DEFINITION OF TERMS

Acquired Immunodeficiency Syndrome (AIDS)

A life-threatening disease caused by a virus and characterized by the breakdown of the body's immune defenses.

AGAMMAGLOBULINEMIA

An almost total lack of immunoglobulins, or antibodies

ALLERGEN

Any substance that causes an allergy

ALLERGY

An inappropriate and harmful response of the immune system to normally harmless substances.

ANAPHYLACTIC SHOCK

A life-threatening allergic reaction characterized by a swelling of body tissues including the throat, difficulty in breathing, and a sudden fall in blood pressure.

ANTIBODY

A soluble protein molecule produced and secreted by B cells in response to an antigen, which is capable of binding to that specific antigen.

ANTIGEN

Any substance that, when introduced into the body, is recognized by the immune system.

ANTIGEN-PRESENTING CELLS

B cells, cells of the monocyte lineage (including macrophages as well as dendritic cells), and various other body cells that "present" antigen in a form that T cells can recognize.

ANTINUCLEAR ANTIBODY (ANA)

An autoantibody directed against a substance in the cell's nucleus.

ANTISERUM

Serum that contains antibodies.

ANTITOXINS

Antibodies that interlock with and inactivate toxins produced by certain bacteria.

APPENDIX

Lymphoid organ in the intestine

ATTENUATED

Weakened; no longer infectious

AUTOANTIBODY

An antibody that reacts against a person's own

tissue.

AUTOIMMUNE DISEASE

A disease that results when the immune system mistakenly attacks the body's own tissues.

AUTOIMMUNE DISEASE

Rheumatoid arthritis and systemic lupus erythematosus are autoimmune diseases.

B CELLS

Small white blood cells crucial to the immune defenses. Also known as B lymphocytes, they are derived from bone marrow and develop into plasma cells that are the source of antibodies.

BONE MARROW

Soft tissue located in the cavities of the bones.

The bone marrow is the source of all blood cells.

COMPLEMENT

A complex series of blood proteins whose action

"complements" the work of antibodies.

Complement destroys bacteria, produces

inflammation, and regulates immune reactions.

COMPLEMENT CASCADE

A precise sequence of events usually triggered by an antigen-antibody complex, in which each component of the complement system is activated in turn.

CONSTANT REGION

That part of an antibody's structure that is characteristic of each antibody class.

CO-STIMULATION

The delivery of a second signal from an

antigen-presenting cell to a T cell.

The second signal rescues the activated T cell from

energy, allowing it to produce the lymphokines

necessary for the growth of additional T cells.

CYTOKINES

Powerful chemical substances secreted by cells

Cytokines include lymphokines produced by lymphocytes and monokines produced by monocytes and macrophages.

CYTOTOXIC T CELLS

A subset of T lymphocytes that can kill body cells infected by viruses or transformed by cancer.

DENDRITIC CELLS

White blood cells found in the spleen and other

lymphoid organs.

Dendritic cells typically use threadlike tentacles to

enmesh antigen, which they present to T cells.

EPITOPE

A unique shape or marker carried on an antigen's surface, which triggers a corresponding antibody response.

GRAFT-VERSUS-HOST DISEASE (GVHD)

A life-threatening reaction in which transplanted immunocompetent cells attack the tissues of the recipient.

HELPER T CELLS

A subset of T cells that typically carry the T4 marker and are essential for turning on antibody production, activating cytotoxic T cells, and initiating many other immune responses.

HEMATOPOIESIS

The formation and development of blood cells, usually takes place in the bone marrow.

HISTOCOMPATIBILITY TESTING

A method of matching the self-antigens (HLA) on the tissues of a transplant donor with those of the recipient. The closer the match, the better the chance that the transplant will take.

HUMAN LEUKOCYTE ANTIGENS (HLA)

Protein in markers of self used in histocompatibility testing. Some HLA types also correlate with certain autoimmune diseases.

HYBRIDOMA

A hybrid cell created by fusing a B lymphocyte with a long-lived neoplastic plasma cell, or a T lymphocyte with a lymphoma cell.

A B-cell hybridoma secretes a single specific antibody.

B lymphocyte + neoplastic plasma cell

T lymphocyte + lymphoma cell

HYPOGAMMAGLOBULINEMIA

Abnormally low levels of immunoglobulins.

IDIOTYPES

The unique and characteristic parts of an antibody’s variable region, which can themselves serve as antigens.

IMMUNE COMPLEX

A cluster of interlocking antigens and antibodies.

IMMUNE RESPONSE

The reactions of the immune system to foreign substances.

IMMUNOASSAY

A test using antibodies to identify and quantify substances. Often the antibody is linked to a marker such as a fluorescent molecule, a radioactive molecule, or an enzyme.

IMMUNOCOMPETENT

Capable of developing an immune response.

IMMUNOGLOBULINS

A family of large protein molecules, also known as antibodies.

IMMUNOSUPPRESSION

Reduction of the immune responses, for instance by giving drugs to prevent transplant rejection.

IMMUNOTOXIN

A monoclonal antibody linked to a natural toxin, a toxic drug, or a radioactive substance.

