The cytokine IL-9 has been implicated in allergic reactions, including food allergy, but its contribution to parenteral versus oral antigen-induced anaphylaxis remains unclear.
Osterfeld, H., Ahrens, R., Strait, R., Finkelman, F. D., Renauld, J.-C., & Hogan, S. P. (2010). Differential roles for the IL-9/IL-9 receptor alpha-chain pathway in systemic and oral antigen-induced anaphylaxis. Journal of Allergy and Clinical Immunology, 125(2), 469-476. https://doi.org/10.1016/j.jaci.2009.09.054 (Original work published 2010)