6.6 Prion diseases
Finally, we should look at the particular problems associated with prion diseases, or transmissible spongiform encephalopathies, such as variant Creutzfeld Jacob Disease (vCJD) and kuru. Prion diseases are caused by altered forms (prions) of small membrane glycoproteins, which are normally expressed on a number of cell types in the body, including neurons and lymphocytes. Once prions have appeared, the endogenous protein becomes folded in the same conformation as the prion, so the prions appear to ‘replicate’ and act like an infectious agent.
Why will it be very difficult to develop a vaccine against prion diseases?
The prion protein has the same primary amino-acid structure as the endogenous protein, so it is perceived as a ‘self-molecule’ by T cells and an immune response cannot develop.
In theory, the conformational differences between the prion and the endogenous protein might allow it to be recognised by B cells and antibodies, because they recognise the overall shape (conformation) of an antigen. However, in practice any differences seem to be too small to be immunogenic, possibly since the B cells do not receive help from T cells.