Background IgG4-related disease (IgG4-RD) is a novel disease entity characterised by elevated serum IgG4 levels, IgG4(+) plasmacytic infiltration and fibrosis in various organs. We hypothesised that, if elevated IgG4 titers would be caused by antigen-driven immune responses, clonally expanded, IgG4(+) B cells and plasma cells might be present in affected tissue and peripheral blood.
Objectives To analyse the presence of IgG4(+) expanded B-cell clones in peripheral blood (PB) before and after successful therapy of patients with IgG4-associated cholangitis (IAC), and to compare this to healthy and disease controls using a newly developed high throughput sequencing (HTS) protocol for analysis of the B-cell receptor (BCR) repertoire.
Methods In 6 IAC patients the BCR repertoire was assessed in PB before and after 4 and 8 weeks of prednisolone (median 40mg, range 20–40 mg) treatment. As controls 6 healthy controls (HC) and 6 treatment-naive disease controls with PSC and pancreaticobiliary cancer were analysed (DC). In two patients a paired duodenal papilla biopsy was obtained at baseline. After isolation of mRNA the BCRheavy-chain was amplified, including the CDR3 region, thus fingerprinting unique clones. In our HTS protocol the number of clonal reads can be used as a measure for ‘dominance’; clones with a frequency of >0.5% were considered dominant.
Results At baseline, a mean of 15.1% of all clones was IgG(+) in IAC (similar in HC/DC). Among the IAC IgG(+) clones, the most dominant ones were IgG4(+) (mean rank: 1st in IAC versus 63th in HC (p < 0.005) and 55th in DC (p < 0.005)). Across all isotypes in every IAC patient IgG4(+) BCR clones were present among the 10 most dominant BCR clones which was not observed in any of the controls. The papilla contained the same dominant IgG4(+) clones that were detected in the paired blood samples. After 4 and 8 weeks of therapy, the contribution of IgG4(+) clones specifically to the BCR-repertoire was negligible (median 0.19%, IQR 0.16–0.21%), mirroring a sharp decline in serum IgG4 in conjunction with regression of clinical symptoms.
Conclusions Our findings indicate that IgG4(+) clones are abundantly present within the repertoire of IAC patients, in contrast to healthy or disease controls. The inflamed tissue was shown to contain the same expanded IgG4(+) clones, suggesting an antigen-driven immune response in IgG4-RD. A possible central role for IgG4(+) B cells is furthermore supported by the finding that IgG4(+) clones in peripheral blood specifically disappear upon successful corticosteroid therapy.