Isolation, identification, and characterization of the human airway ligand for the eosinophil and mast cell immunoinhibitory receptor Siglec-8.
J Allergy Clin Immunol 2020;
147:1442-1452. [PMID:
32791164 DOI:
10.1016/j.jaci.2020.08.001]
[Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 07/24/2020] [Accepted: 08/03/2020] [Indexed: 02/07/2023]
Abstract
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.
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