The Immune System in Action

The Immune System in Action - Part 1

Introduction

AIDS researchers continue to make progress in battling HIV, addressing the fight with a variety of new and promising approaches...but this presentation isn't about the fight against the AIDS virus.

We instead take a look at the battlefield where the fight takes place, putting you into the world of the immune system.

A mumps virus enters the body, then enters a cell. There it makes copies of itself. How does the immune system respond? It's up to you to figure it out. A play-by-play explanation will follow, as well as an explanation of what makes an attack by the AIDS virus unique...and devastating

The immune system fights one of the many battles that it engages in each and every day to keep the body healthy.

The Immune System in Action - Part 2

What Happens

The enemy in its war is a nasty little virus -- a mumps virus. That virus quickly finds and enters a healthy cell within the body, where it uses that cell's machinery to make many copies of itself.

The Immune System in Action - Part 3

What Happens 2

Within the body, a macrophage determines that these viruses are the enemy and moves in toward one of the invaders. The macrophage devours the virus and rips the virus apart.

The macrophage then displays fragments of the virus, called antigens, on its surface.

Although the macrophage at this point is able to destroy more and more viruses, there is no way it could do so faster than the viruses are being made. Something else has to be done.

The Immune System in Action - Part 4

What Happens 3

The macrophage seeks out a helper T cell. Not from any helper T, though. The cell has to recognize the fragments of the virus on the macrophage's surface. Once the macrophage encounters such a T cell, it and that T cell become united. The connecting of these cells sets into motion a series of events -- events that, through a multifaceted yet focused attack, lead to the annihilation of the mumps viruses.

The Immune System in Action - Part 5

How the Viruses were Wiped Out

Upon binding with each other, the macrophage and helper T cell release chemicals that send special immune cells into action. These chemicals stimulate the production of helper T cells and macrophages. They also stimulate the production another type of T cell: the killer T cell.

By now, many viruses have invaded the body's cells. The job of the killer T cells is to search out, attack, and destroy those cells already infected with the virus.

The Immune System in Action - Part 6

How the Viruses were Wiped Out 2

The newly-created helper T cells take a different approach to the invaders. The helper Ts release their own chemical message in order to stimulate the production of B cells, another very important player in the immune system's counter attack. These B cells transform into plasma cells which, in turn, flood the body with millions upon millions of antibodies.

The Immune System in Action - Part 7

How the Viruses were Wiped Out 3

Like macrophages, antibodies seek out foreign invaders. Unlike macrophages, they're very selective about what they attack. The ones produced by this last batch of B cells are after the strain of mumps virus that intitiated the counter attack, and only that strain. Many of these antibodies attach themselves to any mumps viruses they encounter. Attached antibodies acted as flags that say, "Here's one!"

The Immune System in Action - Part 8

How the Viruses were Wiped Out 4

Macrophages, now more abundant (thanks to the chemical released by your macrophage and the helper T), consume the flagged viruses. Sure, the macrophages would have gone after the viruses without the help of antibodies, but with the antibodies' help, they find and destroy the viruses much more efficiently.

The flags also attract molecules called complements. Complements seek out any antibody-virus combinations and pierce the viruses, thus killing them off.

The Immune System in Action - Part 9

How the Viruses were Wiped Out 5

Within the span of a few days, the virus that first entered your body and its decendants are completely wiped out.

After the final battle, the numbers of antibodies, macrophages, B cells, and helper and killer T cells decrease dramatically. What remains, though, are memory B cells and memory T cells. If the virus ever enters the body again, these will quickly move into action and most likely wipe out the invader before it ever gains a stronghold.

The Immune System in Action - Part 10

Battling AIDS

You've seen how the immune system successfully fights invaders such as the mumps virus. Why isn't it able to do the same with {aids} HIV?
The reason is that the virus attacks the immune system's T cells, thus disrupting the body's immune response. Still, the immune system puts up a valiant fight, producing a billion new cells every day to combat the virus. A billion isn't enough, though, because a billion copies of the virus are also produced every day.

The two forces continue to fight -- day after day, month after month, sometimes year after year -- until the immune system exhausts itself. Once this happens, the number of T cells drop dramatically. And with this vital component of the immune system missing, the body is left susceptible to other diseases.

Notes - Fighting Other Invaders

The attacker in this animation was a virus. The immune system would respond similarly if the body were attacked by bacteria or other microorganisms.

The Real World

The sequence of events presented in this feature may seem somewhat involved -- and yet, exactly how the immune system works is decidedly more complex and still not fully understood. Although much has been learned in the past decade, there is much left to be discovered.