We have already seen how white blood cells will
attack, swallow, and digest an invader. But what are
these white blood cells and how do they work?
Blood Cells: neutrophils & lymphocytes
five types of white blood cells, but only two are of importance
in this discussion. One type is the neutrophil, which
accounts for about 60% of all white cells. During infections,
these cells divide and are dumped into the blood stream and
lymph fluids to combat the infection. They fight invaders by
"eating" bacteria and other foreign matter. The neutrophil
membrane wraps around the invader and traps it inside the neutrophil.
Once inside, digestive enzymes in the neutrophil destroy the
The cell nucleus in new, young neutrophils tends to break into
pieces as they age. Thus, by counting the percentage of neutrophils
that have a single, intact nucleus, a doctor can know that the
body is responding as expected to an infection.
the right, two white blood cells surrounded by red blood
cells. The one indicated by the arrow is a mature neutrophil.
The one just to the left is a lymphocyte.
the left, three mature neutrophils at the bottom, a lymphocyte
near the top, and a monocyte (arrow). The monocyte
matures into a large macrophage cell.
other important type of white cell is the lymphocyte,
which comes in two forms, a B-type and an T-type. The B-type
makes circulating antibodies. The B-type is made in lymph
nodes and bone marrow.
The T-type lymphocyte ("T" is for
killer) either kills foreign cells on contact or helps
by releasing chemicals that assist in killing invaders. T-cells
recognize the surface proteins on other cells and when they
come in contact with an intruder, the invading cells are killed.
are made in a gland at the base of the neck, called the thymus.
This gland is very large in young people, but almost disappears
in old age. Production of T-cells can be reactivated
at any time, if a foreign antigen is presented. T-cells also
play a role in the rejection of transplanted tissue and in
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