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Updated: Feb 24, 2026
Isolation of Peritoneum-derived Mast Cells and Their Functional Characterization with Ca2+-imaging and Degranulation Assays
Published on: July 4, 2018
Mast cell degranulation via MRGPRX2 by isolated human albumin fragments
T Karhu1, K Akiyama2, O Vuolteenaho3
1Research Unit of Biomedicine, University of Oulu, Oulu, Finland; Biocenter Oulu, University of Oulu, Oulu, Finland.
Background:
Mast cells are important modulators of the human immune system via their release of several inflammatory mediators and proteases. The release can be activated by different pathways: the classical immunoglobulin E-dependent pathway and by the non-immunological immunoglobulin E-independent pathway. MAS-related G protein-coupled receptor X2 (MRGPRX2) is expressed in mast cells and it is one of the endogenous receptor responsible for the IgE-independent activation of human mast cell. The MRGPRX2 is classified as orphan receptor and unlike most GPCRs, the MRGPRX2 recognizes a wide range of basic molecules. Thus, there still might be several unknown ligands for the receptor.
Methods:
MRGPRX2 activating peptides were isolated from human plasma using consecutive HPLC purification steps. The isolation process was monitored with MRGPRX2 transfected HEK 293 cells. The isolated peptides were sequenced by MS and synthetized. The synthetic peptides were used to determine degranulation of the human LAD 2 mast cell line by measuring β-hexosaminidase release.
Results:
Three endogenous MRGPRX2 activating peptides were isolated from human plasma. These peptides are identified as fragments of albumin. The isolated fragments activate MRGPRX2 and degranulate MRGPRX2 expressing LAD 2 cells in dose-dependent manner.
Conclusions:
The isolated basic peptides generated from human albumin are able to degranulate mast cells via the MRGPRX2.
General Significance:
These endogenous albumin fragments, cleaved from albumin by mast cell secreted proteases, provide a possible pathway for self-perpetuating mast cell dependent inflammation.
Insights
Researchers discovered albumin fragments that activate mast cells through the MAS-related G protein-coupled receptor X2 (MRGPRX2). This finding reveals a new pathway for mast cell activation and inflammation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Mast cells modulate the immune system through inflammatory mediators.
- Mast cell activation occurs via IgE-dependent or IgE-independent pathways.
- MAS-related G protein-coupled receptor X2 (MRGPRX2) mediates IgE-independent mast cell activation and recognizes basic molecules.
Purpose of the Study:
- To identify endogenous ligands for the MRGPRX2 receptor.
- To investigate the role of albumin fragments in mast cell activation.
Main Methods:
- Peptide isolation from human plasma using HPLC.
- Monitoring MRGPRX2 activation with transfected HEK 293 cells.
- Peptide sequencing by mass spectrometry (MS) and synthesis.
- Measuring mast cell degranulation (β-hexosaminidase release) using LAD 2 cells.
Main Results:
- Three endogenous peptides activating MRGPRX2 were isolated from human plasma.
- These peptides were identified as fragments of human albumin.
- Albumin fragments dose-dependently activated MRGPRX2 and degranulated LAD 2 mast cells.
Conclusions:
- Basic peptides derived from human albumin activate mast cells via MRGPRX2.
- These albumin fragments may contribute to self-perpetuating mast cell-dependent inflammation.
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