They chose Salmonella vaccine strains because they have been documented to induce mucosal immunity in human vaccines such as that for typhoid fever, he noted.
After they had been orally vaccinated, the animals were divided into low- and high-responder groups based on antibody titers to the PrPSC protein, then challenged with an oral dose of the prions.
Under normal circumstances, 100% of mice given the experimental form of scrapie would die from the disease after an incubation period of 180-200 days. But the authors found that the mice with a high gut secretory anti-PrP titer immumoglobulin A (IgA) titer and a high systemic IgG titer remained asymptomatic at 400 days (long-rank test P<0.0001 versus sham controls).
"When the animals were sacrificed, there was no evidence of prion infection in their brains or in their systemic lymphoreticular organs," Dr. Wisniewski said. "The control animals universally died from the prion infection after 190 to 200 days. Animals that developed lower levels of anti-PrP antibodies had a slight delay in their incubation period, but they also came down with illness."