Identification of galectin-3 as an autoantigen in patients with IgG 4 -related disease.

BACKGROUND: 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.

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 IgG4 -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 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).

CONCLUSION: 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.