When they encounter antigen, they produce antibodies.

The immune system protects the body against infections and diseases. This is sometimes also called the lymphatic system. It consists of tissues and organs that produce, store and carry white blood cells that fight infections and other diseases. This system includes the bone marrow, spleen, tonsils, thymus gland, lymph nodes and lymph vessels. Lymph clear liquid passes through the lymphatic system and carries cells that help fight infections and other diseases. Lymph nodes are rounded masses of lymphoid tissue that is surrounded by a capsule of connective tissue. Lymph nodes filter lymph, and they store white blood cells. They are located along lymphatic vessels. Lymph vessels of thin tubes that transport lymph and white blood cells through the lymphatic system. They branch, like blood vessels in all tissue. Thymus organ in the chest behind the breastbone. T lymphocytes grow and multiply in the thymus. Spleen organ on the left side of abdomen near the stomach. It produces white blood cells, filters the blood, stores blood cells, and destroys old blood cells. White blood cells are made by bone marrow cells and help the body fight infection and other diseases. There are many types of white blood cells.

Antigen third-party agent that causes response in the immune system. may be bacteria, viruses, etc. There's a different antigens for each cold you ever had and every type of flower, which ever you sneeze. White blood cells patrol the body. When they encounter antigen, they produce antibodies. Antibody binds to an antigen. Each antigen is formed differently. The immune system has to produce antibodies that fits exactly. Some antibodies, antigens, destroy, when furosemide they communicate with them. Other help white blood cells to destroy the antigen. .