lyse target cells.

Classical Pathway

A complement activation pathway triggered by antigen-antibody complexes (Ag-Ab complexes).

Alternative Pathway

A complement activation pathway triggered by foreign cell surface constituents such as pathogens or injured tissue.

Agglutination

In vitro antigen-antibody reactions that result in visible clumping.

Sensitization

The first step of agglutination in which antibody binds to antigen without visible agglutination.

Lattice Formation

The second step of agglutination in which antibody-coated cells cross-link to form visible agglutination.

Zeta Potential

The distance between red blood cells caused by charged ions, which affects lattice formation.

Prozone

The reaction zone characterized by antibody excess, resulting in small complexes and lack of visible agglutination.

Zone of Equivalence

The reaction zone where antigen and antibody concentrations are optimal, forming large complexes and maximum agglutination.

Postzone

The reaction zone characterized by antigen excess, resulting in small complexes and lack of visible agglutination.

Prozone, Equivalence, Postzone Curve

A representation showing how agglutination peaks at the zone of equivalence with large complexes and drops off in prozone (antibody excess) and postzone (antigen excess).

Forward Grouping

An ABO/D typing procedure using commercial anti-A, anti-B, and anti-D to detect A, B, and D antigens on patient red cells.

Reverse Grouping

An ABO serum testing procedure using A1 and B reverse grouping cells to detect ABO antibodies in patient serum or plasma.

Antibody Screen

A testing procedure using screening cells to detect antibodies in patient serum or plasma with specificity to red cell antigens.

Crossmatch

A laboratory procedure to determine serologic compatibility between donor red cells and patient serum or plasma before transfusion.

Anti-A1

A split component of Anti-A antibody that reacts specifically with A1 cells but not A2 cells.

Anti-H

A weak, cold-reacting antibody found in the serum of group A1 and A1B individuals, tested with U. europaeus reagent to assess H antigen presence.

ABO Antigen Biosynthesis Pathway

The pathway where L-fucosyl transferase converts a Type-2 precursor chain into the H structure (sugar L-fucose), which is converted to A antigen by N-acetyl galactosaminyl transferase or B antigen by D-galactosyl transferase.