|
Our immune system protects us against threats. These
include viruses, bacteria and parasites causing
infectious diseases, from ordinary flu to full-blown
malaria. The white blood cells of the defense system
are produced in the marrow of our bones. The cells
are carried in the blood to specialized organs, where
they develop and communicate to launch immune
responses against infections. Immune responses are
aggressive and must be controlled. They should be
activated only when the body is threatened by
disease. To learn how to start or stop the immune
system we must understand how microorganisms and sick
cells are recognized by white blood cells.
Some white blood cells, like
macrophages, destroy and eat bacteria and damaged
cells. The B cells produce antibodies, which can
neutralize viruses, bacteria or toxic proteins in the
blood and other body fluids. The T cells can trace
microorganisms that leave the body fluids to invade
cells. Each T killer cell carries receptors for one
type of foreign substance, "antigen". T cells can
bind to infected cells and kill them. This can
prevent spread of the microorganism within the body.
But how can the T cells specifically identify or
"recognize" the infected cells?
|
