Peptides of major basic protein and eosinophil cationic protein activate human mast cells

The eosinophil granule proteins, major basic protein (MBP) and eosinophil cationic protein (ECP), activate mast cells during inflammation; however the mechanism responsible for this activity is poorly understood. We found that some theoretical tryptase-digested fragments of MBP and ECP induced degranulation of human cord blood-derived mast cells (HCMCs). The spectrum of activities of these peptides in HCMCs coincided with intracellular Ca²⁺ mobilization activities in Mas-related G-protein coupled receptor family member X2 (MRGPRX2)-expressing HEK293 cells. Two peptides corresponding to MBP residues 99–110 (MBP (99–110)) and ECP residues 29–45 (ECP (29–45)), respectively, induced degranulation of HCMCs and intracellular Ca²⁺ mobilization in MRGPRX2-expressing HEK293 cells in a concentration-dependent manner. Stimulation with MBP (99–110) or ECP (29–45) induced the production of prostaglandin D2 by HCMCs. The activities of MBP (99–110) and ECP (29–45) in both HCMCs and MRGPRX2-expressing HEK293 cells were inhibited by MRGPRX2-specific antagonists. In conclusion, these results indicated that MBP and ECP fragments activate HCMCs, and it may occur via MRGPRX2. Our findings suggest that tryptase-digested fragments of eosinophil cationic proteins acting via the MRGPRX2 pathway may further our understanding of mast cell/eosinophil communication.