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Background:Forcipomyia taiwana is a tiny blood-sucking midge whose habitat covers large parts of Taiwan and southern China. Female midges bite during the day, causing intense pruritis and swelling in allergic individuals. In this study, we investigated the immune responses of different allergic reactions to midge bites. Methods:F. taiwana (midge)-specific IgE, -IgG and -IgG subclasses were examined by ELISA in 62 human subjects. Peripheral blood mononuclear cells (PBMC) from 6 subjects with solely delayed reactions (SDR) to midge bites and 6 nonallergic controls (NAC) were cultured with midge extract at various time points and assayed. Proliferation of PBMC was measured by MTT assay. Expression of cytokine mRNA was measured by real-time PCR and protein levels by cytometric bead immunoassay or ELISA. Protease activity in midge extract was determined by the Azocoll method. Results: Midge-specific IgE among subjects with an immediate reaction were significantly elevated compared to SDR and NAC subjects. There were no differences in the level of midge-specific-IgG, -IgG₁, -IgG₂, -IgG₃ and -IgG₄ among subjects with different biting reactions. Midge extract elicited significantly more PBMC proliferation, higher expression of IFN-γ, IL-10, IL-6 and TNF-α in SDR subjects than in NAC. Protease activity was detected in midge extract. Protease inhibitors E64 and pepstatin suppressed midge-extract-induced IL-8 production. Conclusions: Our results suggest that an immediate reaction to midge bites is IgE-mediated. IFN-γ, IL-6 and TNF-α are involved in delayed reactions to midge bites. A protease-activated pathway may also be involved in the intense, itchy reactions to midge bites.

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