Biology Reference
In-Depth Information
CHAPTER 1
ANTIBODIES BINDING ANTIGENS
INTRODUCTION
Under normal circumstances, we are constantly exposed to foreign
substances including chemicals, bacteria, viruses, etc. In order to defend
ourselves against the adverse effects of these substances, we have developed
various immunological mechanisms over years of evolution. The so-called
innate process involves certain cells capable of eating such foreign
substance. For example, carbon particles from smoke are picked up by
macrophages lining our lungs. The macrophages cannot digest these carbon
particles which in turn are not toxic. They just stay around. For city
dwellers, their lungs gradually turn black after many years of such exposure.
On the other hand, if the foreign substance is a pathogenic bacterium, the
macrophage may try to digest the bacterium. Or, on entering the
macrophage, the bacterium may survive and start to divide, thus killing the
macrophage. Such immunological battles go on continuously during our
entire life.
In order to improve our chance of survival, we have developed a more
efficient line of defense. If our macrophages have managed to kill off a
certain type of pathogenic bacteria, the so-called adaptive process of defense
somehow remembers this incident, by producing special protein molecules
known as antibodies. If we encounter the same bacteria a second time, one
end of these antibodies will be able to bind to some surface molecules of
these bacteria known as antigens. The other end of the antibodies will bind
to certain special receptors on the surface of the macrophages to improve the
efficiency of these macrophages to eat them. Since the number of different
antigens in the world is of the order of millions or billions, we need to have
a system capable of producing millions or billions of different antibodies
just for survival in the existing environment. Any deficiency of this system
due to genetic defect, infection, aging, etc. can result in disease processes.
In fact, we are able to produce specific antibodies capable of binding foreign
