Explaining your immune system using Aliens: Special Edition

Aliens (1986) is James Cameron’s action sequel to Alien (1979) where Ellen Ripley returns to exomoon LV-426 to find it infested with aliens and a newt. The Special Edition is longer which you can get on DVD and contains a scene that we’re going to need.

Your immune system is the amazing coordination of white blood cells that are fighting ‘ill-making particles’ (pathogens) in your blood and tissues right now. We are going to use the film, slightly out of order, to explain how it works. First we skip the safe, talky bit and get quickly to Ripley and the Colonial Marine Unit being attacked by aliens from all sides.

First line of defence

Your skin is the main reason you are not ill all the time. Pathogens can’t get through and are soon washed off. Assuming you wash. You do wash don’t you? Here are the team putting a barrier between themselves and the aliens by barricading themselves in the colony command centre. Good work team!

 

Second line of defence

Our marines represent white blood cells (leucocytes) — that make up a small part of your blood but all of your immune system. This, second line of defence is the non-specific immune system where white blood cells called phagocytes destroy any particle that looks foreign. In your body this is done by engulfing them, breaking them up then spitting out the bits. For our film we can show any picture of someone wildly shooting a gun.

Randomly shooting at an alien.

Third line of defence

This shooting is all very well but we are going to need a more specialist approach to combat such a specialist creature. Memory would be helpful too, in case we encounter this creature again — you know, in case there are any more sequels. Ripley is already our memory cell in this film which is principally why she is there. Her briefing to the Weyland-Yutani Corporation allowed a bigger and faster response the second time.

The specific immune system uses two different approaches: Bullet With Your Name On It, and Kill The Infected. The first is a custom, ranged weapon that shoots at free-floating pathogens; the second is mercy-killing of already-infected, human cells.

Bullet With Your Name On It

 

In the Special Edition, the marines assemble sentry guns to keep the aliens away from the command centre. These bullets represent antibodies — free-floating molecules that attach to proteins on the pathogen’s coat (antigens), stick them together making them unusable, and mark them for destruction by phagocytes. Plasma cells generate 2000 of these each second which is a rate of fire you wouldn’t want happening by mistake, so we have a clever double-check mechanism before it starts.

First a type of phagocyte — a macrophage — engulfs a pathogen, breaks it up, and displays bits of it on its outside. There isn’t a scene in Aliens where this happens. John Hurt? He sort of displays the pathogen on his outside but he’s in the wrong film.

Macrophage being inspected by a T cell.

There are many white blood cells called T cells, each covered with a different receptor. These correspond with the many types of antigens (coat proteins) a pathogen might bring with it. When the right type of T cell binds with the bits of pathogen on the outside of the macrophage it duplicates into activated T helper cells.

Meanwhile, a white blood cell called a B cell has also engulfed a pathogen and has also presented bits of it on the outside. When an activated T helper cell binds with this the double-check is complete and it releases a chemical that stimulates the B cell to duplicate into B memory cells (like Ripley) and Plasma cells — the sentry guns. Blammo.

Kill the Infected

In Aliens the marines find surviving colonists have huddled together in the atmosphere processing station so go down there to give them a foil blanket and a bit of Kendal Mint Cake. There they find ‘Mary’, alive but impregnated with alien eggs. Fitting with our metaphor, Mary whispers “Kill me” — which we’ll take, even though that may not be exactly what subsequently happens.

 

Our own cells will present bits of the invading pathogen on the outside if they are infected. A white blood cell called T killer patrols around checking outer proteins on our cells. When it finds an antigen that fits its receptors it will duplicate into an army of T killer cells, plus some T memory cells, that march off dispatching any body cell that is displaying the same antigen. Cold.

Working together, these systems keep us remarkably well. Our bodies end up better off than LV-426 colony Hadleys Hope — not that I will tell you what happens. Next time you are at home fighting a cold be sure to watch Aliens: Special Edition as this massive battle takes place!

