The immune system is composed of a number of cells, tissues and organs that work in association and attacks the disease causing microorganisms and protect the human body. The cells of the immune system are the leukocytes or the white blood cells. They are of two main types that work in combination and destroy organisms and substances that invade the body.

Leukocytes are divided into two main types as: phagocytes and lymphocytes. Lymphocytes are the cells that help the body to remember the organisms and then recognize and destroy them when they invade the body again.

Types of Lymphocytes

There are two types of Lymphocyte: B lymphocytes and T lymphocytes. Lymphocytes are produced in the bone marrow and they either remain there and mature to form B lymphocytes or move to the thymus gland and mature to form T lymphocytes. Both the cells have different functions. The B cells make antibodies that attack bacteria and toxins while the T cells attack body cells themselves when they have been taken over by viruses or have become cancerous. Lymphocytes secrete products (lymphokines) that modulate the functional activities of many other types of cells and are often present at sites of chronic inflammation.