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

The antigenic trigger that drives expansion of circulating plasmablasts and CD4⁺ cytotoxic T cells in patients with IgG₄-related disease (IgG₄-RD) is presently unknown.

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 IgG₄-RD by using mass spectrometry.

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.

mAbs expressed from the 2 dominant plasmablast clones of a patient with multiorgan IgG₄-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 IgG₄ isotype (28% of the IgG₄-RD cohort, P = .0001) and IgE isotype (11% of the IgG₄-RD cohort, P = .009). No significant responses were seen from the IgG₁, IgG₂, or IgG₃ isotypes. IgG₄ anti-galectin-3 autoantibodies correlated with increased plasma galectin-3 levels (P = .001), lymphadenopathy (P = .04), total IgG level increase (P = .05), and IgG₄ level increase (P = .03).

Affinity chromatography using patient-derived mAbs identifies relevant autoantigens in patients with IgG₄-RD. IgG₄ galectin-3 autoantibodies are present in a subset of patients with IgG₄-RD and correlate with galectin-3 plasma levels. The marked increases in levels of circulating IgG₄ and IgE observed clinically are, at least in part, caused by the development of IgG₄- and IgE-specific autoantibody responses.