INFLAMMATORY RESPONSE

Redness, warmth, swelling, pain, and loss of function produced in response to infection, as the result of increased flood flow and an influx of immune cells and secretions.

INTERLEUKINS

A major group of lymphokines and monokines

LANGERHANS CELLS

Dendritic cells in the skin that pick up antigen and transport it to lymph nodes.

LYMPH

A transparent, slightly yellow fluid that carries lymphocytes, bathes the body tissues, and drains into the lymphatic vessels.

LYMPHATIC VESSELS

A bodywide network of channels, similar to the blood vessels, which transport lymph to the immune organs and into the bloodstream.

LYMPH NODES

Small bean-shaped organs of the immune system, distributed widely throughout the body and linked by lymphatic vessels.

Lymph nodes are garrisons of B, T, and other immune cells.

LYMPHOID ORGANS

The organs of the immune system, where lymphocytes develop and congregate. They include the bone marrow, thymus, lymph nodes, spleen, and various other clusters of lymphoid tissue. The blood vessels and lymphatic vessels can also be considered lymphoid organs.

LYMPHOKINES

Powerful chemical substances secreted by lymphocytes.

These soluble molecules help direct and regulate the immune responses.

MACROPHAGE

A large and versatile immune cell that acts as a microbe-devouring phagocyte, an antigen-presenting cell, and an important source of immune secretions.

MAJOR HISTOCOMPATIBILITY COMPLEX (MHC)

A group of genes that controls several aspects of the immune response. MHC genes code for self-markers on all body cells.

MAST CELL

A granule-containing cell found in tissue. The contents of mast cells, along with those of basophils, are responsible for the symptoms of allergy.

MONOCLONAL ANTIBODIES

Antibodies produced by a single cell or its identical progeny, specific for a given antigen.

As a tool for binding to specific protein molecules, monoclonal antibodies are invaluable in research, medicine, and industry.

MONOKINES

Powerful chemical substances secreted by monocytes and macrophages.

These soluble molecules help direct and regulate the immune responses.

NATURAL KILLER (NK) CELLS

Large granule-filled lymphocytes that take on tumor cells and infected body cells.

They are known as "natural" killers because they attack without first having to recognize specific antigens.

NUCLEIC ACIDS

Large, naturally occurring molecules composed of chemical building blocks known as nucleotides.

There are two kinds of nucleic acids, DNA and RNA.

OKT3

A monoclonal antibody that targets mature T cells.

OPSONIZE

To coat an organism with antibodies or a complement protein so as to make it palatable to phagocytes.

PEYER’S PATCHES

A collection of lymphoid tissues in the intestinal tract.

PHAGOCYTES

Large white blood cells that contribute to the immune defenses by ingesting microbes or other cells and foreign particles.

PLASMA CELLS

Large antibody-producing cells that develop from B cells.

POLYMORPHS

Short for polymorphonuclear leukocytes or granulocytes.

PROTOZOA

A group of one-celled animals, a few of which cause human disease (including malaria and sleeping sickness).

RHEUMATOID FACTOR

An autoantibody found in the serum of most persons with rheumatoid arthritis.

RNA (Ribonucleic Acid)

A nucleic acid that is found in the cytoplasm and also in the nucleus of some cells. One function of RNA is to direct the synthesis of proteins.

SERUM

The clear liquid that separates from the blood when it is allowed to clot.

This fluid retains any antibodies that were present in the whole blood.

SCID

Severe combined immunodeficiency disease (SCID)

A life-threatening condition in which infants are born lacking all major immune defenses.

SPLEEN

A lymphoid organ in the abdominal cavity that is an important center for immune system activities.

STEM CELLS

Cells from which all blood cells derive. The bone marrow is rich in stem cells.

SUBUNIT VACCINE

A vaccine that uses merely one component of an infectious agent, rather than the whole, to stimulate an immune response.

SUPERANTIGENS

A class of antigens, including certain bacterial toxins, that unleash a massive and damaging immune response.

SUPPRESSOR T CELLS

A subset of T cells that turn off antibody production and other immune responses.

T CELLS

Small white blood cells that orchestrate and/or directly participate in the immune defenses. Also known as T lymphocytes, they are processed in the thymus and secrete lymphokines

THYMUS

A primary lymphoid organ, high in the chest, where T lymphocytes proliferate and mature.

TIL (Tumor-infiltrating Lymphocytes)

These immune cells are extracted from the tumor tissue, treated in laboratory, and reinjected into the cancer patient.

TISSUE TYPING

See histocompatibility testing.

TOLERANCE

A state of nonresponsiveness to a particular antigen or group of antigens.

TONSILS AND ADENOIDS

Prominent oval masses of lymphoid tissues on either side of the throat.

TOXINS

Agents produced by plants and bacteria, normally very damaging to mammalian cells, that can be delivered directly to target cells by linking them to monoclonal antibodies or lymphokines.

VACCINE

A substance that contains antigenic components from an infectious organism.

By stimulating an immune response (but not disease), it protects against subsequent infection by that organism.

VARIABLE REGION

That part of an antibody's structure that differs from one antibody to another.