Adaptive Immunity

Antigen

Any molecule that can be recognized by the immune system and trigger an immune response

Major histocompatibility complex (MHC)

A set of surface proteins essential for the adaptive immune system to recognize foreign molecules

Antibody

Y-shaped protein secreted by plasma cells that specifically recognize, bind, and neutralize antigens

Complete antigen

A substance that contains both immunogenicity (ability to provoke and immune response) and reactivity

Hapten

A small molecule that, alone, cannot elicit an immune response but can do so when attached to a larger carrier molecule, becoming antigenic

Antigenic determinant/epitope

Small region of an antigen that an antibody or T cell receptor can bind

Foreign antigen

An antigen that originates outside the body, such as those found in pathogens (bacteria, viruses, fungi), which can trigger an immune response

Carbohydrate antigen

An antigen found on bacterial cell walls, cancer cells, and red blood cells (ABO blood groups)

Class II MHC protein

Molecules expressed in the surface of antigen-presenting cells (APCs), that present foreign antigens to T cells, initiating an immune response

Class I MHC protein

Molecules found on the surface of all nucleated cells that present endogenous antigens to T cells

Protein antigen

Complex 3D antigens found in viruses and worm parasites; most common and varied type of antigen

Chemical specificity

Precise interaction where an antibody recognizes and binds an epitope on an antigen

Self-antigen

An antigen that is a normal component of the body’s own cells or tissues; under normal conditions, the immune system does not attack these

Hemocytoblast

Stem cells in red bone marrow that develop into lymphocytes

Plasma cell

Cell that produces and release antibodies; they differentiate from B cells

Immunocompetence

Ability of immune cells to properly recognize self vs. non-self

Memory cell

Cell that remembers encountered pathogens and ramps up the immune response if it encounters the same pathogen again

Humoral response

Produces antibodies that circulate in the body’s humors (blood and lymph)

Central tolerance

Destruction of immature B cells that recognize and strongly bind to self-antigens in the bone marrow

Peripheral tolerance

Mature B cells are released from the bone marrow into circulation but are inactive since they have not been exposed to foreign antigens yet. After undergoing sensitization, if a T cell does not activate them, they will undergo apoptosis.

Sensitization

When a B cell first binds to an antigen

Activation

A sensitized B cell presents its antigen on MHC II proteins and receives a signal from a T cell, prompting it to become a plasma cell and release antibodies

Clonal selection

Only lymphocytes with a certain antigen specificity are expanded

Primary immune response

First exposure of the immune system to an antigen, causing a slow build-up of antigen and the creation of memory cells

Secondary immune response

Re-exposure of the immune system to an antigen, causing a fast and large build-up of antibodies; memory cells differentiate into plasma cells

Active immunity

The resistance to pathogens acquired during an adaptive immune response that results in the creation of antibodies

Passive immunity

The transfer of antibodies to an individual without requiring a person to mount their own active immune response

Constant segment

Segments of antibody chains that determine the class of it; does not vary much within the same class

Variable segment

Segments of antibody chains that contain a unique set of amino acids to bind an epitope

IgM

The first antibody to be produce in response to an infection, primarily mediating the immune response before IgG takes over

IgG

Most abundant type of antibody; protects against bacterial and viral infections in blood and bodily fluids by enhancing phagocytosis, neutralizing toxins, and triggering the complement system

IgE

Associated with inflammatory response and allergic reactions since it binds to allergens and triggers histamine release from mast cells and basophils

IgD

Functions mainly as an antigen receptor on B cells and sensitizes them, thereby playing a role in the initiation of immune responses

IgA

Found predominantly in mucous membranes and bodily secretions like saliva, mucus, teras, and breast milk; plays a critical role in mucosal immunity by neutralizing pathogens and toxins

Neutralization

Process of coating a pathogen with antibodies, making it physically impossible for the pathogen to bind to cellular receptors and enter/infect cells

Agglutination

Antibodies bind to cell-bound antigens on the surface of cells and clumps them together, making it difficult for them to move in body tissues

Precipitation

Antibodies bind to soluble antigens and form large, insoluble complexes