Page 21 - The Miracle in 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 invaders (2),
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digests them, and displays their identity markers
on its own surface. This chemical message is pre-
sented 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
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to join the battle (6). Some B cells begin to repro-
duce (7), and these new cells store information to
help the body fight the same invader on another
day (8). Other B cells spew out thousands of anti-
bodies each second (9), forcing bacteria to clump
together (10). Macrophages can then sweep
through, swallowing the clumped bacteria, while
special protein molecules and antibodies 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, engulfing
scattered antibodies, dead bacteria, and other
debris until the infection subsides.