Ig Gene Analysis Reveals Altered Selective Pressures on Ig-Producing Cells in Parotid Glands of Primary Sjögren’s Syndrome Patients

Abstract

In this study, we sought to understand the selective pressures shaping the Ig-producing cell repertoire in the parotid glands of primary Sjögren’s syndrome (pSS) patients before and after rituximab treatment (RTX). In particular, we evaluated the role of potential N-glycosylation motifs acquired by somatic hypermutation (ac-Nglycs) within Ig H chain V region (IGHV) genes as alternative selective pressures for B cells in pSS. Five pSS patients received RTX. Sequential parotid salivary gland biopsies were taken before RTX, at 12 wk and at 36–52 wk after treatment. Parotid biopsies from four non-pSS patients served as controls. Sequence analysis was carried out on the IgA and IgG RNA transcripts expressing IGHV3 genes in all parotid biopsies. Both IgG and IgA sequences from pSS patients exhibited no evidence for positive Ag-driven selection pressure in their CDRs in contrast to non-pSS controls. The prevalence of IgG sequences with ac-Nglycs was significantly higher in pSS patients than in non-pSS controls. Selection pressures shaping the IgG and IgA repertoire within pSS patients’ parotid glands are distinct from those in non-pSS controls, with very little evidence for positive (auto)antigen selection. The higher prevalence of ac-Nglycs on pSS-IgG compared with non-pSS IgG indicates that ac-Nglycs could be an alternative form of selection pressure. We speculate that B cell hyperproliferation within parotid glands of pSS patients may result from Ag-independent interactions such as that between glycosylated B cell receptors and lectins within the microenvironment rather than (auto)antigen-specific stimulation. Our study brings a new perspective into research on pSS.

Acquiring new N-glycosylation sites in variable regions of immunoglobulin genes by somatic hypermutation is a common feature of autoimmune diseases

“…In conclusion, in addition to Vergroesen et al in RA, and our previous work in pSS,2 the meta-analysis described here clearly indicates that there is an increase in ac-Nglycs by somatic hypermutation of immunoglobulin  genes during humoral immune responses in various autoimmune diseases. This phenomenon is thus clearly not restricted to ACPA-expressing B cells in RA as shown by Vergroesen et al .…”

“…We have shown previously2 increased numbers of IgG encoding immunoglobulin variable heavy region gene (IGHV) transcripts with ac-Nglycs derived from B cells and plasma cells residing in the inflamed parotid salivary gland of patients with primary Sjögren’s syndrome (pSS) compared with non-pSS sicca controls (24% vs 6%). Importantly, in pSS the IgG encoding transcripts exhibited no evidence for signs of antigen selection in the complementarity determining regions.…”

Response to: ‘Acquiring new N-glycosylation sites in variable regions of immunoglobulin genes by somatic hypermutation is a common feature of autoimmune diseases’ by Visser et al

“…This is also supported by previous work of the authors on primary Sjögren’s syndrome IgG-BCR sequences 4. The findings presented by Visser et al contribute to the further understanding of the introduction of N- glycosylation sites by autoreactive B cells and its possible impact on selective advantages in B cell selection and/or the breach of tolerance of autoreactive B cells.…”

The Emerging Importance of IgG Fab Glycosylation in Immunity

“…compared with other IgG (auto)antibodies as the result of an increase in IgG Fab glycans (40). Nevertheless, although IgG Fc-glycosylation patterns were associated with disease activity/severity and outcome (41,42) (44). It was suggested that B cell hyperproliferation and selection within the parotid glands may result from Ag-independent interactions of glycosylated BCRs with microbial lectins, as described for lymphoma B cells (see below).…”