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.