Plasma contains proteins,
enzymes, electrolytes, sugar, glucose
and fats and constitutes 55 percent of
the blood. The other 45 percent of the
blood is made up of cells, including
red blood cells (erythrocytes), white
blood cells (leukocytes) and platelets
(thrombocytes).
Red blood cells are
responsible for carrying oxygen to all
other cells in the body. Platelets help
cuts and wounds heal. White blood
cells form the army of the immune
system. Although all these cells depend
on each other to keep a person healthy,
it is the work of white blood cells that
is at the core of our immune system.
Blood and lymph are the
transport mechanisms for leukocytes
(white blood cells), the basic units of
immunity.
Leukocytes
White blood cells, or
leukocytes, come in different sizes and
perform different functions.
Leukocytes all have a nucleus, which
contains the material for growth,
nourishment and reproduction. All
leukocytes arise from a stem cell, or
parent cell, located in the bone
marrow. Stem cells give rise to different
types of blood cells, which then mature
into different types of cells depending
on where in the body the maturation
process takes place.
All the body’s leukocytes fall
into one of three categories:
polymorphonuclear granulocytes,
monocytes and lymphocytes. Each of
these has its own role to play in
immune function.
Polymorphonuclear granulocytes
(polys): These cells form the first line
of defense. They don’t have a
specialized function: they can attack all
foreign intruders. Polys include
neutrophils, eosinophils, basophils
and mast cells.
s Neutrophils: These cells are
extremely mobile. Neutrophils are
phagocytic cells, meaning that they can
engulf other cells, microbes and other
particles. Neutrophils play a major role
in the inflammatory response. They
comprise 55-70 percent of all white
blood cells.
s Eosinophils: These cells are
phagocytes. It is believed that they play
an important role in regulating the
severity of allergic reactions by
secreting an enzyme that breaks down
histamine. They also seem to be
involved in combating parasites.
Eosinophils comprise 1-3 percent of
the total of white blood cells.
s Basophils: These cells are not
phagocytic; however, they are
responsible for releasing histamine, a
chemical involved in the allergic
response. Basophils also release
heparin, an important anticoagulant.
These cells are found in small numbers
in the blood, accounting for less than
1 percent of all white blood cells.
sMast cells: These cells are similar to
basophils, but they do not circulate in
the blood. Mast cells can be found
closer to the skin and are very active
in the allergic response.
Monocytes: These cells make up 3 to
8 percent of all circulating leukocytes.
They are phagocytic. Although
monocytes are active in the immune
response, their most important role is
to mature into macrophages.
sMacrophages: These are very large
and extremely “hungry” phagocytic
cells that can not only circulate in the
bloodstream, but also settle in the
spleen, liver, lymph nodes, tonsils,
lungs and bone marrow. There they
can engulf aging or damaged cells and
microbes. They are also good defenders
against fungi. Along with the
neutrophils, macrophages are the
body’s major phagocytes.
Together,neutrophils,
monocytes and macrophages play a
major role in the inflammatory, or
nonspecific, immune response. These
phagocytes are able to engulf invaders
and abnormal cells and then help to
clean up after the immunological
response. However, as we will see later,
monocytes and macrophages are also
involved in the more specific immune
response.
Lymphocytes: These are very
specialized leukocytes and comprise 20-
50 percent of all leukocytes.
T-cells: These cells are called T-cells
because they mature in the thymus.
They comprise 60-70 percent of
lymphocytes. When humans are still
in the fetal stage of development,
immature stem cells migrate from the
bone marrow to the thymus, where
they become T-cell “parents.” The
progeny of these cells endure a
selection process that weeds out T-cells
that are abnormal or have receptors
that recognize normal body structures.
The cells emerging from this
Aromatherapy &
The Immune System continued
3
process are programmed to respond to
a single enemy. They then migrate to
the spleen and the lymph nodes and
await an attack. These cells now
compose what is called cell-mediated
immunity. T-cell receptors are made
of proteins and they specialize in
identifying viruses and other
organisms that invade a cell.
There are three basic types of T-cells:
sHelper T-cells: Most abundant Tcells.
They stimulate the growth of
cytotoxic and suppressor T-cells. They
also stimulate macrophages to perform
their engulfing duties and B-cells to
produce antibodies.
sCytotoxic T-cells (killer cells): These
cells attach to specific antigens and
secrete enzymes to puncture the shells
of the invaders.
s Suppressor T-cells: These cells
suppress the active immune response.
They keep the immune system from
becoming overactive.
B-Cells: These cells comprise 10-20
percent of all lymphocytes. Once a
stem cell produces a descendant, the
stromal cells of the bone marrow
decide whether this cell will become a
B-cell or another cell type. Once a cell
is designated as a B-cell, a specialized
structure called the surrogate complex
determines which cells will survive and
be allowed to circulate throughout the
body. The B-cells that survive migrate
to the lymph nodes and spleen to await
action. B-cells are especially adept at
catching intruders like bacteria. B-cells
fight intruders by manufacturing
antibodies. This type of immunity is
known as humoral or antibodymediated
immunity. Antibodies are
very specific; each one can bind to only
one specific antigen. This binding
helps destroy that particular antigen.
Antibodies come in five different types:
IgM, IgG, IgA, IgE and IgD. Ig stands
for immunoglobulin.
s IgM: is the first antibody to appear
in response to an invader. It attaches
to the intruder and marks it for
destruction by phagocytic cells. It
remains in the blood stream and it is
very effective against bacteria.
However, its effects are very short-lived.
s IgG is the most abundant antibody
and it provides lifelong immunity
against a specific antigen. It can enter
tissue spaces and is the only antibody
able to pass through the placenta,
giving the fetus its immunity.
s IgA is found in wet surfaces such as
saliva, tears, nasal and vaginal
secretions. It fights off invaders at the
sites of entrance.
s IgE is able to adhere to mast cells
and basophils to release histamines
responsible for allergic reactions. It is
also involved in the fight against
parasites.
s IgD almost exclusively found inserted
into the membrane of B-cells, it seems
to regulate the cell’s activation.
s Natural killer (NK) cells: These are
lymphocytes that are granular in
appearance. Their role is nonspecific.
They can destroy invaders, specifically
cancer and virus-infected cells, without
assistance from other cells.
The Communication System
As expected, in order for all
these specific and non-specific
leukocytes to perform their duties,
there has to be an effective
communication system in place. How
do these cells “speak” to each other?
Through proteins called cytokines.
Manufactured by monocytes,
macrophages and lymphocytes, these
proteins regulate cell growth and
function during inflammatory and
specific immune responses. Among
these proteins are interferons,
interleukins, tumor necrosis factor,
colony-stimulating factor, and
erythropoietin. Cytokines can enhance
inflammatory and immune responses,
and can inhibit these responses in the
fight or flight response. (see section on
Stress and Immunity).
The Immune System at Work
When a macrophage attacks
an antigen, it takes fragments of it to
helper and suppressor T-cells. In turn,
these orchestrate a response. Helper Tcells
always want to send too many
cytotoxic T-cells to fight, while the
suppressor T-cells never want to send
enough. Together they arrive at a
balance. The cytotoxic T-cells are sent
to fight armed with enzymes, when
they find the invader, they can use
these enzymes to drill holes on its shell
causing its insides to pour out.
Phagocytes arrive and clean-up debris.
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