The Miracle Of The Immune System

Step By Step To All-Out War

Until now, we have discussed the general structure of the defence system, its organs, cells, and enemies. In this chapter, we will explore the deadly warfare between our defence system and enemy cells, and the wonderful defence our body mounts. 

The brave battle fought by of our defence system is comprised of three important stages: 

1. Identification of the enemy, first action. 

2. The attack of the real army, all-out war. 

3. Retreat to a normal state.  


The defence system has to clearly identify the enemy before it starts the fight. This is because each engagement differs from the other depending on the type of enemy. Moreover, if this piece of intelligence is not properly handed on, our defence system may inadvertently attack the body's own cells. 

The phagocytes, known as the scavenger cells of the defence system, take the first action. They fight hand-to-hand with the enemy. They are just like infantrymen who fight with bayonets against enemy units. 

Sometimes, phagocytes cannot catch up with the increasing numbers of the enemy, at which point big phagocytic cells, macrophages cut in. We can liken the macrophage to cavalrymen cleaving their way through the middle of the foe. At the same time, macrophages secrete a fluid, which sets off a general alarm in the body to increase the body temperature. 

Macrophages have yet another important characteristic. When a macrophage cell captures and engulfs a virus, it tears off a special portion of the virus, which it carries on itself like a flag. This serves as a sign for the other elements of the defence system as well as an item of information. 

Once the gathered intelligence is forwarded to the helper T cells, by the help of which they identify the enemy, their first task is to immediately alert the killer T cells, stimulating them to multiply. Within a short period, the stimulated killer T cells will become a formidable army. This is not the only function of the helper T cells. They also ensure that more phagocytes arrive at the battlefront while they transfer the gathered intelligence relating to the enemy to the spleen and lymph nodes. 

Once the lymph nodes receive this information, the B cells, which have been waiting for their turn, are activated. (The B cells are manufactured in the bone marrow and then migrate to the lymph nodes to wait for their turn to be of service). 
 

1 THE WAR BEGINS
As viruses start to invade the body, some will be captured by the antigens with the assistance of the macrophages and subsequently destroyed. Some of millions of T helper cells travelling in the circulatory system have the ability to "read" this specific antigen. These particular T cells become active when they bind to the macrophages.
2. FORCES MULTIPLY
Once activated, helper T cells begin to multiply. They then warn the killer T cells and B cells, which are few in number and sensitive to the enemy virus, to multiply. When the number of B cells increases, the helper T cells send them a type of signal to initiate the manufacturing of antibodies.
3. DEFEATING THE INFECTION
At this point, some viruses have successfully penetrated the cells. The only place where viruses can multiply is in the body cells. With the chemical materials they secrete, killer T cells cause the death of these cells by drilling through their membranes, and removing the elements inside. Thus they prevent the virus in the cell from reproducing. By holding directly on to the surface of the virus, antibodies inactivate them and prevent them from invading other cells. In conclusion, cells that are infected are destroyed with the aid of chemical substances, which were prepared prior to the attack.

4. AFTER THE WAR 

After the battle is won, and the disease has been eradicated, suppressor T cells stop the whole offensive system. Memory T and B cells remain in the blood and lymphatic system in order to become immediately activated in case a virus of the same type is met.

The activated B cells go through a number of stages. Every stimulated B cell begins to multiply. The multiplication process continues until thousands of identical cells are formed. Then, the B cells, which are ready for war, start to divide and are transformed into plasma cells. Plasma cells also secrete antibodies, which will be used as weapons during the fight with the enemy. As stated in earlier chapters, B cells are capable of producing thousands of antibodies in a second. These weapons are very handy. They are capable enough to bind to the enemy first, and then to destroy the biological structure of the enemy (antigen).   


If the virus penetrates the cell, the antibodies cannot capture the virus. At this point, the killer T cells come into play again and, by identifying the viruses in the cell with the help of MHC molecules, they kill the cell. 

However, if the virus has been successfully camouflaged, escaping even the notice of killer T cells, then "natural killer cells", briefly called NKs, swing into action. These cells destroy the cells which host viruses in them, and which are imperceptible to other cells. 

After the victory is won, suppressor T cells stop the war. Although the war is over, it is never to be forgotten. Memory cells have stored the enemy in their memory. Staying in the body for years, these cells help the defence to be faster and more effective if the same enemy is encountered again. 

The heroes of this war have not received any military training. The heroes of this war are not human beings able to reason. 

The heroes of this war are cells so minuscule as to hardly cover a full stop when they come together in millions. 
Moreover, this amazing army does not engage in fighting alone. It manufactures all the weapons it will use during the war; it makes all war plans and strategies itself, and cleans up the battleground after the war. If all these processes were left in the control of man, and not cells, would we ever be able to handle such a feat of organization?