Brown Prion Proteins (IMAGE) University of California - San Diego Caption Prion protein aggregates (brown) in the brain of a mouse expressing the human-elk protein. Credit UC San Diego School of Medicine Usage Restrictions Use credit as indicated. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.