Warriors of Your Immune System

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The immune system accounts for one percent of our bodies' 100 trillion cells. All white blood are leukocytes. White cells (like all blood cells) arise in the bone marrow. The brain does not control the immune system.

Active Immunity



Complement proteins


B Cells/Plasma Cells

Fun Facts

Helper T

Killer T



Memory T


Passive Immunity

Suppressor T



White Blood Cells

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Immune System Vocabulary 

Barriers: Skin, mucous and hairs work together to keep invaders out! First line of defense is the skin, which is rich in IgA antibodies. If invaders get past the skin, they need to get by nonspecific defenses like the Macrophages, Natural Killer cells, and complement proteins. Go back to the top


Every tissue in the body is loaded with capillaries, small blood vessels slightly larger than red blood cells. Coursing through the capillaries you find blood plasma transporting nutrients to the tissue and removing waste. Red cells slip by single file releasing their load of oxygen and picking up carbon dioxide for return to the lungs. Lymphocytes can travel in blood vessels or lymphatic vessels. Lymph is a clear fluid that bathes the body's tissues. (Taken From Cells Alive!)

And amongst the red cells is an array of specialized cells - neutrophils, platelets, monocytes, and lymphocytes - ready to spring into action at the slightest nick of the skin. (Taken From Cells Alive!)

Trauma, bacteria and dirt signal to white cells in nearby vessels there is damage to control. Neutrophils, the most active and phagocytic of the white blood cells, become sticky and begin to adhere to the inside of the vessel wall. Adherence slows the cells down, making them "roll" on the inside of the vessel. The neutrophils then become super-adherent and squeeze out between endothelial cells that line the vessel; a phenomenon called "diapedesis". (Taken From Cells Alive!) From there, the white cells must FIND, EAT, and KILL foreign microbes.

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White blood cells (Leukocytes) can be classified as follows:



a.      Neutrophil

b.      Eosinophil

c.      Basophil



a. Lymphocyte (B or T cell)

b. Monocyte (Precursor to Macrophage)

                                    Lymphocytes = B cells and T cells

B Cells:

B cells complete maturation in bones. They are later found in Lymphnodes. Major battles take place at Lymphnodes. Lymphocytes can travel in blood vessels or lymphatic vessels. Lymph is a clear fluid that bathes the body's tissues.

T Cells:

T cells mature in the thymus : The thymus is an organ that is found near the heart. "T" stands for thymus. The thymus is like a nursery or a school. Go back to the top



                                       Second class = Phagocytes. Phagocytes include monocytes, macrophages, and neutrophils.


Phagocyte means, "eating cell", or "cell eater". The monocytes are phagocytes that circulate in the blood. When monocytes migrate to tissues, they become macrophages. Special macrophages can be found in the lungs, kidney, brain, and liver. Neutrophils are similar to macrophages, but smaller.  Go back to the top


Lymphnodes are like fighting arenas because battles occur there. They are found throughout the body: neck, armpits, and groin. B and T platoons wait for invaders there and go to war. A swollen gland is a sign that a battle is raging in the lymphnode. Go back to the top

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Recognition, amplification of defenses/attack, suppression, and memory

Helper T cells: This cell roams the body. It is the commander in chief because identifies the enemy and commands the other cells in the immune system to go to war. It looks at antigen's epitopes (specific antigenic information) to identify the invader. The helper T cell then communicates with phagocytes, B cells and killer T cells and it commands them to replicate and go to war.  Go back to the top



MHC: MHC stands for "major histocompatibility complex". MHC is like the flag on a ship. It is found on the surface of all cells. It signals the body that the cell is friendly. (It is important for the body to distinguish self and non-self.) MHC can also signal an alarm if a virus is reproducing in the cell.




Macrophages place antigens of enemies on its MHC to warn Helper T cells that the body is under attack. After doing this, the macrophages and Helper T cells reproduce and go to war. B cells can also place foreign antigens on its MHC and alert the Helper T cells.  Go back to the top



Antigens: a code, a symbol or a mark that triggers an immune response. It is like a fingerprint. Tissue from another person carries foreign antigens. Identical twins, however, have identical antigens. Go back to the top

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Recognition, amplification of defenses/attack, suppression, and memory

Lymphokines: These are chemicals that cells use to communicate with one another. Lymphokines start the replication process. For instance, after exchanging these chemicals and replicating, copies of the macrophages and helper T cells rush to the spleen and lymphnodes where they stimulate the production of other cells to fight the invader. The spleen filters antigens from the blood.  Lymphocytes, including both T cells and B cells, secrete lymphokines, while monocytes and macrophages secrete monokines. Go back to the top




B Cells become Plasma Cells: Plasma cells produce antibodies. Once stimulated, the B cells replicate and turn into plasma cells that produce chemical antibodies at a rate of 10,000 molecules per second per cell! B cells (plasma cells) are found in lymphnodes. (Lymphnodes are found in your neck, armpits and groin.) Macrophages and Helper T cells can alert B cells to go to war. B cells complete maturation in bones and then move to the Lymphnodes. Each B cell is pre-programmed to make one specific antibody. Go back to the top


