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

Background: The antigenic trigger that drives expansion of circulating plasmablasts and CD4 cytotoxic T cells in patients with IgG-related disease (IgG-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-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-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 isotype (28% of the IgG-RD cohort, P = .0001) and IgE isotype (11% of the IgG-RD cohort, P = .009). No significant responses were seen from the IgG, IgG, or IgG isotypes. IgG anti-galectin-3 autoantibodies correlated with increased plasma galectin-3 levels (P = .001), lymphadenopathy (P = .04), total IgG level increase (P = .05), and IgG level increase (P = .03).

Conclusion: Affinity chromatography using patient-derived mAbs identifies relevant autoantigens in patients with IgG-RD. IgG galectin-3 autoantibodies are present in a subset of patients with IgG-RD and correlate with galectin-3 plasma levels. The marked increases in levels of circulating IgG and IgE observed clinically are, at least in part, caused by the development of IgG- and IgE-specific autoantibody responses.