Acquisition of N-Glycosylation Sites in Immunoglobulin Heavy Chain Genes During Local Expansion in Parotid Salivary Glands of Primary Sjögren Patients

Front Immunol. 2018 Mar 12;9:491. doi: 10.3389/fimmu.2018.00491. eCollection 2018.

Abstract

Previous studies revealed high incidence of acquired N-glycosylation sites acquired N-glycosylation sites in RNA transcripts encoding immunoglobulin heavy variable region (IGHV) 3 genes from parotid glands of primary Sjögren's syndrome (pSS) patients. In this study, next generation sequencing was used to study the extent of ac-Nglycs among clonally expanded cells from all IGVH families in the salivary glands of pSS patients. RNA was isolated from parotid gland biopsies of five pSS patients and five non-pSS sicca controls. IGHV sequences covering all functional IGHV genes were amplified, sequenced, and analyzed. Each biopsy recovered 1,800-4,000 unique IGHV sequences. No difference in IGHV gene usage was observed between pSS and non-pSS sequences. Clonally related sequences with more than 0.3% of the total number of sequences per patient were referred to as dominant clone. Overall, 70 dominant clones were found in pSS biopsies, compared to 15 in non-pSS. No difference in percentage mutation in dominant clone-derived IGHV sequences was seen between pSS and non-pSS. In pSS, no evidence for antigen-driven selection in dominant clones was found. We observed a significantly higher amount of ac-Nglycs among pSS dominant clone-derived sequences compared to non-pSS. Ac-Nglycs were, however, not restricted to dominant clones or IGHV gene. Most ac-Nglycs were detected in the framework 3 region. No stereotypic rheumatoid factor rearrangements were found in dominant clones. Lineage tree analysis showed in four pSS patients, but not in non-pSS, the presence of the germline sequence from a dominant clone. Presence of germline sequence and mutated IGHV sequences in the same dominant clone provide evidence that this clone originated from a naïve B-cell recruited into the parotid gland to expand and differentiate locally into plasma cells. The increased presence of ac-Nglycs in IGHV sequences, due to somatic hypermutation, might provide B-cells an escape mechanism to survive during immune response. We speculate that glycosylation of the B-cell receptor makes the cell sensitive to environmental lectin signals to contribute to aberrant B-cell selection in pSS parotid glands.

Keywords: B-cell; N-glycosylation; Sjögren syndrome; heavy chain; next generation sequencing; parotid Gland.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • B-Lymphocytes / immunology*
  • Cell Proliferation
  • Clonal Selection, Antigen-Mediated
  • Clone Cells
  • Glycosylation
  • High-Throughput Nucleotide Sequencing
  • Humans
  • Immunoglobulin Heavy Chains / genetics*
  • Immunoglobulin Heavy Chains / metabolism
  • Lectins / immunology
  • Lymphocyte Activation
  • Middle Aged
  • Parotid Gland / physiology*
  • RNA / genetics*
  • Salivary Glands / physiology*
  • Sjogren's Syndrome / immunology*
  • Young Adult

Substances

  • Immunoglobulin Heavy Chains
  • Lectins
  • RNA