Development of a Time-Resolved Fluorescence Immunoassay for BAFF and Its Preliminary Clinical Application in Patients with Lupus Nephritis.

This study was designed to develop a time-resolved fluorescence immunoassay (TRFIA) for the detection of B-cell activating factor (BAFF) and to evaluate the preliminary clinical utility of serum BAFF measurement in patients with lupus nephritis (LN). A BAFF-TRFIA was established using 96-well microplates coated with anti-BAFF monoclonal antibodies, combined with anti-BAFF polyclonal antibodies and europium (Eu³⁺)-labeled goat anti-rabbit IgG as the detection antibody. Serum BAFF concentrations were measured in 46 patients with LN and 30 healthy controls to assess the clinical applicability of the assay. The developed BAFF-TRFIA demonstrated a sensitivity of 27.62 pg/mL and a linear detection range of 97.66-25,000 pg/mL. The intra-assay and inter-assay coefficients of variation ranged from 1.44% to 9.17% and from 2.34% to 11.93%, respectively, indicating acceptable assay precision. Serum BAFF concentrations exhibited substantial inter-individual variability in patients with LN. Compared with healthy controls, a broader distribution of BAFF concentrations and several markedly elevated values were observed in the LN group. Relatively higher BAFF concentrations were predominantly observed in patients with class III and class IV LN. In summary, a BAFF-TRFIA with a wide detection range was successfully developed based on a europium (Eu³⁺) chelate. This method enables the quantification of soluble BAFF in biological samples and has been successfully applied to the measurement of serum BAFF in patients with LN. The established assay provides a promising approach for the clinical evaluation of soluble BAFF.