Every day, you are exposed to billions of bacteria, viruses, and parasites from the environment. Your body is an open target all the time that it's really a miracle you're still alive. The secret lies in your immune system which is intricately designed and organized to protect you from these harmful microorganisms.
A component of this complex system is its immune cells. With the protective mechanisms of these cells, it's like having a full army on 24 hour patrol which defends you from dangerous foreign invaders. What happens when you don't have these cells? One of my sources said that as morbid as it may seem, think of someone dead where his immune system stopped working and millions of organisms attack his body until what's left is a skeleton.
So what are these built-in soldiers of yours which help in keeping you alive every day?
These cells are usually among the first to counter attack during an infection. Phagocytes are programmed to search and devour bacteria, viruses and parasites as well as the cells that are damaged by these microorganisms.
There are three of kinds of phagocytes.
- First are the granulocytes which attack foreign bodies in large numbers. Using their powerful enzymes, they engulf enemies.
- Second are the macrophages which compensate for their slower response through their bigger size, longer lives, and their ability to eat more intruders.
- And third are the more recently known dendritic cells which also capture and eat up foreign substances.
Aside from directly attacking foreign bodies, macrophages and dendritic cells have another crucial role in the immune system. After devouring a virus, bacteria or a parasite, they actually carry a part of their victim called antigen on their surface. They then travel to the lymph nodes, spleen and thymus where more powerful immune cells called lymphocytes are found. In there, the phagocytes present the antigen to the lymphocytes (call them your second line of defense, if you may). Lymphocytes have numerous receptors on their surface that match a particular antigen. Once a receptor recognizes the antigen, the lymphocyte is activated to help fight the intruders.
One kind of lymphocytes is the T-cells which are of two types: the Helper T cells and Killer T cells.
- The Helper T cells are actually the first to be activated by an antigen presented by a phagocyte. When this happens, the Helper T-cells produce proteins that in turn activate the Killer T-cells as well as the other immune cells such as the B-cell.
- The activated Killer T cells then look for the cells that are infected by the viruses and bacteria and swiftly kill them.
Another group of lymphocytes alerted by the antigen carried by your macrophages or dendritic cells are the B-cells.
To be fully activated however, B-cells need the proteins of Helper T-cells as mentioned.
Once this full activation occurs, a B-cell divides into two cells: plasma cells and memory cells.
- Plasma cells produce antibodies. These antibodies attach to the antigens of the foreign substances and the cells infected by them. Through these, not only do they stop the intruders from causing further damage, they also mark and gather these enemies, making it easier for the eater cells to devour them.
- Memory cells on the other hand, records the imprint of the antigens. When invaders whose antigens they've recorded attack you again in the future, the immune system is activated a lot faster, meaning the antigen-presentation of the pathogens as well as the conference of the Helper T-cell and Killer T-cell need not happen. Your memory cells just remind the other immune cells that they've once fought this kind of enemies and they'll attack them right away. Often, the response is so quick that the invading microorganisms are wiped out before they can cause you any symptom. Consider Chicken pox; once you have it, you'll never have it again (except in rare cases) - that's because your memory cells (which are also produced by T-cells) simply remember them.
As stated, your immune cells are just a part of your complicated immune system. In fact, this system is so complex that a lot of it is yet to be fully understood. But what is known is enough to assure you that your body is fully equipped to take care of you, as long as you take good care of it too.