QUANTITATIVE DISCRIMINATION OF HEPATIC RETICULOENDOTHELIAL CLEARANCE AND PHAGOCYTIC KILLING

An in vivo assay to quantify simultaneously two important components o f hepatic reticuloendothelial system (RES) function-clearance and phag ocytic killing-was developed in the rat. Intravenously injected E. col i labeled with (NaCr)-Cr-51 and 5-[I-125]-iodo-2'-deoxyuridine were cl eared rapidly from the blood primarily by the liver. While hepatic Cr- 51 levels remained stable for 24 h following inoculation and provided a reliable measurement of clearance, hepatic I-125 decreased over time . Hepatic I-125, calculated by sampling whole liver homogenates, accur ately reflects the number of viable bacteria recovered from quantitati ve cultures of the same homogenates, thus validating this assay as a m easure of bacteria killing. Pre-treatment of rats with substances prev iously shown to affect RES function (gadolinium, zymosan, and sheep er ythrocytes) were found to selectively modulate clearance and/or killin g. The correlation between hepatic isotope levels and viable hepatic b acteria, the gold standard for assessing the capacity of the liver to remove organisms from the blood and kill them, was preserved under con ditions of up- and downregulation of RES function. The ability to quan titatively discriminate two distinct components of the hepatic RES sho uld provide a useful tool for future investigations of altered RES fun ction.