Soluble Tim3 detection by time-resolved fluorescence immunoassay and its application in membranous nephropathy

Background We aimed to develop a time-resolved fluorescence immunoassay (TRFIA) for detecting soluble T-cell immunoglobulin and mucin domain 3 (sTim3) in serum samples and to demonstrate a preliminary application of this method in membranous nephropathy (MN). Methods sTim3 TRFIA was developed, and the sTim3 concentration in the serum of patients with MN and healthy individuals was detected using a sandwich method. Results The sensitivity of the developed sTim3 TRFIA was 0.66 ng/mL, higher than that of an enzyme-linked immunosorbent assay (ELISA) (1.11 ng/mL). The detection range was 0.66-40 ng/mL. The intra-assay coefficient of variation (CV) for sTim3 was 1.64%-4.68%, and the inter-assay CV was 5.72%-9.32%. The cross-reactivity to interleukin 6 (IL-6) and kidney injury molecule 1 (KIM-1) was 0.25% and 0.04%, respectively. The average recovery was 105.26%. The sTim3 concentration in patients with MN was considerably higher than that in healthy individuals (P < .001). The sTim3 concentration in the serum of patients with MN was significantly increased from G1 to G4 based on the Jonckheere-Terpstra test (P < .001). Thus, we used sTim3 as a diagnostic indicator for distinguishing between healthy individuals and patients with MN as well as between different stages of MN. Conclusion We successfully established TRFIA to detect sTim3 in serum. We then applied this method to patients with MN, demonstrating for the first time that TRFIA is a valid diagnostic tool to detect sTim3 in serum.