acquired immunodeficiency syndrome (AIDS)-A life
threatening disease eaused by a virus and eharaeterized by
breakdown of the body's immune defenses.

active immunity-Immunity produeed by the body in response
to stimulation by a disease-eausing organism or a vaeeine.

agammaglobulinemia-An almost total lack of
immunoglobulins, or antibodies.
allergen-Any substanee that eauses 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,
and a sudden fall in blood pressure.

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

antibody-dependent cell-mediated cytotoxicity (ADCC)-An
immune response in which antibody, by coating target cells,
makes them vulnerable to attack by immune cells.

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 nueleus.
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. Rheumatoid
arthritis and systemic lupus erythematosus are autoimmune
diseases.

bacterium-A microscopic organism composed of a single cell.
Many but not all bacteria eause disease.

basophil-A white blood cell that eontributes to inflammatory
reaetions. Along with mast eells, basophils are responsible for
the symptoms of allergy.

B cells-Small white blood eells erueial to the immune defenses.
Also know as B Iymphoeytes, they are derived from bone
marrow and are the souree of antibodies.

biological response modifiers-Substances, either natural or
synthesized, that boost, direct, or restore normal immune
defenses. BRMs include interferons, interleukins, thymus
hormones, and monoclonal antibodies.

biotechnology-The use of living organisms or their products to
make or modify a substance. Biotechnology includes recombi
nant DNA techniques (genetic engineering) and hybridoma
technology

bone marrow-Soft tissue located in the cavities of the bones.
The bone marrow is the source of all blood cells.

cellular immunity-Immune protection provided by the direct
action of immune cells (as distinct from soluble molecules such
as antibodies).

chromosomes-Physical structures in the cell's nucleus that
house the genes. Each human cell has 23 pairs of chromosomes.

clone-A group of genetically identical cells or organisms
descended from a single common ancestor, OR, to reproduce
multiple identical copies.

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 for each antibody class.

cytokines-Powerful chemical substances secreted by cells.
Cytokines include Iymphokines produced by Iymphocytes and
monokines produced by monocytes and macrophages.

cytotoxic Tcells-A subset of T Iymphocytes that carry the T8
marker and can kill hody cells infected by viruses or trans
formed by cancer.

dendritic cells-White blood cells found in the spleen and
other Iymphoid organs. Dendritic cells typically use threadlike
tentacles to enmesh antigen, which they present to T cells.

DNA (deuxyribonucleic acid)-A nucleic acid that is found in
the cell nucleus and that is the carrier of genetic information.

enzyme-A protein, produced by living cells, that promotes the
chemical processes of life without itself being altered.

eosinophil-A white blood cell that contains granules filled with
chemicals damaging to parasites, and enzymes that damp down
inflammatory reactions.

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

fungus-Member of a class of relatively primitive vegetable
organisms. Fungi include mushrooms, yeasts, rusts, molds, and
smuts.

gene-A unit of genetic material (DNA) that carries the direc
tions a cell uses to perform a specific function, such as making a
given protein.

graft-versus-host disease (GVHD)-A life-threatening reaction in
which transplanted immunocompetent cells attack the tissues of
the recipient.

granulocytes-Phagocytic white blood cells filled with granules
containing potent chemicals that allow the cells to digest micro
organisms. Neutrophils, eosinophils, basophils, and mast cells
are examples of granulocytes.

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

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.

HlV(human immunodeficiency virus)-The virus that causes
AIDS.

human leukocyte antigens (HLA)-Protein markers of self
used in histocompatibility testing. Some HLA types also
correlate with certain autoimmune diseases.

humoral immunity-Immune protection provided by soluble
factors such as antibodies, which circulate in the body's fluids
or "humors," primarily serum and Iymph.

hybridoma-A hybrid cell created by fusing a B Iymphocyte
with a long-lived neoplastic plasma cell, or a T Iymphocyte with
a Iymphoma cell. A B-cell hybridoma secretes a single specific
antibody.

hypogammaglobulinemia-Abnormally low levels of immu
noglobulins.

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-The use of 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 toxic drug
or a radioactive substance.

inflammatory response-Redness, warmth, and swelling
produced in response to infection, as the result of increased
blood flow and an influx of immune cells and secretions.
interleukins-A major group of Iymphokines and monokines.

Kupffer cells-Specialized macrophages in the liver.

LAK cells-Lymphocytes transformed in the laboratory into
Iymphokine-activated killer cells, which attack tumor cells.

Langerhans cells-Dendritic cells in the skin that pick up
antigen and transport it to Iymph nodes.
Ieukocytes-All white blood cells.

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

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.

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

lymphocytes-Small white blood cells produced in the
lymphoid organs and paramount in the immune defenses.

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.

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

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

microbes-Minute living organisms, including bacteria, viruses,
fungi, and protozoa.
microorganisms-Microscopic plants or animals.

molecule-The smallest amount of a specific chemical substance
that can exist alone. (To break a molecule down into its
constituent atoms is to change its character. A molecule of
water, for instance, reverts to oxygen and hydrogen.)

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

monocyte-A large phagocytic white blood cell which, when it
enters tissue, develops into a macrophage.

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 Iymphocytes 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.

neutrophil-A white blood cell that is an abundant and
important phagocyte.
OKT3-A monoclonal antibody that targets mature T cells.

opportunistic infection-An infection in an immunosuppressed
person caused by an organism that does not usually trouble
people with healthy immune systems.

Opsonize-To coat an organism with antibodies or a
complement protein so as to make it palatable to phagocytes.
organism-An individual living thing.

parasite-A plant or animal that lives, grows, and feeds on or
within another living organism.

passive immunity-Immunity resulting from the transfer of
antibodies or antiserum produced by another individual.

Peyer's patches-A collection of Iymphoid 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.

platelets-cellular fragments critical for blood clotting and
sealing off wounds.

polymorph-Short for polymorphonuclear leukocyte or
granulocyte.

proteins-Organic compounds made up of amino acids.
Proteins are one of the major constituents of plant and animal
cells.

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

rheumatoidfactor-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.

scavenger cells-Any of a diverse group of cells that have the
capacity to engulf and destroy foreign material, dead tissues, or
other cells.

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.

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.

suppressor T cells-A subset of T cells that carry the T8 marker
and 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 Iympho
cytes, they are processed in the thymus and secrete Iympho
kines.

thymus-A primary Iymphoid organ, high in the chest, where T
Iymphocytes proliferate and mature.
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 Iymphoid
tissues on either side of the throat.

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.

virus-Submicroscopic microbe that causes infectious disease.
Viruses can reproduce only in living cells.