Colour and Vision

The last episode of Forces of Nature with Brian Cox is recommended - all about light and colour, and how it affects life on Earth.
To complement this episode, I'd also very highly recommend the Colour and Vision exhibition at the Natural History Museum (http://www.nhm.ac.uk/visit/exhibitions/colour-and-vision-exhibition.html), as it not only describes the importance of colour in the evolution of life, but also takes a look (no pun intended) at how vision itself evolved.

Make an effort to go!

40 years of life on Mars... ?

The fascinating story of the Labeled Release experiment reached its peak 40 years ago today when the first Viking Lander sent back results from the planet Mars showing microbial life does exist on Martian soil. After some initial celebration NASA decided, on balance, the positive result must have been a mistake. No further biological missions have been sent to the red planet - it is now only geology - and you'll notice missions have changed from 'looking for life' to 'looking for signs that Mars could have supported life'.

Research the story by starting with a gripping account in Michael Brooks' '13 Things That Don't Make Sense' or this online essay by Geoff Olson; then note that a recent paper ran a statistical analysis of the mission data and found to disagree with NASA's ultimate conclusion.

The wild donkeys of Collioure

The small Catalan town of Collioure (Cotlliure) has a little known secret for those patient enough to wait - wild donkeys.
The small population of feral donkeys has been roaming the hills around Collioure for nearly four centuries now, having in all likelihood escaped from the conquering French army in 1642. Other historians state that they might be from one of the ancient monasteries in the hills surrounding the town.
The small population, probably numbering no more than 30 now, has proved to be remarkably adaptable in the face of many adversities thrown its way over the years. In the late 18th century, the last attempt by the Spanish to take control of the town reduced the population, according to the local town hall documents, to perhaps as few as 10 individuals. Many of the donkeys were conscripted into the Spanish army, allowing a cavalry unit to form the first "panzer" group of mounted troops. However, due to the quixotic nature of the animals, the small unit did not survive the hostilities, and ultimately the Spanish siege failed.
The remaining donkeys have continued to adapt to their environment, particularly the changing temperature - very hot during the day, and colder at night. The donkeys are semi-nocturnal, and as a result they have evolved a reflective tapetum, similar to cats, in their eyes. Their fur is also slightly thicker than other donkey species, as they can be found at altitude where temperatures are cooler, particularly at night. It was probably this adaptation that saved the population from extinction in 1870, when a freak snowstorm covered the town and its surroundings.
Nowadays, the small population of hardy survivors is treated with respect and caution. They occasionally roam in to town, to eat the flowers from unsuspecting locals' gardens, but most of the time they graze in peace in the hills surrounding this very pretty part of the world.

Biology Olympiad (Intermediate)

Just a quick note of congratulations to three of the PAL students, who took part in the Intermediate Biology Olympiad organised by the Society of Biology. All three did very well; the results are listed below:

Ariane 52/70 - Bronze medal

Hadi 49/70 - Highly commended

Anna - 48/70 - Highly commended

Perhaps we can get more students involved next year?

Lavender

Here in the south of France there's loads of lavender, and it's got many uses. The name probably comes from the Latin "to wash" (lavare) but might have its origins elsewhere...

If it's not grown decoratively, it is usually used for production of essential oils - lavender essential oil has found its way into much modern quackery:
- calming rub
- stops runny noses
- burns
- cuts and bruises
- ear pain
- monthly cramps
- anti-stress
All of the above can be magically treated by lavender. The oils do have some antiseptic and anti-inflammatory properties, but it's perhaps safest to use lavender in cooking - it's often included in "herbes de Provence". Bees use the flowers to make some very nice honey too, and if you get up close to lavender in the summer you'll find it alive with insects:

And there's money to be made in selling it - a large bunch will cost nearly $500, or in the old days you could get 50 free haircuts. Flower power.

Life in the south of France

At last a return to what might be more regular updates. At least until things start to get very busy again.

So what is it?
Suggestions so far include "Beetleus farageibona" and "Rattus titanicexitus" though neither of these seem likely...
Any ideas?