Are prions living things (like virus or bacteria), or rather a chemical? What are their effects on humans?


Chris - Prions are the names given to these proteins found in the nervous system and also elsewhere in the body, which are responsible for diseases like BSE: Bovine Spongiform Encelopathy, mad cow disease. In humans, the equivalent is CJD: Creutzfeldt-Jakob disease.

These proteins are normal for the brain. We normally make them, but we make them in a shape or form called PrPc. This is a globular protein that looks a bit like a ball of wool and it dissolves really easily. No one actually knows exactly what it does in the nervous system, but it's a normal part of everyone's nervous system and other parts of the body as well including the immune system. But for some reason and probably because of the shape of the protein, this ball of wool can sometimes get tangled into a rigid fibrous shape called a beta-pleated sheet. And when it forms this beta-pleated sheet shape, then what can actually happen is it can make other "ball of wool" shape prions also convert into these rigid beta-pleated sheets, and from where you had 1, you now have 2 and 2 can convert 2 more, making 4, and 4 can go out and convert making 8 and so on. And the whole thing grows exponentially.

They build up in the brain, and they appear to be directly toxic to nerve cells which is why you end up with this spongiform change in the brain because you lose nerve cells and replace them with vacualation or gaps or holes in the brain. It makes your brain a bit like Swiss cheese and they appear to be able to transmit. So if you eat material which is contaminated with prions from a closely related animal like a cow, they can cross the species barrier, get into our body, go the nervous system, and then they make the person develop BSE or human BSE in this instance. So that's the prion story. It won a Nobel Prize for Stan Prusiner who first came up with the idea.

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