Final answer:
Experimental evidence for protein agents causing TSEs includes the presence of abnormal prion proteins in brain biopsies, RT-QuIC assay for early detection, and the transmissibility of TSEs through contaminated meat, supporting the uniqueness of prions as protein-based infectious agents.
Step-by-step explanation:
The experimental evidence that leads to the belief that a protein agent was responsible for Transmissible Spongiform Encephalopathies (TSEs) includes the identification of abnormal prion proteins in affected brain tissues. Histological examinations of brain biopsies showing characteristic amyloid plaques, vacuoles, and the presence of prion proteins are the gold standard for diagnosing TSEs. The RT-QuIC assay is a newer method that can detect the abnormal prion proteins earlier in the infection process. Additionally, the discovery that prion diseases can be transmitted through the consumption of contaminated meat or animal feed corroborates the protein agent theory. Furthermore, prions are resistant to heat, chemicals, and radiation, and do not contain DNA or RNA, making them a unique kind of infectious agent.