The Immune System Because the human body provides an ideal
environment for many microbes, they try to pass your skin
barrier and enter. Your immune system is a bodywide network of
cells, tissues, and organs that has evolved to defend you
against such "foreign" invasions.The proper targets of your
immune system are infectious organisms--bacteria such as these
streptococci; fungi (this one happens to be Candida, the cause
of yeast infections); parasites, including these worm-like
microbes that cause malaria; and viruses such as this SARS
virus. Markers of Self At the heart of the immune response is
the ability to distinguish between "self" and "non-self." Every
cell in your body carries the same set of distinctive surface
proteins that distinguish you as "self." Normally your immune
cells do not attack your own body tissues, which all carry the
same pattern of self-markers; rather, your immune system
coexists peaceably with your other body cells in a state known
as self-tolerance. This set of unique markers on