This is the first of a two-part series on the immune system. Lyrics are immediately below the video.

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Links to Immune System Main Menu (interactive learning, and curriculum)


It’s a dangerous world full of pathogenic germs
Viruses and fungi and bacteria and worms
They’re trying to invade you, to them you’re food and shelter,
And once they get inside it sends your system helter skelter

But you’ve got a system for fighting back,
For recovering your health from infectious attack
With weapons that leave these pathogens in ruins
Yeah we’re talking ’bout the system that makes us immune

It’s the immune system
Sworn to protect you
From dangerous pathogens that try to infect you
Three layers of defense keep the germs away
Letting us live yet another day,

Skin and mucous membranes first, then innate defenses,
For fending off invaders that breach our fences,
Then specific responses, with lymphocytes B and T
Let’s learn about immunity!

Our outermost defense is our impermeable skin
Dead outer cells lined with fibrous keratin
Covered with secreted lactic acid and lysozyme
A bacteria dissolving enzyme

At openings like noses there’s a mucus-membrane lining,
A viscous protein fluid trap for pathogen confining,
And pathogens that enter through the mouth can die quite miserably
When they’re dissolved inside our stomach’s sour acidity.

But even with these barriers, some pathogens break through
Entering through cuts or riding mucus into you
The next step in defense is non-specific and innate
We share it with the plants and fungi and invertebrates!

You’re born with these defenses that’s why they’re called “innate.”
They’re implemented when infection starts, no need to wait
They consist of cells and proteins that make non-specific moves
Against those foreign entities that enter into you.

The primary components here are white blood cells
Sentinels or guards who respond when all’s not well
They’re leukocytes, they fight invaders in generic ways
Engulfing them or chemically blowing them away


Inflammation’s a key part of the innate response
You know it from the swelling and the way a wound feels hot
Tissue damage from infections or injuries
Causes leukocytes like mast cells to release histamines

Which makes capillaries leak though vasodilation,
Leads to redness and to swelling and a painful sensation
Sentinel cells and tissues emit chemical alarms
That draw defenders to the scene defending us from harm.

The first cell to arrive could be a neutrophil
The most abundant type of white blood cell
They’re phagocytes,engulfing viruses and germs
Devouring pathogens like robins eating worms

These neutrophils gorge themselves until they die defending us
Their cellular remains accumulate as pus
Innate responses, they’re anything but simple
Remember that each time you see the pus inside a pimple

Another phagocyte is called a macrophage
Which means “big eater” they attack with rage
Dendritic cells are phagocytes too
Patrolling ‘neath the skin and in the lungs and other tissues

A fever is a body-wide systemic inflammation,
The higher temperature inhibits germ replication,
And might also enhance immune cells’ phagocytic action
As fever ramps up our body’s chemical reactions.


Natural killer cells are also on the innate team
Detecting body cells that display abnormal proteins
Indicating viral infection or cancer
And when they meet abnormal cells here’s their deadly answer

These killers release perforins that perforate with holes
Infected cells’ membranes making them explode
Along with secretion of deadly granzymes
That induce infected cells to commit suicide

Even the infected cells try to do their part
Secreting interferons, proteins that make it hard
For viruses to penetrate the cell membranes
Of uninfected nearby cells which keeps them in the game

Complement’s another part of innate immunity
It’s made of 30 proteins, that work as a community
To open holes in membranes of invading bacteria
Destroying them and clearing out infection from that area.

Now that’s innate immunity, part one of our song,
So join us in immune part two so you can sing along,
As we learn ‘bout defenses acquired and specific
Immunity, it’s really terrific!