Detection and functional resolution of soluble immune complexes by an FcγR reporter cell panel

Fc-gamma receptor (Fc gamma R) activation by soluble IgG immune complexes (sICs) represents a major mechanism of inflammation in certain autoimmune diseases such as systemic lupus erythematosus (SLE). A robust and scalable test system allowing for the detection and quantification of sIC bioactivity is missing. We developed a comprehensive reporter cell panel detecting activation of Fc gamma Rs. The reporter cell lines were integrated into an assay that enables the quantification of sIC reactivity via ELISA or a faster detection using flow cytometry. This identified Fc gamma RIIA(H) and Fc gamma RIIIA as the most sIC-sensitive Fc gamma Rs in our test system. Reaching a detection limit in the very low nanomolar range, the assay proved also to be sensitive to sIC stoichiometry and size reproducing for the first time a complete Heidelberger-Kendall curve in terms of immune receptor activation. Analyzing sera from SLE patients and mouse models of lupus and arthritis proved that sIC-dependent Fc gamma R activation has predictive capabilities regarding severity of SLE disease. The assay provides a sensitive and scalable tool to evaluate the size, amount, and bioactivity of sICs in all settings.

Automated summary

The study developed a test system for detecting and quantifying the bioactivity of sICs, identifying Fc gamma RIIA(H) and Fc gamma RIIIA as the most sensitive Fc gamma Rs. The research has predictive capabilities regarding the severity of SLE disease and provides a sensitive and scalable tool for evaluating the size, amount, and bioactivity of sICs.