The study investigated the role of interleukin 31 (IL-31) and its receptor (IL-31RA) in horses affected by insect bite hypersensitivity (IBH). The findings concluded that the transcription of these elements increased in response to Culicoides nubeculosus – a biting midge – but did not exaggerate in allergic horses or correlate with itching (pruritus).

Study Summary

• The research study focused on understanding the role of IL-31 and IL-31RA in horses suffering from Insect Bite Hypersensitivity or IBH – a common ailment in horses causing allergic reactions, such as itching, due to insect bites, specifically from a biting midge known as Culicoides nubeculosus.
• The study was performed on a total of 52 horses, with some normal and some affected by IBH. These horses were further divided into two groups based on two separate studies carried out in different periods: a low-dose study involved 19 normal and 15 IBH horses during the summer of 2019, and a high-dose study comprised of 8 normal and 10 IBH horses in the winter of 2022-2023.
• The severity of itching was measured using a visual analogue score or a grading system ranging from 1 to 6.

Procedure and Analysis

• Whole blood leukocytes or white blood cells from these horses were exposed to either a saline solution or Culicoides nubeculosus at a low or high dose, and then the transcription of IL-31 and IL-31RA was measured using quantitative RT-PCR tests.
• The transcription of IL-31 and IL-31RA- the process where DNA gets converted to mRNA, essentially indicating the level of proteins being produced, was found to significantly increase after exposure to high-dose Culicoides nubeculosus in both average and IBH horses. There were no notable differences between the two groups. However, after exposure to low-dose Culicoides nubeculosus, while IL-31RA transcription increased in both groups, IL-31 transcription decreased in normal horses.
• The study saw no positive correlation between itchiness scores and IL-31 transcription after exposure to either low- or high-dose Culicoides nubeculosus. This suggests that increased IL-31 levels were not necessarily tied to increased itchiness in the horses.

Conclusion

• The researchers concluded that no exaggerated IL-31 transcription was identified in allergic (IBH) horses suggesting that the underlying disorder in IL-31 signaling might occur later in the process (downstream) or in localized tissues. It may also involve regulation by yet unidentified receptor splice variants or increased sensitivity to other itch-causing agents (pruritogens) activated by IL-31.
• This opens doors for further studies to better understand IL-31 signaling’s role in equine allergic skin disease.