Key Terms

active immunity

immunity developed from an individual’s own immune system

acute inflammation

inflammation occurring for a limited time period; rapidly developing

adaptive immune response

relatively slow but very specific and effective immune response controlled by lymphocytes

afferent lymphatic vessels

lead into a lymph node

antibody

antigen-specific protein secreted by plasma cells; immunoglobulin

antigen

molecule recognized by the receptors of B and T lymphocytes

antigen presentation

binding of processed antigen to the protein-binding cleft of a major histocompatibility complex molecule

antigen processing

internalization and digestion of antigen in an antigen-presenting cell

antigen receptor

two-chain receptor by which lymphocytes recognize antigen

antigenic determinant

(also, epitope) one of the chemical groups recognized by a single type of lymphocyte antigen receptor

B cells

lymphocytes that act by differentiating into an antibody-secreting plasma cell

barrier defenses

antipathogen defenses deriving from a barrier that physically prevents pathogens from entering the body to establish an infection

bone marrow

tissue found inside bones; the site of all blood cell differentiation and maturation of B lymphocytes

bronchus-associated lymphoid tissue (BALT)

lymphoid nodule associated with the respiratory tract

central tolerance

B cell tolerance induced in immature B cells of the bone marrow

chemokine

soluble, long-range, cell-to-cell communication molecule

chronic inflammation

inflammation occurring for long periods of time

chyle

lipid-rich lymph inside the lymphatic capillaries of the small intestine

cisterna chyli

bag-like vessel that forms the beginning of the thoracic duct

class switching

ability of B cells to change the class of antibody they produce without altering the specificity for antigen

clonal anergy

process whereby B cells that react to soluble antigens in bone marrow are made nonfunctional

clonal deletion

removal of self-reactive B cells by inducing apoptosis

clonal expansion

growth of a clone of selected lymphocytes

clonal selection

stimulating growth of lymphocytes that have specific receptors

clone

group of lymphocytes sharing the same antigen receptor

complement

enzymatic cascade of constitutive blood proteins that have antipathogen effects, including the direct killing of bacteria

constant region domain

part of a lymphocyte antigen receptor that does not vary much between different receptor types

cytokine

soluble, short-range, cell-to-cell communication molecule

cytotoxic T cells (Tc)

T lymphocytes with the ability to induce apoptosis in target cells

delayed hypersensitivity

(type IV) T cell-mediated immune response against pathogens infiltrating interstitial tissues, causing cellular infiltrate

early induced immune response

includes antimicrobial proteins stimulated during the first several days of an infection

effector T cells

immune cells with a direct, adverse effect on a pathogen

efferent lymphatic vessels

lead out of a lymph node

erythroblastosis fetalis

disease of Rh factor-positive newborns in Rh-negative mothers with multiple Rh-positive children; resulting from the action of maternal antibodies against fetal blood

fas ligand

molecule expressed on cytotoxic T cells and NK cells that binds to the fas molecule on a target cell and induces it do undergo apoptosis

Fc region

in an antibody molecule, the site where the two termini of the heavy chains come together; many cells have receptors for this portion of the antibody, adding functionality to these molecules

germinal centers

clusters of rapidly proliferating B cells found in secondary lymphoid tissues

graft-versus-host disease

in bone marrow transplants; occurs when the transplanted cells mount an immune response against the recipient

granzyme

apoptosis-inducing substance contained in granules of NK cells and cytotoxic T cells

heavy chain

larger protein chain of an antibody

helper T cells (Th)

T cells that secrete cytokines to enhance other immune responses, involved in activation of both B and T cell lymphocytes

high endothelial venules

vessels containing unique endothelial cells specialized to allow migration of lymphocytes from the blood to the lymph node

histamine

vasoactive mediator in granules of mast cells and is the primary cause of allergies and anaphylactic shock

IgA

antibody whose dimer is secreted by exocrine glands, is especially effective against digestive and respiratory pathogens, and can pass immunity to an infant through breastfeeding

IgD

class of antibody whose only known function is as a receptor on naive B cells; important in B cell activation

IgE

antibody that binds to mast cells and causes antigen-specific degranulation during an allergic response

IgG

main blood antibody of late primary and early secondary responses; passed from carrier to unborn child via placenta

IgM

antibody whose monomer is a surface receptor of naive B cells; the pentamer is the first antibody made blood plasma during primary responses

immediate hypersensitivity

(type I) IgE-mediated mast cell degranulation caused by crosslinking of surface IgE by antigen

immune system

series of barriers, cells, and soluble mediators that combine to response to infections of the body with pathogenic organisms

immunoglobulin

protein antibody; occurs as one of five main classes

immunological memory

ability of the adaptive immune response to mount a stronger and faster immune response upon re-exposure to a pathogen

inflammation

basic innate immune response characterized by heat, redness, pain, and swelling

innate immune response

rapid but relatively nonspecific immune response

interferons

early induced proteins made in virally infected cells that cause nearby cells to make antiviral proteins

light chain

small protein chain of an antibody

lymph

fluid contained within the lymphatic system

lymph node

one of the bean-shaped organs found associated with the lymphatic vessels

lymphatic capillaries

smallest of the lymphatic vessels and the origin of lymph flow

lymphatic system

network of lymphatic vessels, lymph nodes, and ducts that carries lymph from the tissues and back to the bloodstream.

