The disclosed assay can be used for detecting levels of circulating 26S proteasome bound to complement factor 3 or 4 in blood plasma or other body fluids, such as for monitoring levels of inflammation and virus infection in the body of a mammalian, including complement system down regulation in the body of a mammalian as well as for verifying compliance of processed cereals (SPC) and/or functional food with high levels of natural antisecretory protein (NASP).