Chapter 15: The Adaptive Immune Response

Comprehensive vocabulary flashcards covering the key terms, lymphoid organs, antibody functions and classes, and cellular mechanisms of the adaptive immune response from Chapter 15.

Humoral immunity

An adaptive immune response that protects against extracellular antigens (such as bacteria, toxins, and viruses in blood or tissue fluids) using antibodies produced by B cells.

Cell-mediated immunity (CMI)

An adaptive immune response that protects against antigens inside host cells (such as virus-infected and cancer cells) using T cells to coordinate responses or destroy infected cells.

Lymphatic vessels

Vessels that carry lymph containing antigens from body tissues to bring antigens into contact with lymphocytes.

Primary lymphoid organs

The organs where lymphocytes develop and mature, specifically the bone marrow and thymus.

Bone marrow

A primary lymphoid organ that produces blood cells and serves as the site where B cells mature.

Thymus

A primary lymphoid organ to which T cells migrate in order to mature.

Secondary lymphoid organs

Sites where mature lymphocytes gather, encounter antigens, and begin immune responses.

Lymph nodes

Secondary lymphoid organs that help lymphocytes come into contact with antigens carried in lymph.

Spleen

A secondary lymphoid organ where immune cells encounter antigens.

Tonsils

Secondary lymphoid structures that help protect against pathogens entering through the mouth and nose.

Peyer's patches

Secondary lymphoid structures located in the intestines that sample intestinal contents.

MALT

Mucosa-associated lymphoid tissue that protects mucous membranes from microbial invasion.

SALT

Skin-associated lymphoid tissue located under the skin.

Antigen

A molecule that reacts specifically with an antibody, B-cell receptor, or T-cell receptor.

T-dependent antigen

An antigen that requires help from a helper T cell to activate a B cell.

T-independent antigen

An antigen that can activate B cells without helper T-cell assistance, such as lipopolysaccharide (LPS) and molecules with repeating subunits.

Immunogenic

The property of an antigen that makes it capable of triggering an immune response.

Epitope

A specific region or part of an antigen that the immune system recognizes and binds to; also called an antigenic determinant.

Neutralization

A protective outcome of antibody binding where antibodies prevent toxins and viruses from attaching to and entering cells.

Opsonization

A protective outcome where antibodies coat pathogens, making it easier for phagocytes to recognize and engulf them.

Complement system activation

A protective outcome where antibody binding activates the classical complement pathway to help destroy pathogens.

Immobilization and prevention of adherence

A protective outcome where antibodies bind to bacterial flagella or pili, preventing bacteria from moving or attaching to cells.

Cross-linking

A protective outcome where antibodies use their two binding arms to connect separate antigens together.

Antibody-dependent cellular cytotoxicity (ADCC)

A protective outcome where antibodies mark infected or abnormal cells so natural killer (NK) cells can destroy them.

IgM

The first antibody class produced during the primary immune response, the principal class produced in response to T-independent antigens, and an activator of the complement system.

IgG

The most abundant antibody class in blood and tissue fluids that provides long-term protection and can cross the placenta to protect a developing fetus.

IgA

The antibody class that protects mucous membranes and is found in mucus, tears, saliva, and breast milk to protect breast-fed infants.

IgD

The antibody class involved in the development and maturation of the antibody response, whose function in blood is not well understood.

IgE

The antibody class involved in allergic reactions and responses to parasites, which binds to mast cells and basophils.

Primary response

The adaptive immune response that occurs the first time the body encounters an antigen, taking about $10\text{--}14\text{ days}$ for significant antibody production.

Secondary response

A faster and more effective adaptive immune response that uses memory cells from previous exposure to eliminate recognized pathogens before they can cause harm.

Dendritic cells

Cells responsible for activating helper T cells and cytotoxic T cells by presenting antigens to T-cell receptors (TCRs).

Helper T cells (TH)

T cells that direct and coordinate the immune response, activate B cells and macrophages, and produce cytokines.

Cytotoxic T cells (TC)

T cells that recognize intracellular antigens presented by the body's own cells and destroy infected or abnormal host cells by causing apoptosis.

Natural killer (NK) cells

Innate immune cells that destroy stressed cells missing MHC class I molecules and kill antibody-bound abnormal or infected cells via ADCC.

Apoptosis

Programmed cell death.

Cytokines

Chemical signals that help immune cells communicate and coordinate responses.

Plasma cells

Activated B cells that differentiate and produce antibodies.

Memory cells

Long-lived lymphocytes formed during an immune response that respond faster during future exposures to the same antigen.