Immunoreactive

Part of speech: adjective

Definitions

1. Showing a reaction when exposed to a particular antigen, as detected by an immune assay or antibody test
2. Responding to the presence of a specific antigen or substance, typically identified through laboratory immunological methods
3. Capable of triggering a detectable immune response when it encounters a specific protein or foreign molecule

Etymology: Immunoreactive is a modern scientific compound, built by joining "immuno-" to "reactive." The first part comes from "immune," which reached English in the Middle Ages from Middle French "immun," itself from Latin "immunis," meaning free from a duty or obligation. Medical writers later took the prefix "immuno-" to describe the body's defences, so the two parts together describe something that reacts with the immune system. The second part, "reactive," traces back through Old French "re-" and Latin "actus," from "agere," "to do" or "to drive," with the Latin "re-" adding the sense of back or again. "Reactive" passed into English through that Latin and French route, and it carries the idea of responding to a stimulus. Combined with "immuno-," the word names a substance or cell that responds in the immune system.