Page 19 - The Miracle of the Immune System

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THE SOLDIERS OF THE BODY
Within a lymph node a battle rages between
the body's attackers and defenders. When
bacteria pour through a lymphatic channel
(1), a macrophage engulfs some of the in-
10 vaders (2), digests them, and displays their
identity markers on its own surface. This
chemical message is presented to a type of
white blood cell known as a helper T cell
(3), which responds by multiplying (4) and
releasing chemical messages that call more
defenders to arms (5). Other T cells signal
B cells to join the battle (6). Some B cells
begin to reproduce (7), and these new cells
store information to help the body fight the
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same invader on another day (8). Other
B cells spew out thousands of antibodies
each second (9), forcing bacteria to clump
together (10). Macrophages can then sweep
through, swallowing the clumped bacteria,
while special protein molecules and anti-
bodies make bacteria palable for
macrophages (11). Sometimes, the proteins
kill bacteria directly by puncturing their cell
walls (12). Scavenging macrophages then
clean the entire node of battle debris, en-
gulfing scattered antibodies, dead bacteria,
and other debris until the infection sub-
sides.