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Introduction to the Immune System

Immune cells

Do you remember the last time you were sick?  Chances are you remember having had a head cold or the flu, or maybe even a stomach virus.  You might have thought that you were never going to recover, but in a few days, you were feeling yourself again, thanks to your immune system!

Pathogens - What makes you sick?

Bacteria and viruses are usually to blame for bringing on nasty colds, fevers and fatigue, and many serious infections. There are other life forms that can infect you as well, such as parasites and fungi, and also non-living things like chemical toxins. Any microorganism that causes infection is called a pathogen.  Some common pathogens are the Influenza virus that causes the Flu, or the bacterium Streptococcus pneumoniae which causes Pneumonia.

Transmission - How do you get sick?

Pathogens can infect you in many ways which .  Sometimes kissing, sneezing, coughing, or touching contaminated areas can spread infection. This is how the common cold is mainly spread.  Many bacterial diseases can come from leaving open wounds untreated and eating contaminated food; also blood poisoning or food poisoning can develop.  Yet more chronic diseases can spread through transferring blood or sexual contact, like the HIV virus.   There are many ways pathogens spread from person to person, and each pathogen is different, but sometimes all we have to do to get sick is breathe in air-born particles! 

With so many points of entry and so many dangerous microbes out there, it seems that we should be sick all the time.  Luckily, our immune system is working ‘round the clock to fend off infections from outside particles and clean the body of dead or old cells.

What is the immune system?

The immune system is not located in a specific organ. It’s easiest to think of our bodies’ immune system as a complex constellation of different types of cells like B and T cells and tissues like the lymphatic system and the thymus that work together to protect nearly every area of our body.  Each type of cell is prepared to perform certain functions, such as killing damaged or infected cells, carrying messages, making antibodies, or carrying away debris.

You might ask, how does each cell know what job to do?  Are they just born that way?  And how do they differentiate between “good” and “bad” cells, knowing not to attack your own healthy cells? 

Distinguishing self from non-self

In fact, this is the most important function of the immune system: to distinguish what cells and substances belong to your body and are healthy, and which aren’t! What belongs to the body is referred to as “self,” and something that doesn’t belong as “non-self.” Think of the wide variety of different tissues and cells that can be found in your body: hair cells, teeth cells, bone cells, blood cells, calcium in your bone, there are even some friendly bacteria that live in our intestine to help us eat! Your immune system has to be very smart to be able to discern such a variety of things!

Understanding how the immune system works could reveal the key to curing many infections and diseases.  But if you are just beginning to explore the many functions of the immune system, the most important idea to keep in mind is that our immune system has “learned to learn;” in other words, through millions of years of evolution, our immune system has acquired the ability to learn and remember information about the billions of different cells and substances it comes into contact with every day.  Without the ability to learn and remember, you’d keep getting sick from the same thing over and over!

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