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Characterization of the IgA receptor from human polymorphonuclear leucocytes
M Albrechtsen1, G R Yeaman, M A Kerr
1Department of Pathology, University of Dundee, Ninewells Hospital and Medical School, U.K.
Abstract:
Human polymorphonuclear leucocytes (PMNs) will phagocytose yeasts opsonized with specific affinity-purified human serum IgA. PMNs also bind to Sepharose beads coated with IgA or IgG, but not to beads coated with bovine serum albumin (BSA) or horseradish peroxidase (HRP). Binding to IgA-Sepharose stimulates the cells to release lysozyme. Affinity chromatography of 125I-labelled PMN membrane proteins on IgA-Sepharose results in isolation of a polypeptide of apparent 60,000 MW. The protein, which is not bound to IgG-Sepharose under the same conditions, appears as a diffuse band on SDS-PAGE, suggesting it is heavily glycosylated.
Insights
Human polymorphonuclear leucocytes (PMNs) phagocytose IgA-opsonized yeast and bind IgA-coated beads, releasing lysozyme. A 60 kDa glycosylated protein on PMN membranes binds IgA, indicating a novel immune receptor.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Human polymorphonuclear leucocytes (PMNs) are crucial immune cells.
- Immunoglobulin A (IgA) plays a role in mucosal immunity.
- The specific receptors for IgA on PMNs are not fully characterized.
Purpose of the Study:
- To investigate the interaction between human PMNs and IgA.
- To identify potential IgA-binding proteins on the surface of PMNs.
Main Methods:
- Phagocytosis assays using IgA-opsonized yeast.
- Binding assays with IgA- and IgG-coated Sepharose beads.
- Affinity chromatography using IgA-Sepharose to isolate PMN membrane proteins.
- SDS-PAGE analysis to characterize isolated proteins.
Main Results:
- PMNs phagocytose IgA-opsonized yeast and bind to IgA-coated beads.
- Binding to IgA-Sepharose stimulates lysozyme release from PMNs.
- A 60 kDa polypeptide, likely glycosylated, was isolated from PMN membranes using IgA-Sepharose, but not IgG-Sepharose.
Conclusions:
- Human PMNs possess a specific mechanism for interacting with IgA.
- A novel, heavily glycosylated 60 kDa protein on PMN membranes appears to be an IgA receptor.
- This finding suggests a new pathway for IgA-mediated PMN function in immunity.