Immune system biochem

2008-05-04

in Geek stuff, Science

Face on a wall

It seems as though one of the coolest medical products you can make from blood is intravenous immunoglobulin (IVIG). Basically, it consists of antibodies extracted from the plasma of thousands of individual blood donors. It is given to people who have had their own ability to produce antibodies compromised and helps their immune system to attack infections over a period between two weeks and three months.

I remember a children’s television show where white blood cells are represented as the body’s police force. The analogy is fair enough. There are situations where the police force is lazy, so nasty gangs move in. There are situations where nasty gangs simply kill off the police force. Finally, there are situations where the police force goes haywire and starts savaging the population. Autoimmune diseases are the anatomical equivalent of the uncontrolled police force. Apparently, IVIG can help in all three circumstances: as well as in cases of inflammation.

Reading about biochemistry is an excellent way of being reminded just how absurdly complicated life is. I frequently find myself contemplating all the thousands of chemical reactions involved in performing the slightest action – tapping a key, dilating your pupil when a cloud crosses the sun – and being amazed that they can happen so quickly and consistently.

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{ 3 comments… read them below or add one }

R.K. May 7, 2008 at 10:04 am

How do they extract just the antibodies from the donor blood?

Edward May 7, 2008 at 11:59 am

I know very little about IVIG, but to answer R.K.’s question a general level, a multi-step purification process is used to extract and purify the sample and then ensure that the infusate is pathogen-free. A first step would probably be fractionation based on molecular weight and electrical charge properties. Cells, bacteria, and other proteins are quite a bit different from immunoglobulins, so this would be easy to do. Anion exchange chromatography would be a more refined step, and it would also remove some of the pathogens. The tricky part is viruses, which can escape through the cruder measures of purification (although anion exchange does capture some of them). I understand that virucidal agents are added at some point, and there’s been talk of using gamma irradiation. In any case, these guys know what they’re looking for and they do a pretty good job with it. No transmission of hepatitis has been reported since 1994, and HIV has never been transmitted through IVIG.

Milan is correct in his analogy, but I’d like to add a little bit to it. The police force doesn’t just go around killing everyone, but rather only the cells that have a shared feature with something bad. If the immune system has seen a invader that has a feature similar to a normal body cell, then it can be fooled into thinking that the normal cell is a bad guy and kill it off. If it goes and kills, say, all of the cells that serve a particular function then you’ll have some problems. E.g. the police force sees one bearded criminal and gets rid of him, but then mistakenly thinks that all bearded people are corrupt politicians and gets rid of them all… which would be bad.

Oh, and as Milan also alluded to, the whole point of IVIG is that we don’t exactly know what we’re giving. If we knew the precise antibody that was effective against the pathogen, then we could just make a monoclonal antibody specifically targeting that disease (which, by the way, is the new fad). As such, IVIG also has its share of risks… but we give it on the hope that someone somewhere has produced an antibody that will be effective against the particular disease we don’t know how to treat.

R.K May 7, 2008 at 12:53 pm

Edward,

Thanks for the excellent information.

I am willing to bet that the thinking behind this post was sparked by Milan’s fondness for House.

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