An image of pelvic and thigh bones overlays a drawing of leg and pelvic muscles.
The image dissolves to a single thighbone with a mid-section cutaway.
Special white blood cells called lymphocytes
play a key role in the immune system's response to foreign invaders.
There are two main groups,
both of which form in bone marrow.
The cutaway enlarges,
showing the spongy marrow
with a few young cells.
One group, called T-lymphocytes or T-cells,
migrates to a gland called the thymus.
The thymus is shown as a strip of tissue in front of the heart.
Influenced by hormones, they mature there into several types of cells,
including helper, killer, and suppressor cells.
Inside the thymus, a sphere marked H connects with two smaller cells labeled T.
Then there are four T-cells that sprout claw-like appendages.
These different types work together
to attack foreign invaders.
They provide what's called
cell-mediated immunity,
which can become deficient in persons with HIV,
the virus that causes AIDS.
HIV attacks and destroys helper T cells.
The cells disappear. The image returns to the marrow with cells labeled B
rapidly dividing and multiplying before sprouting claw-like appendages.
The other group of lymphocytes are called B-lymphocytes or B cells.
They mature in the bone marrow
and gain the ability to recognize
specific foreign invaders.
The image changes to the thighbone and a B- and T-cell.
A box shows the pelvic muscles and bones
overlain by a network of blood and lymph vessels.
Mature B cells migrate through the body fluids
to the lymph nodes,
spleen, and blood.
A section of the drawing enlarges to show a close up
of the vascular and lymph systems.
In Latin, body fluids were known as humors.
So B-cells provide what's known as humoral immunity.
B-cells and T-cells
both circulate freely in blood and lymph,
searching for foreign invaders.
A cutaway of an artery
shows red blood cells,
T-cells, and B-cells flowing through.