Hello Merry, Prion disease is first of all a Protein misfolding disease which comes under a broad category of neurodegenerative disorders - meaning the structure of the Prion protein (PrP) is altered to (PrPSc) form. This altered PrPSc form will auto-infect normal cellular PrP forms and they join together to form a fibrillar structures. Now, when their stuctural form changes they can't execute the action which they're set out to do. These PrPSc-PrPSc fibrils become elongated starting to disrupt normal cell's activity and they start getting out of the cell. Other loose or uncoupled PrPSc forms escape out through vesicles into the next adjoining cell. This is how the pathogenesis of the prion is mediated. Now the strangest feature of the Prion disease is that it is not attacked by immune cells rather seems to aid their infection. Well basically the infectious form is very stable and is found to be not affected even by high salts and esters. Also in some ways the proteosomes are rendered ineffective to the PrPSc.

There is research going on in this field to identify humoral and cellular immune cells which seem to aid the propagation. The proposed hypothesis is that the Dendrite cells are invaded by the Prions which then start infecting those cells and stop they antigen presenting ability.

Prions are technically "non-foreign". They are just mutated normal proteins that has catalytic capability that can cause more normal proteins to mis-fold and cumulate. Plus these chemical reactions are happening in side brain which is immune restricted organ. That's make them "untouchable". I think.

When presented by antigenpresenting cells under inflammatory conditions prion proteins (and any other protein-regardless of whether being of self or foreign origin, conformationally changed or not) will raise adaptive immune responses. Conversely, in absence of inflammation, even foreign proteins are tolerated.

Hello Merry, Prion disease is first of all a Protein misfolding disease which comes under a broad category of neurodegenerative disorders - meaning the structure of the Prion protein (PrP) is altered to (PrPSc) form. This altered PrPSc form will auto-infect normal cellular PrP forms and they join together to form a fibrillar structures. Now, when their stuctural form changes they can't execute the action which they're set out to do. These PrPSc-PrPSc fibrils become elongated starting to disrupt normal cell's activity and they start getting out of the cell. Other loose or uncoupled PrPSc forms escape out through vesicles into the next adjoining cell. This is how the pathogenesis of the prion is mediated. Now the strangest feature of the Prion disease is that it is not attacked by immune cells rather seems to aid their infection. Well basically the infectious form is very stable and is found to be not affected even by high salts and esters. Also in some ways the proteosomes are rendered ineffective to the PrPSc.

There is research going on in this field to identify humoral and cellular immune cells which seem to aid the propagation. The proposed hypothesis is that the Dendrite cells are invaded by the Prions which then start infecting those cells and stop they antigen presenting ability.

does immune system involved as one of the factor that make a "barrier species" in prion trasmission?

i mean why it could be easier for BSE transmittied in same species (longer time incubation for trasmission to other kind of species)?