Encyclopedia of Health and Medicine

284 The Immune System and Allergies
factors that begins with ANTIBODY–ANTIGEN binding)
is the primary alert mechanism that activates the
mononuclear phagocyte system. Monocytes and
macrophages work in a coordinated fashion, communicating
via CYTOKINES (cell-originated biochemical
messages) with other cells involved in
the IMMUNE RESPONSE.
For further discussion of the mononuclear
phagocyte system within the context of the structures
and functions of the immune system, please
see the overview section “The Immune System
and Allergies.”
See also B-CELL LYMPHOCYTE; CELL STRUCTURE AND
FUNCTION; GENE; GRANULOCYTE; MACROPHAGE; MONO-
CYTE; NATURAL KILLER (NK) CELL; PHAGOCYTE; PHAGOCY-
TOSIS; T-CELL LYMPHOCYTE.
mucosa-associated lymphoid tissue (MALT) A
loosely organized collection of LYMPH tissue that
underlies and integrates with epithelial tissue (the
lining of mucous membranes) throughout the
body. MALT reinforces the body’s immune presence
and response in areas of the body that provide
direct interface with the external
environment. These areas, such as the gastrointestinal
tract and the LUNGS, are most vulnerable to
breaches that could allow pathogens to enter the
body to cause INFECTION.
MALT contains clusters of phagocytic cells such
as macrophages and dendritic cells, which consume
cellular debris, as well as T-cell lymphocytes
and B-cell lymphocytes. T-cell lymphocytes attack
and kill invading pathogens, and B-cell lymphocytes
produce antibodies to protect against future
invasion by the same pathogens. There are several
types of MALT; each has specific functions, according
to its location in the body. Among them are
• BRONCHUS-ASSOCIATED LYMPHOID TISSUE (BALT),
which strengthens the body’s defense against
INFLUENZA and PNEUMONIA
• GUT-ASSOCIATED LYMPHOID TISSUE (GALT), which
helps protect against invasion by gastrointestinal
viruses
• NOSE-ASSOCIATED LYMPHOID TISSUE (NALT), which
intensifies the body’s resistance to airborne
viruses such as those that cause COLDS
• SKIN-ASSOCIATED LYMPHOID TISSUE (SALT), which
helps block BACTERIA, fungi, and other
pathogens from passing through microscopic
breaks in the SKIN
• VASCULAR-ASSOCIATED LYMPHOID TISSUE (VALT),
which infiltrates the epithelium of the BLOOD
vessels
MALT may be the site of solid tumors that
develop in LYMPHOMA (sometimes called MALT
lymphoma). The most common MALT site for
such an occurrence is the gastrointestinal tract.
Researchers believe these lymphomas develop
when a constant assault, such as a persistent infection,
engages the MALT site. B-cell lymphocytes
accumulate to fight the infection. When their
accumulation persists over time, which is abnormal,
the B-cell lymphocytes turn cancerous. The
connection with MALT lymphomas that arise from
GALT is HELICOBACTER PYLORI infection, which also
has a strong connection to STOMACH CANCER.
Researchers believe H. pylori may account for 85
percent or more of gastrointestinal MALT lymphomas,
many of which grow in the STOMACH.
Treatment is highly successful when the diagnosis
of MALT lymphoma occurs early in the CANCER’s
development because the tumors grow slowly and
lack aggression in spreading.
For further discussion of MALT 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; B-CELL LYMPHOCYTE; FUNGUS;
LYMPHOCYTE; MACROPHAGE; METASTASIS; MONONUCLEAR
PHAGOCYTE SYSTEM; PATHOGEN; PHAGOCYTE; PHAGOCY-
TOSIS; T-CELL LYMPHOCYTE; VIRUS.
multiple chemical sensitivity syndrome A constellation
of symptoms that result from exposure
to common chemicals at levels that do not normally
cause response or reaction. Multiple chemical
sensitivity syndrome is difficult to diagnose
and treat. Symptoms are often broad ranging.
There remains disagreement among medical
experts (doctors and researchers) about the diagnostic
criteria and causes of the syndrome. Some
believe multiple chemical sensitivity syndrome is a
component of GENERALIZED ANXIETY DISORDER (GAD)