Structures of the Immune System
LYMPH M cell
lymph nodes adenoids
B-CELL LYMPHOCYTE tonsils
plasma cell THYMUS
memory B-cell PEYER’S PATCHES
T-CELL LYMPHOCYTE APPENDIX
cytotoxic (killer) T-cell MUCOSA-ASSOCIATED
memory T-cell LYMPHOID TISSUE(MALT)
helper T-cell SKIN-ASSOCIATED LYMPHOID
suppressor t-cell TISSUE(SALT)
NATURAL KILLER(NK) CELL NOSE-ASSOCIATED
complement factors LYMPHOID TISSUE(NALT)
MONOCYTE BRONCHIAL-ASSOCIATED
MACROPHAGE LYMPHOID TISSUE(BALT)
GRANULOCYTE GUT-ASSOCIATED LYMPHOID
basophil TISSUE(GALT)
eosinophil VASCULAR-ASSOCIATED
neutrophil LYMPHOID TISSUE(VALT)
MAST CELL
Functions of the Immune SystemThe immune system’s role is to protect the body
from infection. Infection, from the immune sys-
tem’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 MARROWreleases billions of
monocytes and granulocytes, also called polymor-
phonuclear cells (PMNs), into the BLOODcircula-
tion. Monocytes circulate in the blood for about
24 hours and then migrate into the LY M P Htissues,
LIVER, and the various MUCOSA-ASSOCIATED LYMPHOID
TISSUE (MALT) structures throughout the body.
Known as macrophages after their migration,
these cells participate in ANTIGENprocessing as well
as continued PHAGOCYTOSIS(consumption of cellu-
lar debris). Granulocytes (neutrophils, basophils,
and eosinophils) are instrumental in the body’s
inflammatory response, which is integral to HEAL-
INGin normal immune function as well as respon-
sible 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 matu-
rity in the bone marrow and regulate ANTIBODY-
MEDIATED IMMUNITY. T-cell lymphocytes come to
maturity in the THYMUSand regulate CELL-MEDIATED
IMMUNITY. Lymphocytes circulate in the blood and
the lymph, and also reside in lymph organs and
tissues throughout the body. The SPLEENcontains
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 sys-
tem centers on the ability of immune cells to dis-
tinguish 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-THE IMMUNE SYSTEM
AND ALLERGIES
The IMMUNE SYSTEMprotects 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 ARTHRITISand relatedAUTOIMMUNE DISORDERSare rheumatologists.
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