The Human Immune System...
Armed and Ready!

The human immune system seems to bring the military to mind when discussing it. Armed and Ready! Search and Destroy! Ever vigilant! All are very appropriate descriptions of our immune system.

Somehow, it just seems fitting to talk about the human immune system in military terms.

It is always on guard, constantly doing reconnaissance, never sleeping, ready to attack; its troops willing to die to keep us alive.

Perhaps a quick overview of this amazing system is in order to set the stage for a deeper examination.

But before going on, a quote from Elizabeth Taylor is order. She hit the nail on the head when she said,

As we will see in the page on laughter in the Lifestyle section, there is a lot more to health and immunity than just chemicals and cellular response.

First off, a good place to start might be in looking at who or what the human immune system is guarding against.

Our body is under constant attack, 24/7, day in and day out. The invaders never take a holiday so our immune system can't either. Rest assured, when we are asleep, our immune system is wide awake.

Our body is home to over 600 trillion bacteria; some friendly and beneficial; others harmful and out to do damage. There are ten times more bacteria in and on our body than there are cells that make up our body.

Many of the harmful bacteria have become highly adaptive in outsmarting the antibodies designed to kill them. The term Superbugs has been coined to described this new threat to our health.

Viruses are always looking for a host to inhabit and help them multiply. They are true parasites and need a host cell in order to grow and reproduce. They have a nasty habit of penetrating cells in our body and hijacking the cells machinery to reproduce the viral DNA and messenger RNA.

Nature itself has a whole arsenal of molds, spores and pollens, collectively called allergens, that challenge the human immune system.

On top of all that, our body's cells are constantly being damaged by free radicals. Unless these mutated, damaged cells can be eliminated; the seed of a tumor can take root and eventually will become a future cancer diagnosis.

Finally, there are the man-made chemical toxins that we ingest, breathe in and otherwise absorb in our homes and workplaces. These must also be taken care of by the human immune system.

Let’s take a look at the structure of the defending army in the human immune system and how it does its job.

Not so fast! First off we need to clarify a couple of terms.

An active response is the body's own reaction to a threat that attacks on its own or is introduced on purpose as in a vaccination.

The active response creates memory cells that are long lasting and provide immediate protection if the same invaders show up again. The Active response with its memory cells is so efficient that many people won't even know they have been exposed. It takes care of the disease before the symptoms ever appear.

The Passive response is generally medically induced using created antibodies. This response doesn't occur naturally and is usually short lived.

A good example of a specific passive response is the hepatitis A vaccination usually given to international travelers. It only provides temporary protection.

Sometimes booster shots are needed with passive immunity; tetanus, polio and smallpox inoculations all need boosters at appropriate intervals.

Now on to the lines of defense!

The first line of defense in the human immune system is the moat around the castle. It's a physical barrier that we know as skin. We don't usually think of skin as an organ but it is, in fact it's the largest organ.

Diagram: Structure of human skin, the body's first line of defense and largest organ. Note the sweat and sebaceous glands.

As far as defending our body, skin is a waterproof barrier with glands that secrete both antibacterial and antifungal chemicals to fight invaders. The skin's low pH creates an acidic environment in which most invading organisms cannot survive.

OMG! I'm red; I'm swollen; I hurt; I'm hot! I must be inflamed!

The second line of defense in the human immune system is the inflammatory response. Invaders that breach the skin or epithelium layer of the respiratory, gastrointestinal or urinary systems trigger an immediate response, usually within seconds.

The inflammatory response isn't actually what we think of as part of the human immune system. Nevertheless, it is usually referred to as Innate Immunity or the innate immune system; it is what we were born with.

It can be thought of as a "tripwire" that calls out an inflammation SWAT Team when there is a breach in the first line of defense.

Inflammation messengers are the first responders to attack or injury. They are the ones that summon the the fighters in white blood cells to take care of whatever infectious agents have gotten in. The classic manifestations of inflammation are heat, redness, swelling and pain.

The response is always the same, meaning that it is non-specific and doesn't care if the threat is a physical injury or organism. Two big differences between the inflammatory (innate) response and the immune system is that it has no memory and does not create immunity.

Inflammation was thought to be a disease until 1793 when John Hunter found that it was not a disease but, instead, a response by our body to aid in the recovery.

It doesn't have to identify the invader; it's just pure search and destroy. With the inflammatory response, it's "kill 'em all, sort 'em out later". Click on Innate Immunity for a greater discussion on the inflammatory Response.

The human immune system takes over after the inflammation response starts to wind down. This line of defense is characterized by "natural killer cells" which we will meet shortly.

The immune system is very focused, very specific. Its objective is to recognize strangers. The immune system is very suspicious of strangers. It immediately thinks "stranger danger" whenever it meets a cell it doesn't know.

It is programmed to recognize "self" from "non-self" and it has a very long memory. As they say, it never forgets a face, or in this case, an antigen or pathogen. Specifically it is on the lookout for recurring events and generally remembers events for a lifetime.

The pictoral below represents the immune response of a first exposure and the apparent non-infections of subsequent exposures.

In medical terms, we might say the human immune system stays poised and up-regulated; meaning alert and ready to pounce on any stranger it meets.

Another word the medical community uses is "inducible". The immune system can be made to wake up by inoculation, vaccination, or natural exposure. All these occurrences will induce the immune system to go to work.

One more thing to understand about the human immune system is that anything it sees or experiences between conception and birth, a typical nine-month period known as embryogenesis, Will be viewed as friendly, or "self".

Given that, it will respond to any foreign invader that it has not seen since embryogenesis. We only have this immune tolerance once in our lifetime; when we emerge and start breathing on our own, it's over.

In the next page, we will look at the three types of human immune system responses; the humoral, cell mediated and secretory phase. All are collectively called acquired or adaptive immunity. Click on Acquired Immunity to continue.

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