Plasma Galectin-9 Concentrations in Normal and Diseased Condition

BACKGROUND/AIMS: Galectin-9 is a soluble immune modulator with versatile functions, including a role as an immune checkpoint molecule. Therefore, the amount of galectin-9 in the blood may reflect an individual's immunological balance. Many studies have conducted galectin-9 measurements; however, the reported galectin-9 concentration in the blood varies greatly, even within healthy controls. This study investigates the variation between the reported and actual concentrations of galectin-9. METHODS: A GalPharma ELISA and an R&D Systems ELISA kit were directly compared using the same set of plasma and a series of recombinant galectins, including degraded galectin-9. Furthermore, galectin-9 in plasma was concentrated using anti-galectin-9 antibody-conjugated beads, and subjected to western blotting to estimate the quantity and integrity of galectin-9 and assess the consistency of ELISA measurements. RESULTS: The R&D Systems' ELISA indicated a 50-fold higher median concentration of plasma galectin-9 than that indicated by the GalPharma ELISA. This variation is due to aberrantly enhanced reactivity of the R&D Systems' ELISA to degraded galectin-9 present in small quantities in the plasma. The GalPharma ELISA could detect only intact galectin-9 and its results correlated well with the plasma galectin-9 level obtained by western blotting. CONCLUSION: ELISA kits from R&D Systems reacts aberrantly higher against degraded galectin-9 than the intact galectin-9. Therefore, the existence of a small amount of degraded galectin-9 in a test sample hinders the quantification. As galectin-9 is a fragile protein, this is a serious concern when using this kit. Based on quantifications from the GalPharma ELISA, the median (25th-75th percentiles) galectin-9 concentration in healthy subjects in the current study cohort was calculated as 110 pg/mL (67 -154 pg/mL).