Serum from AIH patients with anti-RXFP1 activity inhibits relaxin-2 signaling through RXFP1 in an IgG-dependent manner. (a) Putative structure of RXFP1, as depicted using ChimeraX; the region corresponding to the RXFP1 peptide identified by PhIP-seq is highlighted in red, along with annotation of functional domains (for schematic representation, see panel inset). (b) Assay of relaxin-2–induced induction of cAMP by RXFP1, in THP-1 cells preincubated with [1:100] dilution of patient serum negative (green) or positive (red) for RXFP1 antibodies; relaxin concentration, x axis; cAMP response reported as a percentage of untreated control signal, y axis. (c) Measurement of relaxin-2 EC50 in ng/μl (y axis) for patient serum negative (green) or positive (red) for RXFP1 antibodies. (d) Depletion of IgG using protein A-G beads (x axis, right) or mock-depleted serum (x axis, left) was performed prior to incubating THP-1 cells with patient serum at [1:250]; resultant impact on relaxin-2 signal was expressed as a percentage of untreated signal (y axis).