Cells Of The Immune System

February 16th, 2010

The cells of the immune system work together to protect the body against antigens, foreign bacterial, viral or parasitic invaders. The immune system is very complex and each cell has a unique function of keeping the body healthy. These cells can be classified into two different types: phagocytes and lymphocytes.

Phagocytes

These cells are dedicated to search and destroy missions against bacterial, viral, or dead cells. The three main types are macrophages, dendritic cells, and granulytes.

Macrophages: Important to immune response, macrophages act as antigen scavengers. They originate in the blood stream as white blood cells called monocytes; once mature, they leave the blood stream and are called macrophages. They operate in the spleen or lymph nodes to capture and present antigens to T and B cells for immune response.

Dendritic Cells: Serving the same function as macrophages, dendritic cells are even more effective because they travel the blood stream and other tissues of the body, including the spleen and lymph nodes to capture antigens for immune response.

Granulocytes or Polymorphonuclear (PMN) Leukocytes: This group attacks antigens in large numbers and eats them until they die. Some are also specialized against parasitic invaders.

Macrophages and dendritic cells also serve another very important function: antigen presentation. They capture and present antigens to T and B cells as an alert for immune response.

Lymphocytes

These white blood cells begin life in the bone marrow but then travel throughout the lymphatic system. The function of the lymphatic system is to feed the body new cells and filter out dead cells and foreign bodies. Lymphocytes rely on lymph vessels to transport throughout the lymphatic system.

The two broad subtypes of lymphocytes are T cells and B cells:

T-Cells: These lymphocytes are named after the thymus, where they mature after they leave the bone marrow. They usually settle in the spleen or lymph nodes for activation, but they are also sometimes found in liver, lung, blood, and intestinal and reproductive tracts. There are two different types of T-Cells:

T Helper: the main regulator of immune defense, the job of this T-cell is to initiate or increase immune responses by activating other white blood cells to fight off infections. T Helpers must be activated themselves by the antigen presentation of macrophage or dendritic cells.

T Killer/Suppressor: These cells specialize in destroying viral-infected and sometimes bacterial-infected cells of the body. They can also attack cancer cells and sometimes parasites.

B Cells: When a B cell meets an antigen, it relies on T cells for activation. Once it is activated, the B cell begins the process of cell division. During this process, two new cell types are created: plasma cells and B memory cells.

Plasma cells: these cells serve the key purpose of creating antibodies, which help search and destroy antigens. Plasma can produce antibodies at an astounding rate of tens of thousands per second.

Memory cells: these cells live in the body for a long time and serve to remember specific antigens. This works so that the next time the invader makes its way into the body, it is quickly recognized and destroyed.

Natural Killer Cells. Also called NK cells, these cells are very similar to the T Killer/Suppressor cells. These effector cells serve to kill some tumors, like melanomas, lymphomas andviral-infected cells, particularly herpes and cytomegalovirus-infected cells.

They are dissimilar to T-cells, however, in their function to kill antigens without dependency on a conference in the spleen or lymph nodes first. They do work against antigens more effectively when set in motion by the T Helper cells.

http://nobelprize.org/educational_games/medicine/immunity/immune-detail.html

http://www.thebody.com/content/art1788.html

http://www.microbiologybytes.com/iandi/2a.html

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