·     It defends the body against pathogenic microbesand germs that are exposed to the human body everyday. The body’s defensivemechanism is achieved through a series of steps called the immune response.This attacks disease-causing microbes which are likely to invade the body’ssystem.

The immune system is also composed of specialised cells, varioustissues, organs and proteins that work together to protect the body. One of themain 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 organsand tissues involved in the immune system are called lymphoid organs which are;spleen, bone marrow, thymus, appendix, lymph nodes, tonsils and the Peyer’spatches found throughout the small intestinal duct. Primarily, leukocytes comein two types; phagocytes and lymphocytes. The phagocytic cells chew harmfulmicroorganism whilst the lymphatic cells allow the body recognise previousinfectious microbes and help the body to destroy them. Lymphocytes alsoconsists of two types of cells; B- cells and T-cells. B-cells produce antibodiesto attack foreign antigens that causes harm to the body.

T-cells, however, hastwo main functions; to recognise and destroy malignant cells, and to orchestratean immune response which play a vital role in immunity.