Background: Topical tacrolimus has been widely used in the treatment of inflammatory and immune dermatoses for its immunosuppression effect. However, a transient irritation like itching, burning induced by tacrolimus is common when initial application, which is similar to pseudo-allergic reaction. MAS-related G protein-coupled receptor-X2 (MRGPRX2) in mast cells (MCs) mediates drug-induced pseudo-allergic reaction and IgE-independent pruritis in chronic skin diseases. Whether MRGPRX2 participates in above tacrolimus adverse reaction should be addressed. Further, immunosuppression mechanism of tacrolimus on MCs is greatly ignored. Methods: Wild-type (WT) mice, kit mice and MrgprB2 deficient (MUT) mice were applied to explore the mechanism of initial irritant reaction and immunosuppression of tacrolimus on the skin MrgprB2 in MCs in vivo. LAD2 cells and MRGPRX2-knockdown LAD2 cells were used to confirm the regulation of MRGPRX2 by tacrolimus in vitro. Results: Tacrolimus could trigger IgE-independent dermatitis when initial application through MrgprB2-related MCs degranulation. Using FK-DNS, a fluorescently labeled tacrolimus, we found tacrolimus could bind to MRGPRX2 directly. Interestingly, after long-term tacrolimus treatment, the initial itching and inflammatory reaction faded away without IgE change. Hence, longstanding treatment with tacrolimus suppressed MRGPRX2/B2 expression and decreased inflammatory cytokines release. Conclusion: Our study provides for the first time a novel target for tacrolimus, demonstrating that short-term tacrolimus treatment induces pseudo-allergic reaction via MRGPRX2/B2 in MCs, while long-term treatment dampens MRGPRX2/B2 expression, leading to decreased inflammatory cytokines release and immune cells recruitment, which may contribute to its potent immunosuppression effect in the treatment of inflammatory and immune skin diseases.

Background: Secukinumab (an interleukin (IL)-17 inhibitor) has been reported to be able to alter gut microbiome composition in psoriatic patients. However, it still remains unclear the gut microbiota alteration and related functional changes caused by successful secukinumab therapy in psoriatic patients. In this study, fecal samples from healthy people as comtrol (H; n=35), psoriatic patients without therapy (BT; n=32) and patients after 5-month successful secukinumab treatment (AT; n=11) were collected., Then gut microbiomes were investigated using next-generation sequencing targeting 16S ribosomal RNA. Results: Successful secukinumab therapy caused a significantly elevated microbiota richness and biodiversity, as well as an alteration in the gut microbiota composition than psoriasis without therapy and healthy control. The psoriatic patients after secukinumab successful therapy showed a microbiota profile characterized by increased proportions of the phylum Firmicute, families Comamonadaceae and Erwiniaceae, and a reduction in the phylum Bacteroidota, compared to the other two groups. Besides, we discovered that secukinumab treatment group exhibited more significant abundance in contains mobile elements phenotype, form biofilms phenotype, gram positive phenotype, and less abundance in gram negative phenotype and potentially pathogenic phenotype by BugBase. Functional analysis showed the different COG pathways and KEGG pathways such as downregulated cardiovascular diseases pathway and upregulated infectious diseases between secukinumab therapy group and the other two groups.Conclusions: Secukinumab therapy enhanced the diversity of gut microbiota and altered the composition of the gut microbiome, which actually may construct a more stable homeostasis of gut microbiome with less potentially pathogenicity.

Thimerosal has been used as a preservative in a variety of products which may cause contact dermatitis. It is the second most common allergen in positive patch test reactions, though being a clinical irrelevant allergen. It is believed that thimerosal may cause contact dermatitis through delayed-type hypersensitivity response. However, recent studies have demonstrated the association between Mas-related G protein coupled receptor X2 (MRGPRX2) on mast cells and pseudo-allergic reaction. It is possible that thimerosal may cause contact dermatitis via MRGPRX2 mediated mechanism. To investigate the role of MRGPRX2/MrgprB2 in contact dermatitis induced by thimerosal, we developed a novel skin pseudo-allergic reaction mouse model, footpad swelling and extravasation assays in vivo and mast cell degranulation assay in vitro were studied. The results showed that thimerosal induced contact dermatitis in dorsal skin and footpad swelling in wild-type mice, but had no significant effect in MrgprB2knockout mice. Thimerosal-induced dermatitis is characterized by infiltration of inflammatory cells and elevation of serum histamine and inflammatory cytokines, rather than elevation of serum IgE level. Moreover, thimerosal increased the intracellular Ca 2+ concentration in HEK293 cells overexpressing MrgprB2/MRGPRX2. Downregulation of MRGPRX2 resulted in the reduced degranulation of human mast cells from LAD2 cell line. Collectively, we demonstrate that MrgprB2 mediated thimerosal-induced mast cell degranulation and pseudoallergic reaction in mice, thimerosal also activated human mast cell via MRGPRX2, indicating that MRGPRX2 may be a key contributor to human contact dermatitis.