C-C Chemokine Receptor Type 5, or CCR5, is a protein in your white blood cells. We don't know its exact function, but we're pretty sure it interacts with T cells, and it may play a key role in inflammations that result from infection. All in all, it's a pretty standard white blood cell protein. That's what HIV counts on.
Some forms of HIV use CCR5 as their point of entry into your immune system. When that happens, shit gets bad. That's why most early drugs given to HIV positive people target CCR5. It's more or less the main point of entry for the AIDS virus.
|It's like that drainage grate at Helm's Deep. Only, you know, AIDS.|
Now let's take a quick two and a half thousand year trip to the past and take a look at Ancient Athens. In 430 BC, the second year of the Peloponnesian War, Athens was struck with a massive, horrific plague that wiped out a fourth of its population. It was at this point in human history when CCR5 started to change. Medicine back then consisted mainly of blood-letting, the type of thing that lands you in a psyche ward nowadays. Back then you paid people to do it to you.
As a result, natural selection weeded out a lot of people via disease. Many survived, of course. Some of them had a bizarre natural resistance, which we now call CCR5-Δ32, or Delta 32. It's a gene mutation. A tiny variation in your genetic makeup that essentially deletes a certain segment of the CCR5 protein. As smallpox and various other diseases spread across Europe, the Delta 32 mutation became more common in the survivors, conferring various immunities to a lucky minority.
|Alas, this did not include immunity to ludicrous superstitious violence.|
Today, Delta 32 is found in about 10-15% of European-descended humans. The segment of CCR5 that it deletes turns out to be a chief cause of all kinds of problems. That includes the aforementioned HIV. I suppose you can see what I'm getting at. If you are of European descent, there is as much as a 15% chance that you are, if not immune, then highly resistant to the AIDS virus.
That's evolution at work. Think of the untold thousands of people who had to die so that this mutation could become as prevalent as it is. Think of how many people would have to suffer today for it to become a common feature in human beings. This relatively new strength, like all the strengths we enjoy as a species, came at a massive cost over thousands of years.
Luckily, we've gotten pretty good at tinkering with evolution since then. Rather than opening our veins and hoping all the sick pours out with our blood, we use real science to develop real medicine that really works. And the discovery of the Delta 32 mutation is a boon for medicine. We don't know how, and we don't know for sure it'll work, but it's very possible that this natural resistance might hold the key to curing HIV, a disease that only twenty years ago was synonymous with a death sentence.