The Immune System
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is a group of cells, molecules, and tissues that help
defend the body against diseases and other harmful invaders.
provides protection against a variety of potentially damaging substances that
can invade the body. These substances include disease-causing organisms, such
as bacteria, fungi, para ....
Middle of paper
.... as foreign by a body's immune system is called an
antigen. Several types of cells may be involved in the immune response to
antigens.
When an antigen enters the body, it may be partly neutralized by
components of the innate immune system. It may be attacked by phagocytes or by
performed antibodies that act together with the complement system. The human
immune system contains approximately 1 trillion T cells and 1 trillion B cells,
located in the lymphoid organs and in the blood, plus ap ....
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