mast cell A granulated LEUKOCYTEthat resides in
tissues throughout the body. When the IMMUNE
RESPONSE stimulates mast cells, they release
PROSTAGLANDINS, HISTAMINE, and other biochemicals
from their granules. Mast cells are primarily
responsible for the symptoms that are the hall-
mark of the HYPERSENSITIVITY REACTION: INFLAMMA-
TION, itching, SKIN RASH, coughing, and sneezing.
Mast cells have an abundant presence in the tis-
sues of mucous membranes such as the NOSE, pul-
monary tract (TRACHEA and bronchi), and
gastrointestinal tract. Mast cells also infiltrate the
connective tissues. They respond to the stimula-
tion of complement factors and to IMMUNOGLOBULIN
E (IgE) antibodies.
For further discussion of mast cells within the
context of the structures and functions of the
immune system, please see the overview section
“The Immune System and Allergies.”
See also ANTIBODY; COMPLEMENT CASCADE; COUGH;
LIVING WITH ALLERGIES; MUCOSA-ASSOCIATED LYMPHOID
TISSUE(MALT); SNEEZE.
monoclonal antibodies (MAbs) Antibodies pro-
duced in a laboratory using RECOMBINANT DNAtech-
nology. MAbs derive from cloned mouse SPLEEN
cells (hence the designation “monoclonal”) con-
taining the desired ANTIBODYfused with human
myeloma cells. Mouse cells have proteins very
similar to the proteins of human cells. Human
myeloma cells, because they are cancer cells, have
the ability to replicate without limitation. The
myeloma cells arise from B-cell lymphocytes,
which produce antibodies.
When scientists fuse the two cells together,
they achieve cells (called hybridomas) that com-
bine the desired ANTIGEN sensitization with the
ability to endlessly replicate antibody-producing
cells. After fusion, scientists can attach radioac-
tive molecules for diagnostic imaging or to
deliver fatal radiation to specific cells (called con-
jugated MAbs). Doctors then can inject MAbs into
people to stimulate the IMMUNE RESPONSE as a
mechanism for fighting INFLAMMATION(such as in
RHEUMATOID ARTHRITIS) and certain types of cancer
or to specifically target certain cells for death
without affecting other cells. Indiscriminate cell
death is a significant limitation of current
CHEMOTHERAPY.
A key limitation of therapeutic MAbs is that the
body recognizes them as nonself and configures
antibodies against them. MAbs are highly effective
for the first treatment, then may be less effective
or initiate a HYPERSENSITIVITY REACTION in subse-
quent treatment efforts.THERAPEUTIC MONOCLONAL ANTIBODIES (MABS)
abciximab (ReoPro) alemtuzumab (MAb Campath)
bevacizumab (Avastin) cetuximab (Erbitux)
daclizumab (Zenapax) infliximab (Remicade)
lym-1 (Oncolym) muromonab-CD3 (OKT3)
omalizumab (Xolair) rituximab (Rituxan)
tositumomab (Bexxar) trastuzumab (Herceptin)For further discussion of MAbs within the con-
text of the structures and functions of the immune
system, please see the overview section “The
Immune System and Allergies.”
See also B-CELL LYMPHOCYTE; CANCER TREATMENT
OPTIONS AND DECISIONS; IMMUNOTHERAPY; INTERFERONS;
INTERLEUKINS; MOLECULARLY TARGETED THERAPIES.monokines CYTOKINESthat convey biochemical
messages among monocytes (white BLOODcells in
the blood circulation) and macrophages (white
blood cells that reside in the tissues). Monokines
direct the actions of these immune cells during the
IMMUNE RESPONSE, stimulating and coordinating
numerous functions. There is some overlap
between monokines and LYMPHOKINES(which lym-
phocytes produce).
See also COMPLEMENT CASCADE; IMMUNE SYSTEM;
INTERFERONS; INTERLEUKINS; LEUKOCYTE; LYMPHOCYTE;
MACROPHAGE; MONOCYTE.mononuclear phagocyte system The combined
activity of the IMMUNE SYSTEM’s phagocytes—mono-
cytes in the BLOODcirculation and macrophages in
the tissues—to consume cellular debris. These cells
are scavengers within the body, responsible for
cleaning up after B-cell lymphocytes, T-cell lym-
phocytes, and natural killer (NK) cells. They also
clear the debris that results from normal cell death
(APOPTOSIS). They are called mononuclear because
their cell structure contains a single nucleus; neu-
trophils, which are also phagocytes, have multiple
nuclei (and are called polymorphonuclear). The
COMPLEMENT CASCADE(an interaction of proteins ormononuclear phagocyte system 283