Dual effect of tacrolimus on mast cell-mediated allergy and inflammation through Mas-related G protein-coupled receptor X2

Background: Topical tacrolimus, although widely used in the treatment of dermatoses, presents with an immediate irritation on initial application resembling a pseudo-allergic reaction. Mas-related G proteincoupled receptor X2 (MRGPRX2) in mast cells (MCs) mediates drug-induced pseudo-allergic reaction and immunoglobulin E (IgE)-independent pruritis in chronic skin diseases. However, the immunosuppression mechanism of tacrolimus on MCs via MRGPRX2 has not been reported.Objective: To investigate the role of MRGPRX2 and the mechanism of action of tacrolimus on its short-term and long-term applications.Methods:Wild-type mice, Kit(W-sh/W-sh) mice, and MrgprB2-deficient (MUT) mice were used to study the effect of tacrolimus on in vivo anaphylaxis model. LAD2 cells and MRGPRX2-knockdown LAD2 cells were specifically used to derive the associated mechanism of the tacrolimus effect.Results: Short-term application of tacrolimus triggers IgE-independent activation of MCs via MRGPRX2/B2 in both in vivo and in vitro experiments. Tacrolimus binds to MRGPRX2, which was verified by fluorescently labeled tacrolimus in cells. On long-term treatment with tacrolimus, the initial allergic reaction fades away corresponding with the downregulation of MRGPRX2, which leads to decreased release of inflammatory cytokines (P < 0.05 to P < 0.001).Conclusion: Short-term treatment with tacrolimus induces pseudo-allergic reaction via MRGPRX2/B2 in MCs, whereas long-term treatment downregulates expression of MRGPRX2/B2, which may contribute to its potent immunosuppressive effect in the treatment of various skin diseases.(c) 2023 Japanese Society for Investigative Dermatology. Published by Elsevier B.V. All rights reserved.