CHAPTER 1 CELLS AND ORGANS OF THE IMMUNE SYSTEM2
undergo m After birth, most stem cells are found in
the b m Marrow is found in tubular, flat, and long
bones a c of a connective tissue framework, called
stroma, w s red or yellow pulp. Red pulp, which
is t m source of hemopoietic stem cells, is found in flat
bones s as the hip bone, breast bone, ribs, and vertebrae.
The ca material at the epiphyseal plate of long bones
contains r pulp. Yellow pulp is the major marrow constituent
in l t bones and is comprised of aggregated fat cells.
Stem ce f red pulp produce four major cell lineages:
(1) er (2) platelets, (3) myeloid cells (polymor-
phonuclear leukocytes, basophils, eosinophils, monocyte/
macrophages), and (4) lymphocytes. These lineages undergo
maturation in the bone marrow before being released into
blood.
BLOOD
Blood co red and white cells. Red cells are responsible
for c oxygen to tissues, and white blood cells play a key
role in fighting infections.
White Blood Cells
Peripheral b contains red blood cells, white blood cells,
and p Based on the presence or absence of cytoplas-
mic g white blood cells can be defined as granulocytes
and n Granulocyte subsets include polymor-
phonuclear leukocytes, eosinophils, and basophils. Monocytes
and sm l are generally considered nongranulo-
cytic. H a small subpopulation of lymphocytes, called
large granular lymphocytes (LGLs), does contain granules.
Polymorphonuclear Neutrophils
Polymorphonuclear neutrophils (PMN) (also referred to as
polymorphonuclear leukocytes [PML]) constitute 50% to
70% o t white blood cells in peripheral blood. Their main
function i t ingest and destroy foreign protein and bacteria.
PMNs h a multi-lobed nucleus, which is usually divided
into three or more segments (Figure 1-1).
The c contains four distinct types of granules:
(1) primary or azurophilic granules, (2) secondary granules,
(3) gelatinase granules, and (4) secretory vesicles.
Primary Granules
These g contain myeloperoxidase and lysozyme, which
play m roles in the destruction of intracellular bacteria.
Myeloperoxidase converts hydrogen peroxide into hypochlo-
rous acid w reduces pH and initiates the destruction of
the b cell wall. Lysozyme is an enzyme that disrupts
the s integrity of bacterial cell walls by breaking poly-
meric β 1-4 linkages.
Secondary Granules
Secondary g contain additional enzymes such as apo-
lactoferrin and collagenase, which prevent bacterial growth
and in PMN mobility. Apolactoferrin binds free iron
and p the bacterial synthesis of heme-containing pro-
teins such as cytochromes.
Tertiary Granules
Tertiary a secretory granules also play a role in immu-
nity a h defense. Tertiary granules contain lysozyme
and g Gelatinase degrades ground substances
between c and increases PMN mobility. Secretory ves-
icles e N-formyl-1-methionyl-1-leucyl-1-phenylal-
anine ( which is a chemoattractant and activating
agent f P
PMNs a p in the bone marrow and undergo a
9-day t 2-week, seven-step maturation process from myelo-
blasts t m cells. Mature cells entering the blood may
remain in circulation (circulating pool) or marginate (mar-
ginating p by attaching to the endothelial lining of the ves-
sels in c beds. Cells in capillary beds express certain
molecules, c selectins, w p attach PMNs
to the vessel wall.
In r to infection or inflammation, PMNs “demar-
ginate” a enter the blood circulation. At the same time, the
bone m releases large numbers of immature neutrophils,
called neutrophilic “bands,” i t c The influx of
immature b cells, commonly referred to by physicians as a
Cytoplasm
Nucleus
B
A
Figure 1-1
A, A polymorphonuclear neutrophils (PMN) in a blood smear also
known as polymorphonuclear leukocyte (PML) (x1000). B, A sche-
matic of a polymorphonuclear leukocyte. Note the multi-lobed nucleus.
(From Carr J, Rodak B: Clinical hematology atlas, ed 3, St Louis, 2009,
Saunders.)