The Immune System's Defense Team

Antibodies are specialized fighter proteins that your body produces in response to specific antigens. The two are attracted to each other, linking up like puzzle pieces, so that the antibody can destroy the antigen. Antibodies kill antigens in several ways, including:

making them clump together so they can't move; macrophages, a type of white blood cell, can then swallow them up;

punching holes in them so their insides leak out and they diel; and

locking up with them and attracting immune cells (macrophages in particular) like flies to honey. The immune cells then gobble them up.
White blood cells
Millions of these cells circulate in the blood and tissues, helping defend your body from infection by destroying foreign materials and providing antibodies. There are five main types.

Lymphocytes are the key elements of the immune system. They remember any antigen they've met before, providing a specific plan of attack against it if it reappears in the body. Lymphocytes circulate and recirculate through the body until they're needed. There are two types:

T cells react against antigens only after being introduced to them by special escort cells. After meeting the antigens, the T cells secrete potent substances that attract fighter cells, such as macrophages and other defense cells, and keep them pumped up and fighting until the battle against the antigen-covered cells is won. (Think of them as the cheerleaders in the antigen battle.) As in real war, however, some battles end in a draw: The immune system may not be able to kill the antigen outright, but only trap it in a web of protein strands so it does little or no harm. This is a job for the T cells: to recruit the fighting cells that surround, enclose, and immobilize a resilient enemy.

B cells are the immune cells that produce antibodies. They have a long memory for their enemies, and may remain in the body for years, ready to wage war quickly and powerfully whenever an antigen they've met before shows up again. This is how vaccination works: A tiny bit of the (usually) killed antigen, such as polio, measles, or the flu, is injected into your blood, stimulating your B cells to create antibodies to it. Then, if you ever encounter the live form of the virus or bacteria, your body can quickly marshal its defenses and produce millions of the required antibodies. If your B cells had never met that particular antigen before, however, there would be no antibody response, or, at least, a much slower response, so the intruder could get the upper hand.
The second main type of white blood cell, macrophages, are large cells that engulf and digest microorganisms and other antigens.

The last three types of white blood cell are neutrophils, eosinophils, and basophils. These cells contribute to inflammation, which is the initial generalized immune response.

Major organs

Thymus. Located in the front of the upper chest, it acts like a nursery for the development of T cells.

Spleen. Located in the upper left side of your abdomen, it filters out foreign organisms that infect your blood, removing old or damaged platelets and red blood cells, storing extra blood and releasing it as needed, and helping form some types of white blood cells. The spleen can be removed if it is damaged, but that may lower your resistance to infection.

Bone marrow. Located in the middle of your bones, most specifically your vertebrae, pelvic, and leg bones, it generates T cells, B cells, and macrophages — cells that travel throughout the body in the blood and tissue fluids.

Lymph nodes. These nodes filter lymph fluid, removing antigens, bacteria, and cancer cells that get trapped in their weblike structure, where macrophages, antibodies, and T cells can destroy them. Hundreds of lymph nodes are located throughout your body, so removing any lymph nodes during breast cancer surgery does not compromise your overall lymph node protection.