Humans and domestic animals are tragically susceptible to a family of rare, fatal brain diseases called transmissible spongiform encephalopathies (TSEs) or prion diseases.[HN2],[HN3] A prominent example is the recent epidemic of bovine spongiform encephalopathy (BSE)[HN4] in the United Kingdom. In March 1996, a new variant of a human TSE, Creutzfeldt-Jakob Disease (nvCJD),[HN5],[HN6] was reported in the United Kingdom in a small group of people, all of whom were much younger than most individuals with CJD (1). The unusual nature of these outbreaks prompted ready speculation that the causative agent for BSE was transmitted from cattle to humans, triggering the nvCJD cases. Although no definitive answer to this question has yet been obtained, several recent papers shed new light on this issue.

Brain damage in prion diseases [HN7] is thought to occur when abnormal prion protein (PrP)[HN8] molecules gain access to the brain and cause normal PrPs to take on the abnormal, disease-causing form. Raymond et al.(2) mimicked this process in a test tube and, in their cell-free biochemical system, analyzed interactions between normal and abnormal PrP molecules obtained from various species. Positive interactions between prions from different species, leading to formation of additional abnormal protein, usually predict the susceptibility of the different species to cross-species transmission of the prion diseases. Using abnormal, protease-resistant PrP from cattle with BSE, these workers found positive interactions with normal PrP of cattle, sheep, and mice (all of which are susceptible to experimental BSE), and negative interactions with hamster (which is resistant to BSE). Normal human PrP gave a weak, but detectable, positive interaction, a result that suggests that the biochemical potential for BSE transmission to humans exists, but that humans may be more resistant than other known susceptible species.