The 2nd paper tracks a molecule, IL-8, which has been found to signal equine allergic immune responses. This may be a component as to how horses and humans develop allergic responses.
Couetil, L., Cardwell, J. M., Leguillette, R., Mazan, M., Richard, E., Bienzle, D., Bullone, M., Gerber, V., Ivester, K., Lavoie, J. P., Martin, J., Moran, G., Niedźwiedź, A., Pusterla, N., & Swiderski, C. (2020). Equine Asthma: Current Understanding and Future Directions. Frontiers in veterinary science, 7, 450.
Elisabeth M. Larson, Susanna Babasyan, Bettina Wagner; IgE-Binding Monocytes Have an Enhanced Ability to Produce IL-8 (CXCL8) in Animals with Naturally Occurring Allergy. J Immunol 15 May 2021; 206 (10): 2312–2321.