Identification of galectin-3 as an autoantigen in patients with IgG4-related disease

Background: The antigenic trigger that drives expansion of circulating plasmablasts and CD4(+) cytotoxic T cells in patients with IgG(4)-related disease (IgG(4)-RD) is presently unknown. Objective: We sought to sequence immunoglobulin genes from single-cell clones of dominantly expanded plasmablasts and generate recombinant human mAbs to identify relevant antigens in patients with IgG(4)-RD by using mass spectrometry. Methods: Paired heavy and light chain cDNAs from dominant plasmablast clones were expressed as mAbs and used to purify antigens by using immunoaffinity chromatography. Affinity-purified antigens were identified by using mass spectrometry and validated by means of ELISA. Plasma levels of the antigen of interest were also determined by using ELISA. Results: mAbs expressed from the 2 dominant plasmablast clones of a patient with multiorgan IgG(4)-RD stained human pancreatic tissue sections. Galectin-3 was identified as the antigen specifically recognized by both mAbs. Anti-galectin-3 autoantibody responses were predominantly of the IgG(4) isotype (28% of the IgG(4)-RD cohort, P = .0001) and IgE isotype (11% of the IgG(4)-RD cohort, P = .009). No significant responses were seen from the IgG(1), IgG(2), or IgG(3) isotypes. IgG(4) anti-galectin-3 autoantibodies correlated with increased plasma galectin-3 levels (P = .001), lymphadenopathy (P = .04), total IgG level increase (P = .05), and IgG(4) level increase (P = .03). Conclusion: Affinity chromatography using patient-derived mAbs identifies relevant autoantigens in patients with IgG(4)-RD. IgG(4) galectin-3 autoantibodies are present in a subset of patients with IgG(4)-RD and correlate with galectin-3 plasma levels. The marked increases in levels of circulating IgG(4) and IgE observed clinically are, at least in part, caused by the development of IgG(4)- and IgE-specific autoantibody responses.