Granulocytes undergo many stages of development before becoming mature neutrophils, basophils, or eosinophils. They contain cellular systems that consume foreign substances by surrounding and digesting of microorganisms and foreign particles or enveloping foreign substances within the plasma membrane. Monocytes originate in the bone marrow as immature monoblasts and promonocytes. Once these early cell forms develop into monocytes, they circulate in the bloodstream for about 24 hours. If the monocytes detect an area of inflammation, they move into tissues to become macrophages - larger phagocytic cells that help lymphocytes to detect foreign microorganisms and launch immune system responses.
Lymphatic tissue contains both fixed and circulating elements.
Many different types of lymphatic cells interact to combat infections and recognize abnormal cells within the body. Fixed lymphoid tissue is found in the lymph nodes, spleen, thymus, tonsils and adenoids, bone marrow, and various sites within the gastrointestinal tract, respiratory system, and liver. It is believed that daughter B-cells complete their development within the bone marrow. B-cells combat infections by changing into plasma cells, which secrete antibodies. Plasma cell antibodies become attached to the invading germ, which is then recognized and destroyed by the blood granulocytes.