Bear Trap

Antibodies: Antibodies belong to a family of large molecules known as immunoglobulins. Each has about a dozen parts and is designed for a specific invader. They float throughout the body and wait for invaders. Antibodies lock on to the antigen of the invader like a key fits into a lock. They neutralize the enemy and tag it for attack. Antibodies are like guided missiles, handcuffs, straight jackets, mines or bear traps. They hold invaders until Macrophages can eat them up. They can kill the enemy with the help of complement proteins.  Go back to the top


Complement proteins: Complement proteins float throughout the body. They can work with antibody to create holes in invaders. They inject liquid into an invader and cause it to pop.  Go back to the top


Macrophages: A macrophage is a phagocyte, or eating cell. Macrophage means "big eater." Macrophages are found in all tissues and act as housekeepers, guards, and frontline defenders. They are voracious eaters and will eat the enemy and dead body cells. They are scavengers. They are garbage collectors.

If a Helper T cell sounds an alert, a macrophage will reproduce itself by the thousands and its new copies will go to war against the enemy.

Macrophages have MHC on their body too. If a single macrophage detects and eats an enemy, it can alert the Helper T cell by placing the enemy's antigens on its MHC; it will run the dead enemy up the flagpole and sound the alarm. It uses lymphokines to communicate with other cells and the brain.  Go back to the top

Scanning electron micrograph of human macrophage (Gray blob) ingesting Streptococcus pyogenes.

(The bacteria are orange.) The spherical cell riding piggyback on the macrophage is a lymphocyte, an important component in the immune response to infection.



Killer T Cells: Copies of Helper T cells will also turn on killer T cells. Killer T cells destroy cells in the body that have been invaded by foreign organisms. These cells inject enzymes that eat away the infected cell. Killer T cells also destroy cancer cells.  Go back to the top

Natural Killer Cells: There are also natural killer cells. They are always on alert and they can kill any foe. Like the killer T, it kills on contact. Go back to the top

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Recognition, amplification of defenses/attack, suppression, and memory

Suppressor T Cells: Once the war is over and the body has won, the Suppressor T Cell slows down or stops the activities of B cells and other T cells. Go back to the top

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Recognition, amplification of defenses/attack, suppression, and memory

Memory T Cell: T and B cells, generated during the initial infection, stay behind and become memory cells. Memory cells stay on the lookout for future invaders. If the same invader tries to invade the body a second time, an overwhelming attack is mounted by these memory cells, and the new invasion is quickly crushed. The body is now immune to that particular organism. This mechanism allows vaccinations to work.  Go back to the top

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Active Immunity: There are 2 ways to become immune to a disease.

One way to acquire immunity is to get a disease and survive. This is natural immunity.

The second way to become immunized against a disease is to get a vaccine. Vaccines are dead or weakened germs that illicit an immune response without causing the disease. In order for vaccines to be effective, they must be safe and they must have good antigens.


Passive Immunity:

Everyone has experienced passive immunity. Passive immunity means that someone else is doing the work of fighting off infection. For example, infants receive antibodies that have traveled across the placenta. Antibodies are also present in the milk of mothers. Serum with antibodies (anti-serum) or "gamma globulin" is sometimes given to travelers in countries with hepatitis. This type of immunity only lasts a couple of weeks.  Go back to the top



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What a virus does in the body: A virus enters the body, and works its way into cell. Viral genes commandeer the cell's own machinery, forcing it to make more viruses. Soon baby viruses spew forth into the blood stream. The cold virus would kill you were it not for the immune system. Within hours, antibodies that routinely patrol the bloodstream encounter free-floating viruses. These antibodies latch on, disabling the virus, until a phagocyte can engulf the invader. If a phagocyte eats an invader, it will display the antigens of the enemy on its MHC. After Macrophages summon the Helper T, they communicate with lymphokines and replicate. The Helper T then summons the B cells to turn into plasma cells and make antibodies. Killer T cells are commanded to track down infected cells. Infected cells are recognized by the bits of virus attached to the MHC of the cell. The Killer T cells shoot the infected body cells with caustic chemicals that lyse the cell, and dissolve the DNA of the cell and the virus. When the war is over, memory T cells are made. Extra antibodies are located in strategic locations in the mucous membranes, saliva, and tears. Go back to the top


Fun Facts:

Four phases of the immune response: recognition, amplification of defenses, attack, and suppression.

Arthritis, an autoimmune disease, occurs when the immune system attacks the body.

An allergy is when the immune system responds inappropriately to a harmless substance.

A Virus is little more than a package of genetic info that takes over a body cell to reproduce.

99.9 % of Bacteria are essentially good.

There is a T cell, B cell and an antibody for every different antigen from smallpox to the common cold. In order to have room for these warriors in the body, there is only of a few of each kind. However, when danger calls, the cell in need will reproduce to become millions.  


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