A novel strategy to identify autoantigens by proteomic analysis of plasma IgG-bound proteins

Autoimmune mechanisms have been hypothesized to underlie a number of human disorders in which both disease pathogenesis and diagnostic biomarkers remain poorly understood. This is partly due to a lack of efficient techniques for identification of plasma autoantibodies associated with specific pathophysiological conditions. We have developed a novel proteomic methodology to comprehensively identify plasma IgG-bound proteins using liquid chromatography tandem mass spectrometry (LC-MS/MS) after denaturing enriched plasma IgG to solubilize and release low molecular weight proteins. In total, we identified 44 proteins using this method that were undetectable in unprocessed plasma, 21 of which were not identified in the Human Plasma Proteome Draft of 2017. Comparison of plasma IgGbound proteins between healthy subjects and patients with isolated adrenocorticotropic hormone deficiency, a rare endocrine disorder speculated to involve autoimmune mechanisms, revealed several distinct IgG-bound proteins specifically detected in patient plasma but not in healthy subjects. Our results suggest that solubilization of low molecular weight proteins bound to enriched plasma IgG and subsequent proteomic analysis by LC-MS/MS could provide a promising strategy for identification of autoantigens in human peripheral blood.