Isolation, identification, and characterization of the human airway ligand for the eosinophil and mast cell immunoinhibitory receptor Siglec-8

J Allergy Clin Immunol. 2021 Apr;147(4):1442-1452. doi: 10.1016/j.jaci.2020.08.001. Epub 2020 Aug 11.


Background: The immunoinhibitory receptor Siglec-8 on the surface of human eosinophils and mast cells binds to sialic acid-containing ligands in the local milieu, resulting in eosinophil apoptosis, inhibition of mast cell degranulation, and suppression of inflammation. Siglec-8 ligands were found on postmortem human trachea and bronchi and on upper airways in 2 compartments, cartilage and submucosal glands, but they were surprisingly absent from the epithelium. We hypothesized that Siglec-8 ligands in submucosal glands and ducts are normally transported to the airway mucus layer, which is lost during tissue preparation.

Objective: Our aim was to identify the major Siglec-8 sialoglycan ligand on the mucus layer of human airways.

Methods: Human upper airway mucus layer proteins were recovered during presurgical nasal lavage of patients at a sinus clinic. Proteins were resolved by gel electrophoresis and blotted, and Siglec-8 ligands detected. Ligands were purified by size exclusion and affinity chromatography, identified by proteomic mass spectrometry, and validated by electrophoretic and histochemical colocalization. The affinity of Siglec-8 binding to purified human airway ligand was determined by inhibition of glycan binding.

Results: A Siglec-8-ligand with a molecular weight of approximately 1000 kDa was found in all patient nasal lavage samples. Purification and identification revealed deleted in malignant brain tumors 1 (DMBT1) (also known by the aliases GP340 and SALSA), a large glycoprotein with multiple O-glycosylation repeats. Immunoblotting, immunohistochemistry, and enzyme treatments confirmed that Siglec-8 ligand on the human airway mucus layer is an isoform of DMBT1 carrying O-linked sialylated keratan sulfate chains (DMBT1S8). Quantitative inhibition revealed that DMBT1S8 has picomolar affinity for Siglec-8.

Conclusion: A distinct DMBT1 isoform, DMBT1S8, is the major high-avidity ligand for Siglec-8 on human airways.

Keywords: DMBT1; GP340; SALSA; Siglec-8; keratan sulfate; mucus layer; nasal lavage; sialic acid; submucosal gland; upper airway.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigens, CD / immunology*
  • Antigens, Differentiation, B-Lymphocyte / immunology*
  • Bronchi / immunology
  • Calcium-Binding Proteins / chemistry
  • Calcium-Binding Proteins / immunology*
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / immunology*
  • Eosinophils / immunology
  • Humans
  • Lectins / immunology*
  • Ligands
  • Mast Cells / immunology
  • Nasal Lavage Fluid / immunology
  • Proteoglycans / immunology
  • Trachea / immunology
  • Tumor Suppressor Proteins / chemistry
  • Tumor Suppressor Proteins / immunology*


  • Antigens, CD
  • Antigens, Differentiation, B-Lymphocyte
  • Calcium-Binding Proteins
  • DMBT1 protein, human
  • DNA-Binding Proteins
  • Lectins
  • Ligands
  • Proteoglycans
  • SIGLEC8 protein, human
  • Tumor Suppressor Proteins