Encyclopedia of Health and Medicine

Structures of the Immune System
LYMPH
lymph nodes
B-CELL LYMPHOCYTE
plasma cell
memory B-cell
T-CELL LYMPHOCYTE
cytotoxic (killer) T-cell
memory T-cell
helper T-cell
suppressor t-cell
NATURAL KILLER (NK) CELL
complement factors
MONOCYTE
MACROPHAGE
GRANULOCYTE
basophil
eosinophil
neutrophil
MAST CELL
THE IMMUNE SYSTEM
AND ALLERGIES
The IMMUNE SYSTEM protects the body from INFECTION. Allergies represent an inappropriate response from the immune
system toward harmless substances. Doctors (MDs and DOs) who treat conditions of the immune system may be
internists or immunologists. Doctors who specialize in treating allergies are allergists, and those who specialize in
treating RHEUMATOID ARTHRITIS and related AUTOIMMUNE DISORDERS are rheumatologists.
M cell
adenoids
tonsils
THYMUS
PEYER’S PATCHES
APPENDIX
MUCOSA-ASSOCIATED
LYMPHOID TISSUE (MALT)
SKIN-ASSOCIATED LYMPHOID
TISSUE (SALT)
NOSE-ASSOCIATED
LYMPHOID TISSUE (NALT)
BRONCHIAL-ASSOCIATED
LYMPHOID TISSUE (BALT)
GUT-ASSOCIATED LYMPHOID
TISSUE (GALT)
VASCULAR-ASSOCIATED
LYMPHOID TISSUE (VALT)
Functions of the Immune System
The immune system’s role is to protect the body
from infection. Infection, from the immune system’s
perspective, is any activity from foreign
entities that causes damage to cells. It does so
through a complex and intricate integration of
organs, tissues, cells, and molecules.
Each day the BONE MARROW releases billions of
monocytes and granulocytes, also called polymorphonuclear
cells (PMNs), into the BLOOD circulation.
Monocytes circulate in the blood for about
24 hours and then migrate into the LYMPH tissues,
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LIVER, and the various MUCOSA-ASSOCIATED LYMPHOID
TISSUE (MALT) structures throughout the body.
Known as macrophages after their migration,
these cells participate in ANTIGEN processing as well
as continued PHAGOCYTOSIS (consumption of cellular
debris). Granulocytes (neutrophils, basophils,
and eosinophils) are instrumental in the body’s
inflammatory response, which is integral to HEAL-
ING in normal immune function as well as responsible
for much of the distress of a HYPERSENSITIVITY
REACTION—ALLERGY—when the immune system
malfunctions.
The workhorse cells of the immune system are
the lymphocytes, which from birth divide into
two camps: B-cell lymphocytes, which patrol the
blood and lymph on the alert for invaders, and T-
cell lymphocytes, which respond to the call of B-
cell lymphocytes when invaders penetrate the
body’s barriers. B-cell lymphocytes come to maturity
in the bone marrow and regulate ANTIBODY-
MEDIATED IMMUNITY. T-cell lymphocytes come to
maturity in the THYMUS and regulate CELL-MEDIATED
IMMUNITY. Lymphocytes circulate in the blood and
the lymph, and also reside in lymph organs and
tissues throughout the body. The SPLEEN contains
about half the body’s supply of lymphocytes.
Perhaps more than any other system of the
body the immune system is one of molecular
function. The entire function of the immune system
centers on the ability of immune cells to distinguish
cells that belong to the body—self
cells—from cells that do not belong to the body—
nonself cells. It does so through molecular mark-