That's the most amazing part of our immune system really - This is totally full on geeky and all but I find it absolutely fascinating:
First - Without getting complicated an antibody is basically a molecule that can bind to an antigen. So think along the lines of when a bacteria enters our body we need a way to not only recognize, but "tag" that bacteria, or put a flag on it to allow our immune systems to see it. Identify it. So an antibody is the flag and each one is unique... it sticks to the bacteria and it says hey, I shouldn't be here. The cells of our immune system now go full tilt to kill it. Remove it from our bodies. It does't have to be a bacteria, but is really any "foreign substance" or protein.
So here is the full on geeky part:
Our bodies have the ability to make somewhere over 1x10^12 unique and different antibody molecules (1,000,000,000,000) so in the trillions of antibodies. Most likely a lot more than that really.
This means that basically at any given point in time, we can literally put whatever we want in our system (bacterial etc) from anywhere on the planet and we will have an antibody that can bind to it... So we are essentially protected from any foreign or "non-self" (not from our bodies) protein known on our planet earth.
Even more geeky, if "Aliens" came to visit us or we went to another planet; as long as they were made out of proteins (amino acids really) or a portion of them was made from amino acids, or their bacteria were made out of amino acids, we will be protected by our immune system. This is how we not only evolved, but survived along side our bacterial friends and foes.
The issue we face is that this war between "us and them" has been going on for so long that some of them have evolved ways to hide from our immune systems. Sometimes they can evade us and live long enough to cause damage and kill us. Other times our immune reaction to them kills us. Sometimes they can secret "missiles" or proteins from a distance that effect us without ever even coming into contact with our cells. Other times they can simply hide out inside our immune cells, replicate, survive and interfere with cellular processes. And sometimes it just takes a while for us to "fine-tune" our antibodies to really "stick" to them firmly (specifically) and during this time they can wreak havoc on us, but even in this case we can plant thousands and thousands of weakly "sticking" flags on them and react to them, so if one particular unique antibody falls off there are thousands more already stuck to it. In any case for the most part we can recognize them and fight them off because our repertoire of various immune system defences is just so powerful and so vast.
If it wasn't, well, we would't be here today and bacteria would have won the war. And it's literally an all out war going on inside of us all day, every day. It's both crazy, and fascinating to think about
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More geeky and specific to our intestines: How big is the actual war going on???
Even just in our intestines alone; simply to protect us from oral antigens (bacteria etc) that we swallow on our food or breathe in and swallow in our mucus/spit we have about
2x10^10 or 20,000,000,000 cells (so multi billions of B-cells) that secrete IgA (antibody) or "flags". And every single day these B-cells secrete between 5 and 15 grams of secretory IgA in our mucus. So that's ~6 x10^23 IgA molecules per gram.... so the amount of sIgA were secrete daily in our intestines alone to protect us from what we eat, swallow, and what reside within us is an amount or number that is so high and so large it's hard to even count or grasp...
Math wise it's this ( I think it's correct) but a math person might want to double check as I hate math:
So every single day in our intestines we secrete 600,000,000,000,000,000,000,000 molecules of secretory IgA per gram x (times) between 5-15 grams secreted each day.
Multiply the above number by 15 (for 15 grams) and this tells us the cells of our intestines alone, every single day secrete up to
9,000,000,000,000,000,000,000,000 secretory IgA molecules simply to protect us from the bacteria in and entering our guts...
That's crazy.
Post Edited (Canada Mark) : 6/28/2015 1:41:20 PM (GMT-6)