Failure to Detect Prion Protein (PrP^res) by Immunohistochemistry in Striated Muscle Tissues of Animals Experimentally Inoculated with Agents of Transmissible Spongiform Encephalopathy

Transmissible spongiform encephalopathies (TSEs) are fatal neurologic diseases. Infection by the causative agent, a prion, induces accumulations of an abnormal form of prion protein (PrPres) in tissues of nervous and lymphoid systems. Presence of characteristic histopathologic changes (spongiform encephalopathy) and detection of protease-resistant PrPres in neural and lymphoid tissues are the basis of currently available methods for diagnosis of TSEs. In this study, samples of striated muscle tissues (tongue, heart, diaphragm, and masseter muscle) from 20 animals (cattle, sheep, elk, and raccoons) were examined for PrPres by immunohistochemistry (IHC). All the animals had developed a TSE after experimental inoculation. PrPres was found by IHC in the brain but not in the muscle tissues of all the animals examined. These findings are contradictory to recently published reports of laboratory animals with TSEs, where these altered prion proteins were detected in tongue and other striated muscles. Further testing of muscle tissues is needed to confirm the findings of the present study.