MRGPRX2 and rheumatoid arthritis: In this work, we find the synovial microenvironment reshapes mast cells into an activated phenotype in RA patients and reveal that the activation of mast cell lines in RA microenvironment is mediated by MRGPRX2, evaluate the efficacy of therapeutic interventions against mast cells in arthritic mice, indicating the crucial role of activated mast cells in disease progression.