PBR28 or PBR-28, a chemical substance that binds to translocator protein TSPO, also known as Peripheral-type benzodiazepine receptor (PBR). TSPO located within the cells such as macrophages reaches high levels of expression in inflammatory conditions and thus can be a biomarker of neuroinflammation. When radioactivity in the form of carbon-11 is tagged to PBR 28 and is administered, its uptake in the inflammatory body regions can be measured using positron emission tomography (PET). PBR28 now is involved in a clinical trial to evaluate the specificity of its binding in the joints of patients with inflammatory joint disease, like rheumatoid and psoriatic arthritis.