Skin-infiltrating T cells and cytokine expression in Icelandic horses affected with insect bite hypersensitivity: a possible role for regulatory T cells.

This study investigates the involvement of different types of T cells and cytokine protein profiles in the skin condition, insect bite hypersensitivity (IBH) in Icelandic horses. The research found imbalances in T helper cells and regulatory T cells in IBH-affected horses, suggesting potential therapeutic approaches based on restoring this balance.

Objective and Importance of the Study

• The central aim of this study was to identify the types of T cells and their accompanying cytokine protein profiles in the skin of Icelandic horses affected by a skin disorder called insect bite hypersensitivity (IBH). This is an IgE-mediated reaction to salivary proteins from biting flies, especially in the genus Culicoides, that causes recurrent skin irritation.
• The findings provide insight into the types and distribution of immune cells involved in IBH in horses, and they suggest potential new treatment strategies for restoring immune balance in affected animals.

Research Procedures and Findings

• The researchers characterized the distribution and number of different T cell types (CD4+, CD8+ and FoxP3+) in the skin of both moderately and severely IBH-affected horses, and compared these with healthy control horses.
• They found a significantly higher number of CD4+ cells in the skin lesions of horses with IBH compared to the skin of healthy horses. The total number of T cells (both CD4+ and CD8+) was also higher in lesioned skin compared to non-lesioned skin.
• They went further to measure the expression levels of different types of cytokines (proteins that mediate and regulate immune and inflammatory responses), including Th2 cytokines (IL-4, IL-5, IL-13), Th1 cytokines (Interferon-γ), regulatory cytokines (Transforming Growth Factor β1, IL-10) and the Treg transcription factor FoxP3 in both skin and blood samples.
• Although the number of FoxP3+ T cells did not differ significantly between the groups, a noticeable observation was that the ratio of FoxP3 to CD4+ cells was significantly lower in lesions from severely affected horses than in moderately affected or control animals.
• IBH-affected horses also had significantly higher specific serum IgE levels against Culicoides nubeculosus than the control horses, indicating an immune response to this specific type of biting fly.

Implications for Future Treatment Strategies

• The results of this research suggest that an imbalance between Th2 cells, which typically help to coordinate immune responses, and Treg cells, which help keep the immune system in check, is a key feature of IBH in horses.
• Given this imbalance, the researchers suggested that future treatments for IBH should seek to restore balance between Th2 and Treg cells. This could potentially help alleviate symptoms of IBH and improve the horse’s quality of life.