The Body As BattlefieldAssaults from outside the body turn it into a battlefield where the aggressors sometimes get the upper hand.
From parasitic worms to protozoa to fungi to bacteria to viruses, organisms of many kinds have learned to live by
entering the body and using their molecular machinery to build more of themselves from the body's building
blocks. To meet this onslaught, the body musters the defenses of the immune system—an armada of its own
molecular machines. Your body's own amoebalike white blood cells patrol the bloodstream and move out into
tissues, threading their way between other cells, searching for invaders.
How can the immune system distinguish the hundreds of kinds of cells that should be in the body from the
invading cells and viruses that shouldn't? This has been the central question of the complex science of
immunology. The answer, as yet only partially understood, involves a complex interplay of molecules that
recognize other molecules by sticking to them in a selective fashion. These include free-floating antibodies—which
are a bit like bumbling guided missiles—and similar molecules that are bound to the surface of white blood cells
and other cells of the immune system, enabling them to recognize foreign surfaces on contact.
This system makes life possible, defending our bodies from the fate of meat left at room temperature. Still, it lets
us down in two basic ways.
First, the immune system does not respond to all invaders, or responds inadequately. Malaria, tuberculosis,
herpes, and AIDS all have their strategies for evading destruction. Cancer is a special case in which the invaders
are altered cells of the body itself, sometimes successfully masquerading as healthy cells and escaping detection.
Second, the immune system sometimes overresponds, attacking cells that should be left alone. Certain kinds of
arthritis, as well as lupus and rheumatic fever, are caused by this mistake. Between attacking when it shouldn't
and not attacking when it should, the immune system often fails, causing suffering and death.
Source:
>1991 "Nanomedicine," Chapter 10, Unbounding the Future (K. Eric Drexler, Christine Peterson, Gayle Pergamit)
>Dec. 1994 "Nanotechnology and Medicine" (Ralph C. Merkle) >http://inventors.about.com/gi/dynamic/offsite.htm?zi=1/XJ/Ya&sdn=inventors&zu=http%3A%2F%
2Fen.wikipedia.org%2Fwiki%2FNanotechnology
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