lymphatic trunks

large lymphatics that collect lymph from smaller lymphatic vessels and empties into the blood via lymphatic ducts

lymphocytes

white blood cells characterized by a large nucleus and small rim of cytoplasm

lymphoid nodules

unencapsulated patches of lymphoid tissue found throughout the body

macrophage

ameboid phagocyte found in several tissues throughout the body

macrophage oxidative metabolism

metabolism turned on in macrophages by T cell signals that help destroy intracellular bacteria

major histocompatibility complex (MHC)

gene cluster whose proteins present antigens to T cells

mast cell

cell found in the skin and the lining of body cells that contains cytoplasmic granules with vasoactive mediators such as histamine

memory T cells

long-lived immune cell reserved for future exposure to a pathogen

MHC class I

found on most cells of the body, it binds to the CD8 molecule on T cells

MHC class II

found on macrophages, dendritic cells, and B cells, it binds to CD4 molecules on T cells

MHC polygeny

multiple MHC genes and their proteins found in body cells

MHC polymorphism

multiple alleles for each individual MHC locus

monocyte

precursor to macrophages and dendritic cells seen in the blood

mucosa-associated lymphoid tissue (MALT)

lymphoid nodule associated with the mucosa

naïve lymphocyte

mature B or T cell that has not yet encountered antigen for the first time

natural killer cell (NK)

cytotoxic lymphocyte of innate immune response

negative selection

selection against thymocytes in the thymus that react with self-antigen

neutralization

inactivation of a virus by the binding of specific antibody

neutrophil

phagocytic white blood cell recruited from the bloodstream to the site of infection via the bloodstream

opsonization

enhancement of phagocytosis by the binding of antibody or antimicrobial protein

passive immunity

transfer of immunity to a pathogen to an individual that lacks immunity to this pathogen usually by the injection of antibodies

pattern recognition receptor (PRR)

leukocyte receptor that binds to specific cell wall components of different bacterial species

perforin

molecule in NK cell and cytotoxic T cell granules that form pores in the membrane of a target cell

peripheral tolerance

mature B cell made tolerant by lack of T cell help

phagocytosis

movement of material from the outside to the inside of the cells via vesicles made from invaginations of the plasma membrane

plasma cell

differentiated B cell that is actively secreting antibody

polyclonal response

response by multiple clones to a complex antigen with many determinants

positive selection

selection of thymocytes within the thymus that interact with self, but not non-self, MHC molecules

primary adaptive response

immune system’s response to the first exposure to a pathogen

primary lymphoid organ

site where lymphocytes mature and proliferate; red bone marrow and thymus gland

psychoneuroimmunology

study of the connections between the immune, nervous, and endocrine systems

regulatory T cells (Treg)

(also, suppressor T cells) class of CD4 T cells that regulates other T cell responses

right lymphatic duct

drains lymph fluid from the upper right side of body into the right subclavian vein

secondary adaptive response

immune response observed upon re-exposure to a pathogen, which is stronger and faster than a primary response

secondary lymphoid organs

sites where lymphocytes mount adaptive immune responses; examples include lymph nodes and spleen

sensitization

first exposure to an antigen

seroconversion

clearance of pathogen in the serum and the simultaneous rise of serum antibody

severe combined immunodeficiency disease (SCID)

genetic mutation that affects both T cell and B cell arms of the immune response

spleen

secondary lymphoid organ that filters pathogens from the blood (white pulp) and removes degenerating or damaged blood cells (red pulp)

T cell

lymphocyte that acts by secreting molecules that regulate the immune system or by causing the destruction of foreign cells, viruses, and cancer cells

T cell tolerance

process during T cell differentiation where most T cells that recognize antigens from one’s own body are destroyed

T cell-dependent antigen

antigen that binds to B cells, which requires signals from T cells to make antibody

T cell-independent antigen

binds to B cells, which do not require signals from T cells to make antibody

Th1 cells

cells that secrete cytokines that enhance the activity of macrophages and other cells

Th2 cells

cells that secrete cytokines that induce B cells to differentiate into antibody-secreting plasma cells

thoracic duct

large duct that drains lymph from the lower limbs, left thorax, left upper limb, and the left side of the head

thymocyte

immature T cell found in the thymus

thymus

primary lymphoid organ; where T lymphocytes proliferate and mature

tissue typing

typing of MHC molecules between a recipient and donor for use in a potential transplantation procedure

tonsils

lymphoid nodules associated with the nasopharynx

type I hypersensitivity

immediate response mediated by mast cell degranulation caused by the crosslinking of the antigen-specific IgE molecules on the mast cell surface

type II hypersensitivity

cell damage caused by the binding of antibody and the activation of complement, usually against red blood cells

type III hypersensitivity

damage to tissues caused by the deposition of antibody-antigen (immune) complexes followed by the activation of complement

variable region domain

part of a lymphocyte antigen receptor that varies considerably between different receptor types