Transcription of interleukin 31 and its receptor by leukocytes after Culicoides sp stimulation is dose dependent but is not exaggerated in allergic horses or correlated with pruritus.

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.