a cancer cell

There is bacteria everywhere.  More of the genetic information in our DNA consists of code put in there by infecting viruses than is actually used to make our bodies and who we are.

Cut open a wet fruit and leave it outside, and within a day, it will brown.  And within a few weeks, it will be consumed.

So disease is everywhere.

Why are we alive?  How do we keep the invaders out?

The answer lies in our immune system.

The challenges it faces are immense.  First, it has to be able to defend you against pretty much anything.  Viruses and bacteria mutate extremely rapidly, so there is an almost endless variety of things that can attack your body.  They each have different characteristics and look like something different.

Protecting our body against this endless onslaught – it’s what our immune system does, and what immunology is about.

So: a) Defend against anything

Next, your immune system has to work really fast.  Let’s say you get cut.  Instantly, a horde of foreign elements enter your body, seeking to take over.  Your immune system has to respond almost instantly to stop the infection at the spot.

At the same time, your immune system needs to plan.  Let’s say the attacking troops have gotten past the first barrier of defenses and have established a base inside of you.  They are multiplying rapidly, taking vital resources, and turning into a threat to your existence.

There, your immune system has to mount a coordinated, multifaceted attack that specifically cripples the invaders at their weak points.

b) Your immune system has to do two things.  Respond instantly to infection with generalized defenses, and develop a coordinated attack against things that have established a beach-hold

It gets better.

Not only does your immune system have to do all this, it also has certain limitations.  First, it can in no way attack your own body.  At the same time as it has to be able to attack anything whatsoever that it encounters, it has to be trained not to attack your own body.  The consequences of that happening are typically not so good.

Second, it somehow develops memory.  Once it defeats an enemy, it forever remembers it, and is able to respond quickly and decisively to future provocation.  In general, if you get sick with something and get healthy again, you will never have to worry about that disease again.

Finally, it has to deal with ridiculously complicated logistical issues.  For instance, every day, most people eat a significant amount of food.  In the food, there very often are bacteria, viruses, and other nasty things that want to grow inside of you.

Your body has to somehow attack and eliminate the invading elements while ignoring the food.

How does it do all that?

This is the first of several posts dedicated to the immune system.  For more, see Immunology Online.