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It defends the body against pathogenic microbes that
are exposed to the human body everyday. The body’s defensive mechanism is achieved
through a series of steps called the immune response. This attacks disease-causing
microbes which are likely to invade the body’s system. The immune system is
also composed of specialised cells, various tissues, organs and proteins that
work together to protect the body. One of the main cells involve in the body’s defensive
activity is the white blood cells, also known as leukocytes. These are produced
in many parts of the body. The organs and tissues involved in the immune system
are called lymphoid organs which are; spleen, bone marrow, thymus, appendix,
lymph nodes, tonsils and the Peyer’s patches found throughout the small intestinal
duct. Primarily, leukocytes come in two types; phagocytes and lymphocytes. The
phagocytic cells chew harmful microorganism whilst the lymphatic cells allow
the body recognise previous infectious microbes and help the body to destroy
them. Lymphocytes also consists of two types of cells; B- cells and T-cells.

B-cells produce antibodies to attack foreign antigens that causes harm to the
body. T-cells, however, has two main functions; to recognise and destroy
malignant cells, and to orchestrate an immune response which play a vital role in
immunity.

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