So… What’s An Antibody? May 7, 2008Posted by Hegemony in Science.
Wow… has it really been this long since I posted? Sorry ’bout that. Life and such.
Antibodies are really some of the most interesting proteins you have. Their use and production are both absolutely remarkable and you owe it to yourself to at least appreciate their existence.
Congratulations, if you’re reading this you’re probably a vertebrate (if not, please do contact me at once, I’ll have some questions). As a vertebrate you have billions of antibodies floating around in your blood stream and tissues. When antibody producing cells are maturing, those that have antibodies that recognize your own cells as foreign are destroyed. You only want antibodies that will “tag” stuff that isn’t part of you. To put it simply an antibody allows for specific clearance of threats. They are what your body uses to recognize what’s “self” and what isn’t. So how does it do that? Well, lets have a visual…
Yeah… I got it from wikipedia. Creative commons and such. The antigen binding site is where all the action happens. Each antibody has a specific pattern of amino acids in that region that give it the ability to bind to a specific foreign particle (an antigen). Each antibody works for only one antigen (hence the little carved out shapes in the diagram… it doesn’t actually look like that). You have antibodies with antigen binding sites that correspond to almost any bacteria or virus that you could encounter. Having antibodies sticking to something is like yelling to you immune system, “Holy crap! This shouldn’t be here!”.
The opposite end of the antibody (the blue bit) is always the same throughout a species. This corresponds to various receptors that allow the foreign junk that it’s stuck to to be dealt with. When antibodies bind foreign things and then use their species specific portion to attach to certain cells it can start a cascade of reactions that activate a stronger immune response. This is basically what a vaccination is doing. It introduces an antigen that causes a strong immune response. This effectively immunizes you against an infectious agent.
Ok… so the cool thing: since each antibody only has high binding affinity for a single antigen you need a lot of antibodies, each with a different variable region. You need to cover all the possible nasty bacteria and viruses you might encounter. Since that variable region is produced from the DNA used to make the protein you’d expect that a huge number of genes would be required, right? Well there aren’t! Because the cells that make antibodies (B-cells) can actually change their DNA. This sort of mutation happens only in the immune system. I won’t trouble you with the specifics, but the DNA for the variable region is randomly altered. Each B-cell does this once and this is what determines what antibody this cell makes for it’s entire life span. So with only a little DNA your cells can make all the different antibodies you need. Neat, huh?