allergen

https://doi.org/10.1351/goldbook.12857
Immunostimulant antigenic substance that may or may not cause a clinically significant effect but which is capable of producing an immune reaction, often immediate-type hypersensitivity.
Source:
PAC, 2012, 84, 1113. (IUPAC glossary of terms used in immunotoxicology (IUPAC Recommendations 2012)) on page 1120 [Terms] [Paper]