Atopic dermatitis (AD) is a complex, often lifelong allergic disease with severe pruritus affecting around 10% of both humans and dogs. To investigate the role of mast cells (MCs) and MC-specific proteases on the immunopathogenesis of AD, a vitamin D₃-analog (MC903) was used to induce clinical AD-like symptoms in c-kit-dependent MC-deficient Wsh^−/− and the MC protease-deficient mMCP-4^−/−, mMCP-6^−/−, and CPA3^−/− mouse strains. MC903-treatment on the ear lobe increased clinical scores and ear-thickening, along with increased MC and granulocyte infiltration and activity, as well as increased levels of interleukin 33 (IL-33) locally and thymic stromal lymphopoietin (TSLP) both locally and systemically. The MC-deficient Wsh^−/− mice showed significantly increased clinical score and ear thickening albeit having lower ear tissue levels of IL-33 and TSLP as well as lower serum levels of TSLP as compared to the WT mice. In contrast, although having significantly increased IL-33 ear tissue levels the chymase-deficient mMCP-4^−/− mice showed similar clinical score, ear thickening, and TSLP levels in ear tissue and serum as the WT mice, whereas mMCP-6 and CPA3 -deficient mice showed a slightly reduced ear thickening and granulocyte infiltration. Our results suggest that MCs promote and control the level of MC903-induced AD-like inflammation.

When mosquitoes probe to feed blood, they inoculate a mixture of salivary molecules into vertebrate hosts’ skin causing acute inflammatory reactions where mast cell-derived mediators are involved. Mosquito saliva contains many proteins with largely unknown biological functions. Here, two Aedes albopictus salivary proteins – adenosine deaminase (alADA) and al34k2 – were investigated for their immunological impact on mast cells and two mast cell-specific proteases, the tryptase and the chymase. Mouse bone marrow-derived mast cells were challenged with increased concentrations of recombinant alADA or al34k2 for 1, 3, and 6 h, and to measure mast cell activation, the activity levels of β-hexosaminidase and tryptase and secretion of IL-6 were evaluated. In addition, a direct interaction between alADA or al34k2 with tryptase or chymase was investigated. Results show that bone marrow-derived mast cells challenged with 10 μg/ml of alADA secreted significant levels of β-hexosaminidase, tryptase, and IL-6. Furthermore, both al34k2 and alADA are cut by human tryptase and chymase. Interestingly, al34k2 dose-dependently enhance enzymatic activity of both tryptase and chymase. In contrast, while alADA enhances the enzymatic activity of tryptase, chymase activity was inhibited. Our finding suggests that alADA and al34k2 via interaction with mast cell-specific proteases tryptase and chymase modulate mast cell-driven immune response in the local skin microenvironment. alADA- and al34k2-mediated modulation of tryptase and chymase may also recruit more inflammatory cells and induce vascular leakage, which may contribute to the inflammatory responses at the mosquito bite site. GRAPHICAL ABSTRACT

Introduction: Ulcerative colitis (UC) is a chronic gastrointestinal disease characterized by symptoms of abdominal pain and diarrhea. Chymase is a serine protease released by the mast cells and is highly expressed in patients with UC. However, its role in disease pathogenesis remains poorly understood. In mice, mast cell protease-4 (MCP-4) is considered as the functional homolog of human chymase, sharing similar enzymatic activity and biological roles.Methods: To investigate the role of MCP-4 in UC, we induced colitis in Mcpt-4-deficient (Mcpt-4^∆Cre) and littermate control (Mcpt-4^fl/fl) mice using 2% dextran sulfate sodium salt (DSS) for 8 days followed by 2 days of water. After sacrifice, colon length was measured, and tissue samples were analyzed by histology (H&E and toluidine blue staining), qPCR, and protein assays. Colonic contents were collected for microbiota and metabolomics analysis.Results: The results show that the Mcpt-4-deficiency exacerbated colitis, as reflected by the significantly greater weight loss, higher histological scores, elevated levels of myeloperoxidase and most of determined cytokines. Furthermore, the Mcpt-4^∆Cre colitis mice displayed a distinct shift in colonic microbiota composition, notably with significantly increased abundance of bacteria (Akkermansia and Turicibacter), associated with potentially worsened inflammation in colitis models. In addition, metabolomic profiling revealed alterations in colonic metabolites involved in key Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, including NF-kappa B signaling, Th1 and Th2 cell differentiation.Discussion: These findings reveal that the mouse chymase MCPT-4 plays important roles in maintaining the intestinal homeostasis during colitis, potentially through regulation of colonic cytokines, microbial and metabolic networks.

The Asian tiger mosquito, Aedes albopictus, is an important vector for the transmission of arboviruses such as dengue virus (DENV). Adenosine deaminase (ADA) is a well-characterized metabolic enzyme involved in facilitating blood feeding and (or) arbovirus transmission in some hematophagous insect species. We previously reported the immunologic function of ADA by investigating its effect on mast cell activation and the interaction with mast cell tryptase and chymase. The 2-D gel electrophoresis and mass spectrometry analysis in the current study revealed that ADA is present and upregulated following mosquito blood feeding, as confirmed by qRT-PCR and western blot. In addition, the recombinant ADA efficiently converted adenosine to inosine. Challenging the Raw264.7 and THP-1 cells with recombinant ADA resulted in the upregulation of IL-1β, IL-6, TNF-α, CCL2, IFN-β, and ISG15. The current study further identified recombinant ADA as a positive regulator in NF-κB signaling targeting TAK1. It was also found that recombinant Ae. albopictus ADA facilitates the replication of DENV-2. Compared with cells infected by DENV-2 alone, the co-incubation of recombinant ADA with DENV-2 substantially increased IL-1β, IL-6, TNF-α, and CCL2 gene transcripts in Raw264.7 and THP-1 cells. However, the expression of IFN-β and ISG15 were markedly downregulated in Raw264.7 cells but upregulated in THP-1 cells. These findings suggest that the immunomodulatory protein, Ae. albopictus ADA is involved in mosquito blood feeding and may modulate DENV transmission via macrophage or monocyte-driven immune response.

The gut microbiota represents a stable and dynamic symbiotic community that maintains host health and shapes immune homeostasis. Environmental exposures can disturb this symbiosis, yet the impact of repeated vector biting on host microbial communities has not been explored. Here, we investigated how repeated Aedes albopictus mosquito bites influence gut microbiota composition and stability in a murine model of dextran sulfate sodium (DSS)–induced colitis. Mice were repeatedly exposed to mosquito bites over several weeks prior to DSS treatment, and fecal microbiota were profiled using 16S rRNA sequencing at baseline, during inflammation (day 7), and recovery (day 14). Mosquito biting acted as a “press disturbance,” increasing microbial richness and community dispersion at baseline compared to unbitten controls. During DSS challenge, mosquito-exposed mice exhibited distinct microbial trajectories relative to DSS-only mice, including altered relative abundance of taxa such as Lactobacillus . These microbiota shifts were associated with changes in host inflammatory readouts, including elevated IL-6 during induction and partial normalization by day 14, as well as modest hematological adjustments. Our findings demonstrate that repeated vector exposure can reshape the gut microbiota, modulating the stability and composition of this core host symbiosis under inflammatory stress. These results highlight the sensitivity of symbiotic microbial communities to ecological perturbations and suggest that vector–host interactions may represent an underappreciated factor influencing host–microbe partnerships.