Measurement of circulating progranulin (PGRN/GP88/GEP) by enzyme-linked immunosorbent assay and application in human diseases

Abstract

The enzyme-linked immunosorbent assay (ELISA) is a well-established methodology for detection of analytes in various biological fluids. The assay described herein has been validated for the detection of PGRN/GP88/GEP in blood (serum/ plasma), urine and cerebrospinal fluid (CSF), and synovial fluid and may also be used for breast milk, ductal lavage, nipple aspirates, and saliva. The ability to measure circulating levels of PGRN/GP88/GEP has proven to have clinical utility for several human diseases such as cancer where changes of PGRN/GP88/GEP can be determined as a mean to monitor disease status or response to therapy. In the case of frontotemporal dementia (FTD), the ability to measure PGRN/GP88/GEP levels in plasma and cerebrospinal fluid may be useful in distinguishing PGRN mutation carriers among FTD populations at large. The assay used is a sandwich ELISA where a highly specific antihuman PGRN/GP88/GEP monoclonal antibody is employed as a capture antibody coated on 96-well microplates. After contact with serum (or other bodily fluid), unbound material is washed away before application of another PGRN/GP88/GEP detecting antibody which in turn is detected by a horseradish peroxidase (HRP) conjugated antibody. After further washing to remove all unbound HRP, a substrate (TMB) is added, and after approximately 6 min, a color is developed and can be read as optical density at 620 nm (or 450 nm if using HCL as a stop solution) in a microplate reader. The test described herein is capable of measuring very low levels of PGRN/GP88/GEP such as 0.2 ng/mL as found in CSF of certain FTD patients. Additionally, we have demonstrated the potential clinical utility of measuring the changes of PGRN/GP88/GEP blood levels in cancer patients undergoing therapy.